AO Spine Masters Series Volume 4 Adult Spinal (BookZZ.org)

AOSpine Masters Series Adult Spinal Deformities

AOSpine Masters Series Adult Spinal Deformities

Series Editor:

Luiz Roberto Vialle, MD, PhD Professor of Orthopedics, School of Medicine Catholic Universit y of Parana State Spine Unit Curitiba, Brazil

Guest Editors: Law rence G. Lenke, MD Jerom e J. Gilden Distinguished Professor Orthopaedic Surgery Professor, Neurological Surgery Chief of Spinal Surgery Director of the Advanced Deformit y Fellowship Washington Universit y School of Medicine St. Louis, Missouri

Kenneth M.C. Cheung, MBBS(UK), MD (HK), FRCS, FHKCOS, FHKAM(Orth) Head, Department of Orthopaedics & Traumatology Jessie Ho Professor in Spine Surgery The Universit y of Hong Kong Queen Mary Hospital Pokfulam, Hong Kong

With 92 f gures

Th iem e New York • St u t tgar t • Delh i • Rio de Jan eiro

Th iem e Medical Pu blish ers, In c. 333 Seven th Ave. New York, NY 10001 Execut ive Editor: William Lam sback Man aging Editor: Sarah Lan dis Director, Editorial Ser vices: Mar y Jo Casey Editorial Assist ant: Haley Paskalides Product ion Editor: Barbara A. Ch ern ow In tern at ion al Product ion Director: An dreas Sch aber t Vice Presiden t , Editorial an d E-Produ ct Develop m en t: Vera Sp illn er In tern at ion al Market ing Director: Fion a Hen derson In tern at ion al Sales Director: Louisa Turrell Director of Sales, North Am erica: Mike Rosem an Sen ior Vice Presiden t an d Ch ief Operat ing O cer: Sarah Van d erbilt Presiden t: Brian D. Scan lan Com p ositor: Carol Pierson , Ch ern ow Editorial Ser vices, In c.

Librar y of Congress Cataloging-in -Pu blicat ion Dat a AOSpin e m asters series. v. 4, Adu lt spin al deform it ies / editors, Luiz Roberto Vialle, Law ren ce G. Len ke, Ken n eth M.C. Ch eu ng. p. ; cm . Adult spin al deform it ies In cludes bibliograp h ical referen ces an d in dex. ISBN 978-1-62623-100-9 (alk. p aper) — ISBN 978-1-62623-101-6 (eISBN) I. Vialle, Luiz Roberto, ed itor. II. Len ke, Law ren ce, 1960– , ed itor. III. Ch eung, Ken n eth M. C., editor. IV. Title: Adult spin al deform it ies. [DNLM: 1. Spin al Diseases—surger y. 2. Orth op edic Procedu res—m eth ods. 3. Spin e—su rger y. W E 725] RD768 617.4'71—dc23 2015001979

Copyrigh t ©2015 by Th iem e Medical Publish ers, In c. Im po rtan t n ote: Medicin e is an ever-ch anging scien ce u n dergoing con t in u al develop m en t . Research an d clin ical experien ce are con t in ually expan ding ou r kn ow ledge, in par t icu lar ou r kn ow ledge of prop er t reat m en t an d drug th erapy. In sofar as th is book m en t ion s any dosage or ap plicat ion , readers m ay rest assu red th at th e au th ors, editors, an d publish ers h ave m ade ever y e ort to en sure th at su ch referen ces are in accordan ce w ith the state o f know ledge at the tim e o f productio n o f the bo o k. Never th eless, th is does n ot involve, im p ly, or express any gu aran tee or respon sibilit y on th e par t of th e pu blish ers in respect to any dosage in st ruct ion s an d form s of app licat ion s st ated in th e book. Every user is requested to exam in e carefully th e m an u fact u rers’ lea et s accom p anying each d rug an d to ch eck, if necessar y in con su ltat ion w ith a physician or sp ecialist , w h eth er th e dosage sch edu les m en t ion ed th erein or th e con t rain dicat ion s st ated by th e m an u fact u rers di er from th e st atem en t s m ade in th e presen t book. Such exam in at ion is part icularly im por t an t w ith drugs th at are eith errarely u sed or h ave been n ew ly released on th e m arket . Ever y dosage sch edu le or ever y form of app licat ion u sed is en t irely at th e u ser’s ow n risk an d respon sibilit y. Th e au th ors an d p ublish ers requ est ever y u ser to rep or t to th e p u blish ers any discrepan cies or in accuracies n ot iced. If errors in th is w ork are fou n d after pu blicat ion , errat a w ill be posted at w w w.th iem e.com on th e p rodu ct descript ion page. Som e of th e p rodu ct n am es, p aten t s, an d registered design s referred to in th is book are in fact registered t radem arks or p ropriet ar y n am es even th ough speci c referen ce to th is fact is n ot alw ays m ade in th e text . Th erefore, th e appearan ce of a n am e w ith ou t design at ion as prop rietar y is n ot to be con st ru ed as a represen t at ion by th e p u blish er th at it is in th e pu blic dom ain . Prin ted in Ch in a by Everbest Prin t ing Ltd. 5 4 3 2 1 ISBN 978-1-62623-100-9 Also available as an e-book: eISBN 978-1-62623-101-6

AOSpine Masters Series Luiz Roberto Vialle, MD, PhD Series Editor

Volum e 1

Met astat ic Spin al Tu m ors

Volum e 2

Prim ar y Sp in al Tu m ors

Volum e 3

Cer vical Degen erat ive Con dit ion s

Volum e 4

Adu lt Sp in al Deform it ies

Volum e 5

Cer vical Sp in e Traum a

Volum e 6

Th oracolu m bar Spin e Trau m a

Volum e 7

SCI an d Regen erat ion

Volum e 8

Back Pain

Volum e 9

Pediat ric Sp in al Deform it ies

Volum e 10

Sp in al In fect ion

Contents

Series Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix Luiz Roberto Vialle Guest Edito rs’ Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi Law rence G. Lenke and Kenneth M.C. Cheung 1

Preoperat ive Evalu at ion an d Opt im izat ion for Surger y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 Scott C. W agner, Daniel G. Kang, Ronald A. Lehm an, Jr., and Law rence G. Lenke

2

Decision Making in Adu lt Deform it y Su rger y: Decom p ression Versu s Sh or t or Long Fu sion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Kenneth M.C. Cheung and Jason P.Y. Cheung

3

Th e Use of Osteotom ies for Rigid Spin al Deform it ies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Stephen J. Lew is and Sim on A. Harris

4

In d icat ion s an d Tech n iqu es for Sacral-Pelvic Fixat ion in Adu lt Sp in al Deform it y . . . . . . . . . 45 Kristen E. Jones, Robert A. Morgan, and David W. Polly, Jr.

5

In st r u m en tat ion St rategies in Osteop orot ic Sp in e: How to Preven t Failu re? . . . . . . . . . . . . . 56 Ahm et Alanay and Caglar Yilgor

6

Th e In ciden ce an d Man agem en t of Acu te Neu rologic Com p licat ion s Follow ing Com p lex Adu lt Spin al Deform it y Su rger y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 Joseph S. Butler and Law rence G. Lenke

7

Postoperat ive Coron al Decom pen sat ion in Ad ult Deform it y . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 Yong Qiu

8

Measuring Outcom e an d Valu e in Adu lt Deform it y Su rger y . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 Robert W aldrop and Sigurd Berven

9

Jun ct ion al Issues Follow ing Adu lt Deform it y Surger y . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Han Jo Kim , Sravisht Iyer, and Christopher I. Shaf rey, Sr.

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Contents 10 Biom ech an ics an d Material Scien ce for Deform it y Correct ion . . . . . . . . . . . . . . . . . . . . . . . . . 120 Manabu Ito, Yuichiro Abe, and Rem el Alingalan Salm ingo 11 Pseu dar th rosis an d In fect ion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 Michael P. Kelly and Sigurd Berven Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

Series Preface

Sp in e care is advan cing at a rapid pace. Th e ch allen ge for today’s sp in e care p rofession al is to qu ickly syn th esize t h e best available eviden ce an d exp er t op in ion in th e m an agem en t of sp in e p at h ologies. Th e AOSp in e Mast e r s Series p rovides ju st th at—each volu m e in th e series delivers p ath ology-focu sed exper t opin ion on procedu res, diagn osis, clin ical w isdom , an d pitfalls, an d h igh ligh ts today’s top research pap ers. To bring th e valu e of it s m asters level edu cat ion al cou rses an d academ ic congresses to a w ider audien ce, AOSpin e h as assem bled in tern at ion ally recogn ized spin e path ology leaders to develop volum es in th is Masters Series as a

vehicle for sharing their experiences and expert ise an d p roviding lin ks to th e literat u re. Each volum e focuses on a curren t com pelling an d som et im es con t roversial topic in spin e care. Th e u n iqu e an d e cien t for m at of t h e Masters Ser ies volu m es qu ickly focu ses t h e at ten t ion of t h e read er on t h e core in for m at ion crit ical to un derst an ding th e topic, w h ile en cou raging th e reader to look fu r th er in to th e recom m en d ed literat ure. Th rough th is ap p roach , AOSpin e is advan cing spin e care w orldw ide. Luiz Roberto Vialle, MD, PhD

Guest Editors’ Preface

Adu lt spin al deform it y (ASD) is a clin ical prob lem of in creasing prevalen ce, an d th u s physician s an d pat ien t s w orldw ide are aw are of it . With in creasing longevit y, th e n orm al degen erat ion of th e sp in e m ay lead to variou s ASD p roblem s su ch as lu m bar d egen erat ive scoliosis w ith or w ith ou t accom panying sp in al kyp h osis. In ad d it ion , ASD in clu des a sp ect r u m of preexisten t ch ildh ood deform it ies, su ch as scoliosis or kyp h osis, th at slow ly p rogress to sym ptom at ic st ages over ad u lth ood. Clin ical m an ifest at ion s m ay in clu de progressive defor m it y, p oten t ial sp in al im balan ce, an d spin al sten osis, w ith resu lt an t axial or low er ext rem it y sym ptom atology. Healt h -related qu alit yof-life assessm en t s often d em on st rate severe adverse e ects of ASD th at can in terfere w ith m any aspect s of physical, em ot ion al, an d psych ological w ell-being. W h en clin ical an d radiographic scenarios warrant, surgical intervention, ranging from sim ple decom pression s to com plex total spine reconstructions, should be considered in app rop riate pat ien ts. We h ave assem bled a global pan el of specialists to sh are w ith us th eir experien ce in th e m an agem en t of ASD, from evalu at ion to t reatm en t , an d in clu d in g su ch issu es as in st r u m en t at ion an d su rgical tech n iqu es, as w ell as preven t ing an d m an aging com p licat ion s. Th orough pat ien t evaluat ion , both m edical an d su rgical, is w arran ted, w ith pat ien t select ion for in dicated su rgical in ter ven t ion on e of t h e m ain keys to a su ccessfu l ou tcom e. Per t in en t issu es,

su ch as bon e den sit y evaluat ion an d preoperat ive opt im izat ion , m u st be ad dressed w ith th e u se of in t raop erat ive adjuvan t s to en sure st able in tern al xat ion to th e spin al colum n in pat ien ts requ iring stabilizat ion w ith or w ith out realign m en t. For pat ien ts w ith progressive d efor m it y p rod u cing segm en t al, region al, or global m alalign m en t , var iou s cor rect ive st rat egies are discussed to safely realign th e spin al colu m n u sing variou s form s of sp in al osteotom ies w ith adjuvan t sp in al in st ru m en t at ion to secu re th e spin al segm en ts in th eir realign ed position . Sp in al xat ion tech n iqu es are esp ecially ch allenging w h en in st rum en t ing th e sacropelvic u n it in long con st ru ct s. Th e various form s of osteotom ies ut ilized range from sim ple facet excision s to ext rem ely com plex th reecolu m n osteotom ies su ch as p edicle su bt ract ion and vertebral colum n resection techniques that are occasion ally required for pat ien ts w ith severe deform it y w ith accom panying im balan ce. En su ring n eu rologic safet y du ring ASD su rger y is p aram ou n t , becau se t h ese op erat ion s h ave an early n eu rologic com p licat ion rate t h at is n ot in sign i can t an d can lead to perm an en t de cits. All of th ese essen t ial p reoperat ive an d in t raoperat ive factors are discu ssed in detail. Even w ith in it ial su rgical su ccess, th e longterm success of surger y for ASD is con t roversial. Variou s factors, su ch as w ou n d in fect ion s, pseu dar th rosis, an d adjacen t segm en t p ath ology, th e m ost com m on being proxim al jun ct ion al kyp h osis (PJK), can lead to deteriorat ion

xii

Guest Editors’ Preface of t h e clin ical ou tcom es over t im e. Th e d u rabilit y of clin ical outcom e m easures for th ese pat ien ts is an im p or tan t focu s along w ith th e n an cial im plicat ion s for t reat ing ASD pat ien t s. Th u s, as in all areas of m edicin e, th e valu e prop osit ion of t reat ing ASD pat ien ts, both w ith n on operat ive an d operat ive procedures, m ust be ascer t ain ed to just ify th e w ide spect r um of in ter ven t ion s available. As in all areas of surgery, selecting the appropriate patient and perform ing th e least aggressive su rger y to solve th e clin ical problem w h ile en su ring long-term su ccess is th e opt im al ap proach .

We h ope th is book w ill h elp spin e su rgeon s from arou n d th e w orld n avigate th e often con t roversial an d com p licated clin ical issu es in volved in t h e m an agem en t of ASD p at ien t s, so t h at t h e ou tcom e can be m a xim ized an d t h e com plicat ion s m in im ized. Law rence G. Lenke, MD Kenneth M.C. Cheung, MBBS(UK), MD (HK), FRCS, FHKCOS, FHKAM(Orth)

Contributors

Yuichiro Abe, MD, PhD At ten ding Spin e Surgeon Depar t m en t of Or th op aedic Su rger y En iw a Hospital En iw a, Japan

Ahm et Alanay, MD Professor Depar t m en t of Or th op ed ics an d Trau m atology Facult y of Medicin e Acibadem Un iversit y Istan bu l, Tu rkey

Jaso n P.Y. Che ung, MBBS, MMedSc, FHKCOS, FHKAM(Orth), FRCSEd(Orth) Clin ical Assistan t Professor Depart m ent of Orthopaedics & Traum atology Th e Un iversit y of Hong Kong Queen Mar y Hospit al Pokfu lam , Hong Kong Ke nneth M.C. Cheung, MBBS(UK), MD (HK), FRCS, FHKCOS, FHKAM(Orth) Head, Depar t m en t of Or th opaedics & Trau m atology Jessie Ho Professor in Spin e Su rger y Th e Un iversit y of Hong Kong Queen Mar y Hospit al Pokfu lam , Hong Kong

Sigurd Be rven, MD Professor in Residen ce Director of Spin e Fellow sh ip an d Resid en t Edu cat ion Program Depar t m en t of Or th op aedic Su rger y Un iversit y of Californ ia–San Fran cisco San Fran cisco, Californ ia

Sim on A. Harris, MA, MB, BChir, FRCSC Fellow Depar t m en t of Or th opedics Toron to Western Hospital, Un iversit y of Toron to Toron to, On tario, Can ada

Jo seph S. Butle r, PhD, FRCS (Tr&Orth) Clin ical Fellow Spin al Deform it y Un it Royal Nat ion al Orth opaedic Hosp ital St an m ore, Middlesex, Un ited Kingdom

Manabu Ito, MD, PhD Director Cen ter for Spin e an d Sp in al Cord Disorders Nat ion al Hospit al Organ izat ion Hokkaido Medical Cen ter Sapporo, Japan

xiv

Contributors Sravisht Iye r, MD Or th opaedic Su rger y Residen t Hosp it al for Special Su rger y New York, New York Kristen E. Jo nes, MD Fellow Depar t m en t s of Or th opaedic Su rger y an d Neu rosu rger y Un iversit y of Min n esota Min eapolis, Min n esota Daniel G. Kang , MD Sp in e Su rger y Fellow Depar t m en t of Or th op edic Su rger y Wash ington Un iversit y St . Louis, Missou ri Michael P. Kelly, MD, MSc Assist an t Professor of Or th op edic Su rger y Assist an t Professor of Neu rological Su rger y Depar t m en t of Or th op edic Su rger y Wash ington Un iversit y Sch ool of Medicin e Sain t Lou is, Missou ri Han Jo Kim , MD Assist an t Professor of Or th op aedic Su rger y Co-Director of Edu cat ion Sp in e Ser vice Hosp it al for Special Su rger y New York, New York Ronald A. Lehm an, Jr., MD Professor of Or th opaedic Surger y Professor of Neurological Su rger y Wash ington Un iversit y Sch ool of Medicin e BJC In st it u te of Health St . Louis, Missou ri Law re nce G. Lenke, MD Jerom e J. Gilden Dist ingu ish ed Professor Distinguished Professor of Orthopaedic Surger y Professor of Neurological Su rger y Ch ief of Sp in al Su rger y Director of th e Advan ced Deform it y Fellow sh ip Wash ington Un iversit y Sch ool of Medicin e St . Louis, Missou ri

Stephen J. Lew is, MD, MSc, FRCSC Associate Professor Un iversit y of Toron to Depart m en t of Su rger y Division of Orth opaedics Toron to Western Hospital for Sick Ch ildren Toron to, On tario, Can ada Ro bert A. Mo rgan, MD Assistan t Professor Orth opaedic Su rgeon Un iversit y of Min n esot a Min n eapolis, Min n esota David W. Po lly, Jr., MD Professor an d Ch ief Spin e Ser vice Un iversit y of Min n esot a Depart m en t of Or th opaedic Surger y Min n eapolis, Min n esota Yo ng Qiu, MD Professor an d Director Depart m en t of Sp in e Surger y Nanjing Dru m Tow er Hosp ital Med ical Sch ool of Nanjing Un iversit y Nanjing, Jiangsu Provin ce, Ch in a Re m el Alingalan Salm ingo, PhD Visit ing Research er Biom edical Engin eering Tech n ical Un iversit y of Den m ark (DTU) Engin eer JJ X-Ray A/S Tech n ical Un iversit y of Den m ark (DTU) Scion Kongen s Lyngby, Den m ark Christo pher I. Shaf rey, Sr., MD Joh n A. Jan e Professor of Neu rological Su rger y Professor of Or th opaedic Su rger y Depart m en t of Neu rological Su rger y Un iversit y of Virgin ia Sch ool of Med icin e Ch arlot tesville, Virgin ia VA

Contributors Scott C. Wagner, MD In st r uctor of Su rger y Division of Su rger y Depar t m en t of Or th op aedics Un iform ed Ser vices Un iversit y of th e Health Scien ces Walter Reed Nat ion al Militar y Med ical Cen ter Beth esda, Mar ylan d Robe rt Waldro p, MD Fellow in Sp in e Su rger y Depar t m en t of Or th op aedic Su rger y Un iversit y of Californ ia–San Fran cisco San Fran cisco, Californ ia

Caglar Yilgo r, MD Assist an t Professor Depar t m en t of Or th opedics an d Trau m atology Facult y of Medicin e Acibadem Un iversit y Istan bu l, Tu rkey

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1 Preoperative Evaluation and Optimization for Surgery Scott C. Wagner, Daniel G. Kang, Ronald A. Lehman, Jr., and Law rence G. Lenke

■ Introduction Adult spinal deform it y is an u m brella term en com p assin g var iou s d evelop m en t al, p rogressive, or degen erat ive con d it ion s th at con t ribu te to an altered th ree-dim en sion al st ru ct ure of th e h u m an sp in e. Th ere are th ree m ain t yp es of adult spin al deform it y: t ype 1, de n ovo, or prim ar y degen erat ive scoliosis; t ype 2, u n t reated adolescen t idiopath ic scoliosis th at h as progressed in to adu lth ood; an d t yp e 3, secon dar y scoliosis related to altered ver tebral an atom y due to p reviou s surger y, t raum a, or m et abolic bon e disease.1 A secon dar y form of adu lt scoliosis is iat rogenic im balan ce caused by previou s spin al surger y.2 Th e m ost clin ically im portan t and m ost com m only encountered t ypes of adult deform it y are t ypes 1 an d 3.1 St r u ct u ral cu r ves th at develop in adu lth ood (t ype 1) gen erally begin an d th en progress as th e in ter vertebral disks degen erate w ith n orm al aging. As disk degen erat ion progresses, posterior elem en t in com peten ce leads to axial rotat ion of th e sp in al m ot ion segm en t s, w ith perm an en t rotator y deform it y in t u rn leading to ligam en tous laxit y an d even t ual lateral listh esis of th e ver tebral bodies.3 Dest ruct ion of th e diskoligam en tous com plex an d en suing degen erat ion of t h e facet join t s leads to abn orm al m ot ion at each vertebral segm ent, subsequently causing react ive ch anges such as osteophytosis at th e en d plates, facet join t hyper t rophy/cysts, an d ligam en t u m avu m hyp ert rophy. In addi-

t ion , th e con cavit y of th e m ajor an d fract ion al cu r ve can cau se foram in al n arrow ing, w h ich is often fur th er exacerbated by disk degen erat ion an d loss of foram in al h eigh t (up/dow n foram in al sten osis). Th ese ch anges cau se n arrow ing of th e spin al can al (cen t ral an d lateral recess) an d n eural foram en ,1 an d collect ively con t ribu te to th e clin ical sym ptom s of adult scoliosis or spin al deform it y. Th u s, un derst an ding th e com plex path om ech an ics an d an atom y of th is d egen erat ive process is vital for sp in e su rgeon s con sidering perform ing deform it y su rger y. As t h e p op u lat ion ages an d life exp ect an cy in creases, t h e p revalen ce of d egen erat ive ad u lt sp in al deform it y w ill con t in u e to in crease.2 In fact , t h e im p act on overall p u blic h ealt h an d disabilit y of t h e Un ited St ates p op u lat ion by adu lt d egen erat ive scoliosis can n ot be overst ated , an d t h ere w ill likely be an in creased n um ber of th ese pat ien ts elect ing surgical correct ion of t h eir d efor m it y an d t reat m en t of th eir sym ptom s.2,4

■ Epidemiology New -on set adu lt degen erat ive deform it ies are con sidered in th e con text of a p opu lat ion older th an 40 years of age, w ith ou t a prior h istor y of adolescen t idiopath ic scoliosis (AIS). Adult scoliosis can be asym ptom at ic, an d th e in ciden ce of spin al cur ves of less th an 10 degrees m ay be

2

Chapter 1 as h igh as 64%.5 In fact , 30% of elderly pat ien t s w ith ou t a previou s h istor y of sp in al deform it y w ill develop n ew struct ural abn orm alities, w ith m en and w om en a ected equally (in contrast to adolescent idiopath ic scoliosis, in w h ich girls are m ore com m on ly a ected th an boys).3 Pat ien t s w ith p rogressive d egen erat ive sp in al deform it ies t ypically presen t in th e sixth decade w ith various sym ptom s, frequen tly in cluding a com bin at ion of back p ain , radicu lopathy, an d n eu rogen ic claudicat ion .3 Adult degen erat ive deform it ies ten d to p rogress u p to 6 degrees per year, averaging 3 degrees per year, if left un t reated,3 an d radiograp h ic param eters th at p redict a high risk for p rogression in clu de a Cobb angle greater than 30 degrees, lateral olisth esis greater th an 6 m m , an d a large degree of apical rot at ion .3 How ever, open surgical spin al d eform it y correct ion in ad u lt p at ien t s is associated w ith a com plicat ion rate of u p to 86%, in clu ding a 7.8% rate of early w ou n d in fect ion , an d is t yp ically associated w ith large am ou n t s of in t raoperat ive blood loss, deep w ou n d in fect ion , an d p ulm onar y em bolism .4,6,7 Th erefore, th orough p reop erat ive evalu at ion an d opt im izat ion is absolu tely p aram ou n t w hen con sidering surgical t reat m en t of adu lt sp in al deform it y, becau se th is p at ien t p opu lat ion is often elderly, w ith m u lt iple associated com orbidit ies, an d at h igh risk for m edical an d su rgical com p licat ion s.8 A m u lt id iscip lin ar y app roach , in clu ding th e prim ar y care p rovider, an in tern ist , an en docrin ologist , a cardiologist , as w ell as th e t reat ing sp in e su rgeon , sh ou ld be undertaken in the perioperative evaluation process to m in im ize th e p oten t ial m edical risks an d m axim ize th e fu n ct ion al ben e t s.

■ Clinical Evaluation Initial Assessment Th e in it ial assessm en t m u st in clu d e t akin g a com p reh en sive h istor y an d p er for m ing a th orough p hysical exam in at ion . A p reviou s d iagn osis of sp in al d efor m it y (e.g., ad olescen t id iop at h ic scoliosis, kyp h osis, congen it al d eform it y), a h istor y of prior spin e surgeries, as w ell as any previous im aging st udies dem on -

st rat ing progression of degen erat ive ch anges an d deform it y w ill provide clin ical cu es to ap p ropriately guide th e rem ain der of th e w orkup. Pat ien t s t ypically presen t w ith a com bin at ion of various com plaints, including upper or low er back p ain , radiat ing low er ext rem it y pain or w eakn ess, p aresth esias/n u m bn ess, n eu rogen ic clau d icat ion , d i cu lt y w it h gait or u p r igh t p ost u re, an d p rogression of t h eir d efor m it y. Ch anges in body h abit us/post ure (par t icularly ch anges in th e t of cloth ing), di cult y w ith gait or decreased w alking dist an ce toleran ce, an d ch anges in th e u se of assist ive devices are elicited du ring th e h istor y-taking process. Back p ain is th e m ost com m on p resen t ing sym ptom , an d com p lain t s of p ain m u st be di eren t iated w ith regard to axial versus radicular sym p tom s. Isolated low back p ain m ay rep resen t p araspin al m uscle fat igu e or m ech an ical in stabilit y at t h e p ain fu l segm en t ,1 w ith in creased p ain severit y often suggest ing sign i can t sagit t al an d coron al im balan ce.3 If radicu lar p ain is presen t in addit ion to axial pain , du rat ion / onset of sym ptom s, exacerbating activities, and lateralit y of th e sym ptom s provide gu idan ce for p oten t ial d ecom p ression .1,3 Rad icu lar ext rem it y p ain can be cau sed by an acu te d isk h er n iat ion , localized foram in al or lateral recess ner ve root com pression from osteophytes/ spondylotic changes, foram inal com pression on the concave side of the fractional cur ve, or t raction on th e convex side of th e deform it y, or m ay be related in stead to single- or m u lt ilevel cen t ral sten osis. Neurologic de cit s are less com m on in adu lt deform it ies, bu t w h en presen t are often related to segm en t al in st abilit y cau sing foram in al com pression or congen it al spin al sten osis, w h ich is exacerbated by degen erat ive ch anges cau sing fu r th er cen t ral can al sten osis.1 Th e op erat ive app roach sh ou ld t ake in to con siderat ion th e exten t an d t ype of decom pression an d fu sion con st ruct , if any, th at is in dicated based on th e pat ien t’s sym ptom atology, as w ell as any recen t ch anges or p rogression of sym ptom s.1 The clinical exam ination includes assessm ent of a sh ift in th e t run k, an d th e relat ion sh ip of th e h ead to th e p elvis in th e coron al an d sagittal plan e is n oted. Asym m et r y of th e sh oulder or p elvic gird les p rovid es u sefu l in for m at ion

Preoperative Evaluation and Optim ization for Surgery w ith regard to th e severit y of th e d eform it y, as do p elvic obliqu it y an d leg-length discrep an cy. Oth er su btle clu es to severit y an d progression of th e deform it y in clu de skin creases arou n d th e t r u n k/abdom en an d st an ding p ost u re (e.g., pelvic ret roversion , h ip /kn ee exion ). Having th e p at ien t perform for w ard an d lateral ben ding d u rin g t h e exam can p rovid e im p or t an t p rogn ost ic in for m at ion , as th e rigid it y of th e cur ve can a ect th e overall ou tcom e of n on op erat ive an d su bsequ en t operat ive in ter ven t ion . Hip an d kn ee exion con t ract u res sh ou ld also be assessed w ith th e pat ien t lying in th e supin e posit ion on th e exam in at ion t able. Th en , w ith th e pat ien t lying in th e pron e posit ion on th e table, th e exibilit y of th e cur ve w ith out gravit y can be determ in ed, an d th e pat ien t’s abilit y to tolerate th e pron e posit ion an d overall physical con dit ion ing can be assessed . Th e pat ien t’s in abilit y to t urn pron e in dep en d en tly m ay in dicate sign i can t decon dit ion ing an d th at th e pat ien t is a h igh -risk su rgical can didate). Neu rovascu lar exam in at ion in clu d es overall gait assessm en t , m otor st ren gt h , d eep ten d on reexes, sen sat ion an d cran ial n er ve fu n ct ion , as w ell as ext rem it y p u lse assessm en t .3 Th e p at ien t sh ou ld also be exam in ed for long t ract sign s, as m yelop athy m ay be a com p on en t of severe th oracic deform it y, as w ell as to en sure th at th e p at ien t does n ot h ave con com it an t cer vical sten osis.

are n oted. Magn et ic reson an ce im aging (MRI) is rou t in ely obtain ed, part icularly in th e p resen ce of radicu lar p ain or n eu rologic sym ptom s, th ough it is n ot u n com m on for th ese older p at ien t s to be u n able to u n dergo an MRI for variou s reason s (e.g., p resen ce of a p acem aker). Also, in t h e revision set t ing, p reviou s sp in al in st r u m en t at ion m ay cau se sign i can t im age ar t ifact an d di cult y in MRI in terpret at ion . In su ch pat ien ts, com puted tom ography (CT) m yelogram is obtain ed in stead of MRI, an d provides in form at ion regarding sign i can t areas of sten osis. We also rout in ely obt ain a CT scan in adult spin al deform it y pat ien ts for p reoperat ive plan n ing, w h ich en ables evalu at ion of th e exten t of sp on dylot ic ch anges an d th e levels/ areas of autofusion , h elps determ in e th e feasibilit y and sizing of spinal xation points, and, in the revision set t ing, h elps analyze th e locat ion/ size of any p reviou s decom pression s, th e h ealing of previously fused regions, and the position of previous spinal instrum entation. In addition, at ou r in st it u t ion , th e CT scan is u sefu l in p atients w ith com plex deform it y (e.g., congenital/ segm en tat ion abn orm alit ies, sign i can t angu lar d efor m it y, p reviou s p ost su rgical ch anges) t h rough th e u se of a t h ree-d im en sion al acr ylic m od el for p reop erat ive p lan n in g, an d can also be u sed in t raop erat ively to id en t ify top ograp h ic lan d m arks an d gu id e p lacem en t of in st ru m en tat ion .

Radiographic Evaluation

Provocative Testing

Rad iograp h ic evalu at ion in clu d es fu ll-len gt h st an d in g an terop oster ior an d lateral rad io graph s of th e sp in e, w ith th e pat ien t’s kn ees an d h ips st raigh t , as w ell as supin e full-length lm s to p rovide in form at ion regarding any spon tan eous deform it y redu ct ion w ith gravit y forces rem oved. Cobb angle m easu rem en ts an d radiograp h ic determ in at ion of spin op elvic im balan ce provide crit ical in form at ion , as th e degree of th e cu r ve an d th e exten t of im balan ce can n ecessit ate discu ssion of op erat ive in terven t ion at t h e t im e of in it ial evalu at ion . For th e purpose of preoperat ive plan n ing, th ese m easurem ents are im perative. Rotatory sublu xat ion, the presence an d locat ion of osteophytosis, an d any an teroposterior or lateral listh esis

Select ive n er ve root /t ran sforam in al cor t icosteroid inject ion s can also be u sed to provide diagn ost ic in form at ion as w ell as a th erapeu t ic e ect.1 We use selective ner ve root/transforam in al inject ion s in p at ien t s w it h a com p on en t of radicu lar/low er ext rem it y pain to h elp determ in e th e speci c n er ve root causing sym p tom s, provide tem porar y relief prior to surgical t reat m en t , an d u lt im ately to localize th e levels in w h ich decom p ression m ay result in sym p tom relief. How ever, the utilit y of selective n erve root/transforam inal injections rem ains unclear, as th e lack of respon se to th e inject ion m ay be at t r ibu t able to t h e inject ion tech n iqu e or to poor pat ien t recall. We sp eci cally ask th e p at ien t abou t th e im m ediate relief of sym ptom s,

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Chapter 1 w ith in 5 to 10 m in u tes follow ing th e inject ion , as a criterion for a diagn ost ic inject ion (sym p tom s likely arising from th at level of inject ion ). In con t rast , an inject ion cau sing relief h ou rs or days later m ay be a fun ct ion of th e system ic an t i-in am m ator y e ect follow ing system ic absorpt ion of th e cor t icosteroid. Sim ilarly, in our experien ce, epidu ral cor t icosteroid inject ion s p rovide lim ited diagn ost ic in form at ion , as th e cor t icosteroid m edicat ion dist ributes th rough ou t m u lt ip le levels an d is also absorbed system ically. How ever, w e o er epidural corticosteroid injections for pat ients w ith signi cant cen t ral or lateral recess sten osis to poten t ially provide tem porar y relief of sym ptom s an d im prove physical fu n ct ion to en able p reoperat ive opt im izat ion of t n ess an d m obilit y. We do n ot rout in ely u se facet blocks or diskography for diagn ost ic assessm en t in th e adu lt spin al deform it y patien t.9 How ever, in patients w ith isolated axial back pain and arthritic facet changes on im aging studies, facet blocks m ay be utilized. Becau se t h e p ain gen erator can be located at any p oin t in t h e sp in e relat ive to t h e ap ex of th e cu r ve, facet blocks are p erform ed sequ en t ially at di eren t levels to isolate speci cally w h ich m ot ion segm en ts are causing th e pain , w ith subsequen t relief of sym ptom s after in ject ion /ablat ion .1

■ Nonoperative Management A trial of nonoperative m anagem ent is indicated for alm ost all pat ien ts presen t ing w ith adult spin al deform ities, par t icularly cur ves of less th an 30 degrees, less th an 2 m m of listh esis, and if the constellation of sym ptom s is relatively m inor. In contradistinction to the treatm ent algorithm of adolescent idiopathic scoliosis, there is n o role for bracing in adu lt spin al deform it y pat ien ts 3 because th e progression of th e cur ve is related to degen erat ive ch anges an d m echanical instabilit y, and not longitudinal grow th of t h e a xial skeleton . Th erefore, th e ben e t of tem porar y p ain relief is ou t w eigh ed by th e p oten t ial d econ dit ion ing of th e p arasp in al m u scles an d by skin com plicat ion s resu lt ing from brace t reat m en t in th is pat ien t pop u lat ion .3,10

How ever, in rare cases in w h ich th e p ain sou rce can n ot be ad equ ately localized , t h oracolu m bar or thoracolum bosacral orthoses (TLO/TLSO) m ay be con sidered for tem p orar y st abilizat ion an d pain relief.1 Low -im pact core st rength en ing p rogram s and physical th erapy are u t ilized to im p rove pat ien t reser ves as w ell as to st abilize th e su rrou n ding m u sculat ure to provide im proved su pport to th e spin al colu m n .3 Non steroidal anti-in am m ator y drugs (NSAIDs) are u sed to provide relief of axial an d, occasion ally, radicular pain and neurogenic claudication. We d o n ot rout in ely provide n arcot ic pain m edicat ion s for n on operat ive t reat m en t , an d pain m an agem en t specialists are con sulted to provide m u lt im odal th erapy w ith opt im izat ion of n onn arcotic pain m edication s (e.g., gabapentin, p regabalin ), alth ough som et im es sh ort periods of n arcot ics or p ain m edicat ion s m ay be n ecessar y. Also if operat ive t reat m en t is decided , w e en courage reduct ion or com plete discon tin u at ion of any n arcot ic pain m edicat ion s to avoid d i cult p ain m an agem en t in th e postoperat ive p eriod.

■ Surgical Indications In dication s for surger y in th ese patients include failure of nonoperative pain m anagem ent w ith signi cantly dim in ish ed qualit y of life/fun ct ion, or progression of deform it y/im balan ce, w ith correlat ion bet w een radiograp h ic an d clin ical n d in gs. As p reviou sly m en t ion ed , lu m bar cu r ves greater th an 30 degrees or w ith 6 m m of listh esis in any p lan e are con sidered for surger y because th e deform it y is at h igh risk for progression . Also, p at ien t s w ith an n u al deform it y p rogression greater th an 10 degrees or w ith in creasing listh esis (lateral, an terior, or posterior) greater than 3 m m , and w hose sym p tom s are progressively w orsen ing, are o ered surgical st abilizat ion . Ult im ately, th e decision to proceed w ith surgical m an agem en t is predicated on several m ajor factors, in clu ding th e pat ien t’s sym ptom atology, age, gen eral m edical h ealth , an d th e p at ien t ’s expect at ion s w ith regard to th e ou tcom e of such a sign i can t procedu re.1 If su rgical opt ion s are to be pu rsued ,

Preoperative Evaluation and Optim ization for Surgery m edical opt im izat ion of th e p at ien t an d detailed preoperat ive su rgical p lan n ing are absolu tely crit ical to prom ote th e su ccess of th e t reat m en t p lan .

■ Optimization for Surgery As previou sly m en t ion ed, t h e presen t ing age of pat ien ts w ith ad u lt spin al deform it ies is t yp ically bet w een 60 an d 70 years, an d system ic m edical com orbidities are com m on.1,3 Diabetes an d cardiac an d vascu lar disease can sign i can tly im pact th e surgical outcom e, part icu larly for a large recon st ru ct ive p rocedure, given th e poten t ial for con siderable in t raoperat ive blood loss an d overall su rgical t im e.1,3 Postop erat ively, elderly pat ien ts also requ ire longer reh abilit at ion , given th eir decreased card iopu lm on ar y reser ves.1 Th erefore, con su lt at ion w ith th e an esth esiologist an d t h e pat ien t’s p rim ar y care p rovid er is recom m en d ed to p u rsu e an in terdisciplin ar y approach for st rat ifying th e pat ien t’s p eriop erat ive m edical risks an d opt im izing m edical com orbidities prior to proceeding w ith su rger y. Halpin et al11 an d Sugrue et al12 described their high -risk protocol for patients un dergoing m ajor sp in al su rger y: p at ien t s are con sidered h igh risk if th e su rgeon an t icip ates longer th an 6 h ou rs of operat ive t im e, m ore th an six ver tebral levels w ill be in cluded, or th at th e procedu re w ill be staged, or if th e p at ien t p resen t s w ith signi cant m edical com orbidities. In these au th ors’ p rotocols, all h igh -r isk p at ien t s are evaluated by a h ospit alist an d an esthesiologist , an d various param eters are evaluated an d optim ized, including nutritional status, pulm onar y st at u s, cardiac an d ren al fu n ct ion , an d h ep at ic fu n ct ion .11,12 Th e case is th en discu ssed at a conference for h igh-risk spin e procedures th at is at ten ded by all m an aging p rovid ers before op erat ive clearan ce is granted.11 At our institution, the use of sim ilar goal-directed, evidence- based p rotocols to coord in ate t h e care of com p lex p at ien t s h as im p roved ou tcom es an d overall pat ien t sat isfact ion postop erat ively.12 Nu t rit ion al st at u s of th e adu lt spin al deform it y patient should be assessed preoperat ively.

Th is evalu at ion is t yp ically accom p lish ed by m easu r in g ser u m albu m in , p realbu m in , tot al p rotein , an d t ran sfer r in , w h ich p rovid e in form at ion regarding p at ien t p rotein reser ves.13 Pat ien t s w it h albu m in levels less t h an 3.5 g p er deciliter h ave been sh ow n to h ave a sign i can t ly h igh er r isk of com p licat ion s an d m ort alit y.14 Prealbum in levels below 11 m g per deciliter requ ire n u t rit ion al su p por t , an d becau se th ese levels are n ot a ected by hydrat ion st at u s, prealbu m in is th e recom m en ded m easurem ent tool for assessing nut ritional stat us.14 Any in su cien cy in th e n ut rit ion al state iden t i ed p reop erat ively sh ou ld be corrected p rior to su rger y, con su lt ing w it h a n u t r it ion ist if n ecessar y. Th e durat ion of n ut rit ion al supp or t is depen den t on th e severit y of th e m aln ou rish ed st ate an d th e pat ien t’s gen eral h ealth , but gen erally is 6 to 12 w eeks in order to at tain appropriate n ut rit ion al opt im izat ion , alth ough som e p at ien t s m ay requ ire a longer p er iod . Postoperat ive n u t rit ion is an im p or t an t asp ect for all p at ien t s follow ing sp in al d efor m it y su rger y, par t icu larly w ith com plex spin al recon st r u ct ive procedu res th at en t ail sign i can t m et abolic dem an d. Th ere is often a balan ce in t im ing for th e st ar t of n u t rit ion by m ou th an d ret u r n of bow el fu n ct ion (i.e., bow el sou n d , at u s, an d bow el m ovem en t ). St ar t ing an oral diet too early m ay resu lt in ileu s or obst ru ct ion , w h ich can sign i can tly in crease th e p atient’s pain and lim it early reh abilitat ion e orts, w h ereas u n n ecessar ily d elayin g th e st ar t of n u t rit ion m ay fail to m eet m et abolic requ irem en t s to opt im ize h ealing an d reh abilit at ion in th e p ostoperat ive p eriod . Th erefore, in cer t ain cases, p ar t icu larly follow ing com p lex sp in al reconstructive procedures, we at tem pt placem en t of a sm all bow el feeding t ube (SBFT) on postoperat ive day 1, w ith th e goal to begin t ube feeds by postoperat ive day 2. If th ere is di cult y in placing th e SBFT dist al to th e pylorus, w e begin paren teral n ut rit ion support th rough cen t ral access. We con t in ue sm all bow el t ube feed s or p aren teral n u t r it ion su p p or t u n t il th e pat ien t is tolerat ing adequate n ut rit ion by m ou th . Per iop erat ive blood m an agem en t is an asp ect of ad u lt sp in al d efor m it y su rger y t h at requires particular at tention. Low preoperative

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Chapter 1 h em oglobin con cen t rat ion an d in creased n um ber of levels fu sed h ave been sh ow n to be sign i can t r isk factors for allogen eic blood t ran sfu sion at th e t im e of surger y.15 Th e risks associated w ith t ran sfu sion are m yriad , an d in clu de ben ign febrile react ion , in fect iou s disease t ran sm ission , an d an aphylaxis. Th erefore, e or ts to reduce th e poten t ial n eed for t ran sfusion sh ou ld be u n der taken preop erat ively. In th e absen ce of any con t rain dicat ion s, w e recom m en d th at p at ien t s w ith ad u lt spin al deform it y take iron supplem en t s for 2 to 4 w eeks p rior to su rger y.14 Th ere is eviden ce to suggest th at preoperat ive recom bin an t h um an er yth ropoiet in (rh EPO) adm in ist rat ion in th e preop erat ive period can reduce th e t ran sfu sion rate w ith ou t in creasing com p licat ion s.16 How ever, at our in st it u t ion th is is n ot a com m on p ract ice given th e sign i can t expen se of rh EPO, an d, in ou r exp erien ce, it s lim ited e ect iven ess in th e adult spinal deform it y patient. We t ypically use oth er perioperat ive adjun ct ive m easures an d blood m an agem en t st rategies, w h ich in clu des th e use of in t raven ou s an t i brin olyt ics (e.g., t ran exam ic acid), cell saver, an d topical h em ost at ic agen ts (e.g., Surgi o, th rom bin), as w ell as p aying m et icu lou s at ten t ion to h em ost asis th rough out th e procedu re (in clu ding packing o segm en t s w ith rolled su rgical sp onges to redu ce blood loss w h en at ten t ion is focu sed on d ecom p ressing or in st rum en t ing m ore cep h alad or cau dad spin al levels). Open an terior su rgical deform it y correct ion for severe spin al deform it y h as been sh ow n to h ave d et rim en t al e ect s on p ostop erat ive pu lm on ar y fun ct ion , part icularly in older adu lt p at ien t s or pat ien t s w ith preexist ing lu ng disease.17,18 Alth ough p u lm on ar y fu n ct ion test ing is n ot rou t in ely p erform ed preop erat ively, w e t yp ically evalu ate p at ien t s w ith pu lm on ar y sym ptom s, di cu lt y w ith or poor en du ran ce w ith daily act ivit y an d am bu lat ion , or com plex or severe thoracic deform ity (often w ith planned th ree-colu m n osteotom y). We u se p u lm on ar y fu n ct ion test ing in th ese pat ien ts to st rat ify th e risk of poten tial postoperative pulm onar y com plicat ion s, an d w e obtain a p u lm on ar y sp ecialist con sult at ion for perioperat ive opt im izat ion . Also, p reoperat ive sm oking cessat ion is im perat ive for at least 8 w eeks p rior to su rger y.

Typ ically, m ajor d efor m it y cor rect ion an d fu sion h as been accom p lish ed via com bin ed an terior/posterior approach es; th e an terior release w ith fu sion is ach ieved via a th oracotom y or th oracoabdom in al approach , follow ed by posterior in st ru m en tat ion , w h ich provides im proved fu sion rates an d bet ter overall correct ion .19 How ever, it is post ulated th at disrupt ion of t h e t h oracic cage d u r in g t h e an ter ior ap proach leads to inju r y to th e resp irator y m ech an ism .18 Becau se of th is th eor y, th ere h as been in terest in p osterior-on ly m an agem en t of severe deform it ies (e.g., via th ree-colu m n osteot om ies such as pedicle subst ract ion osteotom y [PSO] or vertebral colu m n resect ion [VCR]) an d in t h e th eoret ical ben e t s of obviat ing th e an terior approach on pulm on ar y fun ct ion . Th ere is som e eviden ce th at p osterior-on ly su rger y can ach ieve sim ilar postop erat ive radiograp h ic outcom es 19 ; how ever, patien ts w ith such severe deform it ies often p resen t w ith ch ron ic rest rict ive lu ng disease, w it h m in im al p oten t ial for im p rovem en t in lu n g fu n ct ion d esp ite cor rect ion of t h e t h oracic d efor m it y, an d a recen t st u dy fou n d th at , in adu lt p at ien t s, u t ilizat ion of VCR for severe d efor m it y cor rect ion d id n ot im p rove p ostop erat ive p u lm on ar y fu n ct ion .18 Preop erat ive p u lm on ar y fu n ct ion test in g, t h erefore, m ay be w or th w h ile in pat ien t s w ith sign i can t th oracic deform it ies an d baselin e p ulm on ar y disease to est ablish poten t ial reser ves. Th us, it is im port an t to cou n sel older p at ien ts w ith m ore severe deform it ies th at despite th e correct ion a orded by th e surger y, w h ich m ay requ ire exten sive osteotom ies, p u lm on ary fu n ct ion m ay n ot im prove sign i can tly p ostoperat ively.18 Hyp ovit am in osis D, alt h ough ext rem ely com m on , is often m issed in t h e p reop erat ive set t ing, d esp ite t h e p oten t ially ser iou s com p licat ion s ar ising from t h is de cien cy. It is estim ated th at m ore th an h alf of all gen eral m edicin e inpat ien t s are de cien t in vit am in D, th ough th e p revalen ce in pat ien t s u n d ergoing spine surger y rem ain s largely un explored.20 A recen t st udy from a single in st it u t ion fou n d an overall vitam in D de cien cy rate of 57% in pat ien t s un dergoing spin al surger y of any kind, an d th e rate for pat ien ts w ith diagn osed spin al d eform it y w as 18%; th is relat ively low preva-

Preoperative Evaluation and Optim ization for Surgery len ce is likely at t ribu table to an in creased rate of vit am in D supplem en tat ion in th is coh or t .20 It is th us im por tan t to con sider th is diagn osis an d recom m en d adequate vit am in D in take for pat ien ts w ith diagn osed spin al deform it y, especially preop erat ively, as calcium m etabolism is ext rem ely im p or t an t in t h e p reven t ion of osteoporosis. Alon g w it h hyp ovit am in osis D, osteop oro sis is also ver y com m on in th is p at ien t p opu lat ion . Th e m an agem en t of th is seriou s disease requires th e coop erat ion of a m u lt idiscip lin ar y team . Post m en op au sal w om en are at a h igh r isk for d evelop m en t an d p rogression of osteop orosis, w h ich can lead to fragilit y fract u res an d in creased m or t alit y; h ow ever, older m en m ay also p resen t w it h osteop orosis, an d any clin ical su sp icion sh ou ld p rom pt an in it ial w orkup. Th e World Health Organ ization (W HO) recom m ends that all peri- and postm enopausal w om en un dergo screen ing for low bon e m in eral den sit y (BMD),21 an d du al-en ergy X-ray absorpt iom et r y (DEXA) is th e gold stan dard for assessm en t of BMD. We obt ain DEXA BMD m easu rem en t s of t h e lu m bar sp in e an d h ip s for all p reop erat ive p at ien t s, regard less of age or gen d er, to id en t ify osteop orot ic p at ien t s w h o m ay require opt im izat ion /t reat m en t w ith con su lt at ion of an en docrin ologist or p rim ar y care provid er p rior to su rger y. Post m en op ausal w om en diagn osed w ith osteop orosis sh ou ld also receive 1,500 m g calciu m an d 400 IU vit am in D daily. There also exist m edical m odalities for opt im izat ion of BMD, in cluding bisph osph on ates, parathyroid h orm on e (teriparat ide), est rogen m odu lators or h orm on e rep lacem en t , an d calciton in . Th e u se of th ese m edicat ion s sh ou ld be m on itored in con su ltat ion w ith th e pat ien t’s en docrin ologist or p rim ar y care provider. Iden t ifying p at ien t s w ith osteop orosis prior to su rger y facilitates t reat m en t an d opt im izat ion of th eir BMD, an d can im p rove su rgical outcom es by optim izing th e xation strength of th e surgical in st rum en tat ion an d ult im ately im prove bon e h ealing/fu sion . Card iop u lm on ar y, n u t r it ion al, an d bon equ alit y assessm en t s are vit al in t h is p at ien t pop u lat ion . Com orbidit ies are in t u it ively m ore com m on in th e adu lt deform it y p op u lat ion w h en com pared w ith th e adolescen t idiopath ic

scoliosis p opu lat ion , an d th e presen ce an d severit y of t h ese com orbidit ies gu ide th e in it ial m an agem en t of th e deform it y. Alth ough th ere h as been som e eviden ce th at osteopen ia an d osteoporosis do n ot play a sign i can t role in th e p rogression of adult sp in al deform it y,3 in pat ien ts elect ing to proceed w ith su rgical correct ion of scoliosis th e presen ce of osteoporosis can a ect th e abilit y to obt ain p u rch ase in th e bony sp in e. In pat ien ts over 50 years of age un dergoing sp in e su rger y of any t ype, th e inciden ce of osteoporosis h as been repor ted to be 14.5% for m en an d 51.3% for w om en .22 In deed, osteoporosis is associated w ith rep or ted fu sion rates as low as 56%, as w ell as iat rogen ic in st abilit y an d fract u re follow ing su rger y.23 Su rveys h ave fou n d t h at m ost or t h op ed ic sp in e su rgeon s feel u n com for t able m an aging th e t reat m en t of osteoporosis after it h as been diagn osed 24 ; th erefore, prom pt referral to p rim ar y care providers or en docrin e specialists for par t ial or com plete m an agem en t of osteop orosis prior to any plan n ed su rgical proced ure is recom m en ded. Lastly, psych osocial factors m u st be con sidered. Ment al h ealth issues are com m on in th e older adu lt pop u lat ion , an d th e presen ce of depression, anxiet y, psychosis, or other prem orbid p sych ological con d it ion s can adversely a ect su rgical ou tcom es an d p at ien t p ercept ion of su rgical su ccess.11 Th ese factors can be m an aged by e ect ively u t ilizin g a team of social w orkers or case m an agers an d psych iat ric su p p ort , an d sh ou ld n ot be overlooked prior to u n d er t aking m ajor spin al deform it y surger y.

■ Preventing Complications Medical com p licat ion s su rrou n ding adu lt spin al deform it y surger y can range from m ild to ext rem ely severe, w ith an overall com p licat ion rate ranging from 40 to 86% in pat ien ts u n dergoing deform it y surger y.25 Th orough at ten t ion to th e p reoperat ive m edical opt im izat ion p rocess can redu ce th e in ciden ce of postop erat ive com plicat ion s, an d st rategies to m in im ize such com plicat ion s sh ould be judiciously em ployed. Th e m ost com m on m in or com plicat ion in th e

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Chapter 1 postop erat ive p eriod is u rin ar y t ract in fect ion (UTI), w ith a repor ted rate of 9%.25 UTIs can be preven ted pre- an d in t raoperat ively by app ropriate sterile tech n iqu e du ring in ser t ion of th e cat h eter, u n rest ricted cath eter drain age, early rem oval, an d, in som e in stan ces, inst illat ion of ben ign bacteria in th e urin ar y t ract .25 Pu lm on ar y abn orm alit ies, in cluding atelect asis an d pn eu m on ia, are also ver y com m on in th is pop ulat ion . Th ese com plicat ion s can be preven ted in th e preoperat ive set t ing via sm oking cessat ion at least 8 w eeks prior to su rger y, as n oted above, as w ell as appropriate use of bron ch odilators or pu lm on ar y reh abilitat ion p rotocols.25 Of cou rse, m any oth er in t ra- an d p ostoperat ive st rategies exist to m inim ize the num erous com plicat ion s th at m ay occu r, bu t th ese are beyon d th e scope of th is ch apter.

■ Preoperative Planning Levels of Treatment Six levels of operat ive treatm en t w ere described by Silva an d Len ke 3 in 2010: I, decom pression alon e; II, decom p ression an d lim ited in st ru m en ted posterior spin al fusion ; III, decom pression an d lu m bar cur ve in st ru m en ted fu sion ; IV, decom pression w ith an terior an d posterior sp in al in st r u m en ted fu sion ; V, t h oracic in st r u m en t at ion an d fu sion exten sion ; an d VI, in clu sion of osteotom ies for speci c deform it ies. Each level represen t s a un ique approach to surgical m anagem ent of adult spinal deform it y, p redicated on t h e con stellat ion of sym ptom s repor ted by th e patien t , an d design ed to p rovide in depen den t sym ptom m an agem en t . For p at ien t s w ith n eurogen ic clau dicat ion alon e secondary to central canal stenosis, level I treatm en t , w h ich en tails lim ited decom pression , is app rop riate. Th ese pat ien t s often p resen t w ith m in im al back pain , an d radiograph ic an alysis m ay reveal sm all osteophytes w ith less th an 2 m m of su blu xat ion . Addit ion ally, th ese p at ien t s sh ou ld h ave n o cosm et ic or m ajor d eform it y com plain t s, and th e coron al an d sagit tal balan ce m u st be w ith in reason , as isolated cen t ral decom pression in th e presen ce of cur ves greater th an 30 degrees (or w ith kyph osis) can

lead to w orsen ing of th e d eform it y.3 A relat ively large series fou n d th at coron al im balan ce greater th an 4 cm cor related w ith decreased overall p at ien t-related ou tcom e scores on th e Scoliosis Research Societ y-22 (SRS-22) scale an d th e Osw est r y Disabilit y In dex (ODI),26 an d thus these param eters are extrem ely im portant in th e surgical decision - m aking p rocess. How ever, for th e relat ively w ell-balan ced patien t w ith m ore th an 2 m m of sublu xat ion , th e addit ion of p osterior in st ru m en tat ion at th e level of th e decom p ression im p roves st abilit y an d con st it u tes level II of t reat m en t . If su ch pat ien t s also h ave com plain t s of sign i can t lum bar pain associated w ith th e lum bar deform it y greater th an 30 degrees, bu t m ain t ain global sagit t al and coronal alignm ent, the entire lum bar cur ve m u st be in clu ded in th e in st ru m en ted region , w h ich con st it utes level III of t reat m en t .3 Tran sforam in al lu m bar in terbody fu sion (TLIF) m ay also be u t ilized as an adju n ct w h en fu sing to the sacrum to im prove xation and fusion at the t ran sit ion al lum bosacral jun ct ion .3 Loss of lum bar lordosis, often associated w ith at-back syndrom e in adult deform it y pat ien t s, is often m an aged via an an terior fu sion approach . Ut ilizing an terior fusion in addit ion to posterior xat ion con st it u tes level IV an d provides both load sh aring to redu ce p osterior st rain an d addit ion al ceph alocau dad foram in al decom p ression .3 In addit ion to th e aforem en t ion ed criteria, pat ien t s w ith addit ion al sagittal im balan ce can be m an aged by expan ding the fusion proxim al to the thoracolum bar junct ion , w h ich con st it u tes level V of t reat m en t .3 It is also im port an t th at an terior osteophytes be m inim al, and signi cant thoracic kyphosis cont rain dicates th is t reat m en t ap proach .3 On ce sign i can t sagit t al or coron al im balan ce h as d evelop ed , sp in al fu sion w it h ou t adju st m en t of global align m en t w ill be in su cien t to control sym ptom s. A recent retrospect ive st udy exam in ing th e role of preoperat ive coron al an d sagit tal balan ce fou n d th at postop erat ive correct ion of sagit t al balan ce w as th e st rongest predictor of clinical outcom es, w hereas another st udy h as suggested th at severe preoperat ive coron al im balan ce predict s w orse fun ction al recover y.7,26 Historically, pat ien ts w ith severe, rigid spinal deform ities have been m anaged w ith com bined anterior/posterior approaches; how -

Preoperative Evaluation and Optim ization for Surgery ever, th ere h as been in creased in terest in th e u se of com p lex th ree-colu m n osteotom ies to en able an all posterior approach, how ever interest in th e use of com plex three-colum n osteotom ies to en able an all p osterior app roach ; t h e u se of t h ese osteotom ies con st it u tes Level VI of su rgical m an agem en t . Th ese com p lex th reecolum n osteotom ies require h ighly experien ced surgeons and a specialized operating room team to en sure opt im al outcom es an d th e h igh est level of safet y, an d even w ith th is exp er t ise th ere is st ill a 30 to 40% rate of com p licat ion s follow ing th ese procedu res.17

■ Chapter Summary Pat ien t s w ith adu lt sp in al deform it y rep resen t som e of th e m ost com plex su rgical can didates in th e popu lat ion , an d est im ates suggest th at th e n u m ber of p at ien t s elect in g to u n d ergo su rgical cor rect ion w ill con t in u e to in crease. Adu lt scoliosis com prises a diverse spect rum of disease, w ith m u lt ip le p oten t ial et iologies an d n at ural h istories, an d as such th ere is n o on e single app roach to m an agem en t th at can be applied to all adult deform it y pat ien t s. Radiograph ic, clin ical, an d subject ive n dings m u st be assessed p reop erat ively by a m u lt id iscip lin ar y team . Becau se th ese pat ien ts t ypically p resen t after th e sixt h d ecad e of life, w it h m u lt ip le associated m edical com orbidit ies, th e spin e surgeon m ust be aw are of th e poten t ial for sign i can t risk exposure in th e perioperat ive set t ing. A m u lt idiscip lin ar y ap p roach to preop erat ive evalu at ion m u st be em p loyed , an d th e pat ien t’s prim ar y care provider, in tern ist , en docrin ologist , an d cardiologist sh ould be act ively engaged in determ in ing if th e pat ien t is ap propriate for su rger y an d in p rep aring th e pat ien t for th e p rocedu re. If th e pat ien t is not currently being evaluated for m ajor m edical con dit ion s com m on to th is p opu lat ion , su ch as rest rict ive lu ng disease or osteoporosis, th e sp in e su rgeon m ay be th e rst p rovider to initiate assessm ent and recom m end treatm ent. Th e com plexit y of th e th ree-dim en sion al path oan atom y an d associated biom ech an ics th at can sign i can tly a ect p ostop erat ive ou tcom es m u st be u n derstood an d resp ected, an d th e

preop erat ive evalu at ion an d opt im izat ion for su rger y p rocess m u st be t ailored to each in d ivid u al p at ien t . W it h ap p rop riate p at ien t selection, understanding of all treatm ent options an d d ecision algor it h m s, as w ell as u n d erst an d in g t h e im p or t an ce of a team ap p roach to perioperat ive m edical m an agem en t , spin e su rgeon s can exp ect good resu lts for th eir pat ien t s u n dergoing su rgical t reat m en t for adu lt spin al deform it y.

Pearls Back pain is the most com mon complaint in adult spinal deform it y patients. If claudication symptoms are present in addition to axial pain com plaint s, lateralit y of the pain provides guidance for potential decompression and likely instrumented fusion. The rigidit y of the curve can be assessed both clinically and radiographically, and a ects overall outcomes of nonoperative and subsequent operative intervention. Full-length standing anteroposterior and lateral radiographs of the spine are essential, and supine full-length lm s provide information regarding any spontaneous deformit y reduction related to gravit y. Indications for surgery in these patients include failure of nonoperative pain management, as well as correlation bet ween radiographic and clinical ndings. Consultation with the anesthesiologist and the patient’s primary care provider is recomm ended to ensure an multidisciplinary approach for stratifying the patient’s perioperative medical risks and optimizing medical comorbidities prior to proceeding with surgery Preoperative pulm onary function should be evaluated, as increased im pairm ent or m inim al im provem ent in pulm onary function can be expected postoperatively, and patients should be informed about this m at ter. Hypovitam inosis D and osteoporosis are extrem ely com m on in this patient population, and, given the signi cant detrimental e ect on fusion rates and potentially overall clinical outcomes, should be managed in consultation with an endocrinologist. Operative candidates can be classi ed based on severit y and t ype of their symptoms, as well as preoperative radiographic ndings. Consideration should be given to posterior-only deform it y correction techniques, which m ay reduce morbidit y associated with the anterior thoracotomy or thoracoabdom inal approaches.

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Chapter 1 Pitfalls Bracing is not routinely utilized in adult spinal deformit y patients and m ay result in deconditioning and skin complications. Failure to identify and evaluate osteoporosis and subsequently failing to optimize BMD may result in suboptimal xation and construct/fusion failure. Patients may ex their knees and hips, with subsequent pelvic retroversion, to compensate for xed sagit tal imbalance, and the surgeon should ensure that radiographs are obtained without these compensatory mechanisms. Narcotic pain medications should not be routinely prescribed preoperatively, and patients with signi cant narcotic pain medication use preopera-

tively should be weaned to optim ize postoperative pain m anagem ent. Failure to identify preoperative nutritional de ciency m ay result in poor wound healing, di cult y with rehabilitation, and prolonged fusion healing. Complex three-column osteotomies require highly experienced spine surgeons and a specialized operating room team to ensure optim al outcom es and the highest level of safet y. Therefore, the spine surgeon should always consider every other option or technique to obtain realignment and optim ize balance (e.g., positioning, posterior soft tissue/ligam ent releases, facetectom ies, posterior colum n osteotomy) rather than use a threecolumn osteotomy.

Refere nces Five Must-Read Refe rences 1. Aebi M. Th e adult scoliosis. Eur Spin e J 2005;14:925– 948 Pu bMed 2. Mes n A, Len ke LG, Br idw ell KH, et al. Does p reop erat ive narcot ic use adversely a ect ou tcom es an d com plications after spin al deform it y surger y? A com parison of n on n arcot ic- w ith n arcot ic-u sing grou p s. Spin e J 2014;14:2819–2825 PubMed 3. Silva FE, Len ke LG. Ad u lt degen erat ive scoliosis: evalu at ion an d m an agem en t . Neu rosu rg Focu s 2010; 28:E1 Pu bMed 4. Mum m anen i PV, Sh a rey CI, Len ke LG, et al; Min im ally Invasive Surger y Sect ion of th e In tern at ion al Spin e St u dy Group. Th e m in im ally invasive spin al deform it y surger y algorith m : a reprodu cible rat ion al fram ew ork for d ecision m akin g in m in im ally in vasive sp in al d efor m it y su rger y. Neu rosu rg Focu s 2014;36:E6 Pu bMed 5. Sch w ab F, Dubey A, Gam ez L, et al. Adult scoliosis: prevalen ce, SF-36, an d n ut rit ion al param eters in an eld erly volu n teer p op u lat ion . Sp in e 2005;30:1082– 1085 Pu bMed 6. Sch w ab FJ, Haw kin son N, Lafage V, et al; In tern at ion al Spin e St u dy Group. Risk factors for m ajor perioperat ive com plicat ion s in adult spin al deform it y surger y: a m ult i-cen ter review of 953 consecu t ive pat ien t s. Eur Spin e J 2012;21:2603–2610 PubMed 7. Dau bs MD, Len ke LG, Bridw ell KH, et al. Does correct ion of p reop erat ive coron al im balan ce m ake a d i eren ce in ou tcom es of ad u lt p at ien t s w it h deform it y? Spin e 2013;38:476–483 Pu bMed 8. Acost a FL Jr, McClen don J Jr, O’Sh aughn essy BA, et al. Morbidit y an d m or t alit y after sp in al deform it y su rger y in p at ien t s 75 years an d old er: com p licat ion s an d p redict ive factors. J Neu rosu rg Sp in e 2011;15: 667–674 PubMed

9. Grubb SA, Lipscom b HJ, Suh PB. Result s of surgical t reat m en t of pain ful adult scoliosis. Sp in e 1994;19: 1619–1627 Pu bMed 10. van Dam BE. Non operat ive t reat m en t of adult scoliosis. Or thop Clin Nor th Am 1988;19:347–351 PubMed 11. Halpin RJ, Sugrue PA, Gould RW, et al. St andardizing care for h igh -risk pat ien t s in spin e surger y: th e North w estern h igh -risk spin e protocol. Spin e 2010;35: 2232–2238 Pu bMed 12. Sugrue PA, Halpin RJ, Koski TR. Treat m en t algorith m s and protocol pract ice in h igh -risk spin e surger y. Neurosurg Clin N Am 2013;24:219–230 PubMed 13. Klein JD, Hey LA, Yu CS, et al. Periop erat ive n u t r it ion an d p ostop erat ive com p licat ion s in p at ien t s u n d ergoin g sp in al su rger y. Sp in e 1996;21:2676– 2682 Pu bMed 14. Kelly MP, Hu SS. Nut rit ion and pain m anagem en t in th e adu lt spin al deform it y p at ien t . Scoliosis Research Societ y e-text . h t t p://etext .srs.org/. Accessed August 30, 2014 15. Nu t t all GA, Horlocker TT, San t rach PJ, Oliver WC Jr, Dekutoski MB, Br yan t S. Predictors of blood t ran sfu sion s in spin al inst rum en t at ion an d fusion surger y. Spin e 2000;25:596–601 Pu bMed 16. Sh apiro GS, Boach ie-Adjei O, Dh aw likar SH, Maier LS. Th e u se of Ep oet in alfa in com plex spin e d eform it y surger y. Spin e 2002;27:2067–2071 Pu bMed 17. Auerbach JD, Len ke LG, Bridw ell KH, et al. Major com p licat ion s an d com p ar ison bet w een 3-colu m n osteotomy techniques in 105 consecutive spinal deform it y procedures. Spine 2012;37:1198–1210 PubMed 18. Bum pass DB, Len ke LG, Bridw ell KH, et al. Pulm on ar y fun ct ion im provem en t after ver tebral colum n resect ion for severe spin al deform it y. Spine 2014;39:587– 595 PubMed

Preoperative Evaluation and Optim ization for Surgery 19. Good CR, Len ke LG, Bridw ell KH, et al. Can posterioronly surger y provide sim ilar radiographic and clinical result s as com bin ed an terior (th oracotom y/th oracoabdom in al)/p osterior ap p roach es for adu lt scoliosis? Spin e 2010;35:210–218 Pu bMed 20. Stoker GE, Buch ow ski JM, Bridw ell KH, Len ke LG, Riew KD, Zebala LP. Preop erat ive vit am in D st at u s of adult s un dergoing surgical spin al fusion . Sp in e 2013; 38:507–515 PubMed 21. Lan e JM, Nydick M. Osteoporosis: curren t m odes of prevent ion an d t reat m en t . J Am Acad Orth op Surg 1999;7:19–31 Pu bMed 22. Ch in DK, Park JY, Yoon YS, et al. Prevalen ce of osteoporosis in patien ts requiring spine surger y: in cidence an d signi cance of osteoporosis in spin e disease. Osteoporos In t 2007;18:1219–1224 Pu bMed

23. Park SB, Ch ung CK. St rategies of spin al fusion on osteoporot ic spin e. J Korean Neurosurg Soc 2011;49: 317–322 Pu bMed 24. Dipaola CP, Bible JE, Bisw as D, Dipaola M, Grauer JN, Rech t in e GR. Sur vey of spin e surgeons on at t it udes regarding osteoporosis an d osteom alacia screen ing and treatm ent for fract ures, fusion surger y, and pseudoar th rosis. Spin e J 2009;9:537–544 Pu bMed 25. Baron EM, Alber t TJ. Medical com plicat ion s of surgical t reat m en t of ad u lt sp in al d efor m it y an d h ow to avoid th em . Sp in e 2006;31(19, Su pp l):S106–S118 PubMed 26. Glassm an SD, Ber ven S, Bridw ell K, Horton W, Dim ar JR. Correlat ion of rad iograp h ic p aram eters an d clin ical sym ptom s in adult scoliosis. Spine 2005;30:682– 688 Pu bMed

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2 Decision Making in Adult Deformity Surgery: Decompression Versus Short or Long Fusion Kenneth M.C. Cheung and Jason P.Y. Cheung

■ Introduction Degen erat ive scoliosis m ost com m on ly a ect s th e lum bar spin e in th e elderly. It occu rs as a resu lt of facet an d disk degen erat ion , leading to in creased loads an d resu lt ing deform it y. Th e prevalen ce of adu lt scoliosis in th e elderly p op u lat ion m ay be as h igh as 68%,1 an d th is n u m ber w ill on ly in crease as p eop le live longer an d w ant to m aintain their activit y levels. Untreated scoliosis can lead to pain , spin al osteoar th rit is, w orsen ing deform it y, sp in al sten osis w ith rad iculopathy, coron al an d sagit tal im balan ce, associated m uscle fatigue, and psych ological effects from poor cosm esis and reduced m obilit y. Th e m an agem en t of adult deform it y is con t roversial, w ith a lack of h igh -qualit y eviden ce to gu ide t reat m en t , su ch as determ in ing th e best can didates for con ser vat ive versu s su rgical t reat m en t , an d th e best surgical procedures for sp eci c clin ical scen arios. Never th eless, patients tend to present w ith back or leg pain, and con cern s about deform it y progression n eed to be addressed. Thus, an understanding of the possible causes is im por tan t before appropriate recom m en dat ion s for t reat m en t can be m ade.

■ Diagnosis of Back Pain On e of t h e m ost com m on p resen t in g yet di cu lt- to-discern com p lain ts of degen erat ive

scoliosis is back p ain . Th e pain m ay be st at ic or m ech an ical, localized or region al, or associated w ith but tock or leg pain , an d th ere m ay even be n eu rologic sym ptom s. It is im p or t an t to elicit a thorough history docum enting the pain’s severit y, it s aggravat ing an d relieving factors, an d it s fu n ct ion al lim it at ion s th at a ect w ork or recreat ion or reduce th e pat ien t’s abilit y to w alk distan ces. Th is in form at ion h elp s elu cidate th e cause of th e pain , an d th us h elps in determ in ing th e app rop riate t reat m en t . Axial back p ain can be cau sed by degen erat ion of th e in ter vertebral disk (diskogen ic) or disk height loss leading to segm ental instabilit y (degen erat ive sp on dylolisth esis). Th ere cou ld also be single- or m u lt isegm en t facet join t degen erat ion . All th ese n dings are par t of th e degen erat ive cascad e as described by KirkaldyW illis et al.2 Th u s, a t h orough clin ical exam in at ion w ould in clude carefu l palpat ion of th e lu m bar spin e, its m u scu lat u re, an d th e sacroiliac join ts, to look for areas of local ten dern ess th at w ould h elp pinpoin t path ology. Addit ion al ch aracterist ic n dings in clu de th e presen ce of an “in stabilit y catch ” or th e pat ien t’s experien ce of a catch ing p ain in th e low er back w h ile r isin g from a for w ard -lean in g p ost u re, w h ich requ ires su pp or t ing t h eir w eigh t by p u t t ing th eir h an ds on th eir kn ees. Th e pat ien t m ay also h ave a “pain ful catch ,” in w h ich th e raised, st raigh ten ed leg is u n able to m ove dow n bu t su dden ly drops du e to a sh arp pain in th e low er back. Both sym ptom s could poin t to th e pres-

Decision Making in Adult Deformit y Surgery en ce of spin al in stabilit y, likely from a degen erat ive sp on dylolisth esis. Back pain can also result from post ural im balan ce in both th e coron al an d sagit t al plan es. Th is im balan ce is often referred to as th e “con e of econ om y” as discussed by Jean Dubousset .3 Th e con e is p rojected from th e feet u p , an d so th e t ru n k is on ly w ith in a n arrow range. Th is con cept relates to th e p ar t of th e con e w h ere the body can rem ain balanced w ith out extern al support an d using m inim al e ort . Th e m uscular e or t requ ired in an u p righ t p ost u re is m u ch greater w h en th e con e is exceed ed, an d correct ion sh ou ld be con sidered. Coron al im balan ce of th e sp in e can lead to t ru n cal t ran slat ion an d rib -on -p elvis im p ingem en t . Sagit t al p lan e d eform it ies in clu de di culties in standing upright, resulting in m uscular fat igue an d discom for t from com pen sat ing for th e global sagit t al kyp h osis. Th ese global deform it ies m ay fur th er st ress th e sacroiliac an d h ip join ts an d lead to but tock an d groin pain . Usu ally th e locat ion of th e p ain is qu ite accu rate in determ in ing th e problem at ic site, but th e sacroiliac an d h ip join t s are com m on sites of m isd iagn oses of back p ain an d sh ou ld be th orough ly assessed by clin ical exam in at ion . Sh ou lder or p elvic asym m et r y an d sh ou lder or rib p rom in en ce are clu es for coron al deform it ies. Alth ough a for w ard-lean ing post u re cou ld be related to m uscle fat igue caused by sagit tal im balan ce, it could also be due to a xed kyph ot ic d eform it y of th e sp in e it self or a resu lt of h ip exten sor w eakn ess. In addit ion , during th e gait assessm en t , pat ien t s m ay h ave w orsen ing kyp h ot ic p ost u re du e to m u scle decom pen sat ion associated w ith prolonged w alking. Rad iological assessm en t of cau ses of back p ain w ou ld requ ire fu ll-lengt h st an ding p osteroan ter ior an d lateral rad iograp h s of t h e spin e, w h ich m ust in clu de, at a m in im um , C7 to th e h ip join t s, but ideally w ould in clude C1 to th e h ip join t s, so th at balan ce param eters can be easily m easu red. Flexion an d exten sion view s are usefu l, an d in ou r exp erien ce, stan ding exion and prone traction radiographs show th e m axim u m displacem en t of a spon dylolisth esis an d it s m axim u m redu ct ion .4,5 Addition al m agnetic resonance im aging (MRI) of the lu m bar sp in e is n eed ed to assess n eu rologic

im pingem en t as w ell as to ru le ou t oth er causes of back p ain . Som et im es, becau se of t h e sever it y of t h e d efor m it y, a com p u ted tom ograp hy (CT) m yelogram cou ld be a u sefu l adju n ct to id en t ify t h e exact locat ion of n er ve root com p ression . Radiological instabilit y is com m only de ned by th e degree of slip (Fig. 2.1), an d th e ch ange in slip angle (Fig. 2.2) an d disk h eigh t (Fig. 2.3). Th ese rad iograp h ic feat u res can be fou n d on st an d in g lateral rad iograp h s (d egree of slip ) an d dyn am ic exion -exten sion lateral rad io grap h s (slip angle an d disk h eigh t). Oblique lm s can be t aken to look for a p ars defect . For m easu rem en t of th e degree of slip, a lin e is

Fig. 2.1 Measurement of the degree of slip. A line is dropped from the posterior border of the cranial vertebrae to the caudal vertebrae. The distance from this point to the posterior border of the caudal vertebrae is divided by the total vertebral body width of the caudal vertebrae. Grade 1 is de ned as 0 to 25%, grade 2 is ≥25 to 50%, grade 3 is ≥50 to 75%, and grade 4 is ≥75 to 100%.

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Fig. 2.2 Measurement of the slip angle. The angle is m ade by the superior end plate of the caudal vertebrae and the inferior end plate of the cranial vertebrae. The slip angle of a L5-S1 spondylolisthesis is m easured by a line perpendicular to the posterior aspect of sacrum and a line drawn along the inferior end of the end plate of L5.

Fig. 2.3 Measurement of the disk height. A line is dropped from the m idline inferior end plate of the cranial vertebrae to the upper end plate of the caudal vertebrae. The ratio bet ween this distance and the m idline vertebral height of the cranial vertebrae is compared on dynam ic views.

draw n from th e p osterior border of th e cran ial ver tebrae to th e cau dal ver tebrae. Th e dist an ce from th is poin t to th e p osterior border of th e cau dal ver tebrae is divided by th e tot al ver tebral body w idth of th e cau dal ver tebrae. Grade 1 is de n ed as 0 to 25%, grade 2 is ≥25 to 50%, grade 3 is ≥50 to 75%, and grade 4 is ≥75 to 100%. Sp on dyloptosis is de n ed as m ore th an 100% slip. A slip of greater th an 50% is u n stable an d associated w ith progression an d lum bosacral kyph osis. Th e slip angle of an L5-S1 sp on dylolisth esis is m easu red by a lin e draw n p erpen dicu lar to th e posterior aspect of th e sacru m an d a lin e draw n along th e in ferior en d of th e en d plate of L5. In th e cran ial segm en t s, th e slip angle is m ade by th e superior en d plate of th e

cau dal ver tebra an d t h e in fer ior en d p late of cran ial ver tebra. For m easu ring d isk h eigh t , a lin e is draw n from th e m idlin e in ferior en d plate of th e cran ial ver tebra to th e u p per en d plate of th e cau dal ver tebra. A rat io bet w een th is dist an ce an d th e m idlin e ver tebral h eigh t of t h e cran ial ver tebrae is com p ared on dyn am ic view s. In t h ese cases, fu sion su rger y is in d icated to p reven t p rogression of t h e in st abilit y, cor rect any segm en t al d efor m it y, an d t reat th e a xial back pain caused by spin al in st abilit y. Full-length stan ding coron al an d sagit tal radiograp h s are u sed for assessm en t of th e overall coron al an d sagit tal balan ce using th e cen ter sacral ver t ical lin e (Fig. 2.4) an d C7 p lu m blin e

Decision Making in Adult Deformit y Surgery (Fig. 2.5). Th e bisector of th e cen ter sacral vert ical lin e is also u sefu l for n ding th e p roxim al n eut ral ver tebra. Sagit t al balan ce is m easured by th e C7 sagit t al plum blin e, an d lum bar lordosis is u su ally m easu red from th e u pp er en d plate of T12 to th e en d p late of S1. Sh ou lder h eigh t , apical ver tebral t ran slat ion of th e th oracic and lum bar curves, curve m agnitudes, and exibilit y sh ou ld be d ocu m en ted . Com m on local deform it ies seen on radiograph s in clu d e an L2-L3 ap ex defor m it y, lateral list h esis or

Fig. 2.4 Measurement of central sacral vertical line. Using the top of the iliac crest to control for tilting, a vertical perpendicular line is drawn up from the center of S1. The proximal neutral vertebra can be bisected from this line, and in this gure it would be L2.

Fig. 2.5 Measurement of sagit tal C7 plumb line is done by dropping a vertical perpendicular line to the horizontal from the C7 vertebral body and comparing its horizontal position with the position of the posterosuperior corner of the S1 superior end plate. Sagit tal im balance is normally considered to be > 5 cm deviation from the S1 posterosuperior corner, and in this gure there is a positive sagit tal balance.

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rotator y sublu xat ion (Fig. 2.6), lu m bar hyp olordosis, an d sh or t reciprocat ing cur ves. Lateral listh esis or rot ator y su blu xat ion is m easu red by th e horizontal distance bet w een th e superolateral corn er of th e cau dal ver tebra an d th e inferolateral corner of cephalad vertebra. Bending radiograph s can di eren t iate st i cu r ves from exible cu r ves, bu t is m ore im p or tan t for deciding on th e in st ru m en tat ion levels du ring su rger y. MRI is u sefu l to assess d isk degen erat ion an d spin al sten osis. Deform it y correct ion is requ ired for th ese sym ptom s an d m ay requ ire m ore com p lex operat ion s su ch as osteotom ies an d long fu sion s.

to ver tebral rot ator y su blu xat ion , or reduct ion of th e in terpedicular distan ce on th e con cavit y of th e cu r ve. Th ese pat ien t s u sually develop burn ing or ach ing pain st ar t ing in th e bu t tock th at radiates dow n th e ap p rop riately involved derm atom e to th e low er leg. Clin ical iden t i cation of th e involved derm atom e provides a good clue to the likely nerve root a ected. This can then be con rm ed if there is corresponding weakness in the sam e m yotom e. Typically, im pingem ent of the L4 ner ve root leads to anterior shin num bness w ith an kle dorsi exion w eakness (tibialis an terior), an L5 n erve root involves th e p osterolateral calf an d foot dorsu m , w ith exten sor h allu cis longu s w eakn ess, an d an S1 n er ve root involves th e posterior calf an d sole, w ith w eakn ess of th e exor h allucis longu s. Neurogenic claudication com m only presents w ith in sidious on set of but tock, th igh , an d calf pain t riggered by w alking. Th e u su al disabilit y is th u s dim in ish ed w alking toleran ce. Vascu lar clau dicat ion is an im p or t an t di eren t ial diagn osis. Pat ien t s w ith vascular claudicat ion m ay also p resen t w it h d im in ish ed w alking toleran ce d u e to calf cram p ing on exer t ion or a sen sat ion of t igh t n ess t h at p roceed s from d ist al to proxim al. Th is con t rasts to n eurogen ic clau dicat ion w h ere discom for t w ith n u m bn ess proceeds from p roxim al to d ist al. Object ive sen sor y exam in at ion sh ou ld p inp oin t th e sp eci c derm atom e or suggest w h ich n er ve root is com p ressed. Motor w eakn ess u su ally suggest s a m ore long-stan ding n er ve com pression . Vascular exam ination should be perform ed, including obser vat ion for t rop h ic ch anges in th e skin an d n ails of th e low er lim bs an d dim in ish ed dist al p u lses, w h ich w ou ld suggest a vascu logen ic cau se for th e pain . Radiograp h ic assessm en t w as described above (see Diagn osis of Back Pain ).

■ Diagnosis of Leg Pain

■ Factors that May Lead to

Fig. 2.6 Lateral subluxation is m easured by the horizontal distance bet ween the superolateral corner of the caudal vertebra and the inferolateral corner of the cephalad vertebra.

The classic presentation of n erve root com pression is bu t tock p ain t h at radiates to th e low er ext rem it ies an d n eu rogen ic clau dicat ion . Radicu lar or leg p ain p oin ts to sp in al or foram in al sten osis cau sed by facet join t an d ligam en t u m avu m hyper t rophy, foram in al n arrow ing du e

Curve Progression, Hence the Need for Surgical Treatment In general, the issue of w heth er cur ves progress is debated in th e literat u re, an d th e rate of pro-

Decision Making in Adult Deformit y Surgery gression is h igh ly variable. Cu r ves m ay p rogress 1 to 6 degrees p er year (average 3 degrees per year).6,7 Risk factors for p rogression in clu de a prior h istor y of progression an d radiograph ic risk factors su ch as asym m et rical disk d egen erat ion , lateral disk w edging, an d osteophyte form at ion .8–10 Com paring th e t w o sides of a spin al segm en t , less th an 80% of lateral disk w edge an d m ore th an 5 m m of lateral osteophyte di eren ce m ay in dicate an u n st able segm ent.9 Progression h as been suggested to occur w ith Cobb angles greater th an 30 degrees, loss of lum bar lordosis, apical rot at ion larger th an Nash-Moe grade 2 (convex pedicle m igrates 25% of th e ver tebral body w idth an d th e con cave p edicle gradu ally disappears), lateral listh esis of 6 m m or m ore, or a p rom in en t or d eep ly seated L5 d isk (in relat ion sh ip to t h e in tercrest al lin e).11–14 Th e p resen ce of rot ator y su blu xat ion , lateral spon dylolisth esis, an d disk degen erat ion in th e u pp er lu m bar levels also suggests a risk of progressive deform it y.12 Due to spin e coup ling, rotator y deform it y of th e sp in e is related to th e develop m en t of lateral spon dylolisth esis. Th u s, ap ical ver tebral rotat ion m ay also predict scoliosis progression . Spinal segm en t s p roxim al to th e scoliosis sh are th e load to com pen sate for spin e im balan ce. With disk degen erat ion , th is com p en sator y m ech an ism fails, an d progressive deform it y occurs. Fusion su rger y is requ ired to p reven t cu r ve p rogression , an d th e length of fu sion is depen den t on th e presen ce of coron al or sagit tal im balan ce.

■ Management Man agem en t of adu lt deform it ies sh ou ld be tailored to each pat ien t becau se th e sym ptom atology is di eren t in ever y case. Treat m en t is dep en den t on th e experien ce of th e su rgeon , th e p at ien t ’s p referen ce, th e p at ien t ’s age an d fu n ct ion al stat u s, m agn it u de of d eform it y, th e rate of p rogression , an d th e presen ce of com orbidit ies. Som et im es th e cause of pain is di cult to di eren t iate based solely on clin ical an d radiological exam in at ion . In th ese cases, t ran sforam in al epidural inject ion s, select ive n er ve root blocks, and facet joint blocks are com m only u t ilized to iden t ify th e p ain gen erator.

Non op erat ive m an agem en t is u su ally reser ved for p at ien t s w ith m ild sym ptom s arising from sten osis, radicu lar or back p ain , cu r ve m agn it u de of less th an 30 degrees, lateral su b lu xat ion of less t h an 2 m m , an d reason able coron al an d sagit t al balan ce.14 Com m on in d icat ion s for su rger y in clu d e a xial back p ain , sym ptom at ic deform it y, n eu rologic sym ptom s, an d dissat isfact ion w ith appearan ce. Th e n al decision sh ou ld be a balan ce of th e m agn it u de of su rger y, th e qu alit y of life gain , an d th e risk of surgical com plicat ion s. Pat ien ts w ith severe deform it y m ay require m ajor surger y to achieve fu ll correct ion , an d th e risk of com plicat ion s w ill dram atically increase. Com plication rates of up to 80%have been reported in som e series.15,16 Conversely, decom pression on ly or lim ited fu sion m ay be su cien t to provide reason able an d last ing relief for pat ien t s. Th e follow ing sect ion s discu ss th e au th ors’ experien ce in su rgical decision m aking, ch oosing bet w een decom p ression on ly an d sh or t or long fu sion , an d th e pitfalls of m an aging adult deform it y.

■ Critical Factors in Decision

Making for Surgery Th e goal of su rger y for t h ese p at ien t s sh ou ld be to perform th e sm allest operat ion possible th at w ould h elp relieve th e sym ptom s an d preven t a recu rren ce. We n d it h elps to break dow n th e com p on en t s of p at ien t com p lain ts in order to m ake an app ropriate decision . 1. Leg pain a. Ner ve root com pression /spin al sten osis— local decom pression b. Degenerative spondylolisthesis—local decom pression ± fusion 2. Back p ain a. For local degen erat ion or in st abilit y— sh or t fu sion b. For exible or correct able sagit t al or coron al im balan ce—long fusion c. For st i or u n correct able sagit t al or coron al im balance—long fusion + osteotom ies 3. Progressive deform it y a. Long fusion to preven t progression , seldom w ou ld be p erform ed alon e in th e absen ce of sym ptom s above

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■ Surgical Decision Making Decompression Only Decom p ression alon e is in dicated for p at ien t s w it h n eu rogen ic clau d icat ion w it h ou t back p ain or a sym ptom at ic or p rogressive d eform it y. Decom p ression is u su ally in t h e for m of p osterior fen est rat ion or lam in ectom y, alth ough oth er ap p roach es, in clu ding an terior in direct decom p ression an d en doscop ic t ran sforam in al approach es, h ave been described. Each ap proach h as m erit an d w ou ld be depen den t on th e su rgeon’s exp erien ce. A detailed discussion of th eir relative m erits is beyon d the scope of th is ch apter. As a gen eral prin cip le, in th ose pat ien t s u n dergoing decom pression alon e, as m u ch facet join t an d as m any posterior ligam en tou s st ru ct u res as p ossible sh ou ld be preser ved to reduce th e risk of fut ure progression an d iat rogen ic in st abilit y. On e sh ou ld alw ays be prepared to carr y out a local fusion if m ore exten sive bon e resect ion is n ecessar y. Th is is n ot u n com m on as su ch in dividuals often h ave t igh t spin al can als, an d in ciden tal du rotom ies are n ot in frequ en t . If a w ide lam in ectom y is perform ed for th e repair, a local fu sion w ith pedicle screw xat ion m ay be advisable. Usual in dicat ion s for decom pression -on ly su rger y in clu de leg p ain w ith m in im al or n o back pain , Cobb angles of less th an 30 degrees, less th an 2 m m of lateral su blu xat ion , an d n orm al coron al an d sagit t al balan ce in dicated by th e cen ter sacral ver t ical lin e an d C7 p lu m b lin e.14 Desp ite com bin ed back an d leg sym p tom s th at m ay w arran t fusion , decom pression alon e m ay be in dicated for pat ien ts w ith sign i cantly h igh su rgical risk. Th is m ay be th e best opt ion for an elderly pat ien t w ith n eurogen ic clau dicat ion , a m ild d eform it y, an d p oor bon e qualit y. Pat ien ts u n dergoing d ecom p ression alon e sh ou ld alw ays be w arn ed of a risk of progression of th e deform it y th at m ay requ ire a fut u re fu sion procedu re.

Fusion Fu sion su rger y is in d icated for t h e t reat m en t of back p ain du e to d egen erat ive ch anges or in -

stabilit y, as w ell as to preven t progression of th e deform it y. It m ay be perform ed alon e or in com bin at ion w ith decom pression in pat ien t s w ith radicular sym ptom s. Sh or t fu sion m ay be u sefu l to st abilize cur ves w ith sign i can t apical rotat ion or w h en t ran slat ion or lateral listh esis is greater th an 3 m m .6,12,17,18 How ever, if th ere is sym ptom at ic coron al or sagit t al im balan ce, realign m en t an d long fu sion is advisable. Deter m in at ion of fu sion levels for ad u lt scoliosis is based on t h e sever it y of sp in al d efor m it y an d t h e global ap p earan ce an d degen erat ive ch anges of th e en t ire sp in op elvic axis. Th ere is n o u n iversal agreem en t on th e lengt h of fu sion an d th e select ion m eth od of th e en d ver tebrae for in st r u m en tat ion . Sh or t fu sion w ith in th e deform it y n ot exceeding th e en d ver tebrae aim s to stabilize th e spin al segm en ts w ith out correct ing th e w h ole deform it y. It s m ajor advan t age is the low er risk of com p licat ion s from t h e an est h esia or t h e su rger y; th u s it is in dicated in th ose w ith back pain bu t w ith ou t coron al or sagit tal im balan ce. Long fusion s or fusion s exten ding beyon d th e en d ver tebrae is u sefu l for correct ion of large cur vat ures w ith coron al or sagit tal im balan ce, but th is procedure n eeds to be balanced again st in creased com plicat ion rates. Typical p at ien t s w h o m ay be m an aged w ith sh or t fu sion s (Fig. 2.7) are th ose w ith sm aller Cobb angles (less th an 30 degrees) an d m in or rot ator y su blu xat ion (lateral su blu xat ion s of m ore th an 2 m m ).14 Back an d leg pain an d segm en tal in st abilit y cau sed by w ide decom pression s can all be t reated w ith sh or t fusion s. Lon g fu sion s (Fig. 2.8), w h ich gen erally m ean s fu sion to L5 or t h e sacr u m , an d to T10 or above, yield bet ter surgical correct ion of th e scoliosis an d restorat ion of lu m bar lordosis. Th ey are t ypically indicated for pat ien t s w h ose cu r ves are likely to p rogress, su ch as p at ien ts w ith Cobb angles greater than 45 degrees, m ore th an 2 m m of lateral sublu xat ion , an d coron al an d sagit t al im balan ce.14 Th e aim of th e long fusion is to ach ieve balan ce in both th e coron al and sagit tal planes, not absolute Cobb angle correct ion .19 Glassm an et al20 dem on st rated th at p osit ive sagit t al balan ce is th e single biggest p redictor of clin ical sym ptom s in adult deform it y an d takes priorit y over oth er param eters.

Decision Making in Adult Deformit y Surgery Th u s, long fu sion s sh ou ld alw ays be con sidered in p at ien t s w ith global coron al or sagit t al im balan ce to ach ieve bet ter fu n ct ion al ou tcom es. It sh ou ld be born e in m in d th at in st ru m en tat ion sh ould n ot en d at th e level of jun ct ion al kyp h osis or sp on dylolisth esis. Any level of severe rot ator y su blu xat ion sh ou ld be in clu ded w ith in th e fusion block. To balan ce th e spin e,

19

t h e m ost h or izon t al ver tebra sh ou ld be t h e u p p er in st r u m en ted ver tebra (UIV).21 In st r u m en t at ion sh ou ld n ot en d at a level w it h p osterior colu m n de cien cy, w ith listh esis in any direct ion , at a level of a rotated segm en t , w ith jun ct ion al kyph osis, at th e apex of th e deform it y in t h e coron al or sagit t al p lan e, or at a degen erated level. (text cont inues on page 23)

a

Fig. 2.7a–e A 71-year-old man with complaints of axial back pain and bilateral lower limb claudication. (a) The patient has degenerative scoliosis from L3 to L5, with a Cobb angle of 25 degrees. (b) L3–4 and L4–5 spondylolisthesis and spinal stenosis were noted. (continued on page 20)

b

20

Chapter 2

c

d

e

Fig. 2.7a–e (continued ) (c) The L5-S1 was well hydrated, and there was no oblique take-o . (d,e) Short fusion from L3 to L5 was performed with good correction of the segmental instabilit y.

21

Decision Making in Adult Deformit y Surgery

a

Fig. 2.8a–d A 58-year-old m an with axial back pain and lumbar hypolordosis. There is (a) an oblique L5-S1 with degenerative changes and (b) a positive sagit tal im balance. (continued on page 22)

b

22

Chapter 2

c

Fig. 2.8a–d (continued ) (c) The patient was treated with an L3 pedicle subtraction osteotomy and posterior spinal fusion from T10 to the sacrum with S1 and iliac instrumentation. (d) Good restoration of sagit tal balance is observed postoperatively.

d

Decision Making in Adult Deformit y Surgery

Upper Instrumented Vertebra for Long Fusions In gen eral, for long fusion s, th e au th ors’ preferen ce is to en d at T10 or above, becau se in st rum en t at ion an d fu sion s en ding at T12 to L1 h ave been show n to have a higher revision rate, likely related to th e hyperm obile th oracolu m bar region as it t ran sit ion s from an im m obile th oracic sp in e to a m obile lu m bar spin e. Th ere are also ch anges in facet orien tat ion from coron al to sagit t al an d ch anges in sagit t al align m en t from kyph osis to lordosis. Exten ding th e UIV to T10 (level w ith t rue ribs) or fu r th er p roxim ally can provide relat ive p rotect ion to th e adjacen t segm en t w ith th e in creased stabilit y p rovided by th e rib cage. Th e rib cage length en s th e t ran sverse dim en sion s of th e spin e an d gives th e th oracic spin e greater resist an ce to ben ding st resses in m u lt iple p lan es. T11 or T12 d oes not have costosternal articulation s; hence, these levels lack th e biom ech an ical advan tage of th e u pp er levels. In addit ion , oth er factors th at cou ld a ect long-term su r vival of th at segm en t n eed to be taken in to con siderat ion . Th ese factors in clude h ealthy adjacen t spin al segm en ts w ith n o degen erat ion or in st abilit y in any plan e, an d a UIV adjacen t to sp in al segm en t s w ith n orm al sagit tal, coron al, an d axial align m en t an d n earn eut ral rotat ion . Th e UIV sh ou ld lie w ith in th e “st able zon e” de n ed by th e cen ter sacral vert ical lin e, before su rger y, or cou ld be p laced in to th at zon e after su rger y. Cu rren tly, th ere is n o con sen su s st u dy available to recom m en d T10 in st r um en tat ion in all p at ien t s to im p rove long-ter m resu lt s. Disadvan t ages of t h e UIV above T10 in clu d e in creased risk of p er iop erat ive com p licat ion s, an d w ith longer in st rum en tat ion across th e th oracolu m bar sp in e th ere is also a greater risk of pseudar th rosis. Th u s, th e rat ion ale for stop ping at T10 m ay n ot be ap p licable in all cases. Im por tan t decision s on th e exten t of in st r um en t at ion an d fu sion sh ou ld depen d on th e posit ion of th e UIV in relat ion sh ip to th e global spin e. An exten sion to T5 or even h igh er w ould dep en d on th e abilit y of th e lu m bar su rger y to correct th e sagit t al im balan ce. With con t rol of m ore sp in al segm en t s, bet ter sagit t al balan ce m ay be ach ieved m ore easily.

Ult im ately, th e surgical procedure sh ould be tailored to each pat ien t’s n eeds an d based on th e goal of ach ieving a w ell-balan ced, st able, pain less, an d du rable spin e w ith th e few est n um ber of fused segm en t s w h ile reducing th e r isk of com p licat ion s associated w it h largescale operat ion s.

Low er Instrumented Vertebra for Long Fusions For the low er inst rum en ted vertebra (LIV), m ost long fu sion s w ill exten d to th e sacrop elvis or stop at L5. In adolescen t idiop ath ic scoliosis, it m ay be p ossible to stop at L3 or L4 in a lu m bar cur ve, but because of st ru ct ural ch anges an d a xed t ilt fou n d at th e cau dal sp in al segm en t s like L4-L5 in adu lt deform it y, stopp ing at a m ore cran ial segm en t is gen erally n ot advised. Stopp ing at L5 en ables reten t ion of th e lum bosacral m ot ion , avoidan ce of sacroiliac (SI) join t stress, decreased operative tim e and instrum entat ion com plicat ion s, an d a low er pseudar th rosis rate. Pelvic xat ion can also be avoided . On th e oth er h an d, th is p rocedu re places a lot of st ress at th e L5-S1 disk, being th e on ly residu al m obile segm en t , an d th e pat ien t n eeds to be w arn ed of fu t u re breakdow n an d th e n eed for su rger y to fu se th is segm en t . In gen eral, for m any p at ien t s, th e L5-S1 disk is already d egen erated, an d in su ch cases it is probably bet ter to fu se to th e sacru m . Preser vat ion of th e L5-S1 disk en ables som e p elvic m ot ion , w h ich m ay be im por t an t for som e fu n ct ion al dem an ds of pat ien ts, su ch as rid ing a bicycle. Fu sion to th e sacru m is requ ired for disk degen erat ion at L5-S1, spon dylolisth esis or spin al sten osis at th e sam e segm en t , as w ell as obliqu e take-o at L5-S1 or in fract ion al cu r ves greater th an 15 degrees.22 Balan cing is di cu lt w ith ou t fu sion d ow n to t h e sacr u m in cases of oblique t ake-o at L5-S1. In addit ion , th e foram en is sm aller on on e side, leading to u n ilateral L5 radicu lop athy. It is n ot u n com m on to see pat ien ts w ith foram in al, cen t ral, or lateral recess sten osis at L5-S1. If sten osis is p resen t at L5-S1 an d m ore exten sive decom pression is requ ired , fu sing d ow n to th e sacr u m is in evit able. Th e obviou s disadvan tages of fusion to the sacropelvis include in creased operat ive t im e

23

24

Chapter 2 an d m ore exten sive surgical dissect ion to reach th e sacru m . An terior colu m n su p por t m ay also be required to reduce th e rate of pseudar th rosis. Lost m ot ion at L5-S1 m ay also alter th e pat ien t’s gait . Osteotom ies m ay be requ ired if less t h an 30% d efor m it y correct ion can be obt ain ed on ben d ing rad iograp h s. Th is is n ot u n com m on because adu lt deform it ies are usually st i . To avoid overloading th e in st rum en t at ion at th e m et al–bon e in terface, releases an d rebalan cing w ou ld be required. Th ere are t w o t yp es of sagit tal im balan ce in adu lt deform it y. First , th e spin e is globally balan ced but a segm en t al port ion of sp in e is at or kyp h ot ic. Secon d , th ere is global an d segm en tal im balan ce. Coron al im balan ce can also be classi ed in to t w o t yp es w ith th e sh oulders an d pelvis t ilted in opposite direct ion s or w ith t ilt ing in th e sam e direct ion . Poster ior colu m n osteotom ies are t h e best ch oice for segm en t al im balan ce of th e sp in e. A prerequ isite w ould be m obile disk spaces to allow exten sion correct ion . If th e disks are already degen erated an d st i , an terior release is also required. If th e bon e stock is in adequate, an terior st ruct ural graft s can be u sed to im prove fu sion rates. For global im balan ce, both Sm ith -Petersen an d pedicle subt raction osteotom ies can be used. Typically, a Sm ith-Petersen osteotom y is in dicated if th e w eigh t-bearing lin e falls w ith in 3 cm of th e sacr u m , an d a p edicle su bt ract ion osteotom y is reser ved for cases w ith poor bon e stock, an d it can provide 30 degrees of lordot ic correct ion . In pat ien ts w ith com bin ed coron al an d sagit t al im balan ce, pedicle subt ract ion osteotom ies are a viable op t ion if th e sh ou lders an d p elvis are t ilted in th e sam e direct ion , but a vertebral colum n resect ion is th e bet ter opt ion if th e sh ou lders an d pelvis are t ilted in opp osite direct ion s. An ter ior p roced u res are requ ired on ly in r igid deform it ies th at are n ot p assively correctable w ith posterior in st rum en tat ion . Th ey are u su ally used on ly in com bin at ion w ith posterior inst rum en tat ion, as interbody fusion s alone m ay n ot be able to correct th e overall sagit t al align m en t .23 An terior spin al fu sion can fur th er correct lum bar hypokyph osis an d im balan ce, p rovide in direct decom p ression by foram in al

dist ract ion , p reven t p osterior in st r u m en tat ion failure by load sh aring, an d decrease th e rate of pseu dar th rosis, w h ich is especially com m on in sm okers, diabet ics, and osteoporot ic patien ts.14

■ Complications Ad u lt d eform it y su rger y is ch allenging, an d th ere are m any associated com p licat ion s. Repor ted com plicat ion rates reach 80% for adu lt deform it y, w ith u p to 58%of pat ien t s requ iring reoperat ion .15,16 Th ese degen erat ive con dit ion s usually occur in th e elderly w ith m ultiple com orbidities such as pulm onary and cardiac disease, osteoporosis, and nutritional de cien cy. Th ese con dit ion s sh ould be properly opt im ized prior to surger y to decrease perioperative risks. Any of th e above com orbidit ies m ay a ect th e t im ing of surger y as w ell as th e scale of su rgical correct ion . Deform it y correct ion can in directly decom p ress th e n eu ral st ruct ures by rod derot at ion , can t ilever reduct ion m an euvers, an d part icularly by in creasing vertebral disk h eigh t w ith an ter ior in terbody fu sion . Overdist ract ion on t h e con cave sid e m ay lead to loss of lu m bar lordosis. To reduce rigid cu r ves, p osterior colu m n osteotom ies at m ult iple levels are likely required to m obilize th e spin al segm en t s. Fusion s sh ou ld avoid stopping at a level of rot ator y su blu xat ion to p reven t aggravat ing th e sublu xat ion . With lim ited in st ru m en tat ion an d fusion , d egen erat ion m ay be accelerated in th e rem ain ing cur ve as a result of adjacen t segm en t d isease. Stop p ing t h e fu sion w it h in t h e d efor m it y m ay provoke th ese adjacen t segm en t p roblem s. Stopping th e fusion at th e th oracolu m bar ju n ct ion also leads to adjacen t segm en t d isease cran ial to th e segm en t of fu sion . Fusion to T10 or above m ay avoid th is. How ever, som e con sider adjacent segm en t degen erat ion un p reven t able in fusion su rger y as it could be du e to th e n at u ral age-related p rogression of a degen erat ive process coupled w ith th e post surgical e ect of spinal st i en ing created by fusion or in st r u m en t at ion procedu res.24,25

Decision Making in Adult Deformit y Surgery Proxim al adjacen t segm en t d egen erat ion is detected by p rogressive n ar row ing of d isk h eigh t , progressive decrease in lordosis or in crease in kyph osis, osteophyte form at ion , sclerosis of an adjacen t en d p late, or t ran slat ion in t h e coron al or sagit t al p lan es. Proxim al junct ion al problem s such as adjacen t segm en t degen erat ion , com p ression fract u re, or screw failure in th e UIV occurs m ore frequen tly w ith fu sion s en d ing at T11 to L2 as com p ared w ith th ose at T10 or above.26 For th e LIV, d ep en ding on fu sion to L5 or to th e sacru m , di eren t com p licat ion s m ay occu r, including L5-S1 disk degeneration, loss of curve an d balan ce correct ion , iliac screw im plan t problem s, an d p seu dar th rosis. If th e fu sion is stopp ed at L5 w h ere th ere is xed sagit t al im balan ce an d disk degen erat ion at L5-S1, th e rate of disk degen erat ion w ill fu r th er in crease, leading to loss of sagit tal pro le correct ion an d L5-S1 spondylolisthesis.22 In osteoporotic bone, fusion to L5 h as a h igh risk of xat ion failu re, as th e L5 pedicles are m ostly can cellou s an d th ere are t rajector y problem s in obt ain ing a m edial angle for p lacing th e pedicle screw s. Failu re of L5 screw s w ith loosen ing leads to kyph osis or hyp olordosis of th e L4-L5 segm en t . L4-L5 kyp h osis m ay be tolerated in a sh or t fu sion , bu t w ith longer fusion s th e degree of sagit t al im balan ce becom es an issu e. Fusions to the sacrum should be reserved for L5-S1 spondylolisthesis, stenosis, oblique takeo , m oderate or severe L5-S1 degeneration, and p rior lam in ectom y. Problem s w ith long fu sion s to the sacrum in clude h igher com plicat ion rates d u e to a large-scale op erat ion , r isk of sacroiliac join t degen erat ion , altered gait m ech an ics and in creased pseudarthrosis. Instrum en tation com plicat ion s for th ese long fusion s in clude breakage an d back-ou t or loosen ing of screw s. To avoid th is, S1 screw s sh ou ld be bicor t ical th rough th e prom on tor y an teriorly. S1 screw s sh ould also be directed m edially to avoid p en et rat in g t h e L5 n er ve root . Bon e graft in g an terior to L5-S1 an d iliac screw s m ay fu r th er p rotect th e S1 xat ion . To im prove th e L5-S1 xat ion , dist al h ooks, iliac screw s, an d in terbody cages for an terior colu m n su p p or t are also opt ion s. Hooks are an altern at ive xat ion

esp ecially in osteoporot ic bon e bu t m ay cau se sten ot ic p roblem s at L5-S1. Iliac screw s en t ail th e risk of p u llou t 27 an d are usually m ore prom in en t . Screw s sh ould be buried if possible, but , in th in pat ien ts, rem oval m ay be requ ired an d sh ou ld be d on e arou n d 2 years after xat ion . Tech n ically, iliac screw s are m ore di cult to in ser t w ith previous posterior iliac bon e h ar vest ing. Th ere is also a h igh er pseudar th rosis rate at L5-S1, but th is m ay be salvaged by revision surger y w ith an terior recon st r u ct ion an d iliac xat ion as w ell as using bon e m orph ogen et ic p rotein to im prove fusion rates. The low est pseudarthrosis rate of L5-S1 fusions is associated w ith com plete sacropelvic xation and surgery in patients younger th an 55 years of age.28

■ Chapter Summary In adult deform it y, th ere is di cu lt y in m atch ing a patient’s sym ptom s and concerns w ith the su rgical p lan . Clin ician s m u st w eigh poten t ial gains and risks, and all surgical decisions should be in dividually tailored to th e pat ien t . Com orbidit ies sh ould be addressed prior to surger y to avoid perioperat ive com plicat ion s. Usually, th e su rgical opt ion s in clu de decom pression alon e, decom p ression w ith lim ited ar th rodesis, an d deform it y correct ion w ith long fu sion (Table 2.1). Decom p ression su rger y is reser ved for p at ien t s w ith leg p ain bu t m in im al or n o back pain, scoliosis Cobb angles less than 30 degrees, less th an 2 m m of su blu xa t ion , n o th oracic hyperkyph osis, an d acceptable coron al an d sagittal balan ce, or if th ey h ave a poor prem orbid st ate. For sh or t fu sion s, p at ien t s sh ou ld h ave scoliosis Cobb angles less th an 30 degrees, segm en t al in stabilit y (m ore th an 2 m m of lateral su blu xat ion ), back an d leg pain , n o sign i can t im balan ce issues, an d, if destabilizing, decom pression is requ ired for adequ ate relief of sp in al sten osis an d n er ve root com pression . Long fu sion s are reser ved for scoliosis Cobb angles greater than 45 degrees, m ore than 2 m m of subluxation, and coronal and sagittal im balance. To avoid com plications related to instrum en t at ion ,

25

26

Chapter 2 Table 2.1 Decompression Surgery Only Versus Short Fusion Versus Long Fusion Symptom or Condition

Decompression Only

Short Fusion

Long Fusion

Back and leg pain

Back and leg pain

Cobb angle < 30 degrees

Cobb angle > 30 degrees

Stabilit y

Radicular pain, minimal or no back pain Cobb angle < 30 degrees < 2 mm Acceptable coronal and sagit tal balance Stable motion segm ent

> 2 mm Global coronal and sagit tal imbalance Segmental and regional kyphosis

Operated levels

Stenotic levels only

Lim itations

Cannot address global balance, progressive deformit y, segmental instabilit y with wide decompression

< 2 mm Acceptable coronal and sagit tal balance Segm ental instabilit y, > 50% pars/facet excision for decompression Rotatory subluxation segments within fusion block, segmental instabilit y caused by wide decompression Higher surgical risk, cannot address global balance, adjacent level disease

Pain Scoliosis Subluxation Overall balance

UIV: T10 LIV: L5 if no degeneration, spondylolisthesis, stenosis or oblique take-o at L5-S1 Highest surgical risk, comprom ised xation with osteoporosis, high risk of pseudarthrosis, iliac screw prominence

Abbreviations: UIV, upper instrumented vertebra; LIV, lower instrum ented vertebra.

fu sion sh ou ld n ot en d at a level w ith ju n ct ion al kyph osis or sp on dylolisth esis, posterior colu m n de cien cy, a rotated segm en t , a level at th e ap ex of th e deform it y, or a degen erated level. Levels of rotator y su blu xat ion m u st be in clu ded w ith in th e fu sion block. For balan ce, the m ost horizon tal vertebra should be th e UIV. Exten sion of th e fu sion to T10 p rovides th e in creased st abilit y o ered by th e rib cage. Th e LIV at L5 is on ly feasible w ith a n orm al L5-S1 disk, an d n o sp on dylolisth esis or sp in al sten osis or obliqu e take-o at L5-S1. Fu sion s to th e sacru m sh ould be avoided if possible to avoid iliac screw im p lan t p roblem s, p seudarth rosis, sacroiliac joint problem s, and gait dist urban ces, but is usually m andator y for long-standing sagitt al an d or coron al im balan ces. Pearls All surgical decisions for degenerative scoliosis should be individually tailored to the patient. Decompression surgery is reserved for patients with leg pain, minim al or no back pain, scoliosis

Cobb angles less than 30 degrees, less than 2 mm of subluxation, no thoracic hyperkyphosis, acceptable coronal and sagit tal balance, or those with poor premorbid state. Short fusions are for scoliosis Cobb angles less than 30 degrees, segmental instabilit y, back and leg pain, and no signi cant imbalance issues. Long fusions are for scoliosis Cobb angles greater than 45 degrees, more than 2 mm of subluxation, and coronal and sagit tal im balance. Extension of the fusion to T10 provides increased stabilit y o ered by the rib cage. The m ost horizontal vertebra should be the UIV. Pitfalls Fusion should not end at a level with junctional kyphosis or spondylolisthesis, posterior colum n de ciency, a rotated segm ent, at the apex of the deform it y, or a degenerated level. Avoid the LIV ending at L5 with an abnorm al L5-S1 disk, spondylolisthesis, spinal stenosis, or oblique take-o at L5-S1. Fusions to the sacrum should be avoided if possible due to the increased risk of iliac screw implant problems, pseudarthrosis, sacroiliac joint problem s, and gait disturbances.

Decision Making in Adult Deformit y Surgery Refere nces Five Must-Read Refe rences 1. Schw ab F, Du bey A, Gam ez L, et al. Adult scoliosis: prevalen ce, SF-36, an d n u t rit ion al param eters in an elderly volu n teer p opu lat ion . Sp in e 2005;30:1082– 1085 PubMed 2. Kirkaldy-Willis W H, Wedge JH, Yong-Hing K, Reilly J. Path ology an d path ogen esis of lum bar spon dylosis an d sten osis. Sp in e 1978;3:319–328 Pu bMed 3. Du bou sset J. Th ree-d im en sion al an alysis of t h e scoliot ic deform it y. In : Wein steid S, ed. Th e Pediat ric Spine: Prin ciples and Practice. New York: Raven Press; 1994 4. Luk KD, Ch eung KMC. Lum bar spin al inst abilit y. Hong Kong Journ al of Or th opaedic Surger y 1998;2 5. Luk KD, Ch ow DH, Holm es A. Ver t ical in st abilit y in spondylolisthesis: a traction radiographic assessm ent tech n iqu e an d th e principle of m an agem en t . Spin e 2003;28:819–827 PubMed 6. Bradford DS, Tay BK, Hu SS. Adult scoliosis: surgical in dicat ion s, operat ive m anagem en t , com plicat ion s, an d outcom es. Spin e 1999;24:2617–2629 PubMed 7. Grubb SA, Lipscom b HJ, Coon rad RW. Degen erat ive adult onset scoliosis. Spine 1988;13:241–245 PubMed 8. Ben n er B, Eh ni G. Degenerat ive lum bar scoliosis. Spin e 1979;4:548–552 PubMed 9. Jim bo S, Kobayash i T, Aon o K, At sut a Y, Mat sun o T. Epidem iology of degen erat ive lum bar scoliosis: a com m un it y-based coh or t st udy. Spin e 2012;37:1763– 1770 PubMed 10. Kobayash i T, At su t a Y, Takem it su M, Mat su n o T, Takeda N. A p rosp ect ive st u dy of d e n ovo scoliosis in a com m u n it y based coh or t . Sp in e 2006;31:178– 182 Pu bMed 11. Grubb SA, Lipscom b HJ. Diagn ost ic n dings in pain ful adult scoliosis. Spin e 1992;17:518–527 Pu bMed 12. Pritch et t JW, Bortel DT. Degen erat ive sym ptom at ic lum bar scoliosis. Spin e 1993;18:700–703 Pu bMed 13. Robin GC, Span Y, Stein berg R, Makin M, Men czel J. Scoliosis in t h e eld erly: a follow -u p st u dy. Sp in e 1982;7:355–359 PubMed 14. Silva FE, Len ke LG. Ad u lt degen erat ive scoliosis: evalu at ion an d m an agem en t . Neu rosu rg Focu s 2010; 28:E1 Pu bMed 15. Carreon LY, Pu n o RM, Dim ar JR II, Glassm an SD, Joh n son JR. Perioperat ive com plicat ions of posterior lum bar decom p ression an d ar th rod esis in older ad u lt s. J Bon e Join t Surg Am 2003;85-A:2089–2092 PubMed 16. Edw ards CC II, Bridw ell KH, Patel A, Rin ella AS, Berra A, Len ke LG. Long adu lt deform it y fu sion s to L5 an d

th e sacrum . A m atch ed coh or t analysis. Spin e 2004; 29:1996–2005 Pu bMed 17. Sapkas G, Efst ath iou P, Badekas AT, An toniadis A, Kyrat zoulis J, Meleteas E. Radiological param eters associated w ith th e evolu t ion of degen erat ive scoliosis. Bull Hosp Jt Dis 1996;55:40–45 PubMed 18. Tribus CB. Degen erat ive lum bar scoliosis: evaluat ion an d m an agem en t . J Am Acad Or th op Su rg 2003;11: 174–183 Pu bMed 19. Sim m on s ED. Surgical t reat m en t of pat ien t s w ith lu m bar spin al sten osis w ith associated scoliosis. Clin Or th op Relat Res 2001;384:45–53 PubMed 20. Glassm an SD, Ber ven S, Br idw ell K, Hor ton W, Dim ar JR. Correlation of radiograph ic param eters and clin ical sym ptom s in adult scoliosis. Spin e 2005;30: 682–688 PubMed 21. Sim m on s ED Jr, Sim m on s EH. Spin al sten osis w ith scoliosis. Spine 1992;17(6, Suppl):S117–S120 PubMed 22. Bridw ell KH. Select ion of in st rum en t at ion an d fu sion levels for scoliosis: w h ere to st art an d w h ere to stop. Invited su bm ission from th e Join t Sect ion Meet ing on Disord ers of th e Spin e an d Perip h eral Ner ves, March 2004. J Neurosurg Spin e 2004;1:1–8 Pu bMed 23. Ch o KJ, Suk SI, Park SR, et al. Sh or t fusion versus long fusion for degenerat ive lum bar scoliosis. Eur Spin e J 2008;17:650–656 PubMed 24. Gh iselli G, Wang JC, Bh at ia NN, Hsu W K, Daw son EG. Adjacen t segm en t degen erat ion in th e lum bar spin e. J Bon e Join t Su rg Am 2004;86-A:1497–1503 PubMed 25. Kum ar MN, Baklan ov A, Ch op in D. Correlat ion bet w een sagit t al plan e ch anges an d adjacen t segm en t d egen erat ion follow in g lu m bar sp in e fu sion . Eu r Spin e J 2001;10:314–319 Pu bMed 26. Sh u ebarger H, Suk SI, Mardjetko S. Debate: determ ining th e upper in st ru m en ted vertebra in th e m anagem en t of adu lt degen erat ive scoliosis: stopping at T10 versu s L1. Sp in e 2006;31(19, Su p p l):S185– S194 PubMed 27. Weist ro er JK, Perra JH, Lon stein JE, et al. Com plicat ion s in long fusion s to th e sacrum for adult scoliosis: m in im um ve-year an alysis of ft y pat ien t s. Sp in e 2008;33:1478–1483 Pu bMed 28. Kim YJ, Bridw ell KH, Len ke LG, Rh im S, Ch eh G. Pseudarth rosis in long adult spinal deform it y in st r um en t at ion an d fusion to th e sacru m : prevalen ce an d risk factor an alysis of 144 cases. Sp in e 2006;31:2329– 2336 PubMed

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3 The Use of Osteotomies for Rigid Spinal Deformities Stephen J. Lew is and Simon A. Harris

■ Introduction Th e u se of spin al osteotom ies in severe spin al deform it ies h as en abled correct ion s th at w ere n ot con sidered possible in th e past . With advan ced posterior-based tech n iqu es, excellen t correct ion s are ach ieved th rough a single ap proach , sh or ten ing th e du rat ion of su rger y an d reducing the need for m ultiple position changes du ring su rger y. Alth ough th e m ajorit y of correct ion s can be perform ed from th e p osterior d irect ion , select ive d eform it ies m ay requ ire com bin ed an terior procedu res. W it h t h e im p rovem en t in su rgical tech n iqu es an d n eu rom on itor in g m odalit ies, ob t ain ing correct ion s of severe spin al deform it ies is now both possible and reasonably safe.1 Thorough kn ow ledge of advan ced an atom y, carefu l preop erat ive plan n ing, an d sp ecialized in st ru m en tat ion an d im plan ts p rovide th e n ecessar y tools for su ccessfu l su rger y. Th is ch apter review s th e variou s osteotom ies, th e in dicat ion s for th eir u se, as w ell as th e m eth ods of m axim izing correct ion s an d m in im izing bot h sh or tan d long-term com plicat ion s.

■ Planning the Deformity

Correction Alth ough deciding w h eth er or n ot to operate is the rst m ain decision to be m ade, plann ing th e n er d et ails of th e p rocedu re w ill h elp en su re a

sm ooth er ow of th e surger y. Th e m ain plan n ing sh ou ld be don e preop erat ively, an d an algorith m for key decision s sh ou ld be establish ed preop erat ively an d discu ssed w ith th e p at ien t an d fam ily. For exam ple, if th e pat ien t does n ot w ish to assum e th e in creased risk associated w it h ach ievin g a m ore com p lete d efor m it y correct ion , it is im p or t an t to discu ss w h at can be ach ieved w ith lesser releases. Conversely, if correct ion is a key com p on en t of th e p at ien t ’s exp ect at ion s an d th e su rgical team can reliably achieve these goals safely, a three-colum n osteotom y can be perform ed if lesser osteotom ies are u n su ccessfu l.

Determining the Flexibility of the Deformity Using th e least risky proced u re to obt ain a correct ion is key to th e safe ou tcom e of deform it y surger y. If a sim ilar correct ion can be obt ain ed th rough m u lt ip le p osterior colu m n releases, a three-colum n osteotom y m ay not be necessary. Deter m in in g t h e exibilit y of t h e cu r ve can often be d i cu lt , an d in t raop erat ive adju stm ents m ay be required in cases w here the cur ve is m ore st i or less st i th an expected. Helpful clu es to cur ve exibilit y in clu de th e presen ce of w ide d isk spaces, disk sp aces th at open an d close on ben ding lm s, an d cur ve m agn it u d es th at decrease w h en th e p at ien t is in th e p ron e p osit ion or w ith t ract ion view s. If com p u ted tom ograp hy (CT) im aging dem on strates anterior fusions, either congenital or from

The Use of Osteotomies for Rigid Spinal Deformities previou s su rger y, th ese fu sion s w ill n ot correct w ith posterior releases, an d th ree-colum n osteotom ies w ill be required. In con t rast , good correct ion s can be ach ieved w ith p osterior colum n releases through previous posterior fusion m asses th at h ave n ot u n dergon e p reviou s an terior fusions. Proper preoperative w orkup w ith long-casset te an teroposterior (AP) an d lateral side ben ders, CT scan , an d m agn et ic reson an ce im aging (MRI) sh ou ld be don e preop erat ively, so t h at t h e best p ossible p reop erat ive p lan can be m ade. New er tech n ologies w ith th reedim ensional (3D) prin ters can provide surgeon s w ith preoperat ive m odels of th e spin e, to even bet ter p repare for th e u lt im ate p rocedu re.

Exposure Excellen t exp osu re is an essen t ial com p on en t of th e procedure. Severe deform it ies can m ake this m ore challenging; how ever, taking the tim e to obt ain th e n ecessar y exposure w ill greatly facilitate im plan t in ser t ion , an d gen erally im prove th e ow of th e p rocedu re. It is im p or tan t to iden t ify th e spin e levels, areas w ith previous d ecom p ression s, fu sion m asses, an d p reviou s im p lan t s. In cases of revision s, kn ow ledge of p reviou s sp in al in st r u m en t at ion w ill en su re

29

th at th e requ ired in st r u m en t s are available to facilitate im plan t rem oval.

Spinal Cord Blood Flow Th e blood ow to th e spin al cord en ters th e du ra th rough vessels th at t ravel w ith th e exiting n er ve root . Alth ough n er ve roots are com m on ly sacri ced in t h oracic-level osteotom ies, taking a n er ve root at th e level of th e ar ter y of Adam kiew icz could lead to sign i can t det rim en t to th e sp in al cord circu lat ion .2 Th is ar ter y h as variable an atom y, but is p resen t bet w een T8 an d L1 on th e left side in th e m ajorit y of p eople. W h en con sidering osteotom ies aroun d the thoracolum bar junction, protecting and saving th e n er ve roots m ay preser ve key sources of blood ow. For t h oracolu m bar t h ree-colu m n osteotom ies, p reop erat ive an giograp hy can be p erform ed to determ in e th e exact locat ion of th e ar ter y of Adam kiew icz. Th e ar ter y ru n s a ch aracterist ic in t radu ral “h airp in ” loop on im aging 3 (Fig. 3.1). Th e locat ion of th e ar ter y m ay in uen ce th e ch oice of level of th e osteotom y, an d th e surgeon m ay ch oose a level oth er th an th e apex if th e arter y is p resen t at th e ap ex. In juring th is vessel, especially in th e presen ce of

a

b

Fig. 3.1a,b Spot image (a) and inverse (b) shots of angiography of the left T11 segm ental artery showing the characteristic intradural hairpin loop (white arrow), representing the artery of Adam kiewicz. In this patient, the vessel enters the dura

through the left T11 foram en and forms the loop that extends up to T10. With the vessel arising t wo levels proximal to the apex, a vertebral column resection was perform ed at L1 without incident.

30

Chapter 3 hypoten sion , can lead to a loss of in t raoperat ive m otor evoked p oten t ial (MEP) m on itoring th at is often delayed from th e t im e of inju r y. With spin al cord in farct ion as on e of th e m ain risks of sp in al cord level osteotom ies, kn ow ledge of an d at ten t ion to th is ar ter y m ay h elp p reven t t h is d evast at ing com p licat ion , esp ecially in pat ien t s w ith p reviou s an terior p rocedu res, w h ere segm en t al vessels m ay h ave been ligated.

Fixation Ach ieving adequate an d stable xat ion is essen tial to obt ain ing an d m ain tain ing deform it y correct ion . Alth ough th e p edicle screw is th e m ain an ch or in th e m ajorit y of con st r u ct s, altern at ives such as h ooks, lam in ar screw s, fusion m ass screw s or h ooks, w ires, an d ban ds sh ou ld be con sidered w h en pedicle screw xat ion is n ot p ossible.4 Obtain ing adequate proxim al an ch ors is gen erally th e key determ in an t of successful con st ruct s in th oracic osteotom ies. Osteotom ies sh ou ld n ot be at tem pted un less solid proxim al an d distal xat ion is establish ed. Careful plan n ing from th e preoperat ive im ages w ill h elp to iden t ify an d select th e approp riate an ch or for each level. Du ring osteotom y closu re, variou s m eth ods can be u t ilized to protect th e m ain im plan t s. Tem porar y devices or im plan ts can be used to close th e osteotom ies, su ch as cen t ral rod con st r u ct s, sp ar in g t h e m ain screw s.5 Th e u se of p er iap ical red u ct ion screw s, t u bes, or ot h er exten ders on th e screw s, lin king of m ult iple an ch ors to th e rod before can t ilevering th e red uct ion , an d th e u se of a th ree- or four-rod technique w ith connectors can facilitate reduction of th e osteotom y an d correct ion of th e deform it ies w h ile p rotect ing th e m ain an ch ors.

Determining the Desired Correction Th e im aging should be carefully st udied to ident ify th e deform it y an d determ in e th e t ype an d m agn it ude of th e desired correct ion . Carefu l u n derst an ding of th e n orm al sagit t al align m ent, the pelvic param eters, and the m agnitude

of th e deform it y w ill h elp to iden t ify w h ich osteotom ies w ould be required to gain th e desired correct ion .6,7 For xed kyph ot ic deform it ies, correct ion w ill be ach ieved th rough an terior length en ing, posterior sh or ten ing, or a com bin at ion of both . For coron al defor m it ies, cor rect ion w ill be achieved th rough con cave length en ing, convex sh or ten ing, or a com bin at ion of both . For xed lordosis, correct ion can be ach ieved th rough an terior sh or ten ing, posterior length en ing, or a com bin at ion of both . For m u lt iplan ar deform it ies, it is im por t an t to iden t ify th e p rim ar y deform it y or deform it ies, an d tailor an osteotom y or com bin at ion of m an euvers to ach ieve th e desired correct ion . For exam p le, for a xed kyph ot ic scoliosis, a com bin at ion of p osterior sh or ten ing an d convex sh or ten ing cou ld be th e prim ar y m ode of correct ion . If a ver tebral colum n resect ion (VCR) w ere to be perform ed, a larger an ter ior cage p laced on th e con cavit y cou ld m a xim ize cor rect ion . For xed hyp erlordosis, a form al an terior release or resect ion cou ld be com bin ed w ith p osterior colu m n releases to ach ieve th e desired correct ion .8 Th e m agn it u d e of th e deform it y m u st be con sidered. Rough est im ates of p oten t ial correct ion th rough a single osteotom y in clud e 10 degrees of sagit tal or coron al p lan e correct ion th rough a single p osterior colu m n release, 30 to 35 degrees of sagit t al an d 10 to 15 degrees of coron al plan e th rough a single pedicle su bt ract ion osteotom y (PSO), an d 30 to 50 degrees of correct ion th rough a VCR in t h e coron al or sagit tal plan e.9,10 For a VCR, m ore correct ion w ill be achieved through a deform it y w ithout a previous fusion com pared w ith one that is previously fused, as correction w ill be ach ieved only through the osteotom y site and not through th e adjacen t segm en t s in cases of previou s fu sion m asses. Properly est im at ing th e desired correct ion relat ive to th e deform it y w ill h elp plan th e n um ber and t ypes of osteotom ies requ ired to ach ieve th e desired correct ion .11

Deciding the Level of the Osteotomy For p osterior colu m n releases (Sm ith Petersen , Pon te), m u lt ip le p er iap ical osteotom ies w ill

The Use of Osteotomies for Rigid Spinal Deformities h elp ach ieve a grad u al, m u lt ilevel cor rect ion for deform ities w ith m obile an terior colum n s. For th ree-colu m n osteotom ies (PSO, PSO varian ts, VCR), th e preferred ver tebra w ou ld be at th e ap ex of th e deform it y, n ot t ilted in th e coron al or sagit t al p lan es, an d w ou ld be ap p ro p r iate for proxim al an d distal xat ion . Oth er con siderat ion s in clu de th e locat ion of th e arter y of Adam kiew icz an d th e presen ce of pseudar th rosis in cases of revision s, in w h ich cases it w ou ld p referable be in clu de th e n on fused levels in th e osteotom y.

w om an w ith an kylosing sp on dylit is (Fig. 3.2). Preoperat ive im aging w ith long-casset te radiograp h s an d CT d em on st rated t h e au tofu sion of h er sp in e. Her ch ief com p lain t s are sagit t al im balan ce an d di cult y w ith for w ard gaze. Her pelvic in ciden ce m easu res 55 degrees, th e lu m bar lord osis 10 degrees, w ith a sacral slop e of 5 d egrees an d a p elvic t ilt of 50 d egrees. With th e desired lum bar lordosis being 10 degrees less th an th e p elvic in ciden ce, an d th e desired p elvic t ilt being less th an 25 degrees, sh e w ou ld requ ire ~ 35 degrees of lu m bar lordosis. This can best be ach ieved th rough a single lu m bar PSO. As for h er th oracic spin e, sh e h as sign i can t com p lain t s related to h er gaze. Her th oracic kyph osis from T5 to T12 m easu res 25 degrees, w h ich is w ith in th e n orm al range. Her T2-T5,

Planning an Osteotomy Pu t t ing all th e in form at ion togeth er w ill h elp to determ in e th e best opt ion for deform it y correct ion . A represen tat ive case is a 66-year-old

a

b

Fig. 3.2a–d Representative case of a 66-year-old wom an with ankylosing spondylitis as demonstrated on the preoperative standing posteroanterior radiograph (a) and the sagit tal CT reconstruction (b). Abnormal sagit tal alignm ent is characterized by a low sacral slope (SS), high pelvic tilt (PT) and insu cient lumbar lordosis (LL, T12-S1) for the given pelvic incidence (PI). To m aintain a balanced

c

d

relationship of the PI and LL, an L2 pedicle subtraction osteotomy (PSO) was performed. Forward gaze was improved with a T3 PSO to correct the proximal thoracic kyphotic deformit y. Stabilization of this correction was achieved with a C2 to pelvis construct as demonstrated on the standing postoperative long-casset te posteroanterior (c) and lateral (d) radiographs.

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Chapter 3 h ow ever, m easures 45 degrees, w h ich is greater th an th e 10 to 15 degrees exp ected for th is region . A single PSO in th is region w ould provide th e n ecessar y correct ion to im p rove h er gaze. Th is p at ien t u n der w en t a T3 an d an L2 PSOs w it h a C2-to -p elvis st abilizat ion t h rough a sin gle-stage procedure, addressing both of h er deform it ies an d p roviding h er w ith th e n ecessar y sagit t al balan ce.

Single Procedure or Staged Alth ough it m ay be preferable to com plete th e su rger y in on e stage, cer tain factors m ay n ecessit ate perform ing th e procedure in t w o or m ore st ages. Th ese factors in clu de excessive bleeding, long du rat ion of th e surger y, m edical com orbidit ies, an d di cu lt ies w ith n eu rom on itoring. Recogn izing th ese d i cu lt ies preop erat ively m ay h elp to elect ively plan perform ing th ese su rgeries over t w o sep arate days. Th e ben e t s of staging in clude m inim izing operat ive team fat igu e, p ost pon ing th e bleeding p ort ion of th e p rocedu re to th e secon d day, an d th e possibilit y of obt ain ing p rop er im aging to ch eck th e p osit ion of th e in st ru m en t at ion p rior to th e secon d stage. Th e t im ing bet w een stages is con t roversial. Som e advocate a sh or t t im e of 1 to 2 days, w h ereas oth ers recom m en d 1 to 2 w eeks to allow pat ien t s to ach ieve th eir n orm al n u t rit ion al st at u s before p roceed ing. Logist ical issues of operat ive t im e an d surgical team availabilit y, as w ell as p at ien t an d fam ily issu es, also n eed to be con sid ered in t h e decision .

The Surgical Team Having a st rong, coh esive su rgical team w ith op en com m u n icat ion is essen t ial to t h e su ccess of th ese com p lex recon st r u ct ion s. Ideally, th e team sh ou ld in clu de an experien ced sp in e su rgeon an d an esth esiologist , skilled su rgical assistan ts, a n ursing team fam iliar w ith th e in st r u m en t at ion an d p rocedu re, an experien ced n eurom on itoring an d radiology tech n ologist , an d a blood con ser vat ion team . Open com m un icat ion is im por tan t , an d su ch issues as blood pressu re p aram eters, blood con ser vat ion st rategies, n eurom on itoring ch anges, an d in form a-

t ion abou t th e su rgical eld an d th e stage of th e p rocedu re sh ou ld be review ed frequ en tly th rough ou t th e case.12

Obtaining Fusion Across the Osteotomy Obt ain ing a solid fu sion across th e osteotom y is im p or tan t in preven t ing early im plan t failu re at the level of the osteotom y. Alth ough m ultiple rods can in crease th e rigidit y of th e con st r uct s, h aving st able an terior an d posterior colum n s w ith bridged st ruct ural bon e across all defects is key to obtain ing fu sion . An terior grafts are n ot su cien t to overcom e large posterior colu m n d efect s. Resected r ibs can be p reser ved in th e procedure an d used to bridge posterior colu m n defect s follow ing osteotom y closu re.13 Tech n iques of fash ion ing th e rib an d th e h ost bed, w iring ribs in place, or using m in i-screw s from th e cran iofacial in tern al xat ion set s to secu re th e ribs w ill h elp re-create th e st ru ct u ral con t in u it y of th e p osterior colum n .

■ Osteotomy Options Spin al osteotom ies can be divided into six m ain t ypes 14 (Fig. 3.3): Posterior colu m n : 1. Par t ial facet 2. Com plete facet Par t ial body: 3. Pedicle subt ract ion osteotom y (PSO) 4. Transdiskal pedicle subtraction osteotomy Com p lete body: 5. Ver tebral colu m n resect ion (VCR) Mult ip le ver tebrae: 6. Mult ip le ver tebral colu m n resect ion In th is classi cat ion , th e ap p roach m odi er w as ad d ed . If t h e p roced u re w as p er for m ed from p oster iorly, t h e osteotom y w ou ld h ave a “P” after t h e n u m ber. If a com bin ed an ter ior an d posterior su rger y w as perform ed, an “A/P” w ou ld be added after th e n u m ber. For exam p le, if a PSO w as perform ed from posteriorly, it w ould be con sidered a t ype 3P osteotom y. A VCR perform ed th rough a com bin ed an terior

The Use of Osteotomies for Rigid Spinal Deformities

a

b

c

d

e

f

an d posterior approach w ou ld be con sidered a t ype 5 A/P.

Types 1 and 2: Posterior Column Osteotomies Release of th e facet join ts an d th e posterior ligam entous structures, including the ligam entum avum , provides signi cant m obilit y to the posterior colu m n . For any correct ion to occu r, th e an terior colu m n h as to be m obile. With th e com bin at ion of a m obile an terior colu m n an d a

a

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c

Fig. 3.4a–f Long casset te standing (a) posteroanterior, (b) lateral, and (c) sagit tal computed tom ography (CT) reconstruction of a 17-year-old boy with an L2 congenital kyphosis. Note the global compensation of the deformit y through thoracic and lumbar hyperlordosis. Posterior column osteotom ies were

Fig. 3.3a–f Schem atic of the comprehensive anatomic spinal osteotomy classi cation proposed by Schwab et al. In this classi cation, Type 1 (a) is a partial facet resection, t ype 2 (b) is a complete facet resection, t ype 3 (c) is a pedicle subtraction osteotomy, t ype 4 (d) is a transdiskal pedicle subtraction osteotomy, t ype 5 (e) is a vertebral column resection, and t ype 6 (f) is a multi-level vertebrectomy. (From Schwab F, Blondel B, Chay E, et al. The comprehensive anatomical spinal osteotomy classi cation. Neurosurgery 2014;74:112–120, discussion 120. Reprinted with perm ission.)

released posterior colum n , sign i can t correct ion can be ach ieved in both th e coron al an d sagit tal plan es (Fig. 3.4). For kyph osis correct ion , th is osteotom y p rovides a com bin at ion of posterior sh ortening and an terior length ening. Type 1 osteotom ies involve resect ion of th e in ferior facets. Th is can provide som e m obilit y in t h e p oster ior colu m n . Typ e 2 osteotom ies involve rem oval of th e superior facet an d ligam en tou s st ru ct u res. Resect ion of th e su perior facet is t h e key to t h e release. Th is can be ach ieved w ith out resect ing th e in ferior facets,

d

e

f

perform ed at L1-L2 and L2-L3, with correction of the deformit y and stabilization from (d) L1 to L3, allowing for (e) the spontaneous norm alization of the thoracic kyphosis and a decrease in (f) the compensatory lumbar hyperlordosis.

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a

b

Fig. 3.5a,b (a) Schematic of a posterior column osteotomy with resection of the superior facets. (b) Osteotomy closure is achieved with a temporary central hook-rod construct reducing the inferior facet to the proxim al surface of the pedicle. Note the exible anterior column allowing anterior

lengthening with osteotomy closure. (From Lewis SJ, Goldstein S, Bodrogi A, et al. Comparison of pedicle subtraction and Smith-Petersen osteotomies in correcting thoracic kyphosis when closed with a central hook-rod construct. Spine 2014;39:1217– 1224. Reprinted with permission.)

esp ecially w h en sign i can t dist ract ion of th e facets occurs, as is th e case w ith large kyph ot ic deform it ies. Preser vat ion of th e in ferior facet du ring th e osteotom y can h elp to m ain tain posterior-colum n bone stock, aiding in th e posterior fu sion . Use of a h ook-based tem p orar y cen t ral rod to facilit ate osteotom y closure follow ing th e p osterior colu m n release p rodu ced ~ 10 degrees of correct ion per osteotom y level in th e th oracic sp in e (Fig. 3.5).

sociated abn orm ally h igh PI, a sacral PSO can be p erform ed to decrease th e PI an d n orm alize th e PI–LL relat ion sh ip.16 Th e m ain com p licat ion s associated w it h PSOs are bleeding, poten t ial n er ve root injur y or en t rapm en t , an d pseudar th rosis. Th e tech n ique is discussed below. Careful at ten t ion to detail can h elp m in im ize th e poten t ial m orbidit y th at can be seen w ith th ese cases.

Type 3: Pedicle Subtraction Osteotomy Th e PSO is a p oster ior-based closin g-w edge osteotom y. It is id eally su ited for kyp h osis cor rect ion an d can reliably p rodu ce 25 to 35 degrees of lordosis even in th e p resen ce of a solidly fu sed an terior colu m n 15 (Fig. 3.6). Perfor m in g t h e PSO asym m et r ically can en able con com it an t coron al p lan e correct ion . A PSO can be p er for m ed in bot h t h e t h oracic an d lu m bar spin es. In cases of p elvic in ciden ce (PI) an d lu m bar lordosis (LL) m ism atch w ith an as-

Technique Mult iple variat ion s of th e tech n ique h ave been described, bu t th e p rin cip les of th e p rocedu re are com m on to all of th em .

Decompression Follow ing exposu re an d im plan t in ser t ion , th e pedicle is isolated from all of its bony at t ach m en t s: laterally, th e t ran sverse process; dist ally, t h e p ars; an d p roxim ally, t h e su p er ior facet . A com plete lam in ectom y of th e involved level is p erform ed as w ell as of som e or all of

The Use of Osteotomies for Rigid Spinal Deformities a

b

c

d

e

Fig. 3.6a–e Long casset te standing (a) lateral and (b) sagit tal CT reconstruction of a 67-year-old man who underwent a previous anterior and posterior L2-L4 fusion for an L3 burst fracture. Intraoperative views with (c) the temporary central rod in place

and postoperative long casset te (d) lateral and (e) sagit tal T2 magnetic resonance imaging (MRI) demonstrating restored sagit tal alignment following an L3 PSO and T10 to pelvis construct.

th e adjacen t levels to en su re adequ ate sp ace for th e du ral sac cen t rally upon closure. Com plete resect ion of th e pedicle is requ ired to create a single foram en for t w o n er ve root s—th e n er ve root of th e osteotom y level as w ell as th e n er ve root of th e level proxim al. Th e com plete posterior elem en ts of th e vertebra of th e osteotom y level sh ould be resected. A t riangu lar posterior-based w edge of bone is then rem oved from th e body, leaving a sm all am ou n t of an terior bon e of th e ver tebral body. Th e an terior colu m n acts as a h inge du ring closu re. For th oracic-level osteotom ies, th e t ran sverse p rocesses are rem oved to reveal th e m edial rib. Th e rib is dissected free from all it s soft t issu e at tach m en ts, t aking care to avoid en tering t h e p leu ral sp ace. Th e r ib is t h en cu t 5 to 6 cm lateral from t h e ver tebra. Su bp er iosteal dissect ion is don e to free u p th e m edial rib, w h ich is th en det ach ed from th e lateral aspect of t h e ver tebral body. Dissect ion alon g t h e lateral pedicle an d body is th en perform ed to free th e m ediast in um from th e ven t ral ver tebral body. Spoon ret ractors can th en be placed aroun d th e an terior ver tebra to fu r th er protect th e m ediast in al st r u ct u res. Ret ract ing th e spin al cord sh ould be avoided during th e decom pression to m in im ize iat rogen ic inju r y.

Minimizing Bleeding During the Osteotomy Th e ep idu ral vein s r u n a predict able cou rse; iden t ifying, coagu lat ing, an d cu t t ing t h em can m in im ize blood loss du ring th e p rocedu re. Th e vein s r u n th rough th e ep idu ral fat an d sh ou ld be coagulated w h ile separat ing th e fat from th e du ra. A secon d ser ies of vein s r u n alon g th e m edial asp ect of th e pedicle, dist ally along th e cou rse of th e exit ing n er ve root an d proxim ally over th e p edicle an d deep to th e su p erior facet . W h en reach ing arou n d ven t rally, care sh ou ld be m ade to avoid th e segm en t al vessels r u n n ing along th e m idp or t ion of th e lateral ver tebral body. As w ell, failu re to sep arate th e p lan e of th e m ediast in u m from th e ven t ral body can lead to sign i can t m ediast in al ven ou s bleeding du ring dissect ion lateral to t h e ver tebral body. It is im p erat ive to st ay alon g t h e lateral asp ect of t h e ver tebra w h en dissect ing an teriorly.

Osteotomy Closure Closure of the osteotom y is perform ed after ensu ring adequ ate resect ion of th e posterior w all of t h e ver tebral body an d after com p lete resect ion of th e pedicles h as been perform ed. If di cult y is encountered closing the osteotom y,

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Chapter 3 t h e su rgeon sh ou ld con sid er resect in g m ore bon e an ter iorly for ad equ ate d ecom p ression . In adequate bon e resect ion is th e m ain reason osteotom ies do n ot close. To judge th e redu ct ion of th e posterior colu m n , th e in ferior facet of th e level proxim al to th e osteotom y can be p reser ved an d redu ced to th e superior facet of th e level dist al to th e osteotom y. Th is w ill en su re a st able p osterior colu m n w ith st ru ct u ral bon e con t in u it y an d preven t oversh or ten ing du ring closu re. Closu re can be ach ieved th rough t h e u se of a h ookbased cen t ral rod (Fig. 3.7), th rough com pression of th e periapical an chors w ith tem porar y short rods, or w ith three- or four-rod constructs u sing side-to-side rod con n ectors. If p osterior colu m n con t in u it y can n ot be ach ieved th rough osteotom y closure, st ruct ural bon e graft (from adjacen t ribs or large spin ou s processes) can be u sed to ll th e posterior defects.

Type 4: Transdiskal Variant Mod ifying t h e p roxim al resect ion of t h e PSO to exten d across t h e d isk sp ace p rovid es for a

a

Fig. 3.7a,b Schematic of (a) a pedicle subtraction osteotomy closed with (b) a central rod. Note the reduction of the inferior facet of the proximal level to the superior facet of the distal level, re-creating a new facet joint and continuit y of the posterior column. (From Lewis SJ, Goldstein S, Bodrogi A,

greater resect ion an d en ables bon e-on -bon e con t act th rough th e an terior colu m n . Th is variat ion is p ar t icu larly u sefu l in cases of diskit is w ith kyph ot ic collapse (Fig. 3.8) an d post t raum at ic kyph osis.17

PSO w ith Previous Anterior Implants An terior im plan ts at th e level of th e plan n ed osteotom y presen t a ch allenge w h en perform ing posterior-based p rocedu res. Th e im p lan ts can be rem oved eith er th rough a form al an ter ior ap p roach or t h rough an an ter ior reach aroun d procedure from a posterior approach 18 (Fig. 3.9). Posteriorly th e t ran sverse processes are rem oved, and dissection is perform ed along th e lateral asp ect of th e p ed icle. Th e an terior im plan t s are iden t i ed. Taking care to preser ve th e exit ing n er ve root , a m et al cu t t ing bu r can be used to cut th e an terior rod proxim al an d dist al to th e an terior screw. Som e of th e lateral body is th en rem oved to iden t ify th e n eck of th e screw, w h ich is th en cu t w ith th e bu r. Th e segm en t of t h e an ter ior screw w it h t h e at t ach ed rod is rem oved . Th e osteotom y is t h en

b

et al. Comparison of pedicle subtraction and Smith-Petersen osteotom ies in correcting thoracic kyphosis when closed with a central hook-rod construct. Spine 2014;39:1217–1224. Reprinted with permission.)

The Use of Osteotomies for Rigid Spinal Deformities

c

a

g

b

d

e

f

h

Fig. 3.8a–h Long cassette (a) lateral and (b) sagittal T2-weighted MRI of a 73-year-old woman with known tuberculosis unresponsive to medical treatment. Note the destruction and kyphotic collapse of the T10-T11 disk space and (c) adjacent vertebral bodies with an associated epidural abscess noted on (d) gadolinium -enhanced T1-weighted MRI. Long casset te (e) posteroanterior and (f) lateral views demonstrate a T4 to L2 posterior reconstruction. (g) A transdiskal pedicle subtraction

osteotomy was perform ed by resecting the posterior elements and pedicles of T11, the proximal vertebral body of T11, the T10-T11 disk, and the distal vertebral body and end plate of T10. (h) A new vertebral body was creating by reducing the proximal body of T10 to the distal vertebral body of T11. Note the inferior facet of T10 was reduced to the superior facet of T12 to m aintain the integrit y of the posterior column.

p er for m ed in t h e u su al fash ion an d t h e rem ain ing sh aft of th e screw is rem oved w ith th e ver tebral body resect ion (Fig. 3.10).

m ore exten sive resect ion s involving m u lt ip le ver tebrae to ach ieve th e n eeded correct ion . Com m on in d icat ion s for VCR in clu de severe kyp h oscoliosis, con gen it al d efor m it ies (Fig. 3.11), an d rigid deform it ies secon dar y to previous su rger y.20 Th e p roced u re is p er for m ed in a sim ilar fash ion to a PSO. Alt h ough t h e PSO is often p er for m ed for p r im ar ily sagit t al p lan e d eform it ies, th e VCR can accom m odate m u lt ip lan ar deform ities. These deform ities often have m ajor rotational and translational com ponents, causing

Type 5: Vertebral Column Resection For large m u lt ip lan ar deform it ies, resect ion of a com p lete ver tebral body can p rovid e t h e m obilit y in t h e sp in e to ach ieve th e n eed ed cor rect ion .19 Severe kyp h ot ic d efor m it ies, like those seen follow ing t uberculosis, often require

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a

b

c

d

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f

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h

Fig. 3.9a–h Long casset te (a) posteroanterior and (b) lateral view, sagit tal T2 MRI (c), and CT coronal (d), sagit tal (e), and representative axials (f) of a 69-year-old wom an with coronal and sagit tal malalignment following a previous anterior T12 to L5 fusion and circum ferential extension to the sacrum and pelvis. Thoracic kyphosis (T5-T12) measures 45 degrees, lumbar lordosis (T12-S1) measures 7 degrees, the pelvic incidence m easures

51 degrees, the sacral slope m easures 5 degrees, and the sagit tal vertical axis measures 12 cm. (g,h) The patient underwent an o set L2 pedicle subtraction osteotomy through a posterior approach and proximal extension to T4, as demonstrated in the standing postoperative long-caset te posteroanterior (g) and lateral (h) ragiographs. The L2 anterior screw was rem oved from the same posterior approach.

sign i can t ch allenges to th e exp osu re, th e dissect ion , an d th e decom p ression , especially on th e con cave side (Fig. 3.12a,b). Care m ust be taken w h en dissect ing aroun d th e ver tebral body on th e con cavit y, to en su re th at th e dissect ion does n ot en ter th e m ediast in u m . Sim ilarly, w ith th e severe rotat ion , th e spin al cord w ill be sh ifted again st t h e con cavit y (Fig.

3.12c,d), m aking it vu ln erable to inju r y w ith rem oval of th e con cave pedicle. Th ese ch allenges are n ot as di cu lt w h en perform ing a PSO for sagit t al plan e deform it ies. Th e steps for a VCR are sim ilar to th ose for a PSO: exposure, follow ed by in ser t ion of im plants, rem oval of the tran sverse processes, rem oval of the m edial ribs and rib heads, exposure

b a

c

d

Fig. 3.10a–e (a) Intraoperative view of the lateral and anterior dissection perform ed to identify the previously placed anterior instrum entation through a posterior exposure. Note the preservation of the exiting nerve root. A m etal-cut ting high-speed drill is used to cut the anterior rod proximal and distal to the screw. After removal of som e of the lateral vertebral body, a further cut is m ade along the neck of the screw. (b) The screw head with the at tached

e

rod is removed. (c) The shaft of the screw is extracted when completing the osteotomy. (d,e) A schematic demonstrates the removal of the anterior implant. (From Lewis SJ, David K, Singer S, et al. A technique of anterior screw removal through a posterior costotransversectomy approach for posterior-based osteotomies. Spine 2010;35: E471–E474. Reprinted with permission.)

The Use of Osteotomies for Rigid Spinal Deformities a

b

c

Fig. 3.11a–g (a) Anteroposterior and (b) lateral long casset te radiographs of a 19-year-old man with congenital kyphoscoliosis. (c,d) Three-dimensional reconstructions demonstrates a T11 hemivertebra at the apex of the deformit y. The patient underwent (e) posterior resection of T11 and T12 and (f,g) posterior reconstruction from T5 to L4. A

d

e

f

39

g

portion of the resected vertebra was used as an anterior strut bet ween T10 and L1 to maintain the integrit y of the anterior colum n. Closure of the osteotomy was perform ed with proximal to distal convex rod placem ent with the temporary concave rod, with loosened set screws in place to prevent translation.

a

b

c

d

Fig. 3.12a–d Axial (a) CT and (b) MRI of a nonrotated thoracic spine with kyphosis. Note the position of the rib heads and the central position of the spinal cord. (c) Comparative CT of a patient with a severe scoliosis. Note the marked rotation of the

vertebra, the convex lateral vertebral body abut ting the posterior aspect of the convex rib, the very ventral position of the concave rib, and the posterior position of the convex rib head. (d) Axial MRI shows the spinal cord shifted against the concave rib.

40

Chapter 3 of t h e ven t ral ver tebral body, p oster ior d ecom pression , rem oval of th e con cave p edicle, tem porar y con cave rod, convex rem oval of th e pedicle, an d release of th e p roxim al an d distal disks. The vertebral body can be rem oved p iecem eal or en bloc. For p iecem eal rem oval, a sh ell of ven t ral ver tebral body cor tex can be left beh in d to protect th e m ediast in al st r uct u res an d ser ve as a bar r ier for t h e an ter ior st r u t graft or cage. For en -bloc resect ion , circu m feren t ial release of th e disks n eeds to be p erform ed to perm it adequ ate release an d rem oval. Release of th e con cave side of th e disk is th e m ost di cult . Often th e adjacen t m edial ribs on th e con cavit y n eed to be rem oved to provide su cien t access for th e release. Th e t ap for th e pedicle screw s can be u sed as a joyst ick from th e con vexit y to facilitate th e com p lete rem oval of th e ver tebral body. Th e u se of p rop er ret ractors to protect th e m ediast in al st ru ct u res du ring an terior body resect ion is p aram ou n t . W h en p er for m ing VCR w it h m arked rot at ion , it is easiest to en ter th e can al th rough th e convex foram en to st ar t t h e d ecom p ression . Th e com p lete p oster ior elem en t s of t h e level to be resected sh ould be rem oved, along w ith th e lam in ae of th e adjacen t levels. Th is w ill provide good visu alizat ion of th e spin al cord u pon osteotom y closu re. Th e con cave pedicle is carefu lly rem oved an d a tem porar y rod is th en placed on th e con cavit y. Th e m ajorit y of th e rem ain ing dissect ion an d vertebrectom y can be perform ed from th e convexit y w ith out th e tem p orar y rod being in th e w ay. A st ruct ural an terior suppor t graft , eith er a par t of th e resected ver tebra or a cage, is in serted an teriorly to gu ide th e redu ct ion an d prevent overshortening. A lam inar spreader can be used to dist ract ven t rally from th e con cave side to facilitate th e graft/cage in ser t ion . Closu re of th e VCR sh ou ld be don e w ith a convex rod. Th e tem p orar y con cave rod is left in place, w ith the set screw s loosened, preventing translat ion w ith ou t h in dering osteotom y closure. Reduction is often easiest from proxim al to distal. Single- and dual-rod reduction techniques h ave been described. Reducing a proxim al an d dist al convex rod to a cen t ral con n ector h as also been d escr ibed . Being fam iliar w it h m u lt iple tech n iques an d th e equipm en t available

w ill en able th e surgeon to tailor th e m eth od to th e given sit u at ion .

Type 6: Multilevel Vertebral Column Resection Severe kyp h ot ic angu lar deform it ies, often secon dar y to rem ote in fect ion s, are am en able to posterior-based ver tebral resect ion s. A single level is often in su cien t . Mult iple levels of th e rem n an t s of th e d efor m ed ver tebrae are resected (Fig. 3.13). Follow ing resect ion , ven t ral distraction aids in lengthening the an terior colu m n for placem en t of an an terior cage/st rut . Posterior sh orten ing th rough th e rod w ill com plete th e correct ion .

■ Osteotomies for Fixed

Lordosis Th e correct ion of xed hyperlordosis requ ires a com bin at ion of an terior sh or ten ing an d poster ior lengt h en in g. Th is is m ost reliably accom p lish ed t h rough a for m al an ter ior release follow ed by a posterior correct ion (Fig. 3.14). Sim ilar to severe kyph osis, w h ere th e ver tebral colum n is displaced p osteriorly, in xed hyperlordosis th e spin e is disp laced ven t rally. Th is ven t ral displacem en t favors an an terior ap proach , w ith th e spin e being su per cial to th e an terior abdom in al w all. In cases of th oracic hyperlordosis, severe n arrow ing of th e m ediast in u m occu rs, w ith bron ch ial com p ression occurring in th e m ore severe cases. Even in cases w ith respiratory issues, these patients paradoxically ben e t from form al an terior approach es to decrease th e lordosis an d h elp in crease th e kyp h osis, th ereby in creasing th e an teroposterior diam eter of t h e m ediast in u m , relieving th e bron ch ial com pression . An terior sh or ten ing can be accom plish ed w it h m u lt ip le-level d iskectom ies for global hyperlordosis or th rough resect ion of disk an d bon e for m ore focal deform it ies (Figs. 3.15 an d 3.16). A posterior-colum n release an d in st rum en t at ion is th en perform ed. Con tou ring th e posterior rod in th e ap prop riate sagit t al p lan e w ill then reduce th e lordot ic deform it y. Form al

The Use of Osteotomies for Rigid Spinal Deformities

a

b

c

Fig. 3.13a–e (a) Anteroposterior and (b) lateral views of a 59-year-old man with severe kyphosis secondary to remote infection. (c) CT sagit tal view shows four vertebrae autofused ventrally with a severe focal kyphosis, and hyperlordosis of the distal

a

b

Fig. 3.14a–d Supine (a) anteroposterior and (b) lateral long casset te radiographs of a 17-year-old boy with severe neuromuscular lordoscoliosis with previous Baclofen pump insertion. (c,d) Following

d

e

lumbar and thoracic spines. (d,e) Long casset te radiographs demonstrating correction following multilevel vertebrectomy, placement of an anterior cage, and posterior T6 to pelvis instrumentation.

c

d

L1 to S1 anterior diskectomies, intraoperative traction and a posterior T2 to pelvis instrumentation and fusion was perform ed.

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a

b

c

Fig. 3.15a–f (a) Anteroposterior and (b) lateral long casset te radiographs of a 47-year-old woman with a remote Harrington rod instrum entation and fusion for adolescent idiopathic scoliosis. She presented with distal degeneration and sagit tal malalignm ent. (c,d) An L3 pedicle subtraction osteotomy and anterior lum bar interbody fusions at L4–5 and L5-S1 were perform ed, resulting in xed lum bar hyperlordosis. Because of the patient’s severe unhappiness with her sagit tal alignm ent, an anterior L2–3 diskectomy and resection of the proximal portion of the L3 vertebral body followed

a

b

Fig. 3.16a–c Lateral radiographs of the patient in Fig. 3.15 demonstrating (a) the L3 pedicle subtraction osteotomy and (b) the planned resection for the reverse Sm ith–Petersen osteotomy. (c) Close-up lateral view of the lumbar spine following closure of the combined anterior/posterior osteotomy. (From

d

e

f

by a L2–3 posterior column release were performed. The posterior fusion mass release was gently distracted and held open with mesh cages, while an appropriately contoured rod was inserted from distal to proximal to reduce the osteotomy. (e,f) This resulted in a more balanced sagit tal plane. (From Lewis SJ, Gray R, David K, Kopka M, Magana S. Technique of Reverse Smith Petersen osteotomy (RSPO) in a patient with xed lumbar hyperlordosis and negative sagit tal imbalance. Spine 2010;35: E721–E725. Reprinted with permission.)

c

Lewis SJ, Gray R, David K, Kopka M, Magana S. Technique of Reverse Smith Petersen osteotomy (RSPO) in a patient with xed lumbar hyperlordosis and negative sagit tal imbalance. Spine 2010;35:E721–E725. Reprinted with perm ission.)

The Use of Osteotomies for Rigid Spinal Deformities posterior dist ract ion after th e circu m feren t ial release m ay cau se u nw an ted dist ract ion of th e entire spine instead of just the posterior colum n, m aking th e redu ct ion to an u n d er- con tou red rod th e preferred m eth od .

Careful preoperative clinical and radiographic evaluation will help to assess the exibilit y of the deform it y, to determine the xation options, and to decide on the location, num ber, and t ype of osteotom ies required to achieve the desired correction. Accurate intraoperative spinal cord m onitoring, including m otor evoked potentials, is essential to the safe completion of these procedures. Underst anding the tim ing and m agnitude of neuromonitoring changes will direct key intraoperative decisions. Although pedicle screw instrumentation is the primary method of curve control, alternative xation methods such as fusion m ass screws or laminar hooks are important backup strategies, especially in revision surgery or dysplastic anatomy.

■ Chapter Summary Th e ap p roach to severe sp in al d efor m it ies h as sign i can t ly ch anged w it h t h e im p roved tech n iqu es, im agin g, an d in st r u m en t at ion t h at are available. An im p roved ou tcom e w ill be ach ieved w ith carefu l preoperat ive plan n ing, a d eep u n d erst an d in g of t h e d eform it ies, an d th e kn ow ledge an d abilit y to perform th e various correction techniques. Creating an environm ent w ith experienced and skilled surgical and p er iop erat ive team s w ill h elp to p red ict an d m an age t h e com p lexit ies associated w it h t h e successful treat m ent of these ch allenging cases.

Pitfalls The artery of Adam kiewicz has a variable anatomy from T8 to L1, m ost com monly on the left side. When considering osteotom ies around the thoracolumbar junction, protecting and saving the nerve roots may preserve key sources of blood ow. Careful and controlled reduction of three-column osteotom ies is essential to prevent cord translation and subsequent injury. Complete visualization of the cord and harmonious collaboration with the surgical team, electrophysiological monitoring team , and nursing sta is essential for spinal cord safet y.

Pearls Obt aining appropriate preoperative im aging studies can help to bet ter understand the com plexities of the deform it y and the patient’s anatomy, and to plan for potential di culties in the procedure.

Refere nces Five Must-Read Refe rences 1. Dor w ard IG, Len ke LG. Osteotom ies in th e posterioronly t reat m en t of com plex adult spin al deform it y: a com p arat ive review. Neu rosu rg Focu s 2010;28:E4 PubMed 2. Dom m isse GF. Th e blood supply of th e spinal cord. A crit ical vascu lar zon e in spin al surger y. J Bon e Joint Surg Br 1974;56:225–235 PubMed 3. Boll DT, Bulow H, Blackh am KA, Asch o AJ, Sch m it z BL. MDCT angiography of th e spin al vasculat ure and th e ar ter y of Adam kiew icz. AJR Am J Roen tgen ol 2006;187:1054–1060 PubMed 4. Lew is SJ, Aru n R, Bodrogi A, et al. Th e use of fusion m ass screw s in revision sp in al d efor m it y su rger y. Eur Spin e J 2014;23(Suppl 2):181–186 Pu bMed 5. Lew is SJ, Goldstein S, Bodrogi A, et al. Com parison of ped icle su bt ract ion an d Sm ith -Petersen osteotom ies in correct ing th oracic kyph osis w h en closed w ith a

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8.

9.

cen t ral h ook-rod con st r u ct . Sp in e 2014;39:1217– 1224 Pu bMed Schw ab F, Patel A, Ungar B, Farcy J-P, Lafage V. Adult spin al deform it y-postoperat ive st an ding im balan ce: how m u ch can you tolerate? An over view of key param eters in assessing align m en t an d plan n ing correct ive su rger y. Spin e 2010;35:2224–2231 PubMed Rose PS, Bridw ell KH, Len ke LG, et al. Role of pelvic in cidence, th oracic kyph osis, an d pat ien t factors on sagit t al plan e correct ion follow ing pedicle subt ract ion osteotom y. Spine 2009;34:785–791 PubMed Lew is SJ, Gray R, David K, Kopka M, Magana S. Technique of Reverse Sm ith Petersen osteotom y (RSPO) in a patient w ith xed lum bar hyperlordosis and negative sagittal im balance. Spine 2010;35:E721–E725 PubMed Ch o K-J, Bridw ell KH, Len ke LG, Berra A, Baldus C. Com p arison of Sm ith -Petersen versu s p edicle su b -

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Chapter 3 t ract ion osteotom y for t h e cor rect ion of xed sagit t al im balan ce. Spin e 2005;30:2030–2037, discussion 2038 PubMed 10. Dor w ard IG, Lenke LG, Stoker GE, Cho W, Koester LA, Sides BA. Radiograph ic an d clin ical ou tcom es of p osterior colu m n osteotom ies in sp in al deform it y correct ion . Spin e 2014;39:870–880 Pu bMed 11. Br idw ell KH. Decision m akin g regard in g Sm it h Petersen vs. p edicle su bt ract ion osteotom y vs. vertebral colum n resect ion for spin al deform it y. Spin e 2006;31(19, Su pp l):S171–S178 Pu bMed 12. Jar vis JG, St ran t zas S, Lipkus M, et al. Respon ding to neurom on itoring changes in 3-colum n posterior spinal osteotom ies for rigid pediat ric spin al deform it ies. Spin e 2013;38:E493–E503 PubMed 13. Lew is SJ, Kulkarn i AG, Ram persaud YR, et al. Posterior colum n recon st ruct ion w ith autologou s rib graft after en bloc t u m or excision . Sp in e 2012;37:346– 350 PubMed 14. Schw ab F, Blon del B, Ch ay E, et al. Th e com preh en sive an atom ical sp in al osteotom y classi cat ion . Neu rosu rger y 2014;74:112–120, discussion 120 Pu bMed 15. Lafage V, Sch w ab F, Vira S, et al. Does vertebral level of pedicle subt ract ion osteotom y correlate w ith de-

gree of spin opelvic param eter correct ion ? J Neurosu rg Spin e 2011;14:184–191 PubMed 16. Lafage V, Bh arucha NJ, Sch w ab F, et al. Mult icen ter validat ion of a form ula predict ing postoperat ive spin opelvic align m en t . J Neu rosurg Spin e 2012;16: 15–21 Pu bMed 17. Halpern EM, Bacon SA, Kit agaw a T, Lew is SJ. Posterior t ran sdiscal th ree-colum n sh or ten ing in th e surgical t reat m en t of ver tebral discit is/osteom yelit is w ith collapse. Spine 2010;35:1316–1322 PubMed 18. Lew is SJ, David K, Singer S, et al. A techn ique of an terior screw rem oval through a posterior costotransversectom y approach for posterior-based osteotom ies. Spin e 2010;35:E471–E474 Pu bMed 19. Ham zaoglu A, Alan ay A, Ozt urk C, Sarier M, Karadereler S, Gan iyu su foglu K. Posterior ver tebral colu m n resect ion in severe spin al deform it ies: a tot al of 102 cases. Spin e 2011;36:E340–E344 Pu bMed 20. Len ke LG, O’Lear y PT, Bridw ell KH, Sid es BA, Koester LA, Blan ke KM. Posterior ver tebral colum n resect ion for severe pediat ric deform it y: m in im u m t w o-year follow -up of thir t y- ve con secut ive pat ien t s. Spin e 2009;34:2213–2221 PubMed

4 Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deformity Kristen E. Jones, Robert A. Morgan, and David W. Polly, Jr.

■ Introduction Fusion at tem pts across L5/S1 in adult spin al deform it y are plagu ed by a h igh rate of pseu dar th rosis an d im p lan t breakage/failu re du e to th e u n iqu e an atom ic an d biom ech an ical ch aracterist ics of th e lum bosacral jun ct ion .1,2 In a single-in st it ut ion review of adult deform it y pat ien ts w ith con st ru cts greater th an fou r levels, con st r u ct s en ding at S1 h ad a sign i can tly h igh er rate of pseudar th rosis com pared w ith con st r u ct s en ding at L5 or m ore cep h alad levels.1 Oth er pseu dar th rosis risk factors w ere age older th an 55 years, m ore th an 12 levels in cluded in th e con st ruct , an d T10-L2 kyph osis of greater t h an 20 d egrees. Th e ad d it ion of sacral-p elvic xat ion in creases t h e st rengt h an d st abilit y of con st r u ct s span n ing th e lu m bosacral ju n ct ion an d is a form idable tool in the spinal deform it y surgeon’s arm am entarium for correct ing spin al im balan ce.

■ Anatomic and

Biomechanical Considerations As a t ran sit ion zon e from th e m obile lu m bar spin e to th e st i pelvis, th e lum bosacral jun ct ion exp erien ces sign i can t forces ch allenging ar th rodesis at tem pt s across th e segm en t . De-

sp ite bearing axial loads of m ore th an dou ble body w eigh t , th e osseou s an atom y of th e sacru m p rovides relat ively lit tle st rength for xat ion .3 Th e sacr u m con sist s of a t h in r im of cor t ical bon e su r rou n d in g a can cellou s core, w ith large pedicle diam eter preclu ding th e en gagem en t of both m edial an d lateral cor t ical w alls via pedicle screw in st rum en tat ion . Th e lum bosacral jun ct ion is a biom ech an ically dist in ct locat ion th at is su bjected to th e h igh est level of t ran slat ion al sh ear force an d th e m ost lim ited range of m ot ion w ith in th e spin e, w ith th e L5/S1 disk bearing th e largest su m m at ion of load vectors.2,4–6 Th ese u n iqu e st resses, com bin ed w it h th e relat ively sm all am oun t of sacral cor t ical bon e available for xat ion , resu lt in in creased pseu dar th rosis an d im plan t breakage/failure in long in st ru m en t at ion con st r ucts en ding at S1.2,7 McCord et al6 in t rodu ced th e con cept of th e lum bosacral pivot p oin t at th e ju n ct ion of th e L5-S1 d isk an d t h e m id d le osteoligam en tou s colu m n to d escr ibe t h e con siderable exion m om en t s an d can t ilever forces act ing at t h e lu m bosacral ju n ct ion . Exten d in g xat ion an terior to th is p ivot poin t in creases con st r u ct st rength . Screw in sert ion in to th e ilium provides th e longest xat ion length an terior to th is pivot p oin t , an d w as fou n d to be th e on ly in st rum en t at ion t ype at th e lum bosacral jun ct ion th at sign i can tly in creased th e m axim um exion m om en t at failu re. Com p ared w ith t h e w eak can cellous com position of the sacrum , the

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Chapter 4 posterior iliu m o ers abu n dan t cor t ical bon e for an ch or ing in st r u m en t at ion an d en ables in creased screw length an d diam eter, m aking sacral-pelvic xat ion a usefu l tech n ique for in creasing con st ru ct st rength .

■ Indications for Sacral-Pelvic

Fixation Th e r igid xat ion p rovid ed by sacral-p elvic in st r u m en t at ion is a u sefu l adju n ct to t reat ing a w id e ar ray of p at h ological en t it ies. Sacralp elvic xat ion is in dicated for lu m bosacral ar t h rod esis exten d in g cep h alad to t h e L2 vertebra, augm en t at ion for p oor qu alit y or osteop orot ic bon e, sacrectom y for t u m or or in fect ion , u n st able sacral fract u res, cor rect ion of at-back syn drom e via lu m bar osteotom y, correct ion of p elvic obliqu it y, an d h igh -grade spon dylolisth esis.8 Th e addit ion of iliac xat ion in th ese con dit ion s sign i can tly redu ces th e st ress placed on S1 in st ru m en tat ion an d in creases con st r u ct st rength . As w ith all spinal surger y, selection of the appropriate approach for each individual patient an d m et icu lou s at ten t ion to su rgical tech n iqu e is th e key to su ccessfu l t reat m en t . Alth ough sacral-pelvic xat ion is n ot requ ired for m any p at ien t s un dergoing lu m bosacral arth rodesis, th e force vectors required for th e creat ion an d m ain ten an ce of proper sagit tal align m en t relat ive to th e pat ien t’s in dividual bon e qualit y m ust be con sidered.

■ Sacral-Pelvic

Instrumentation Selection and Techniques

be used to supplem en t S1 pedicle/alar screw s but sh ould n ot be relied on for an ch oring a long con st r u ct .

S1 Pedicle Screw s Th e sizable m edially convergen t sacral pedicles accom m odate large screw length an d diam eter w h ile sim ultan eously preven t ing “ lling” th e pedicle to ach ieve bicor t ical p u rch ase of th e m ed ial an d lateral p ed icle w all w it h a sin gle screw . Th e largely can cellou s sacral p ed icles p rovid e relat ively lit t le p u llou t st ren gt h in u n icor t ical xat ion , an d u n icor t ical p ed icle screw s sh ould be avoided.3 Bicor t ical xat ion an ch ored in to th e an terior sacral cor tex provides increased pullout strength com pared w ith un icort ical S1 pedicle screw s; h ow ever, addit ion al t rajectories can be em p loyed to fu r th er en h an ce pu llou t st rength . Luk et al9 com pared bicortical S1 pedicle screw insertion torque and pu llou t st rength to th at of S1 pedicle screw s advan ced t h rough t h e S1 su p er ior en d p late. S1 p ed icle screw s t raversin g t h e en d p late h ad sign i can tly h igh er in ser t ion al torque an d pu llou t st rength com p ared w ith bicor t ical S1 screw s. Tricort ical xat ion , de n ed as a screw t rajector y tow ard th e m ed ial sacral prom on tor y, capt u res p u rch ase in th e dorsal, an terior, an d su p erior en d -plate cor tex (Fig. 4.1b). Leh m an et al10 foun d th at th is t ricort ical t rajector y d oubles th e in sert ion al torque com pared w ith bicor t ical S1 pedicle screw s p arallel to th e S1 en d plate. Tricor t ical S1 screw st rength h as n ot been directly com p ared w ith t ran s– en d-plate screw strength; both provide enhanced strength com p ared w it h t yp ical bicor t ical p u rch ase p arallel to t h e S1 en d p late. Tr ian gu lat ion of t h e p ed icle screw t rajector y in creases p u llou t st rength com pared w ith st raigh t-ah ead t rajector y and sh ou ld be un iversally em ployed.

Sacral Fixation Screw s at S1 can be placed through the pedicles in a m edially convergent m anner w ith bicortical en d-plate or tricort ical purchase, or through th e ala in a divergen t m an n er (Fig. 4.1a). Sublam in ar h ooks an d w ires an d S2 pedicle screw s can

Sacral Alar Screw s Alar screw in ser t ion u t ilizes a lateral t rajector y in to low -den sit y can cellou s sacral bon e. Bicort ical alar xat ion is tech n ically p ossible bu t fraugh t w ith risk of inju ring th e L5 n er ve root s

Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deform it y

a

b

Fig. 4.1a,b Sacral screw trajectories. (a) Trajectories for S1 pedicle (A) and alar (B) screw placement. (b) Intraoperative view demonstrating probe insertion in tricortical S1 screw trajectory. Tricortical purchase utilizing dense sacral promontory cortical bone should be employed to m axim ize screw pullout strength.

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Chapter 4 or com m on iliac vessels draped anteriorly across the ala.3 Thus, alar screw s are ut ilized m ainly as unicortical supplem ents to bicortical/tricort ical S1 p edicle screw con st ru ct s. A Ch op in or Colorad o plate or a Tacom a block can be u t ilized to con n ect S1 an d alar screw s. Disadvan t ages of th is tech n iqu e in clu de con st rain ed screw st ar ting poin t an d p oten t ial im pairm en t of th e ideal t rajector y.

Sacral Sublaminar Wires and Hooks Alt h ough su blam in ar w ires an d h ooks lack su cien t biom ech an ical st rength to ser ve as an ch ors to lon g con st r u ct s, t h ey can be u sed as supplem en ts for sh or t-segm en t fusion s.3,11 Hooks are opt im ally p laced in th e dorsal sacral n eu roforam in a w h ere im p roved cor t ical p u rch ase can be ach ieved . Th e Har r in gton in st r u m en t at ion system in it ially em p loyed sacral h ooks as an ch ors to long con st ructs, but th e rate of pseu darth rosis an d h ook dislodgm en t at L5/S1 w as u n accept ably h igh . Sacral su blam in ar w ires an d h ooks sh ou ld n ot be u sed as an ch ors to long con st ru cts.

Transsacral Fixation Kellogg Sp eed rst d escr ibed t ran sver tebral st r u t graft ing at L5/S1 from an an terior ap proach for pat ien ts w ith h igh -grade spon dylolisth esis. Th e Sp eed tech n iqu e involves driving a bular st rut graft th rough th e L5 ver tebral body an d in to th e sacru m via an terior exposu re, an d is a u sefu l tech n iqu e in lieu of in terbody cage placem en t , w h ich h as an in creased risk of an terior su bsiden ce for pat ien t s w ith h igh -grade spon dylolisth esis.13 Due to th e risk of th e an terior exposure to th e lu m bosacral ju n ct ion , in clu ding inju r y to th e great vessels du ring m obilizat ion or sym path et ic plexu s dysfu n ct ion cau sing ret rograde ejaculation in m ales, H.H. Bohlm an popularized t h e p oster ior ap p roach for t ran sver tebral b u lar st r u t graft in g at L5-S1 for p at ien t s w it h h igh -grade spon dylolisth esis. An terior xat ion t h rough L5/S1 can also be p er for m ed via a p aracoccygeal ap p roach in a m in im ally in vasive fash ion u t ilizing syn t h et ic im p lan t s. As w ith all con st ru ct s, th e addit ion of posterior colum n supp or t in creases st abilit y.

Iliac Fixation S2 Screw s S2 p edicle screw st rengt h is t yp ically lim ited by a sh or t pedicle length an d a locat ion dorsal to th e lu m bosacral pivot poin t described by McCord et al6 an d Kebaish .11 S2 p edicle screw s and S2 screw s directed laterally in to the ala can be used as adjun ct suppor t to sh or t-segm en t fu sion s bu t lack th e biom ech an ical st rength to an ch or long con st ru cts.12

Jackson Intrasacral Rod Technique Jackson in t rasacral rods are in ser ted ver t ically th rough th e ala from S1 to th e level of S2 an d th en can be con n ected to a con st ru ct in clu ding S1 p ed icle screw s. In ser t ion is tech n ically d ifcu lt an d can be p reclu ded by alar an atom ic var iat ion s. Th is tech n iqu e h as been sh ow n to be biom ech an ically in fer ior to a lu m bosacral p ed icle screw s–iliac screw con st r u ct an d is m en t ion ed for h istorical con text on ly.5

An ch or ing a con st r u ct w ith iliac xat ion creates a longer lever ar m to resist can t ilever forces across th e lum bosacral ju n ct ion via exten sion an terior to th e lu m bosacral pivot poin t , in creasing biom ech an ical st rength of sacralp elvic con st r u ct s.6 In cor p orat ion of t h e iliu m in to a con st r u ct o oad s st ress from sacral screw s an d decreases th e rate of sacral in st ru m entation failure and pseudarthrosis across the lu m bosacral ju n ct ion .4,14

Transiliac Fixation Harrington Threaded Sacral Rod Develop ed for p elvic xat ion in adju n ct w ith Harrington distraction rods, this device is m en t ion ed for h istor ical p u r p oses. Tw o sep arate posterior iliac in cision s are u sed to in ser t th e th readed rod th rough th e posterior iliac w ings w ith com pression applied. Pseudarthrosis rates h ave been repor ted above 40%m an d th e dis-

Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deform it y t ract ion forces of Harrington rods can resu lt in sagit tal p lan e im balan ce.2,8

Kostuik Transiliac Bar In ser ted from th e m idlin e, th e Kost uik t ran siliac bar is placed 1 to 2 cm an terior to th e poster ior su p er ior iliac sp in e an d t h en at t ach ed via cu stom con n ectors to S1 p ed icle or alar screw s. Th e bar is sm ooth an d h as a con tou red sh ap e th at accom m odates th e m idlin e sacral dorsal p rom in en ce, an d h as been repor ted to h ave a h igh fu sion rate of u p to 97%.8

Iliac Fixation Luque L-f xation Th e rst to develop segm ental inst rum en tation, Lu qu e exten ded lu m bosacral con st ru ct s to th e pelvis u sing L-sh ap ed rods w h ose en ds w ere in serted in to th e p osterior iliu m at th e posterior su perior iliac sp in e. Th is circum ven ted th e dist ract ion p roblem associated w ith th e Harrington tech n iqu e an d im proved fu sion rates, but piston ing occurring bet w een th e rods decreased th e stabilit y of th e Luque L- xat ion in torsion an d exion .2,8

Galveston Technique Ben L. Allen an d Ron L. Fergu son develop ed th e Galveston tech n iqu e in th e 1980s. Sm ooth rods in serted from th e posterior su perior iliac sp in e in to th e iliu m w ere con n ected to segm en t al lu m bosacral in st r u m en tat ion . Rod con tou ring requ ired sign i can t exper t ise. To obviate th e n eed for th is, rods w ith pre-ben t sagit tal con tour an d bilateral iliac xat ion w ere created in a single piece.3 This construct still required substantial rod m anagem ent skills. Because the sm ooth rods had inferior pullout strength com pared w ith threaded screw s, iliac screw s quickly becam e a m ore popular m eth od of xation.

Iliac Screws Iliac xat ion w ith single or stacked un ilateral or bilateral screw s is perform ed w ith fully or

par t ially th readed screw s. Th e p u llou t st rength an d rot at ion al st abilit y is su p er ior to n on th readed rod tech n iqu es. Th e st ar t ing p oin t for screw in ser t ion is at th e level of th e p osterior su p erior iliac sp in e w ith a t rajector y t arget ing eith er t h e su pra-acet abu lar n otch or th e an terior su perior iliac spin e (Fig. 4.2). Th e screw t rajector y is p lan n ed via visu alizat ion of t h e “iliac teard rop ” on eit h er u oroscopy or com p u ted tom ograp hy (CT) im age gu idan ce. Th e iliac teardrop is a region above th e acetabu lum bordering th e m edial iliac w all, th e lateral iliac w all, an d th e zen ith of th e sciat ic n otch . Th e screw ach ieves greatest p u rch ase in th e lateral m argin of th e teardrop , directed th rough th e cor t ical bon e ju st above th e sciat ic n otch . San tos et al15 an alyzed variou s screw length s an d diam eters an d fou n d a sign i can t in crease in in ser t ion al torqu e for iliac screw s of lengt h ≥ 80 m m an d diam eter ≥ 9.5 m m . No di eren ce in insertional torque existed bet ween the supraacetabu lar n otch an d th e an teroin ferior iliac sp in e-directed t rajector y. Given th e risk of acetabular joint violation w ith the supra-acetabular t rajector y, th e au th ors con cluded th at opt im al iliac screw s are in serted in th e an teroin ferior iliac spin e t rajector y w ith length ≥ 80 m m an d diam eter ≥ 9.5 m m . Iliac screw s can be used in com bination w ith sacral screw s to p rovid e in creased con st r u ct st ren gt h an d are biom ech an ically su p er ior to ot h er p elvic xat ion opt ion s. Com p ar in g t h e Galveston tech n iqu e to iliac screw s in a series of 20 n eu rom u scu lar scoliosis p at ien t s, iliac screw s en abled bet ter cor rect ion of p elvic obliquit y an d decreased im plan t breakage.16 In a biom echanical com parison bet w een the m od i ed Galveston tech n iqu e w ith iliac xat ion bu t n o S1 xat ion versu s S1 p ed icle screw s plus iliac screw s, or S1 an d S2 screw s w ith ou t iliac xat ion , Tis et al17 foun d th at con st r ucts w ith iliac screw s con ferred sign i can t st rength via decreased range of m ot ion in m u lt idirect ion al exibilit y test ing an d in creased load to failu re. Br idw ell’s grou p 4 p er for m ed a laborator y invest igat ion com paring m ult idirect ion al exibilit y an d exu ral load to failu re am ong t h e follow ing con st ru ct t yp es: lu m bosacral p edicle

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Chapter 4

b

c

a

Fig. 4.2a–d Iliac screw placement using intraoperative computed tomography (CT)-based fram eless navigation. (a) Iliac screw insertion point is at the posterior superior iliac spine, directed toward the anterior inferior iliac spine. (b) The teardrop view is utilized to optimize screw purchase in the lateral cortical wall, just above the sciatic notch. (c) The sagit tal view is used to demonstrate screw angulation toward the anterior inferior iliac spine, avoiding violation of the acetabulum. (d) Stacked iliac screw construct in patient with progressive deformit y from high-grade spondylolisthesis previously fused in situ, requiring sacral osteotomy for deform it y correction.

d

screw s, in terbody cage, an d iliac screw s. Iliac screw or interbody cage placem en t signi cantly redu ced m ult idirect ion al exibilit y at th e lum bosacral junction com pared w ith pedicle screw s alon e, but iliac screw xat ion w as su perior in protect ing sacral screw s from p u llou t or p low th rough .4 Lebw oh l et al5 p erform ed a laborator y biom ech an ical an alysis com paring con st ruct st i -

n ess, S1 screw st rain , an d u lt im ate failure load am ong several tech n iqu es of supplem en tar y sacral xat ion , using S1 pedicle screw s w ith an d w ith ou t S2 screw s, as w ell as an in t rasacral rod an d iliac screw s. All tech n iqu es decreased th e S1 screw st rain in exion -exten sion , bu t on ly iliac screw s decreased S1 screw st rain in axial loading. In destructive testing w ith exion loading, only iliac screw s signi cantly increased

Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deform it y th e load to failu re. Th e au th ors con clu d ed t h at th e ad d it ion of iliac xat ion sign i can t ly in creases t h e biom ech an ical st ren gt h of sacral con st r u ct s. A sign i can t disadvan t age to iliac screw s is th e p oten t ial p rom in en ce of t h e screw h ead at th e posterior superior iliac spin e (PSIS). Alth ough t h e st ar t ing poin t can be m od i ed or th e PSIS n otch ed to allow bu r ying of th e screw h ead , im p lan t p rom in en ce can n ot be com pletely elim in ated. An oth er disadvan t age is th e requirem en t of an o set con n ector for segm en tal lu m bosacral in st r u m en tat ion .

Transsacral Iliac Fixation S2-Alar-Iliac Screws Develop ed to address th e problem at ic im p lan t prom in en ce an d o set locat ion of iliac screw s, S2-alar-iliac (“S2-iliac”) screw s are associated w ith a low er com plicat ion rate related to im p lan t p rom in en ce-related p ain , n ecessit at ing screw rem oval, com pared w ith t radit ion al iliac xat ion .11 Im plan t prom in en ce is m in im ized, w ith th e m ean distan ce of th e in ser t ion poin t to th e skin 15 m m deep er for th e S2-iliac tech n ique com pared w ith t radit ion al iliac screw in sert ion at th e PSIS.18 Th e S2-iliac screw star ting poin t is 2 to 4 m m lateral an d 4 to 8 m m cau dal to t h e d orsal S1 foram en , w it h a t rajector y tow ard th e an terior in ferior iliac spin e (Fig. 4.3a) at an angle of ~ 40 degrees lateral an d 20 to 30 degrees cau dal.11,18 Th e iliac teard rop is again em p loyed for t rajector y align m en t . Un like t radit ion al iliac screw s, S2-iliac screw s do n ot t yp ically requ ire an o set con n ector for join ing rods to lu m bosacral p edicle screw con st ru ct s (Fig. 4.3b). Biom ech an ical test ing of S2-iliac screw s h as sh ow n equ ivalen t st abilit y to conven t ion al iliac screw s.19 Th e S2-iliac screw t rajector y resu lt s in crossing th e sacroiliac join t , w h ich h as n ot been sh ow n to be problem at ic in th e rst 5 years of follow -up of th is tech n ique, bu t w h ich requires ongoing su r veillan ce (Fig. 4.3c,d). Alt h ough h aloing arou n d iliac screw s m ay be obser ved in over 25%of pat ien ts, iliac screw pullout or breakage is ver y rare.1,11,14

Adjunctive Anterior Interbody Support Polly an d colleagu es 20 foun d th at load-bearing in terbody st ruct u ral graft s in crease con st ru ct st i n ess an d th erefore can decrease th e st rain on posterior in st ru m en tat ion , in addit ion to in creasing th e surface area available for ar th rodesis. Th ey also fou n d th at th e locat ion of th e in terbody graft in th e sagit t al plan e h as biom ech an ical sign i can ce, w ith an teriorly p laced grafts having increased sti ness com pared w ith cen t ral or posteriorly placed in terbody grafts. Com pared w ith st an d-alon e pedicle screw an d com bin at ion p ed icle-iliac screw con st r u ct s, pedicle-iliac screw con st ru cts com bin ed w ith in terbody cages sign i can tly reduce segm en t al m ovem en t across th e lu m bosacral ju n ct ion in laborator y an alysis.4

■ Patient Positioning Patients undergoing sacral-pelvic instrum entation via open or m inim ally invasive techn ique sh ou ld be p osit ion ed pron e on an operat ing table th at en ables th e creat ion or m ain ten an ce of an atom ic lum bar lordosis. Fixat ion of th e lu m bosacral ju n ct ion in a at or kyp h ot ic an gulat ion m ust be absolutely avoided due to th e resultant sagit tal im balance. Allow ing the abdom en to hang freely w ithout ventral com pression h elps m in im ize in t ra-abdom in al pressu re an d ven ous bleeding.

■ Operative Techniques Sacral Fixation Pedicle screw pu llou t st rengt h is in creased by m edializat ion of in ser t ion t rajector y com p ared w ith “st raigh t-ah ead” in ser t ion w ith out m edial angu lat ion of th e screw t ip.3,12 An obese body h abit u s, an iliac crest overh ang, or t rian gu lated ver tebral bodies m ay p resen t obst acles to adequ ate m ed ializat ion of p edicle screw t rajectory (Fig. 4.4a). If this problem is encountered

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a

b

c

Fig. 4.3a–d S2-alar-iliac screws. (a) Intraoperative CT-guided planning demonstrating starting point and trajectory of S2-alar-iliac screw. (b) Postoperative CT scan showing alignment of S2-alar-iliac screw head with lum bosacral pedicle screws, elim inating

d

the need for an o set connector t ypically required by traditional iliac screws. (c,d) X-rays dem onstrating usage of S2-alar-iliac screws to anchor long construct for deformit y correction.

Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deform it y

53

a

b

Fig. 4.4a–c Complications of sacral-pelvic xation. (a) Failure to adequately direct pedicle screws in m edial trajectory, combined with signi cant screw perforation of anterior cortex, resulting in screws abut ting internal iliac veins bilaterally. (b,c) Asymptomatic halo formation (arrows; dotted line) around iliac screws does not necessitate revision unless resulting in pain or lumbosacral pseudarthrosis.

c

w h ile using a m idlin e open skin in cision , th e bailout tech n ique requires split t ing th e fascia in a p aram edian fash ion for a t ran sm u scu lar approach to en able a m ore lateral star t ing poin t an d m edializat ion of th e t rajector y. Vigilan ce is requ ired to p reven t an u n in ten d ed st raigh t -ah ead t rajector y from violat in g t h e an terior sacral or lum bar cor tex w ith result an t injur y to n eurovascu lar st ruct u res. Th e aort ic bifurcation occurs at approxim ately L4/L5, w ith th e com m on iliac vessels t raveling laterally from th e bifurcat ion . Th e L4 an d L5 n er ve roots t raverse th e an terolateral sacral cor tex prior to join ing th e lum bosacral plexus located at th e level of th e sacral ala, an d th e colon is in close opposit ion to th e ven t ral surface of S2. A relat ive “safe zon e” exist s in t h e ven t ral m id lin e of th e sacral prom on tor y; h ow ever, in dividu al p at ien t vascu lar an atom y sh ou ld be in cid en t ally visu alized an d ap p reciated on p reop era-

t ive sp in e im agin g p r ior to p roceed in g w it h in st rum en t at ion .

Iliac Fixation Misdirect ion of iliac or S2-iliac screw s th rough th e sciat ic n otch can cau se inju r y to th e su p erior glu teal arter y or sciat ic n er ve, w h ich is a rare but serious com plicat ion . Violat ion of th e acet abu lu m m u st be avoid ed . Fam iliar izat ion w it h t h e iliac teard rop view en ables cor rect screw t rajector y select ion . Placem en t of screw s in to th e ilium requ ires sign i can t in ser t ion al torqu e th at can cau se breakage of the screw driver unless care is taken to sequen t ially t ap th e screw t rajector y com pletely to th e desired depth . On ce iliac screw in ser t ion is in it iated , on e sh ou ld n ot p au se d u r ing in ser t ion , as t h e m ech an ical t h erm al en ergy gen erated by screw in ser t ion in t h e

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Chapter 4 bone assists in tem porarily lessening insertional torque, a ben e t th at is lost w h en screw in sert ion p au ses. Iliac screw h ead p rom in en ce an d o set distan ce from lum bosacral pedicle screw h eads is m in im ized ut ilizing th e S2-alar-iliac t rajector y.

Revision of Screw s As m en t ion ed, iliac screw s m ay u n dergo asym ptom at ic h aloing (Fig. 4.4b,c). Un less p ain , im plant breakage, or instabilit y of the construct occu rs, screw revision is n ot required. If iliac screw replacem en t is requ ired, u sing larger diam eter screw s confers m ore stabilit y than using longer screw s.

■ Chapter Summary Sacral-pelvic xat ion is a pow erfu l tool for in creasing th e st rength an d stabilit y of lum bosacral con st r uct s. Ext rem e biom ech an ical forces at th e lu m bosacral ju n ct ion an d relat ively p oor bon e qualit y of th e sacrum result in a h igh rate of lum bosacral pseudar th rosis an d im plan t failure in adu lt spin al deform it y correct ion . Sacral-pelvic xat ion is in dicated for lu m bosacral arth rodesis exten ding ceph alad to th e L2 ver tebra, augm en tat ion of con st ructs for p oorqu alit y or osteoporot ic bon e, sacrectom y for t u m or or in fect ion , u n stable sacral fract u res, correct ion of at-back syn drom e via lu m bar osteotom y, correct ion of pelvic obliqu it y, h igh grade sp on dylolisth esis, or as a salvage m ech an ism during revision for p seu dar th rosis. Sacral xat ion is opt im ally perform ed using bi- or t ricor t ical S1 m edially directed pedicle screw s. Alar an d S2 screw s an d h ooks th rough th e d orsal sacral foram in a m ay be ad ded for su p plem en t at ion , bu t lack th e biom ech an ical st rength to an ch or long con st ru ct s in adu lt sp in al deform it y. Care m u st be taken to opt im ize screw size for cor t ical p urch ase w h ile avoiding

injur y to n eu rovascular st ruct u res an terior to th e lu m bosacral jun ct ion . Iliac xat ion is opt im ally perform ed using iliac or S2-alar-iliac th readed screw s, in a t rajector y tow ard th e an teroin ferior iliac spin e, w ith length ≥ 80 m m an d diam eter ≥ 9.5 m m . Kn ow ledge of sacral-p elvic an atom y an d u se of th e iliac teardrop view on in t raoperat ive im aging is key for iliac screw placem en t . Th e addit ion of in terbody st r u ct u ral graft s in creases th e su rface area for arth rodesis an d st i n ess of th e con st r u ct an d sh ou ld be perform ed for long con st ructs at th e lum bosacral jun ct ion . Th e sp in al d efor m it y su rgeon m u st h ave excellen t kn ow ledge of in d icat ion s, in st r u m en t at ion opt ion s, an d tech n iqu es of sacralpelvic xat ion. Fam iliarizat ion w ith sacral-pelvic an atom y is n ecessar y to opt im ize t h e size an d t rajector y of in st r u m en t at ion an d avoid com p licat ion s.

Pearls Sacral-pelvic xation increases the strength and rigidit y of constructs spanning the lum bosacral junction. Iliac xation decreases the rate of sacral instrumentation failure and reduces the incidence of lumbosacral pseudarthrosis. S2-alar-iliac screws provide strong biom echanical xation, minim al implant prom inence, and favorable implant alignm ent with lum bosacral pedicle screws for ease of rod contouring. Pitfalls Sacral pedicle and alar screws have inadequate strength to anchor constructs extending cephalad to L2, predisposing the patient to lum bosacral pseudarthrosis unless sacral-pelvic xation strategies are employed. Acetabular joint impingement or sciatic notch violation with resultant neurovascular injury can occur during placem ent of iliac screws unless intraoperative imaging with teardrop view is used.

Indications and Techniques for Sacral-Pelvic Fixation in Adult Spinal Deform it y Refere nces Five Must-Read Refe rences 1. Kim YJ, Bridw ell KH, Len ke LG, Ch o KJ, Edw ards CC II, Rin ella AS. Pseu dar th rosis in ad u lt sp in al deform it y follow ing m u lt isegm en tal in st rum en t at ion an d arth rodesis. J Bon e Join t Surg Am 2006;88:721–728 PubMed 2. Kost u ik JP. Treat m en t of scoliosis in the adult th oracolum bar spin e w ith special reference to fusion to th e sacr um . Or th op Clin Nor th Am 1988;19:371–381 PubMed 3. San tos ER, Rosn er MK, Perra JH, Polly DW Jr. Spin opelvic xat ion in deform it y: a review. Neurosurg Clin N Am 2007;18:373–384 Pu bMed 4. Cun n ingh am BW, Lew is SJ, Long J, Dm it riev AE, Lin ville DA, Bridw ell KH. Biom ech an ical evaluat ion of lu m bosacral recon st r u ct ion tech n iqu es for spon dylolisth esis: an in vit ro p orcin e m odel. Sp in e 2002; 27:2321–2327 PubMed 5. Lebw oh l NH, Cu n n ingh am BW, Dm it riev A, et al. Biom ech an ical com parison of lum bosacral xat ion tech n iqu es in a calf sp in e m odel. Sp in e 2002;27: 2312–2320 PubMed 6. McCord DH, Cu n n ingh am BW, Sh on o Y, Myers JJ, McAfee PC. Biom ech an ical an alysis of lu m bosacral xation. Spine 1992;17(8, Suppl):S235–S243 PubMed 7. Kim YJ, Bridw ell KH, Len ke LG, Rin ella AS, Edw ards C II. Pseudar th rosis in prim ar y fusion s for adult idiopath ic scoliosis: in ciden ce, risk factors, an d ou tcom e an alysis. Sp in e 2005;30:468–474 PubMed 8. Moshirfar A, Ran d FF, Spon seller PD, et al. Pelvic xat ion in spine surger y. Historical over view, indications, biom ech an ical relevan ce, and curren t tech n iques. J Bone Joint Surg Am 2005;87(Suppl 2):89–106 PubMed 9. Luk KD, Ch en L, Lu W W. A st ronger bicort ical sacral pedicle screw xat ion th rough th e S1 en dplate: an in vit ro cyclic loading an d pu ll-ou t force evalu at ion . Spin e 2005;30:525–529 Pu bMed 10. Leh m an RA Jr, Kuklo TR, Belm on t PJ Jr, An dersen RC, Polly DW Jr. Advan t age of pedicle screw xat ion directed in to th e apex of th e sacral prom on tor y over bicor t ical xat ion : a biom ech anical an alysis. Spine 2002;27:806–811 Pu bMed

11. Kebaish KM. Sacrop elvic xat ion : tech n iqu es an d com plicat ion s. Spine 2010;35:2245–2251 PubMed 12. Koller H, Zen n er J, Hem p ng A, Ferraris L, Meier O. Reinforcem ent of lum bosacral instrum entation using S1-pedicle screw s com bin ed w ith S2-alar screw s. Op er Or th op Trau m atol 2013;25:294–314 PubMed 13. Cun n ingh am BW, Polly DW Jr. Th e use of in terbody cage devices for spin al deform it y: a biom ech anical perspect ive. Clin Orth op Relat Res 2002;394:73–83 PubMed 14. Tsuch iya K, Bridw ell KH, Kuklo TR, Len ke LG, Baldu s C. Min im um 5-year an alysis of L5-S1 fusion using sacropelvic xat ion (bilateral S1 an d iliac screw s) for spin al deform it y. Spin e 2006;31:303–308 PubMed 15. San tos ER, Sem bran o JN, Mu eller B, Polly DW. Opt im izing iliac screw xat ion : a biom ech an ical st u dy on screw length , t rajector y, an d diam eter. J Neu rosu rg Spin e 2011;14:219–225 PubMed 16. Peelle MW, Len ke LG, Bridw ell KH, Sides B. Com parison of pelvic xat ion tech n iques in n eurom uscular sp in al deform it y correct ion : Galveston rod versu s iliac an d lum bosacral screw s. Spin e 2006;31:2392– 2398, discussion 2399 PubMed 17. Tis JE, Helgeson M, Leh m an RA, Dm it riev AE. A biom ech an ical com parison of di eren t t ypes of lum bopelvic xat ion . Spin e 2009;34:E866–E872 PubMed 18. Ch ang TL, Spon seller PD, Kebaish KM, Fish m an EK. Low p ro le p elvic xat ion : an atom ic p aram eters for sacral alar-iliac xat ion versus t radit ional iliac xat ion . Spin e 2009;34:436–440 PubMed 19. O’Brien JR, Yu W, Kaufm an BE, et al. Biom ech an ical evalu at ion of S2 alar-iliac screw s: e ect of length an d quad-cort ical purch ase as com pared w ith iliac xat ion. Spin e 2013;38:E1250–E1255 Pu bMed 20. Polly DW Jr, Klem m e W R, Cun n ingh am BW, Burn et te JB, Hagger t y CJ, Oda I. Th e biom ech an ical sign i can ce of an terior colum n suppor t in a sim u lated sin gle-level spin al fusion . J Spin al Disord 2000;13:58–62 PubMed

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5 Instrumentation Strategies in Osteoporotic Spine : How to Prevent Failure? Ahmet Alanay and Caglar Yilgor

■ Introduction Osteop orosis is an im balan ce bet w een bon e form at ion an d resorpt ion th at prim arily a ects t rabecu lar bon e. Progressive bon e m in eral loss an d con com itan t bony arch itect ure ch anges resu lt in p ain , deform it y, in creased risk of fract u re, an d possible n eu ral com p ression . Th e spin e is th e m ost com m on site of osteoporot ic fract u res. Alth ough m ost pat ien ts w ith acu te ver tebral com p ression fract u res im p rove regardless of th e t reat m en t ap p lied, n o pat ien t exp erien ces sp on t an eou s restorat ion of t h e ver tebral h eigh t an d ach ieves a realign ed sp in e. Th erefore, sp in al in st r u m en t at ion is even t u ally requ ired for som e p at ien t s. W it h agin g com es a h igh er in cid en ce of com orbid it ies t h at fu r t h er com p licates t h e m an agem en t of osteop orot ic sp in e. Th e eld erly today h ave m ore act ive lifest yles th an d id t h e eld erly of p reviou s gen erat ion s, an d th ey refu se to accept d isabilit y an d d efor m it y as a p ar t of t h e agin g p rocess. Mod i able con d it ion s su ch as p u lm on ar y, coron ar y, an d cerebrovascu lar d isease an d d iabetes m ellit u s sh ou ld be addressed in collaborat ion w ith th e con su lt ing m edical an d an esth esiology sp ecialists to m in im ize th e surgical risk an d opt im ize th e ou tcom e. Pat ien t s w h o sm oke, h ave a n u t rit ion al de cien cy, are dep ressed, or are su bject to oth er life st ressors sh ou ld be cou n seled preop erat ively to redu ce th e im p act of th ese factors.

Perform ing adu lt spin al recon st ru ct ion in pat ien ts w ith osteop en ia requ ires carefu l preoperat ive plan n ing, as osteopen ia h as im pact on both idiopath ic an d degen erat ive disorders. Sim ilarly, careful preop erat ive p lan n ing is requ ired w h en p erform ing a recon st r u ct ion on you nger pat ien t s w ith secon dar y osteop orosis du e to factors su ch as hyp ercor t isolism , hyp erthyroidism , hyperparathyroidism , alcohol abuse, an d im m obilizat ion . In pat ien t s w ith low bon e m in eral den sit y (BMD), spin al im plan t s can n ot be placed as securely as in pat ien ts w ith n orm al BMD, an d th u s ap plicat ion of correct ive forces th rough th e w eak bon e–im p lan t in terface is di cu lt . To avoid failure in su ch sit uat ion s, it is im portan t to u n derstan d th e biom ech an ics of th e osteoporot ic spin e an d to recogn ize th at osteop orosis is a system ic disease. Th e m ain su rgical goal sh ou ld be set to t reat th e sym ptom s. Th is ch ap ter discusses th e pre- an d postoperat ive m easures that can be taken in treating pat ients w ith osteoporosis, an d th e surgical st rategies th at can be used to redu ce th e risk of failure.

■ Understanding the

Modes of Failure in Osteoporotic Spine In the osteoporotic spine, the t w o m ost com m on surgical problem s are failure of the xation

Instrum entation Strategies in Osteoporotic Spine or of th e bon e–im plan t in terface, an d adjacen t segm en t failu re, eith er of w h ich m ay resu lt in pseu dar th rosis. In th e early postop erat ive p eriod, p edicle an d adjacen t ver tebral fract u res are th e m ost com m on failu res, w h ereas in t h e late p h ase, p seu dar t h rosis w it h in st r u m en t at ion failu re, adjacen t disk degen erat ion , an d late com pression fract u res w ith p rogressive kyph osis occu r m ore frequ en tly. Because the osteoporotic spine is less able to w ith st an d force, even th e st resses an d st rain s th at are en t ailed in th e act ivit ies of daily living can cause postoperative im plant failure, w hich m ay present as a sudden pain, a neurologic problem , or im plan t prom in en ce.

Fixation Failure Becau se t h e elast ic m od u lu s of t h e bon e is sm aller t h an t h at of t h e im p lan t , an d becau se th e force t ran sm ission s follow th e p ath of least resist an ce, th e bon e su r rou n d ing t h e screw s fails before t h e im p lan t d oes. Th is p h en om en on is called screw toggling, an d, un der repet itive cycling loading, pedicle screw s t ypically fail by ceph alocaudal toggling. Th en loosen ing an d eventually pullout occur, stripping or fracturing th e p edicle. Th e th in n er lateral w all of t h e p edicle is m ore often fractured than the m edial wall. Th e packing of a stripped screw h ole w ith cort icocancellous graft does not usually augm ent the pullout strength of osteoporot ic pedicles, w hich is a p ossible salvage m eth od in h ealthy bon e.1 In a cem en t-augm en ted pedicle, th e screw can be pu lled ou t alon e, cau sing n o dam age to th e bon e or th e cem en t , or th e screw an d th e cem en t can be p u lled ou t toget h er, creat in g eith er an en larged h ole in th e pedicle or a p ed icle fract ure. Th e dorsal lam in a h as a th icker cor t ical sh ell than does the ventral aspect, w hich contributes to it s success in th e osteoporot ic spin e. Th e m ain failu re m ech an ism of th e lam in ar h ooks is lam in a breakou t , breaking th e “ring” form ed by th e lam in a, posterior vertebral body, an d m edial pedicle w alls. Fract ure of the upper-instrum ented vertebra is an oth er com m on ly seen failu re in th e osteoporot ic spin e.

Adjacent Segment Problems After xat ion of th e osteoporot ic spin e, alm ost 80%of th e proxim al jun ct ion al kyph osis occurs du e to adjacen t ver tebra fract u res.2 In st abilit y an d adjacen t disk degen erat ion are oth er possible m ech an ism s of adjacen t segm en t failu re. Th e preoperat ive st at us of th e adjacen t segm en t an d disk is th e greatest p red ictor of t h e developm ent of postoperat ive adjacent segm en t failure. One m ust avoid ending a fusion adjacent to a severely degen erated disk or to a segm en t w ith xed obliqu it y or sublu xat ion .

Nonunion and Pseudarthrosis Sim ilar to a h ealthy bon e, an osteop orot ic bon e is also su bject to p seu dar th rosis, especially in fusions extending to the sacrum . Know n risk factors in clu de th oracolu m bar kyp h osis, p osit ive sagit tal balan ce greater th an 5 cm , presen ce of h ip osteoar th rit is, an d in com plete sacropelvic xat ion .

■ Preoperative Measures Quantifying Bone Quality Grading scales from X-rays, du al-en ergy X-ray absorptiom etr y (DEXA), quantitative com puted tom ography (QCT), an d m icrodensitom etr y can be u sed to diagn ose an d quan t ify osteoporosis in an adu lt su rgical can didate. QCT p rovides sep arate BMD est im ates of t rabecu lar an d cort ical bon e, an d h as a h igh er sen sit ivit y du e to it s im aging in a cross-sect ion al plan e. Alth ough QCT is u sefu l in p red ict in g t h e fract u re r isk, th ere is n o clear con sen su s on a cor relat ion bet w een th e quan t it y of osteoporosis an d th e t ype of st rategies th at sh ould be ap plied. Th e DEXA values acqu ired from th e fem oral n eck sh ou ld be in ter p reted w it h cau t ion becau se th e bon e den sit y in th e sp in e decreases earlier th an in oth er skelet al sites in th e early post m en opau sal years du e to t u rn over in th is h igh ly t rabecu lar bon e. Bon e den sit y at various skeletal sites begin s to coin cide at about age 70. Also, DEXA acqu ired from t h e ver tebrae m ay be falsely elevated due to degen erat ive ch anges.

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Chapter 5 Th erefore, th e su rgeon m u st be ready to deal w ith a w eak bon e regardless of th e preoperat ive DEXA valu es.

Medical Treatment It is w ell docum en ted in th e literat ure th at BMD correlates w ith im plan t pu llou t st rength . Th erefore, preoperative m edical treatm en t w ith bisphosphonates, recom binant parathyroid horm on e (rPTH), calciton in , select ive est rogen receptor m odu lators, calcium , or vit am in D sh ou ld be con sidered. It is also im p or tan t to determ ine w h ether the bene t of m edical treatm en t is su cien t en ough to o set th e delay in su rgical t reat m en t . Th e ch oice, t im ing, an d durat ion of postoperative pharm acological treatm ent for osteoporosis also rem ain controversial because these drugs m ay in terfere w ith bon e h ealing.

■ Intraoperative Measures Th e loss of th e qu an t it y as w ell as th e arch itect u re of th e osteop orot ic bon e m ay in crease th e risk of sp in al su rger y or m ake th e su rgical goals di cult to ach ieve. In th ese sit u at ion s, speci c pedicle screw ch aracterist ics an d in sertion techniques can be adopted, and surgical strategies such as addressing the pathom orphology of the osteoporotic vertebrae, han dling soft t issu e m et icu lou sly, en h an cing an ch or poin ts, ap p lying p rop hylact ic ver tebrop last y, u sing in terbody su p p or t , an d p rotect ing t h e bon e– im p lan t in ter face are u t ilized to im p rove t h e rate of su ccessfu l xat ion . Th ese tech n iqu es an d st rategies are discu ssed in th e follow ing su bsect ion s.

Pathomorphology of the Osteoporotic Vertebrae It is w ell establish ed that the bone qualit y varies in di eren t part s of th e ver tebrae. Th e vertebral body itself is th e m ost a ected par t of th e osteoporotic vertebrae. The lam ina, on the other h an d, w h ich is predom in an tly cor t ical, is rela-

t ively sp ared an d is p oten t ially a st ronger an ch or. Th e m or p h om et r y of t h e p ed icles are variable. Th is pat tern of bon e loss cau ses th e pedicle screw xat ion to be less e ect ive in th e osteoporot ic bon e. Th e xat ion of th e pedicle screw s is ach ieved eith er by taking advan tage of th e relat ively st ronger cor t ical bon e w ith in th e p edicle by in creasing th e screw diam eter and avoiding tapping the screw path, or by augm en t in g t h e p ed icle screw in var iou s w ays. Su blam in ar xat ion w ith w ires, cables, h ooks, an d ban ds is also a good altern at ive because th e lam in a is less a ected by osteoporosis. Th e BMD also varies in di eren t region s of th e sacr u m . Medial side h as a h igh er BMD th an th e lateral side, an d th e su p erior sacral en d plate h as th e h igh est . Th e screw s sh ou ld th erefore be directed m edially in a t riangu lar fash ion an d tow ard th e sacral prom on tor y. Th e T2 p ed icle is gen erally st ron ger t h an T3–T6 p ed icles, m aking T2 a good opt ion for screw xat ion or p ed icle h ooks as a st rong u pper an ch or poin t .3

Pedicle Screw Factors No con sen su s h as yet been reach ed on t h e op t im al screw diam eter, lengt h , an d sh ap e for xat ion in th e osteop orot ic bon e. How ever, several p edicle screw ch aracterist ics, togeth er w ith th e h ole preparat ion an d screw in ser t ion tact ics, are sh ow n to ach ieve a bet ter xat ion an d preven t im p lan t failu re.

Pedicle Screw Characteristics Dou ble-th readed p edicle screw s h ave a can cellou s th read ed t ip follow ed by a cor t ical th read. Th e w ider p itch of can cellou s th read p rovides add it ion al gr ip in t h e can cellou s bon e, an d th e screw advan ces faster w ith h igh er in sert ion torqu e. Th e cort ical th read in th e pedicle area provides h igh er grip an d less toggle due to den ser th reads.4 Con ical (tapered) screw s also in crease in sert ion al torqu e, bu t th ey can n ot be reversed or backed out , because doing so eradicates th e screw ’s con tact w ith th e bon e. Th e expan dable pedicle screw u ses a n ovel screw design th at en ables th e distal p ar t of th e

Instrum entation Strategies in Osteoporotic Spine screw to en large w ith in th e ver tebral body as a posteriorly directed force is applied to th e screw to resist p u llou t failu re. Th e t ip of th e screw becom es an ch ored again st th e in n er cortex of th e dorsal ver tebral body, resu lt ing in a 76% in crease in h olding st rength in com parison to conven t ion al pedicle screw s,5 by t aking advan t age of th e relat ively un com prom ised cor t ical bon e rath er th an d ep en ding solely on w eaken ed osteoporot ic can cellous bon e. How ever, in pat ien ts w ith severely low BMD, expan dable screw s m ay be u n able to overcom e th e ext rem e biom ech an ical d isadvan t age, resu lt ing in failu re. Moreover, screw revision rem ain s an issue in th e clin ical applicat ion of th ese screw s.

Pedicle Screw Tract Augmentation It is possible to augm ent the pedicle screw tract by preparing th e h ole, inject ing polym ethylm eth acr ylate (PMMA) bon e cem en t in to th e h ole, an d in ser t ing th e screw after w ards. Augm en t at ion m ay also be d on e w it h bioact ive cem ents, calcium phosphate, or calcium sulfate u sing t rad it ion al or fen est rated p edicle screw s. Coat ing th e pedicle screw w ith hydroxyapat ite is a t im e-dep en den t augm en t at ion tech n iqu e th at in creases osteoin tegrat ion .

Cement Augmentation and Fenestrated Screws A cadaveric biom ech an ical an alysis of PMMAaugm en ted pedicle screw xat ion using a n ovel fen est rated bon e t ap in creased th e p u llou t st rength by 199% an d 162% in p rim ar y an d revision p rocedures, resp ect ively.6 Clin ical series also d em on st rated good ou tcom e w it h n o screw loosen ing, m igration , or pullout detected in th e follow -u p X-rays, n o fract ure at th e augm en ted levels, an d n o im plan t failure requiring rein ter ven t ion .7,8 Alth ough PMMA augm en tat ion of th e pedicle screw s provides good xat ion in pat ien t s w ith low BMD, it is n ot free of com plicat ion s. Ext ravasat ion , in t racan al leakage, hypoten sion , in crease in pu lm on ar y ar ter y p ressu re, pulm on ar y cem en t em boli, su per cial in fect ion s, an d th erm al n er ve inju ries w ere repor ted . Th erefore, st rategies w ere developed to reduce th e

likelih ood of cem en t leakage. High er viscosit y cem ent can be used, and uoroscopy can provide additional assistance. It is generally recom m en ded to inject 1 to 3 m L of cem en t becau se u sing a larger am oun t fails to dem on st rate any sign i can t ben e t in p ullou t st rength .6 At ten t ion w as also paid to th e m eth od of PMMA augm en t at ion . Inject ing cem en t in to a cavit y p rep ared by an in at able balloon follow ed by in ser t ion of th e p edicle screw dem on st rated alm ost t w ice th e p u llou t st rength of screw s augm en ted w ith standard cem ent injection.9 Fenestrated screw s have been used m ore recen tly, w ith p rom ising resu lts.10 Alth ough clin ical long-term resu lt s are yet to be seen , th ere is a p oten t ial th eoret ical advan t age of using fen est rated screw s over inject ing cem en t follow ed by screw in ser t ion . Inject ing th e cem en t in to th e p rep ared h ole lls th e t ract , an d w h en in sert ing th e pedicle screw, th e cem en t coat s th e screw th reads an d t h ereby redu ces e ect ive screw purch ase. Altern at ively, cem en t inject ion th rough a fen est rated screw en ables th e cem en t to in lt rate in th e ver tebral body w ith ou t altering th e bon e–im plan t in terface.11 Alth ough it is w idely used w ith prom ising resu lt s, PMMA is toxic, is u n able to u n d ergo rem odeling after m icrofract ure w ith in th e cem en t , an d is d i cu lt to rem ove in revision su rger y. Hen ce, osteobiologic cem en t is an area of in terest an d developm en t for screw augm entation. Calcium phosphate and calcium sulfate avoid th e exoth erm ic react ion an d redu ce th e risk of leakage. Moreover, th ey are bioresorbable and potentially osteoconductive, and in tegrate in th e n at ural p rocess of bony rem odeling. A cadaveric st u dy com paring osteobiologic cem en t an d PMMA for th e u se of screw augm en t at ion foun d n o sign i can t di eren ces in axial pu llou t st rength .12

Hydroxyapatite Coating Th e in creased osteoin tegrat ion of th e hyd roxyapat ite-coated pedicle screw s is t im e depen den t; w ith t im e, opt im u m stabilit y is ach ieved. It h as been sh ow n in an osteoporot ic an im al m odel that hydroxyapatite-coated pedicle screw s are 1.6 t im es m ore resistan t to pu llou t an d th at th ey h ave su p erior biological bon ding to th e

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Chapter 5 surrounding bone, occurring as early as 10 days after surger y.13 How ever, th ey do n ot allow for th e ap p licat ion of addit ion al forces du ring in t raoperat ive correct ion m an euvers.

Insertion Technique and Insertional Torque The starting point, hole preparation, tapping, the in sert ion angle, an d th e t rajector y of a p edicle screw, as w ell as it s length , depth of pen et rat ion , an d diam eter, a ect it s in ser t ion al torqu e an d th ereby its resistan ce to failure.

Length of Screw and Depth of Screw Penetration Th e length of a pedicle screw is lin early related to its pullout st rength . As th e screw pen et rates fur th er in to th e ver tebral body, th e cu tou t load to failu re in creases. By en gaging t h e ven t ral cor tex of t h e ver tebral body, screw s can be p laced in a bicor t ical fash ion to p rovid e u p to an addit ion al 30% of pullout st rength .14 Th e risk–ben e t rat io sh ould be con sidered, an d care m u st be taken to avoid inju r y to adjacen t st r uct u res w h en u sing th is tech n ique.

th e ver tebral body form ed by longer an d t rian gulated screw s.16 Thoracic Spine In th e an atom ic t rajector y, th e screw is in lin e w ith th e pedicle axis an d th erefore is directed to th e in ferior corn er of th e ver tebral body in th e sagit t al p lan e. In th e st raigh tfor w ard tech n ique, th e screw is parallel to th e ver tebral en d plate an d t riangu lat ion in th e t ran sverse p lan e can be ach ieved. Th is tech n iqu e provides at least 39% h igh er m axim u m in ser t ion al torqu e an d 27% greater pullout st rength .17 Pedicle-rib screw s in crease th e e ect ive t ran sverse diam eter w hen com pared w ith the pedicle alone and can be u sed for safer in ser t ion of t h e screw s, alth ough it m ay decrease th e pullout st rength by 25%.18 Th e star t ing poin t sh ou ld be selected in accordan ce w ith th e t rajector y used. Lumbar Spine Placing th e p edicle screw s in convergen ce also in creases t h e p u llou t st rength in t h e lu m bar spin e.

Th e diam eter of t h e p edicle screw sh ou ld be as w ide as possible to en able bet ter cor t ical bon e purchase. Increasing the diam eter in creases th e pu llou t st rength in m ilder cases; h ow ever, in severe osteoporosis th e p u llou t force is low regardless of th e screw diam eter. In stead, using larger diam eters m ay cau se dilat ion or fract u re of th e pedicle th at decreases it s st rength .15

Sacrum and Pelvis Sacral xat ion is a big ch allenge in th e osteoporot ic spin e. Restorat ion of th e sagit tal balan ce is m ore im por t an t th an th e xat ion itself. W h en th e fu sion is exten ded to th e sacr u m an d a long fusion is perform ed, m ult iple an d bicort ical screw xat ion sh ould be used in addit ion to con siderat ion of an terior colu m n su p por t or iliac xat ion . Th e t ricor t ical tech n iqu e, w h ich en t ails d irect in g t h e screw s in to t h e sacral p rom on tor y, in creases t h e in ser t ion al torque.19

Starting Point, Insertion Angle, and Trajectory

Hole Preparation and Tapping

W h en th e screw s are placed parallel, th e volu m e of can cellou s bon e bet w een t h e t h read s of th e screw determ in es th e resist an ce to p u llout for each screw. Triangulated screw s provide bet ter pullout st rength w ith a larger volum e of can cellou s bon e available for resist an ce to pu llout becau se th e con st r uct is con t ributed by th e volu m e of bon e w ith in th e t rapezoid area in

Appropriate preparat ion of th e h ole im proves screw p u rch ase. High in sert ion al torqu e im proves th e screw pu llou t st rength . In h ealthy ver tebral bodies, th e screw s are p laced after tapping to avoid m icrofract u ring w ith in th e den se bony m at rix of th e bon e d u ring screw insertion. In osteoporotic cancellous bone, how ever, tapping resu lt s in rem oval of bon e w ith in

Diameter

Instrum entation Strategies in Osteoporotic Spine th e pedicle t rack an d p reven t s bon e com p ression arou n d th e screw th reads. Even screw rem oval and im m ediate reinsertion decreases the m ech an ical in ser t ion torqu e. Th erefore, u n dertapping or n ot tapping at all is advised in osteoporot ic bon e. W h en com pared w ith sam e-size t ap p in g, u n d er-t ap p ing by 0.5 an d 1.0 m m in creases t h e in ser t ion al torqu e by 47% an d 93%, respect ively.20 Under-tapping is m ore bene cial in the lum bar spin e th an in th e th oracic spin e. Th is m ay be d u e to t h e fact t h at t h e t h oracic p ed icle screw s are p robably m ore d ep en d en t on cort ical pu rch ase w ith in th e p edicle w alls.

Enhancing Anchor Points Th e w eak lin k in t h e osteop orot ic sp in e in st r u m en t at ion is t h e im p lan t–bon e in ter face. Fixat ion st rategies for osteop orot ic bon e are targeted tow ard t aking advan tage of th e relat ively st ronger cor t ical bon e. An ch or opt ion s, in ad d it ion to screw s, in clu d e h ooks, w ires, cables, an d ban ds.

Load Sharing by Multilevel Fixation Becau se th e im plan t–bon e in terface in th e osteoporot ic bon e is pron e to failure, th e n um ber of poin ts of xat ion m ust be in creased to dist ribu te th e con tact forces m ore even ly. Longer con st r u ct s w ith at least t h ree set s of xat ion poin t s at each en d can be ben e cial, keeping in m in d th e added m orbidit y en t ailed w ith u sing addit ion al screw s. As previously stated, using hooks, w ires, cables, and bands as w ell as cross-links help in im proving the perform an ce of the pedicle screw s.

Selection of Fusion Levels En d -in st r u m en ted ver tebrae sh ou ld be carefu lly selected . En d in g t h e con st r u ct in a kyph ot ic region or at th e ap ex of kyp h osis sh ou ld be avoided. An oth er frequ en t decision -m aking dilem m a in th e osteoporot ic sp in e is w h eth er or n ot to fu se to sacr u m . Cer tain scen arios th at requ ire lu m bosacral xat ion are sym ptom at ic L5-S1

sp on dylolist h esis, over 15 d egrees of scoliosis at th e L5-S1 segm en t , an d th e n eed to ach ieve prop er sagit t al balan ce.21 Stop p ing at L5 en t ails th e risk of in creased adjacen t segm en t disease, w h ereas fusing to th e sacr um is foun d to h ave m ore com p licat ion s.21 L5 pedicles are u su ally short and con tain m ore cancellous bone. Th erefore, it m ay be risky to en d a long fu sion at L5 in osteoporot ic p at ient s becau se L5 pedicle screw s m ay fail.

Cross-Link Th e u se of a r igid or sem ir igid cross-lin k, esp ecially w h en th e screw s are t riangulated, in creases th e torsion al st i n ess by m aking th e con st r u ct p erform e ect ively as a qu adrilateral fram e. Th e use of a cross-lin k is especially advan tageous in longer con st ructs, as it preven t s rods from telescop ing.

Hooks, Wires, Cables, and Bands Th e u se of su blam in ar an d p ed icu lolam in ar h ooks, w ires, cables, an d ban d s t akes advan t age of t h e cor t ical bon e com p osit ion of th e spin al lam in a. A p olyester ban d m ay be u sed to in crease th e surface of bony con tact an d to t any an atom y. It m ay be used in a su blam in ar, subpars, transversal, or lam in ot ransversal fashion to enable t ran slat ion , dist ract ion an d com pression , in sit u ben ding, an d rod derot at ion .

Prophylactic Vertebroplasty In th e set t ing of osteoporosis, jun ct ion al failu re, especially in th e cran ial levels, is n ot a rare occu r ren ce. Preven t ion is t h e best w ay to overcom e adjacen t segm en t failu re. Prop hylact ic vertebroplast y entails cem ent augm en tation of th e adjacent nonin st rum ented segm ent/ segm en t s. Alth ough th ere is a p au cit y of clin ical an d biom ech an ical st u dies, p rophylact ic ver tebroplast y seem s to be h elp fu l in decreasing th e revision ar th rod esis rates becau se of adjacen t ver tebrae fract u res.22 Furth er st udies are n eeded to clarify th e op t im u m am ou n t of cem en t requ ired an d h ow

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Chapter 5 m any levels sh ou ld be p rop hylact ically cem en ted . E cacy at th e d ist al adjacen t level also n eeds to be fu r th er an alyzed.

Interbody Support in Osteoporotic Spine An terior colum n suppor t is ben e cial in load sh aring becau se th e graft or cage lessen s th e

st ress directed tow ard th e screw –rod const ru ct . An ter ior in terbody su p p or t m ay fu r t h er im p rove sagit t al sp in al balan ce an d rates of ar th rodesis. In terbody graft s ser ve a m ore crit ical role at th e cau dal en d of th e con st ru ct , par t icu larly at th e lu m bosacral ju n ct ion . Graft s can be placed w ith a bias tow ard th e con cavit y of th e deform it y to assist cor rect ion . Figs. 5.1, 5.2, an d 5.3

a

b

Fig. 5.1a,b (a) Preoperative posteroanterior X-ray. (b) Preoperative lateral X-ray.

Instrum entation Strategies in Osteoporotic Spine

a

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b

Fig. 5.2a,b (a) Preoperative sagit tal magnetic resonance im aging (MRI) view. (b) Preoperative transverse MRI view.

dem onstrate the use of the intraoperative m easures m entioned above in a 64-year-old patient w it h a BMD of –3.2 com p lain in g of back an d leg p ain . In severe osteoporosis, th ere is a risk of su b siden ce of th e graft or cage in to th e en d p lates th at m ay lead to an ter ior colu m n collap se an d su bsequ en t kyp h ot ic d efor m it y. Th e cage sh ou ld be placed to con t act th e p erip h eral apophyseal ring w h ere th e cor t ical bon e is st ronger. A graft w ith an elast ic m odu lu s th at is sim ilar to th e n at ive bon e also redu ces th e risk of subsiden ce. Ch oices of in terbody graft m aterials include bon e (autograft or allograft), m etal, carbon ber, p olyar yleth ereth erketon e (PEEK), an d oth er syn th et ic m aterials. Iliac crest autograft is t yp ically t h e best m atch , bu t it is asso ciated w it h w ell-est ablish ed h ar vest -related m orbidit y.

Role of Anterior Fixation in the Osteoporotic Spine Continuous loading of an terior screw constructs on a low -BMD spine can lead to screw cutout. Although new er im plan t designs dem on strate im proved anchorage,23 anterior xation has a lim ited role in the osteoporotic spine because it is the m ost a ected part of the vertebrae.

Role of Semirigid Fixation in the Osteoporotic Spine Th e load in g of t h e sp in e in var iou s a xes of m ot ion creates in creased st ress at th e bon e– im plan t in terface. Th e di eren ce of th e rigidit y w ith in th e in st r um en ted an d n on in st r um en ted segm en t s of th e sp in e can accelerate adjacen t segm en t degen erat ion an d p oten t ially cau se pseu dar th rosis. Sem irigid xat ion m ay provide su cien t stabilizat ion to facilitate bony fu sion w h ile perm it t ing som e degree of exibilit y to o oad st ress at th e adjacen t segm en t an d th e bon e–im plan t in terface.

Protection of the Bone –Implant Interface Handling intraoperative soft tissue m eticulously, providing exten sive release, p erform ing osteotom ies to in crease exibilit y an d th us m in im ize th e correct ive forces, m ain t ain ing sagit t al align m en t , an d obtain ing a solid fu sion are essen tial for th e protect ion of th e bon e–im p lan t in terface.

Meticulous Soft Tissue Handling Care sh ou ld be t aken to p reser ve t h e su p rasp in ou s ligam en t , in t rasp in ou s ligam en t , an d

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a

b

Fig. 5.3a,b (a) Last follow-up posteroanterior X-ray of the sam e patient dem onstrating the use of cem ent-augmented pedicle screws, anterior interbody support, prophylactic vertebroplast y,

and cross-link. (b) Last follow-up lateral X-ray of the same patient demonstrating the use of cementaugmented pedicle screws, anterior interbody support, prophylactic vertebroplast y, and cross-link.

Instrum entation Strategies in Osteoporotic Spine ligam en t u m avu m bet w een th e cran ial fu sed level an d th e adjacen t segm en t , as w ell as bet w een th e cran ial levels of fu sion . Doing so provides a segm en t of h igh er p osterior ten sion , w h ich m ay preven t th e developm en t of ju n ct ion al d eform it y an d in st abilit y. Su p ra- an d in fra- adjacen t facet s sh ou ld be p reser ved an d th e cran ial d isk sp ace sh ou ld n ot be violated w ith pedicle screw s.

Extensive Release Th e release of th e diskoligam en tou s an d bony con st rain t s su ch as d iskectom y, facetectom y, or var iou s osteotom ies sh ou ld be opt im ized before red u ct ion to d ecrease th e st ress applied to th e bon e–im plan t in terface w h en perform ing spin al correct ive m an euvers.

d ling soft t issu e m et icu lou sly, p rovid in g exten sive releases, m aintaining sagit tal alignm ent, and using an terior in terbody suppor t decreases th e dem an d on xat ion in th e p ostoperat ive period. Extern al brace im m obilizat ion an d rest r ict ion of th e sp in e ran ge of m ot ion as w ell as physical th erapy an d reh abilit at ion are m easures that can be taken in the postoperative period to ser ve the sam e purpose. As stated earlier, th e t im ing of postop erat ive p h arm acological osteoporosis t reat m en t rem ain s con t roversial. If a brace is to be u sed, it m u st be cu stom m olded postoperatively, after surgical deform ity correct ion is est ablish ed . Reh abilit at ion sh ou ld focu s on gait t rain ing, balan ce, an d gen eral con d it ion in g, toget h er w it h ran ge-of-m ot ion an d exibilit y exercises of t h e h ip an d kn ee. Th ere is n o con sen su s yet on th e du rat ion of brace applicat ion .

Maintaining Sagittal Alignment Align ing t h e osteop orot ic sp in e to p hysiological coron al an d sagit t al con tou rs n eu t ralizes th e defor m ing forces, redu ces t h e ju n ct ion al forces, an d d ecreases t h e en ergy requ ired for am bulat ion .

Obtaining Fusion Obt ain ing a rap id an d solid fu sion en su res long-term spin al stabilit y, redu cing th e load on in st r um en t s an d on th e relat ively p oor bon e– im plan t in terface. A th orough fu sion procedu re w ith appropriate bon e-bed preparat ion an d appropriate use of bon e graft s or subst it utes is th erefore of p ar t icu lar im por t an ce in th e osteoporot ic spin e. Th e u se of bon e m orph ogen et ic protein m ay facilitate an earlier an d m ore vigorous fusion , an d decrease th e risk of im plan trelated failure. The use of bone m orphogenetic protein m ay also be associated w ith com p licat ion s related to soft t issu e sw elling, in app ropriate bon e form at ion arou n d n eu ral elem en t s, an d su bsequ en t radiculit is.

■ Postoperative Measures Enhan cing the purchase of intern al xation and protect ing th e bon e–im p lan t in terface by h an -

■ Chapter Summary Prim arily a ect ing th e t rabecu lar bon e, osteoporosis cau ses p rogressive bon e m in eral loss an d con com it an t bony arch itect u re ch anges th at resu lt in p ain , d efor m it y, in creased fract u re r isk, an d p ossible n eu ral com p ression . Alth ough m ost pat ien t s w ith acute, pain fu l ver tebral com p ression fract u res im p rove regardless of th e t reat m en t applied, n o pat ien t spon tan eou sly restores th e ver tebral h eigh t an d ach ieves a realign ed spin e. Spin al in st ru m en t at ion is even t u ally requ ired in som e osteoporot ic pat ien ts. In th e set t ing of osteoporosis, h ow ever, th e xat ion of th e spin al im plan ts is in secu re, an d app licat ion of correct ive forces th rough a w eak bon e–im p lan t in terface is di cult , com plicat ing th e surgical t reat m en t . Th e rst step for an adu lt spin al su rgical can didate is th e diagn osis an d qu an t i cat ion of th e osteoporosis. Un derstan ding th e biom ech an ics an d th e m odes of failu re of th e osteop orot ic sp in e is im por t an t . Th e ver tebral body itself is th e m ost a ected p ar t of th e osteop orot ic ver tebrae. Th e lam in a, on th e oth er h an d, w h ich is predom in an tly cor t ical, is relat ively sp ared an d is p oten t ially a st ronger an ch or. Th e m orph om et r y of th e pedicles is variable. Failure of th e

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Chapter 5 xat ion or of th e bon e–im plan t in terface, adjacen t segm en t failures, an d pseudarth rosis are th e th ree m ain problem s in osteop orot ic spin e. Several p re- an d postop erat ive m easu res m ay be t aken , as w ell as ap p lying several su rgical st rategies in t raop erat ively to p reven t failu re. Th e p ed icle screw ch aracter ist ics toget h er w it h h ole p rep arat ion an d screw in ser t ion t act ics are sh ow n to ach ieve a bet ter xat ion . An terior colum n suppor t is ben e cial in load sh ar ing, im p roving sagit t al balan ce an d red u cing th e rates of arth rodesis. Th e resu lt s of cem ent augm entation of the pedicle screw s and th e adjacen t n on in st r u m en ted ver tebrae seem p rom ising, bu t it is n ot a com p licat ion -free procedu re.

Pearls In elective cases, increasing the BMD preoperatively with parathyroid hormone might be considered. Under-tapping is advised in the osteoporotic bone to increase the insertional torque. Triangulated screws provide bet ter pullout strength, with a larger volum e of cancellous bone available for resistance to pullout because the construct is contributed by the volum e of bone within the trapezoid area in the vertebral body formed by the longer and triangulated screws. The use of a cross-link is especially advantageous in longer constructs, as it prevents rods from telescoping. The use of hooks, wires, cables, and bands take advantage of the relatively stronger cortical bone for xation of osteoporotic bone.

Cem ent-augm ented pedicle screws are advantageous for bet ter xation and for allowing additional corrective forces. Prophylactic vertebroplast y is helpful in decreasing the revision arthrodesis rates because of adjacent vertebrae fractures. The release of the diskoligamentous and bony constraint s such as diskectomy, facetectomy, or various osteotom ies should be optim ized before reduction when perform ing spinal corrective procedures to decrease the stress applied to the bone–implant interface. A custom -m olded postoperative brace helps protect the bone–implant interface. Pitfalls Avoid ending a fusion adjacent to a severely degenerated disk or to a segment with xed obliquit y or subluxation. DEXA scans in elderly patients must be interpreted with caution because degenerative changes may falsely elevate the BMD values. In the osteoporotic bone, t apping result s in rem oval of bone within the pedicle track and prevent s bone com pression around the screw threads. Avoid ending a construct in a kyphotic region or at the apex of kyphosis. Avoid dam aging the supra- and intraspinous ligaments and ligam entum avum bet ween the cranial fused level and the adjacent segm ent, as well as bet ween the cranial levels of fusion. Avoid damaging the supra- and infra-adjacent facets and violating the cranial disk space with pedicle screws.

Refere nces Five Must-Read Refe rences 1. Halvorson TL, Kelley LA, Th om as KA, W h itecloud TS III, Cook SD. E ects of bone m ineral densit y on pedicle screw xation. Spin e 1994;19:2415–2420 PubMed 2. DeWald CJ, St an ley T. In st r u m en t at ion -related com p licat ion s of m u lt ilevel fu sion s for adu lt sp in al deform it y p at ien t s over age 65: su rgical con sid erat ion s an d t reat m en t opt ion s in p at ien t s w it h p oor bon e qu alit y. Sp in e 2006;31(19, Su p p l):S144–S151 Pu bMed 3. Bu t ler TE Jr, Ash er MA, Jayaram an G, Nu n ley PD, Robin son RG. The st rength an d st i n ess of thoracic im plan t an ch ors in osteoporot ic spin es. Spin e 1994;19:1956–1962 Pu bMed

4. Mum m anen i PV, Haddock SM, Liebsch n er MA, Keaveny TM, Rosen berg WS. Biom ech an ical evaluat ion of a double-threaded pedicle screw in elderly vertebrae. J Spin al Disord Tech 2002;15:64–68 PubMed 5. McKoy BE, An YH. An exp an dable an ch or for xat ion in osteop orot ic bon e. J Or t h op Res 2001;19:545– 547 PubMed 6. Fran kel BM, D’Agost in o S, Wang C. A biom ech an ical cadaver ic an alysis of p olym et hylm et h acr ylateaugm en ted pedicle screw xat ion. J Neurosu rg Spin e 2007;7:47–53 PubMed 7. Ch ang MC, Liu CL, Ch en TH. Polym ethylm eth acr ylate augm en t at ion of pedicle screw for osteoporot ic spi-

Instrum entation Strategies in Osteoporotic Spine nal su rger y: a n ovel tech n ique. Spin e 2008;33:E317– E324 PubMed 8. Aydogan M, Ozt u rk C, Karatoprak O, Tezer M, Aksu N, Ham zaoglu A. The pedicle screw xat ion w ith vertebroplast y augm en t at ion in th e su rgical t reat m en t of th e severe osteoporot ic spin es. J Spin al Disord Tech 2009;22:444–447 PubMed 9. Bur val DJ, McLain RF, Milks R, In ceoglu S. Prim ar y ped icle screw augm en t at ion in osteop orot ic lu m bar ver tebrae: biom ech an ical an alysis of p edicle xat ion st rength . Spin e 2007;32:1077–1083 PubMed 10. Ch ang MC, Kao HC, Ying SH, Liu CL. Polym ethylm ethacrylate augm entation of cannulated pedicle screw s for xat ion in osteoporot ic spines an d com parison of its clin ical result s an d biom ech an ical ch aracterist ics w ith th e n eedle inject ion m eth od. J Spin al Disord Tech 2013;26:305–315 PubMed 11. Wang MY, Hoh DJ. Bon e m et abolism an d osteop orosis an d it s e ect s on spin al disease an d su rgical t reat m en t s. In : Win n HR, ed. Youm an s’ Neurological Surger y. Ph iladelph ia: Elsevier; 2011 12. Roh m iller MT, Sch w alm D, Glat tes RC, Elalayli TG, Spengler DM. Evaluat ion of calcium sulfate paste for augm en t at ion of lu m bar p edicle screw p u llou t st rength . Spin e J 2002;2:255–260 PubMed 13. Hasegaw a T, In u fu sa A, Im ai Y, Mikaw a Y, Lim TH, An HS. Hydroxyapat ite-coat ing of pedicle screw s im proves resist an ce again st p u ll-ou t force in th e osteoporot ic can in e lum bar spin e m odel: a pilot st udy. Spin e J 2005;5:239–243 PubMed 14. Zin drick MR, Wilt se LL, Widell EH, et al. A biom ech an ical st udy of in t rapedun cular screw xat ion in th e lu m bosacral spin e. Clin Or th op Relat Res 1986; 203:99–112 PubMed 15. Yazici M, Pekm ezci M, Cil A, Alan ay A, Acaroglu E, On er FC. Th e e ect of pedicle exp an sion on p edicle m or p h ology an d biom ech an ical st abilit y in t h e im -

m at u re p orcin e sp in e. Sp in e 2006;31:E826–E829 PubMed 16. Hadjipavlou AG, Nicodem us CL, al-Ham dan FA, Sim m on s JW, Pope MH. Correlat ion of bon e equivalen t m in eral den sit y to pull-out resist an ce of t riangu lated pedicle screw con st ruct . J Spin al Disord 1997;10: 12–19 PubMed 17. Leh m an RA Jr, Polly DW Jr, Ku klo TR, Cu n n ingh am B, Kirk KL, Belm on t PJ Jr. St raigh t-for w ard versus an atom ic t rajector y tech n ique of th oracic pedicle screw xat ion : a biom ech anical an alysis. Spin e 2003;28: 2058–2065 PubMed 18. White KK, Oka R, Mahar AT, Low ry A, Gar n SR. Pullout strength of thoracic pedicle screw instrum entation: com parison of the transpedicular and extrapedicular tech n iqu es. Spin e 2006;31:E355–E358 Pu bMed 19. Leh m an RA Jr, Kuklo TR, Belm on t PJ Jr, An dersen RC, Polly DW Jr. Advan t age of pedicle screw xat ion directed in to th e apex of th e sacral prom on tor y over bicort ical xat ion : a biom echan ical an alysis. Spin e 2002;27:806–811 PubMed 20. Ku klo TR, Leh m an RA Jr. E ect of var iou s t ap p in g d iam eters on in sert ion of th oracic pedicle screw s: a biom ech an ical an alysis. Spin e 2003;28:2066–2071 PubMed 21. Bridw ell KH, Edw ards CC II, Len ke LG. Th e pros an d con s to saving the L5-S1 m ot ion segm en t in a long scoliosis fusion con st ru ct . Spin e 2003;28:S234–S242 PubMed 22. Ch iang CK, Wang YH, Yang CY, Yang BD, Wan g JL. Prop hylact ic ver tebroplast y m ay redu ce th e risk of adjacen t in t act ver tebra from fat igu e inju r y: an ex vivo biom ech an ical st udy. Spin e 2009;34:356–364 PubMed 23. Goldh ah n J, Rein h old M, St au ber M, et al. Im p roved an chorage in osteoporot ic ver tebrae w ith n ew im plant designs. J Orthop Res 2006;24:917–925 PubMed

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6 The Incidence and Management of Acute Neurologic Complications Follow ing Complex Adult Spinal Deformity Surgery Joseph S. Butler and Law rence G. Lenke

■ Introduction Sign i can t advan ces h ave been m ade in adu lt spin al deform it y (ASD) su rger y over th e past several years. Im p rovem en ts in p edicle screw tech n ology an d th e in creasing use of th reecolu m n osteotom ies h ave m ade m ore p ow erfu l deform it y correct ion s possible. Non eth eless, loss of n eu rologic fu n ct ion after ASD su rger y rem ain s a seriou s an d poten t ially devast at ing com p licat ion , w ith profou n d con sequ en ces for health-related qualit y of life. Intraoperative neurophysiology m on itoring h as becom e a reliable an d e ect ive m odalit y to opt im ize n eurologic safet y du ring ASD su rger y.1,2 Fu r th erm ore, th e in creasing use of im age-gu ided n avigat ion system s h as led to sign i can t im provem en t s in the accuracy of pedicle screw placem ent.3,4 This ch apter discusses th e m an agem en t of acute n eu rologic com plicat ion s in com p lex ASD su rgery and proposes a treatm ent algorithm to deal w ith th ese com p licat ion s in safe an d e ect ive m an n er.

■ Prevalence Th e in ciden ce of n eu rologic com p licat ion s in ASD pat ien t s un dergoing deform it y correct ion

su rger y h as been di cu lt to determ in e. Mu lt iple aw s exist in th e p u blish ed dat a, w ith a lack of h igh -qu alit y prospect ive st u dies, sign ifican t dat a variabilit y, an d a lack of rigorou s an d validated m easurem en ts of n eurologic fun ct ion . Non eth eless, th e in ciden ce of n eu rologic d e cit s follow in g ASD su rger y h as been p reviou sly rep or ted as ran gin g from 0% to over 10%.5–9 Tw o previous st udies, on e from a single in st it u t ion , an alyzed p rosp ect ively collected dat a to iden t ify com plicat ion s, but n eith er on e u sed a validated scoring system to qu an t ify n eu rologic fu n ct ion .10,11 All st u d ies cou ld m ore accu rately be described as ret rospect ive st udies of p rospect ively collected dat a. Bu t an accu rate rate of n eurologic com plicat ion s after com plex ASD su rger y is cr it ical for in for m ed d ecision m aking for both p at ien t s an d su rgeon s. Fu rt h er m ore, it is cr u cial to be able to m easu re ch anges in n eurologic com plicat ion rates in a st an dardized fash ion so as to accurately evaluate n ew tech n iques, tech n ologies, an d t h erap ies in ASD su rger y. The Scoli-Risk-1 trial is a recent prospective, m u lt icen ter obser vat ion al st udy at tem pt ing to accu rately assess th e n eu rologic com p licat ion rate follow ing com plex ASD surger y using th e Am erican Spinal Injury Association (ASIA) scoring system (Fig. 6.1).12 A total of 276 pat ien ts

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Neurologic Complications Following Adult Spinal Deformit y Surgery

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Chapter 6 w ere en rolled from 15 in tern at ion al cen ters. At h ospit al disch arge, 23.1% of pat ien t s h ad a m easu rable low er ext rem it y m otor de cit (i.e., less th an 5/5 m otor st rength in all ve m ajor leg m u scles) d ecreasing to 17.8% at 6 w eeks an d 10.7% at 6 m on t h s p ostop erat ive. Th is st u dy gives a clearer in dicat ion of th e expected n eurologic com plicat ion rate in ASD pat ien ts, poten t ially set t ing a stan dard for fu t u re clin ical t rials aim ed at low ering th e rate of postop erat ive n eu rologic de cits.

■ Mechanisms of Neurologic

Complications Th ere are several p rop osed cau ses of in t raop erat ive n eu rologic d e cit s d u r in g ASD su rger y. In t raop erat ive sp in al cord , cau da equ in a, or n er ve root d e cit s m ay resu lt from direct n eurologic t rau m a during in st r um en tat ion su ch as th e p lacem en t of pedicle screw s, h ooks, or sublam in ar w ires. Fur th erm ore, in t raoperat ive correct ive m an euvers m ay lead to n eu rologic d e cit secon dar y to eith er d ist ract ion of th e n eu ral elem en t s or excessive ten sion on local vascu lat u re, lead ing to decreased blood ow an d cord isch em ia. Spin al cord isch em ia m ay also resu lt from p rolon ged ext rem e hyp oten sion (m ean ar ter ial p ressu re [MAP] < 55 m m Hg), hyp oxia secon dar y to decreased h em oglobin level, or vascu lar com p rom ise after ligat ion of th e segm en t al vessels in an an terior procedu re.13

■ Patient Evaluation and

Preoperative Planning Neu rologic com p licat ion s are m ost st ron gly associated w ith prolonged com p lex su rger y, a large am ou n t of blood loss, com bin ed an terior/ posterior p rocedu res, m u lt ist age su rger y, con genital kyphosis or scoliosis, large or rigid spinal cu r ves (Cobb an gle > 90 d egrees), p reexist in g m yelop at hy or n eu rologic d e cit , an d in t ram ed u llar y sp in al cord t u m ors. Fu r t h er r isk factors in clu d e tet h ered cord , Ar n old - Ch iar i

m alfor m at ion , syr in gom yelia, an d sp lit cord m alform at ion s. A com plete pat ien t h istor y an d th orough physical exam in at ion st ill rem ain essen t ial elem en t s to an adequ ate p reoperat ive w orku p. Pat ien t s sh ould be assessed for a h istor y of congen it al deform it ies su ch as kyph osis an d scoliosis, neuro brom atosis, and skeletal dysplasia, w hich would infer a considerably increased risk of iatrogenic neurologic com plications. Th e physical exam in at ion sh ou ld in clu de a th reedim en sion al assessm en t of th e spin e to evalu ate patient posture, neurologic status, hip exion contract ures, leg length in equalit y, pelvic obliqu it y, body h abit u s, an d n ut rit ion al st at u s. Met icu lou s exam in at ion of t h e m otor, sen sor y, an d re ex fun ct ion as w ell as gait assessm en t is cr it ical in screen in g p at ien t s for p oten t ial in t rasp in al an d brain stem an om alies su ch as tethered cord, Arn old-Chiari m alform ation, syringom yelia, an d split cord m alform at ion s. Adequate radiological im aging is crucial for optim al surgical and neurologic outcom e. How ever, it is tech n iqu e-d ep en d en t , requ ir ing visu alizat ion of th e en t ire spin e in th e coron al an d sagit tal plan es, in cluding th e h ip join ts, w ith all im aging taken w ith th e pat ien t st an ding w ith th e kn ees fully exten ded for accurate m easu rem en t of sagit t al balan ce (sagit t al vert ical axis [SVA]), th oracic kyp h osis, lu m bar lordosis, an d spin opelvic param eters in clu ding pelvic in ciden ce (PI), sacral slop e (SS), an d pelvic t ilt (PT). Lateral dyn am ic st an ding lum bar X-rays m ay iden t ify focal in st abilit y or spon dylolisth esis. Ben ding lm s an d su p in e X-rays w ith out th e e ect s of gravit y h elp assess th e exibilit y of a d eform it y. On ce t h e ap p rop r iate radiograp h ic st u d ies h ave been obt ain ed , t h e sagit t al an d coron al balan ce can t h en be assessed. Magn et ic reson an ce im aging (MRI) is u sed as a rout in e preoperat ive radiograph ic st udy to assess central canal stenosis, facet hypertrophy, pedicu lar an om aly, foram in al en croach m en t , an d degen erat ive disk disease. It also h elp s determ in e th e presen ce of in t raspin al an om alies. Pat ien t s w ith suspected low bon e m ass or w ith est ablish ed osteop orosis sh ou ld h ave a du alen ergy X-ray absorpt iom et r y (DEXA) scan p erform ed to opt im ize su rgical plan n ing.

Neurologic Complications Following Adult Spinal Deformit y Surgery

■ Intraoperative Preparation Met icu lou s in t raop erat ive p reparat ion is required for the safe an d e ective m anagem ent of in t raoperat ive com p licat ion s. Before in du ct ion of an esth esia, th e su rgical team sh ould discuss w ith th e an esth esia an d n eurom on itoring team s an d operat ing room st a th e pat ien t’s m edical sit u at ion , th e in ten ded proced u re, an d su rgical t im e fram e. An ar terial lin e m ay be u sed to m on itor MAP. Som atosen sor y evoked poten t ial (SSEP) an d m otor evoked poten t ial (MEP) leads are placed an d ch ecked before th e p at ien t is t u r n ed to t h e p ron e p osit ion . Th e u p p er ext rem it ies are p ad d ed an d p osit ion ed to avoid st retch or com p ression of t h e brach ial p lexu s, an d care is t aken to en su re t h at t h e p ressu re areas are w ell p ad d ed . Forced -air w arm ing blan ket s preven t hypoth erm ia, part icu larly in procedu res of long du rat ion . Main tain ing adequate blood pressure is essen tial. How ever, a balan ce sh ou ld be m ain tain ed to m in im ize in t raoperat ive blood loss an d t ran sfusion s, yet en suring adequ ate spin al cord p erfu sion . A MAP of < 55 m m Hg h as been associated w ith an in creased risk of spin al cord isch em ia.14 How ever, m ild hypoten sive an esth esia is often u sed to m in im ize blood loss, par t icu larly du ring th e su rgical app roach , w ith th e MAP m ain t ain ed at 65 to 70 m m Hg. Ap proxim ately 30 m inutes before perform ing correct ive m aneuvers, th e an esth esia team sh ould gradu ally elevate th e MAP to > 70–80 m m Hg to m ain t ain ad equ ate cord p er fu sion d u r ing sp in al colu m n m an ip u lat ion an d d efor m it y correct ion .

■ Intraoperative

Neuromonitoring Stagnara Wake -Up Test Th e St agn ara w ake-u p test h as been w id ely u sed in t h e in t raop erat ive assessm en t of n eu rologic fu n ct ion . It assesses p r im ar y m otor cor tex, an terior m otor p ath w ays of th e sp in al cord, n er ve roots, an d p erip h eral n er ves. How ever, it gives on ly a gross approxim at ion of th e

fu n ct ion of th ese elem en t s an d d oes n ot directly m easu re any com pon en t s of th e sen sor y system .15 Th is test involves a tem porar y reduct ion in anesth esia, after w h ich th e pat ien t is asked to m ove th e u pp er an d low er ext rem it ies. Th e test is lim ited, as it is en t irely relian t on pat ien t com plian ce an d can n ot be u sed in p at ien ts un able to follow com m an ds because of in tellect u al an d d evelop m en t al d isabilit y, young age, or preoperat ive w eakn ess. Th e test it self car r ies r isk, in clu d in g self-ext u bat ion , loss of in t raven ou s access or of safe p at ien t p osit ion ing on t h e t able, air em bolism , an d p ostoperat ive recollect ion of th e even t . The w ake-up test w as historically the benchm ark for in t raoperat ive n eu rologic assessm en t , an d is st ill u sed at som e cen ters in conju n ct ion w it h advan ced n eu rom on itoring tech n iqu es as a m ean s of con r m in g n eu rologic st at u s. Properly adm inistered, the w ake-up test should be 100% accu rate in d etect in g gross m otor ch anges.15 Alth ough th e lim it at ion s of th e test preven t assessm en t of n e m otor ch anges, it w ill aler t th e surgeon to th e m ost clin ically sign i can t n eu rologic de cits. It is used w h en th ere is any p roblem obt ain ing spin al cord m on itoring (SCM) sign als (su ch as in a pat ien t w ith th oracic m yelopathy) an d also in pat ien t’s w h o h ave h ad SCM ch anges m eet ing evoked poten t ial w arn ing criteria w h en th e respon ses can n ot be im p roved. It also sh ou ld alw ays be perform ed at th e en d of th e su rgical p rocedu re prior to the patient’s leaving the operating room .

Somatosensory Evoked Potentials Som atosen sor y evoked p oten t ials assess t h e posterior colum ns of the spinal cord, in addition to th e cerebral cor tex an d m ixed periph eral n er ves. Th e posterior colu m n s are respon sible for propriocept ion as opposed to pain an d tem perat u re. Alth ough p rop riocept ive loss is n ot as debilit at ing as a m otor de cit , it can h ave a sign i can t im pact on act ivit ies of daily living. As SSEPs are sen sit ive to focal posterior colum n an d global spin al cord issues, th ey act as a good su rrogate for oth er n eu ral path w ays. How ever, th ere are sit u at ion s w h en a m otor de cit m igh t n ot be dem on st rated on SSEP m on itoring. For exam ple, anterior vascular territory com prom ise

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Chapter 6 w ithout concom itant posterior vascular changes m igh t n ot be add ressed by SSEP m on itoring. Som atosen sor y evoked p oten t ials con t in u e to be th e m ost frequ en tly used in t raoperat ive m on itor in g m et h od to assess t h e in tegr it y of t h e d orsal colu m n bu t can n ot be relied on to m on itor m otor fu n ct ion d irect ly. Rep or t s of p ostop erat ive p arap aresis in t h e absen ce of in t raoperat ive SSEP sign al ch ange un derscores th is im p or t an t lim it at ion .16 SSEP depen dabilit y falls o w h en applied to pat ien ts w ith preexist ing n eurologic con d it ion s. In dividu al n er ve root injury is not e ectively m onitored by SSEPs. Missed n er ve root or isolated m otor p ath w ay com p licat ion s are n ot failu res of th e m odalit y but rather are issues outside of SSEP m onitoring capabilit y, h ighligh ting the need for alternat ive or adjunct m onitoring approaches. Warning criteria for SSEPs at ou t in st it ut ion in clude greater th an a 60% d ecrease in am p lit u d e or a 10% in crease in laten cy of th e sign al as com p ared w ith baselin e valu es.

Motor Evoked Potentials Motor evoked p oten t ials m on itor cor t icospin al t ract act ivit y via st im u lat ion at th e level of th e m otor cor tex or sp in al cord an d are select ive for m otor p at h w ays. MEP m on itor ing relies on in ter ven in g t h alam ic syn ap ses to p reven t an t idrom ic ring of sp in al sen sor y t ract s. Th e st im u lat ion site for t ran scran ial MEP (tcMEP) is th e cerebral cor tex. MEP en d-p oin t dat a are ascer t ain ed from th e spin al cord (D-w ave) or from th e en d m uscle com poun d m otor act ion p oten t ial (CMAP). St im u li are p resen ted as sin gle h igh voltage or m ult iple sm all st im u li. Sou rces of st im u lat ion in clu de m agn et ic an d elect r ical. For m agn et ic tcMEP, a coil over t h e cor tex p rovid es t h e st im u lat ion . Elect r ical st im u lu s of th e m otor cor tex is p rovid ed by su bderm al elect rod es. Alth ough occasion ally associated w ith scalp edem a an d un reliable recordings, corkscrew elect rodes are preferable given th eir low im pedan ce an d secure posit ion ing in th e scalp. Periph eral dat a are com m on ly elect rom yograp h ic via CMAP. Th e CMAP is best m on itored at sites rich in cort icosp in al t ract in n er vat ion su ch as th e distal lim b m u scles. Com m on recording sites are abdu ctor p ol-

licis brevis or ad d u ctor h allu cis brevis w it h viable altern at ives of long forearm exors an d exten sors in th e upper ext rem it y an d t ibialis an terior in th e low er ext rem it y. Alth ough th ere does n ot ap p ear to be any m on itoring advan t age to in creasing th e n u m ber of m on itored m uscles, in creased m uscle group test ing m igh t p rovide a ben e t in iden t ifying posit ion ingrelated inju r y.

Electromyography Th e clin ical ap plicat ion s of elect rom yograp hy (EMG) an d its speci cit y for th e m otor system led to th e in t rodu ct ion of sp on t an eou s EMG (sEMG) recordings. sEMG m yotom es are preselected to coordin ate w ith operat ive levels, an d m uscle relaxan ts m ust n ot be ut ilized du e to dam pen ed or even absen t act ivit y. Con t in u ous elect rical act ivit y to a m yotom e is recorded an d obser ved an d m ay be in d icat ive of root ir rit at ion . W h en a n er ve root is n oted to be excessively m an ip u lated or im p in ged , t r igger in g a bu rst of act ivit y, w it h m ore severe n er ve m an ip u lat ion an d st retch of a n er ve root t rain activit y is also noted. One w ould generally note silen ce if th e n er ve root is clean ly severed. Dist al record ing sites are t yp ically p aired w ith an in t ram u scu lar n eed le or w ire elect rodes in ser ted after in du ct ion bu t before surger y. Triggered EMG (tEMG) h as also been used as it is post ulated th at a h igh st im u lu s in ten sit y tEMG w ill dem on st rate an in t act cor tex of a pedicle h ole th rough w h ich a screw is passed. In applicat ion , bon e h as h igh im pedan ce requiring high thresh old to stim ulate the adjacent n er ve. W h en tEMG requires h igh st im ulat ion , it dem on st rates th e in tegrit y of th e pedicle cor tex an d lack of perforat ion . Direct st im u lat ion of a m isplaced p edicle h ole w ith a breach , can act ivate th e adjacen t n er ve root an d evoke a CMAP in th e appropriate m yotom es at low er st im u lu s in ten sit ies th an w ou ld be exp ected w it h an im p er forate p ed icle cor tex. Clin ical cor relat ion is of cou rse requ ired , bu t t EMG at tem pts to provide data on a path w ay from pedicle screw or t ract to th e distal site an d can be u sed in th oracic spin e operat ion s if th e rect us abdom in is or in tercost als m u scu lat u re are m on itored as th e distal recording site.

Neurologic Complications Following Adult Spinal Deformit y Surgery

■ Multimodality

Intraoperative Monitoring Som atosen sor y evoked p oten t ials are t h e m ost com m on n eu rom on itoring m odalit y em ployed, bu t are n ot alw ays a su cien t proxy for all cord fun ct ion . Failing to recogn ize th e lim itat ion s of SSEPs can lead to devast at ing con sequ en ces. It m u st be em p h asized t h at n o single m odalit y su cien tly m on itors all spin al cord path w ays. If th e goal of in t raop erat ive n eu rom on itoring is to d etect th e on set of de cit s for bot h sen sor y an d m otor p ath w ays, t h en n o sin gle m odalit y m eets th e goal; h ow ever, a com bin at ion of test ing m eth ods m igh t . Mu lt im odalit y in t raop erat ive m on itoring u ses all elect rop hysiological tech n iqu es an d can p rovide in t raop erat ive in form at ion abou t th e n eural st r u ct u res at risk. It p erm it s assessm en t of both ascen ding an d descen ding path w ays con cu rren tly, providing a cer t ain degree of redu n dan cy becau se m any t yp es of in t raop erat ive injuries w ill com prom ise both m otor an d sen sor y p ath w ays.

■ Intraoperative Neurologic

Complications Sign i can t ASD su rger y requ ires con t in u ou s n eurom on itoring, especially during placem en t of in st r um en t at ion an d deform it y correct ion . Im m ediate act ion is required w h en dam age to th e sp in al cord or a p erip h eral n er ve is su spected at any t im e d u ring th e p rocedu re in resp on se to ch anges of > 50% am plit ude an d > 10% laten cy in t h e SSEP/MEP sign als. An algor it h m m ay aid t h e p r im ar y su rgeon in d eter m in ing t h e cau sat ive factor an d in it iat ing appropriate t reat m en t . Reassessm en t of n eurom onitoring signal strength is perform ed after each step . Th e sp eci c t im ing of each of th e step s listed below is n ot u n iversal; rath er, t im ing sh ou ld be determ in ed on a case-by-case basis. Each su bsequ en t step is in it iated if t h e p at ien t fails to d em on st rate im p rovem en t in n eurologic fun ct ion after th e p reviou s sequen tial corrective m aneuvers have been perform ed.

Here is a gen eral ch ecklist of factors to con sider w h en SCM ch anges occur: Ten-Item Ch ecklist in Respo nse to Lo sing SCM Data o r Meeting Warning Criteria (SSEPs o r Neuro genic MEPs) 1. Check with personnel to make certain SCM data issue is real (experience m at ters). 2. Be aware that an increase in blood pressure (MAP ≥ 80–90 m m Hg/systolic blood pressure > 120 mm Hg) may require a quick dose of epinephrine/norepinephrine or a dopamine drip; provide blood products if needed (hemoglobin ˃ 9). 3. Release any traction on patient’s spinal column (halo, halo-fem oral, etc.). 4. Palpate the dura, checking for impingement (if spinal canal is open), such as prior osteotom ies/ lam inectomies. 5. Reverse any corrective maneuver; also consider shortening of spinal colum n. 6. Con rm the absence of spinal subluxation. Consider using temporary bilateral rods during closure. 7. Consider implant malposition (screw/hook/wire) if temporally related, which might indicate dural impingem ent. 8. Order a wake-up test if the m onitoring data have not improved or reached baseline. Also, this is a good time to take a deep breath and re ect on possible additional issues. 9. Con rm that elevated MAP is being maintained. 10. Consider apical spinal cord decompression to relieve tight neural tissue.

Increase Spinal Cord Perfusion Im m ediately follow ing iden t i cat ion of n eurom on itoring sign al ch anges, t h e h em odyn am ic an d oxygen at ion st at us of th e pat ien t sh ou ld be opt im ized to im prove perfusion to th e spin al cord. Th e MAP is elevated to > 80 m m Hg or 20% above baselin e.17 Hem oglobin an d blood glu cose levels are evalu ated an d cor rected if required. Body tem perat ure sh ould be m ain tain ed at > 36.5°C to opt im ize n eurom on itoring. Th ese m easu res h ave been sh ow n to in crease sp in al cord perfu sion .18

Stagnara Wake -Up Test Ch anges in n eu rom on itoring sign al suggest ive of persisten t n eurologic de cit m ay be cause

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Chapter 6 for con sid erin g a con r m ator y test . Prior to th e in du ct ion of an esth esia, p at ien t s sh ou ld be cou n seled th at th ey w ill be asked to perform several com m an d s u pon aw aking from an esth esia. Frequ en t assessm en t of th e p at ien t’s n eu rom on itor in g st at u s is recom m en d ed as in st r u m en t at ion is p laced an d cor rect ive m an eu vers p er for m ed . Th is en ables t h e su rgeon to m ost reliably p inp oin t t h e p ossible in cit in g factor, su ch as a m alposit ion ed im p lan t or ten sion on th e cord cau sed by correct ive m an euvers. Th u s, p oten t ially p roblem at ic in st r u m en t at ion can be rem oved or cor rect ion rela xed w h ile w ait ing for t h e p at ien t to aw aken from an esth esia for th e w ake-u p test . How ever, on e m u st also u n d erst an d t h at a t im e lag can occu r bet w een th e ap plicat ion of a cor rect ive force (e.g., d ist ract ion ) an d t h e d im in u t ion /loss of SCM sign als. Th u s, p ru d en t resp on ses to any SCM ch ange th at m eet s t h e w arn ing criter ia m u st be m ad e based on th e m any factors involved , in clu d in g t h e MAP, any recen t cor rect ion m an euvers, an d th e t ype of dat a.

Release of Correction Th e su rgeon sh ou ld con sider releasing th e ten sion on th e sp in e w h en all param eters (e.g., MAP, tem perature, hem oglobin level) have been reason ably addressed an d th ere is st ill an ab sen ce of exp ected m otor fu n ct ion w it h t h e w ake-u p test . After release of correct ion , a secon d w ake-up test can be con sidered w h en SSEP/MEP sign als in dicate persistent abnorm alit y. If an im p rovem en t in t h e w ake-u p test or in n eu rom on itoring is discovered after th e release of su rgical correct ion , th e su rgeon h as th e opt ion of fu sing th e spin e in sit u or attem pt ing a m ore m odest correct ion . W h en n o im provem en t in n eurologic fu n ct ion is elicited after th e release of ten sion , all screw s an d h ooks sh ould be reassessed. Th e st abilit y of th e spin e also sh ould be evaluated. W h en rem oval of in st rum en tat ion w ould com prom ise th e stabilit y of th e spin al colum n , such as after ver tebral body resect ion , th e surgeon m ay be forced to m ain tain th e exist ing in st rum en tat ion an d fu se th e sp in e u n der th e least am ou n t of ten sion . If osteotom ies h ave been p erform ed, th e

canal should be exam ined for fragm ents of bone, Gelfoam , or bon e w ax, w h ich m ay be con t rib u t ing to cord com pression . Pedicle screw p osit ion sh ou ld be crit ically exam in ed in ligh t of a m on itor ing ch ange. Th e p osit ion of each screw can be reassessed u sing on e m easu re or a com bin at ion of several. High st im u lat ion th resh olds of each xat ion poin t , as in d icated by t r iggered elect rom yograp hy, th eoret ically in dicate in t racor t ical screw p osit ion secon dar y to in creased resist an ce to cu rren t ow th rough cor t ical bon e. Any pedicle screw w it h a m arked ly low er elect rom yograp hy th resh old (< 60%) in relat ion to t h e rest of t h e con st r u ct sh ou ld be reassessed , as t h is m ay in dicate a p ossible pedicle w all breach .19 Screw posit ion can also be evalu ated w it h th e u se of in t raoperat ive u oroscopy. A p edicle screw t ip p ast t h e m idlin e of t h e ver tebral body n oted on p osteroan ter ior rad iograp h s is suggest ive of a m ed ial p ed icle breach . In t h e presen ce of any or all of th ese sign s, t h e screw m ay be rem oved to reassess th e t ract w ith direct p alp at ion . A sm all lam in otom y m ay also be p er for m ed to evalu ate t h e in tegr it y of t h e m ed ial p ed icle cor tex w it h or w it h ou t screw rem oval. Early rem oval of in st r u m en t at ion m ay in crease t h e p ossibilit y of n eu rologic im p rovem en t , p rovid ed t h e sp in e w ill n ot be sign i can t ly d est abilized w it h rem oval of in st r u m en t at ion . Th e abilit y to obtain adequate postoperat ive im aging st u d ies is on e p oten t ial advan t age of rem oval of in st r u m en t at ion . Th e qu alit y of com p u ted tom ograp hy (CT) an d MRI scan s is su p erior w h en n o in st ru m en tat ion is p resen t to create ar t ifact . Even t itan ium con st ructs can prod u ce ar t ifact on CT or MRI scan s. An MRI scan m ay be don e in th e presen ce of t it an iu m in st ru m en tat ion ; oth er w ise, a CT scan can be ordered. If th e in st ru m en t at ion is retain ed an d st an dard CT or MRI scan n ing is in con clu sive, a CT m yelogram can be p er for m ed . If an abn orm alit y (e.g., screw m alp osit ion , h em atom a) is iden t i ed , u rgen t ret u r n to t h e op erat ing room is in d icated for d ecom p ression or rem oval of in st r u m en tat ion . If su cien t im aging can be p erform ed an d th ere is n o iden t i able site of com pression , close p at ien t obser vat ion is adequ ate.

Neurologic Complications Following Adult Spinal Deformit y Surgery

■ Steroid Protocol Alt h ough it s u se is d ebated , m et hylp red n isolon e is cu rren tly th e on ly recogn ized p h arm acologic in ter ven t ion for th e t reat m en t of acu te spin al cord injur y (SCI).13 Th e u se of steroids h as n ot been exten sively st u d ied in th e in t raoperat ive set t ing; h ow ever, w e cu rren tly adm in ister steroid s to p at ien t s w h o h ave a con t in ued n egat ive w ake-up test (i.e., absen ce of m otor fu n ct ion ) after release of ten sion from correct ive an d d ist ract ive m an euvers. Th e cu rren t recom m en ded protocol is a loading in t raven ous bolus dose of 30 m g/kg adm in istered over 15 m in u tes, follow ed by 5.4 m g/kg/h as a 23-h ou r in fu sion (if st ar ted w ith in 3 h ou rs from th e t im e of inju r y).13 Th e u se of m ethylpredn isolon e for th e m an agem en t of in t raop erat ive SCI is n ot w ell docu m en ted. Th u s, t h e su rgeon m u st w eigh th e poten t ial ben e ts of im proved n eurologic recover y again st th e p ossible in creased risk of in fect ion . Th e Am erican Associat ion of Neu rological Su rgeon s/Congress of Neurological Surgeons (AANS/CNS) Joint Section on Disorders of th e Spin e an d Perip h eral Ner ves Gu idelin es Com m it tee h as in dicated th at m ethylpredn isolon e for eith er 24 or 48 h ours is an opt ion in th e t reat m en t of pat ien ts w ith acute SCIs th at sh ould be un der taken on ly w ith th e kn ow ledge th at the eviden ce suggesting h arm ful side e ects is m ore consistent th an any suggest ion of clin ical ben e t . In t raven ou s lidocain e (2 m g/kg) for vasodilatat ion h as been described for t reat m en t of a post u lated isch em ic spin al cord after segm en tal vessel ligat ion .20 In experim en tal an im al m od els, in t rath ecal an d in t raven ou s vasodilators h ave been sh ow n to en h an ce spin al cord perfu sion an d n eu ron al p rotect ion . How ever, w e h ave n o clin ical experien ce w ith th is m ed icat ion an d th u s can n ot com m en t sp eci cally on its u sefu ln ess.

■ Postoperative Management A pat ien t w ith an in t raoperat ive n eu rologic in su lt sh ou ld be ad m it ted to th e in ten sive care u n it p ostop erat ively for close m on itor ing of

h em odyn am ic param eters as w ell as for n eu rologic exam in at ion s. MAP m u st be m ain tain ed at > 80 m m Hg w ith th e ju diciou s u se of in t raven ou s u id replacem en t , blood t ran sfu sion (if in dicated), or vasopressors w h en n ecessar y to m ain t ain cord perfu sion . A β-agon ist (e.g., dopam in e) can be u sed to m ain tain m ean ar terial blood pressure if uid replacem en t alon e is in su cien t . A n eu rologic exam in at ion sh ou ld be perform ed an d docu m en ted ever y h ou r for th e rst 12 to 24 h ou rs. Th is m ay pose a p roblem if th e p at ien t rem ain s in t u bated an d sedated. In th is case, it is p aram ou n t th at t h e p at ien t be ligh ten ed from sedat ion on an h ou rly basis for e ect ive assessm en t of n eu rologic fu n ct ion .

■ Delayed Postoperative

Neurologic Complications Neu rologic com p licat ion s in th e p ostoperat ive p er iod sh ou ld be m an aged w it h t h e sam e d iligen ce an d m et icu lou s care as d escr ibed for an in t raop erat ive SCI. Alt h ough relat ively u n com m on , d elayed p ostop erat ive SCI m ay be at t ribu ted to p rogressive spin al cord isch em ia secon dar y to t ract ion or to th e developm en t of an ep idural h em atom a. As w ith any acute SCI, adequate perfusion of th e spin al cord is p aram ou n t . Blood pressu re sh ou ld be m et icu lou sly m on itored, an d MAP sh ou ld be m ain tain ed at > 80 m m Hg in an effor t to su st ain spin al cord perfusion . Vasopressors (e.g., dopam in e) m ay be requ ired to at tain adequate blood pressu re an d cord perfusion . Hem oglobin levels sh ou ld also be ch ecked to avoid excessive postoperat ive an em ia. Pat ien t tem perature should be m aintained above 36.5°C. A steroid protocol m ay be in it iated as in dicated above for th e pat ien t w ith con t in ued n eurologic loss. Obtain ing im aging st udies before ret urn ing th e p at ien t to th e op erat ing room m ay aid in delin eat ing th e cau se of th e de cit . Th is w ill en able th e su rgeon to p lan th e p rop er cou rse of act ion , w h eth er th at involves reexp lorat ion for localized decom pression of an evolving epidural h em atom a, release of correct ion , or rem oval of in st r u m en tat ion to correct spin al cord isch -

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Chapter 6 em ia secon dar y to excessive ten sion ing. Reim aging w ith CT or MRI scan s can be om it ted if obtain ing th ese st udies w ou ld resu lt in a sub st an t ial t im e d elay. Early d ecom p ression m ay im p rove n eu rologic ou tcom e for t h e p at ien t w ith n ew -on set n eu rologic de cit in th e acute postop erat ive p eriod. Conversely, if n o abn orm alit y is iden t i ed on CT or MRI scan , th e p at ien t m ay be obser ved closely w ith su p por t ive t reat m en t .

■ Chapter Summary Th e su rgical t reat m en t of com p lex ad u lt sp in al deform it y h as advan ced sign i can tly in recen t t im es w ith th e u se of pedicle screw -based in st r u m en t at ion an d th e in creasing role of com plex three-colum n osteotom ies to optim ize deform it y correct ion . Th e correct ion of large m agn it u d e coron al an d sagit t al p lan e deform it y is becom ing m ore com m on . How ever, t h e tech n ical dem an ds involved in restorat ion of spin opelvic align m en t an d sagit tal an d coron al balan ce in large-m agn it ude deform it ies h as a signi cant risk of neurologic com plications, w ith poten t ially d evastat ing clin ical an d fu n ct ion al sequ elae. It is im p or tan t th at sp in al su rgeon s use an algorithm for the safe and e ective m anagem en t of neurologic sequelae associated w ith ASD surger y so as to opt im ize pat ien t m an agem en t an d fun ct ion al ou tcom e.

Pearls Neurologic safet y during spinal deform it y surgery requires preoperative preparation, intraoperative multimodalit y spinal cord monitoring, and postoperative diligence. A com bination of SSEP, MEP, and EMG m onitoring is necessary for com prehensive assessm ent and evaluation of neurologic function during ASD surgery. Appropriate responses to any loss of degradation of SCM data and to warning criteria should include a spectrum of responses aimed at optim izing spinal cord blood supply and m inimizing any direct or indirect tension or pressure on the neural elem ents. To con rm the patient’s neurologic integrit y, one must always perform a detailed m otor exam of the lower extrem ities at the end of the surgical procedure before the patient is extubated and leaves the operating room . Pitfalls One m ust identify those patients who are at high risk of neurologic complications during ASD surgery, including those with preexisting neurologic abnormalities, an abnorm al neural axis on MRI exam , or large and sti kyphotic deform ities. Not responding to or trusting the SCM personnel and data in a tim ely fashion can have devastating neurologic sequelae. One m ust be careful with those patient s kept intubated/sedated following extensive ASD surgery in order not to miss a delayed neurologic complication due to the inabilit y to obtain an adequate neurologic exam on a frequent basis.

Refere nces Five Must-Read Refe rences 1. Dorm an s JP. Est ablish ing a st an dard of care for n eu rom on itoring during spin al deform it y su rger y. Spin e 2010;35:2180–2185 Pu bMed 2. Malh ot ra NR, Sh a rey CI. Int raoperat ive elect rophysiological m onitoring in spin e surger y. Spin e 2010; 35:2167–2179 PubMed 3. Gelalis ID, Pasch os NK, Pakos EE, et al. Accu racy of pedicle screw p lacem en t: a system at ic review of p rospect ive in vivo st udies com paring free h an d, uoroscopy guidan ce and n avigat ion tech n iques. Eu r Spin e J 2012;21:247–255 Pu bMed 4. Tian NF, Huang QS, Zh ou P, et al. Ped icle screw in sert ion accuracy w ith di erent assisted m eth ods: a system at ic review an d m et a-an alysis of com parat ive st udies. Eu r Spin e J 2011;20:846–859 PubMed

5. Daubs MD, Len ke LG, Ch eh G, Stobbs G, Bridw ell KH. Adult spin al deform it y surger y: com plicat ions an d outcom es in pat ien t s over age 60. Spin e 2007;32: 2238–2244 Pu bMed 6. Kim YB, Len ke LG, Kim YJ, et al. Th e m orbid it y of an an ter ior t h oracolu m bar ap p roach : adu lt sp in al d eform it y pat ien t s w ith greater th an ve-year follow -up. Spine 2009;34:822–826 PubMed 7. Kim YJ, Bridw ell KH, Len ke LG, Ch eh G, Baldu s C. Result s of lum bar pedicle subt ract ion osteotom ies for xed sagit tal im balance: a m in im um 5-year follow - up st udy. Spin e 2007;32:2189–2197 Pu bMed 8. Lap p MA, Br idw ell KH, Len ke LG, et al. Longter m com p licat ion s in ad u lt sp in al d efor m it y p at ien t s h avin g com bin ed su rger y a com p ar ison of

Neurologic Complications Following Adult Spinal Deformit y Surgery p r im ar y to revision p at ien t s. Sp in e 2001;26:973– 983 Pu bMed 9. Rh ee JM, Bridw ell KH, Len ke LG, et al. St aged p osterior surger y for severe adult spin al deform it y. Spin e 2003;28:2116–2121 Pu bMed 10. Bridw ell KH, Lew is SJ, Len ke LG, Baldus C, Blan ke K. Pedicle subt ract ion osteotom y for th e t reat m en t of xed sagit t al im balan ce. J Bon e Join t Surg Am 2003; 85-A:454–463 Pu bMed 11. Buch ow ski JM, Bridw ell KH, Len ke LG, et al. Neu rologic com p licat ion s of lu m bar p ed icle su bt ract ion osteotom y: a 10-year assessm en t . Spin e 2007;32: 2245–2252 Pu bMed 12. Len ke LG, Feh lings MG, Sh a rey CI, et al. Prospect ive, m ult icen ter assessm en t of acute n eurologic com plications follow ing com plex adult spin al deform it y surger y: th e Scoli-Risk-1 t rial. Spin e 2014 subm it ted 13. Win ter RB. Neu rologic safet y in sp in al deform it y su rger y. Spin e 1997;22:1527–1533 Pu bMed 14. Ow en JH. Th e applicat ion of int raoperat ive m on itoring du ring su rger y for spin al deform it y. Sp in e 1999; 24:2649–2662 PubMed 15. Vau zelle C, St agn ara P, Jouvin rou x P. Fun ct ional m on itoring of spinal cord act ivit y during spin al surger y. Clin Orth op Relat Res 1973;93:173–178 PubMed

16. Lesser RP, Raudzen s P, Lü ders H, et al. Postoperat ive n eurological de cit s m ay occur despite un ch anged intraoperative som atosensor y evoked potent ials. Ann Neurol 1986;19:22–25 Pu bMed 17. Naslun d TC, Hollier LH, Mon ey SR, Facun dus EC, Sken deris BS II. Protect ing th e isch em ic spin al cord du ring aor t ic clam p ing. Th e in u en ce of an esth et ics and hypoth erm ia. An n Su rg 1992;215:409–415, discussion 415–416 PubMed 18. Rayn or BL, Len ke LG, Kim Y, et al. Can t riggered elect rom yograph th resh olds predict safe th oracic pedicle screw placem ent? Spine 2002;27:2030–2035 PubMed 19. Bracken MB, Sh epard MJ, Holford TR, et al. Adm in ist rat ion of m ethylpredn isolon e for 24 or 48 h ours or t irilazad m esylate for 48 h ou rs in th e t reat m en t of acute spin al cord injur y. Result s of th e Th ird Nat ion al Acute Spin al Cord Injur y Ran dom ized Con t rolled Trial. Nat ion al Acute Spin al Cord Injur y St u dy. JAMA 1997;277:1597–1604 PubMed 20. Klem m e W R, Burkh alter W, Polly DW Jr, Dahl LF, Davis DA. Reversible isch em ic m yelopathy during scoliosis su rger y: a possible role for int ravenous lidocain e. J Pediat r Or th op 1999;19:763–765 Pu bMed

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7 Postoperative Coronal Decompensation in Adult Deformity Yong Qiu

■ General Introduction of

Adult Scoliosis Adu lt scoliosis is de n ed as an abn orm al deform it y in an adu lt , w ith Cobb angle greater th an 10 degrees in th e coron al plan e, w ith or w ith out sagit tal im balan ce or abn orm al pelvic orien t at ion .1 In th e elderly popu lat ion , a variet y of prevalen ce rates h ave been repor ted as a resu lt of di eren ces in de n it ion s of scoliosis, sam ple size, eth n icit y, an d screen ing tools. In a st udy of volun teers w h o w ere over 60 years of age, Sch w ab et al 2 fou n d t h at 68% of t h e su bject s m et th e de nit ion of scoliosis. As repor ted by Xu et al,3 th e p revalen ce of scoliosis w as 13.3%in a coh ort of 2395 adults older th an 40 years of age. Adu lt scoliosis m ay stem from progression of scoliosis d u r in g ch ild h ood or ad olescen ce (Fig. 7.1), or m ay be n ew ly develop ed in adu lth ood th rough degenerat ive ch anges (Fig. 7.2). Th e form er condition is referred to adult idiop at h ic scoliosis, w h ereas t h e lat ter is ter m ed degen erat ive scoliosis or d e n ovo scoliosis. In con t rast to ad olescen t s, ad u lt s w it h scoliosis ch aracter ist ically p resen t w it h back p ain , radicu lopathy, an d n eu rogen ic clau dicat ion . Cosm esis is a con cern of som e you ng adu lt scoliosis pat ien ts. Th ey often com plain of w aist asym m et r y an d ribs abut t ing th e p elvis, as a resu lt of im balan ce in th e coron al plan e or th e sagittal p lan e.

For adu lt scoliosis, n on op erat ive care is u sually the rst-line treatm ent option. Nevertheless, su rger y m ay be in evitable w h en n on operat ive m easu res fail. Th e p rim ar y in d icat ion s for su rgery of adult scoliosis are (1) progressive deform it y, (2) poor spinal balance causing functional d i cu lt ies, (3) large d eform it y t h reaten in g cardiop u lm on ar y com prom ise, (4) n eu rologic m an ifest at ion s, (5) persisten t p ain th at fails to respond to non operative treatm ent, and (6) un acceptable cosm etic appearance.1,4–6 Bess et al,7 in a m ult icen ter review of 290 pat ien t s w ith adult scoliosis, repor ted th at operat ive t reatm en t for older p at ien t s w as prim arily d riven by pain an d disabilit y, in depen den t of rad iograp h ic m easurem en t s, an d, for you nger pat ien t s, by in creased coron al plan e deform it y. Although operative m anagem ent of adult scoliosis is a grow ing ch allenge, a variet y of surgical opt ion s h as been em ployed, in clude posterior, an terior, or com bin ed approach es. Silva an d Len ke 6 prop osed six dist in ct levels of su rgical opt ion s for adult degen erat ive scoliosis: I, decom p ression alon e; II, d ecom p ression an d lim ited in st r um en ted posterior spin al fusion ; III, decom pression an d lum bar cur ve in st ru m en ted fu sion ; IV, d ecom p ression w ith an terior an d p osterior spin al in st ru m en ted fu sion ; V, th oracic in st rum en t at ion an d fusion exten sion ; an d VI, in clu sion of osteotom ies for sp eci c deform it ies. Fu sion levels sh ou ld st ar t p roxim ally at a st able ver tebra, t yp ically above T6 or below

Postoperative Coronal Decompensation in Adult Deformit y

d

a

b

c

e

Fig. 7.1a–e (a,b) A 57-year-old woman with a history of adolescent idiopathic scoliosis. (c–e) Both coronal and global sagit tal balance was well main-

tained, and the L2/3 disk height was much bet ter preserved on the convex side than on the concave side.

T10, an d en d dist ally at a n eut ral an d stable ver tebra. Th e p roxim al level n ever star t s at th e thoracic kyphosis apex, avoiding proxim al jun ction al kyp h osis, w h ereas th e dist al level n ever en ds at a level w ith rot ator y su blu xat ion . Th e decision of w h eth er to in clu de L5 or th e sacrum in th e fusion is con t roversial.8,9 Fu sion d ist ally to L5 o ers th e th eoret ical bene t s of p reser ved lum bosacral m ot ion , sh orter su rgical t im e, an d a decreased likelih ood of pseudarth rosis; on th e oth er h an d, it carries th e potential for accelerated sym ptom atic advanced d egen erat ion at th e L5/S1 disk, w h ich in t u rn u lt im ately result s in axial discom for t , radicu lopathy, an d loss of lu m bosacral lordosis. In con t rast to L5, fusion s exten ded to th e sacr um ach ieve a high er stabilit y of xation as well as a bet ter correction of sagit tal im balance, but this p rocedu re also ru n s th e risk of an in creasing ch an ce of pseudar th rosis, a greater frequen cy of m ajor com p licat ion s, an d a h igh er rate of in st ru m en t at ion failu re.8,9 A recen t st udy also foun d fusion to th e sacrum to be on e of th e risk factors of proxim al jun ct ion al kyph osis.10 Non con t roversial in dicat ion s for fu sion to th e sa-

cr u m in clu d e t h e follow ing 6 : (1) an obliqu e t ake-o of L5 on th e sacr u m , (2) a lu m bosacral fract ion al cu r ve > 15 degrees, (3) advan ced degen erat ion of t h e L5/S1 disk or th e L5/S1 facet joints, (4) L5/S1 spon dylolisthesis, and (5) prior h istor y of d ecom p ression at t h is segm en t . W h en fusion to th e sacru m can n ot be avoided, it is im p ortan t to p erform an in terbody fusion bet w een L5 an d S1 to decrease th e risk of a n on u n ion .

■ Di erentiating Betw een

Degenerative and Idiopathic Scoliosis An essen t ial prem ise of th e t reat m en t of spin al d eform it y in p ar t icu lar is u n d erst an d ing it s et iology. Aebi1 develop ed in 2005 a classi cat ion for adu lt scoliosis based on th e et iology: t yp e 1, de n ovo scoliosis; t ype 2, p rogressive idiopath ic scoliosis; t ype 3a, secon dar y degen erat ive scoliosis, due to a preexist ing condition , eit h er in t r in sic (adjacen t cu r ve) or ext r in sic

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a

b

c

d

Fig. 7.2a–d Adult degenerative scoliosis in a 65-year-old woman. (a) Standing X-ray lm s showed a right-sided lumbar curve, rotatory subluxation at L3/4, and regional kyphosis from L3 to L5 as well as sagit tal imbalance. (b) Magnetic resonance imaging

of advanced disk degeneration showed dark disks with narrowed disk height. (c,d) Computed tomography scans demonstrated the vacuum phenomenon as well as canal stenosis in the lower lumbar region.

Postoperative Coronal Decompensation in Adult Deformit y (low er lim b length d iscrepan cy) to th e spin e; an d t ype 3b, scoliosis secon dar y to m etabolic bon e disease. How ever, it is di cult to di eren t iate th e clin ical et iology in eld erly pat ien t s w h o are u n able to p rovid e eit h er a m ed ical h istor y or in for m at ion abou t t h eir sp in al d efor m it y. As t h ere is a p au cit y of in for m at ion in th e literat ure, th is ch apter describes several experience-based radiographic criteria that m ay h elp to di eren t iate bet w een de n ovo an d idiopath ic scoliosis.

Apical Disk Height In d e n ovo scoliosis, asym m et r ical d isk d egen erat ion h as been regard ed as t h e in it iat in g factor t h at con t r ibu tes to t h e occu r ren ce of degen erat ive scoliosis. Asym m et ric degen erat ion in th e ap ical disks leads to asym m et ric disk collap se, in du cing a cu r vat u re by p ivot ing on th e apical facet join t at th e con cave side, w h ich in t urn exacerbates m ore degen erat ion of th e disks on th e con cave side th an on th e convex side an d th en st ar t t h e viciou s circle. Bao et al11 also foun d th at region al lum bar disk d egen erat ion correlated w ith th e coron al Cobb angle, con rm ing th at asym m et ric disk d egen erat ion con t ribu ted to t h e d evelop m en t of d e n ovo scoliosis. We obser ved t h at t h e convex d isk h eigh t w as sign i can t ly less in d e n ovo scoliosis (Fig. 7.2) th an in idiopath ic scoliosis (Fig. 7.1).

Curve Pattern Th e m ajorit y of degen erat ive scoliosis a ect s th e lu m bar or th oracolu m bar spin e, an d th eir cur ve pat tern s m ay be di eren t from th at of idiopath ic scoliosis. Because the original pathogen esis of de n ovo scoliosis is th e degen erat ion of disk an d facet join ts, th e apex of th e lum bar cur ve is often located at th e in ter vertebral space. Th e m ost com m on apex of de n ovo scoliosis is th e in ter ver tebral sp ace of L2/3 or L3/4, often w it h a sh or ter cu r ve sp an . In ad d it ion , th e levels involved in t h e d egen erat ive cu r ve are gen erally th ree to four levels, w h ereas four

to six levels are m ore com m on in idiop at h ic cur ves.

Regularity of Apical Vertebra In addit ion to cur ve pat tern s, th e apical ver tebra in de n ovo scoliosis is often irregularly wedged. Osteophytes, end-plate abruption, and osteoporotic m inor fracture are com m only seen in degen erat ive ver tebrae, so th e sh ape of vertebra m ay n ot be regu larly t rap ezoid . In con t rast , w edging of ap ical ver tebra, if any, is u sually regu lar in idiop ath ic lu m bar scoliosis.

Compensatory Curve Above the Main Curve Regu lar com pen sator y cu r ves proxim al to th e m ain cur ve in idiopath ic scoliosis m ay develop du ring adolescen ce, an d ser ve as a w ay to rebalance the distal thoracolum bar/lum bar cur ve in th e coron al plan e (Fig. 7.1). Th at explain s w hy global coron al im balan ce is less frequen t in adolescen t id iopath ic scoliosis cases w ith dou ble cu r ve p at tern s, ow ing to th e com p en sator y cur ve an d it s com pen sator y abilit y from th e diskal, p elvic, an d cer t ain ly sp in al m u scu lar st ru ct u re as w ell. Th is balan cing pat tern m ay con t in u e in to ad u lth ood an d last for a long tim e. This feat ure of com pensator y cur ves could ser ve as an im p or tan t rad iograp h ic sign to differen t iate th ese t w o en t it ies. Patients w ith de novo scoliosis often present early w ith coron al or sagit t al im balan ce due to th e less e ect ive com pen sat ive cu r ves above th e im balan ce. In con t rast w ith sagit t al im balan ce, th ere is paucit y of in form at ion in th e literat u re on th e in ciden ce of coron al im balan ce in d e n ovo scoliosis. Based on ou r st u dy,11 abou t on e t h ird of p at ien t s w it h d e n ovo scoliosis m ay presen t w ith coron al im balan ce du e to a lack of com p en sator y cu r ves. Sim ilar to th e fu n ct ion al scoliosis seen in young in dividuals w ith disk h ern iat ion or oth er low er back diseases, t r u n k sh ift ing is n ot u n com m on in de novo scoliosis w ith stenosis because of the pain alleviat ing m ech an ism . Th is t r un k sh ift ing or

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Chapter 7 coron al im balan ce w ith sp in al cu r ve m ay becom e st ru ct ural w ith t im e.

Correlation Betw een the Cobb Angle and Imbalance Th e discrepan cy bet w een t h e Cobb angle an d im balan ce in d e n ovo scoliosis is an in teresting n ding. Degen erat ive cur ves alw ays are sh or ter th an th e idiop ath ic cu r ves an d h ave a sm aller Cobb angle. As m en t ion ed earlier, coron al im balan ce is an im por t an t feat ure of de novo scoliosis, w hatever the Cobb angle, w hereas sign i can t im balan ce is m ostly w it n essed in adu lt id iop at h ic scoliosis w it h severe cu r ves. Th erefore, a sm all Cobb angle w ith obvious coron al im balan ce in dicates th at th e cur ve m igh t be degen erat ive (Fig. 7.2).

Correction Ability of Rotatory Subluxation Ver tebral rot ator y sublu xat ion (VRS) is a t riaxial deform it y, predom in an tly at th e L3/L4 level, w ith fem ale predom in an ce. Alth ough it is m ore likely to occu r in pat ien ts w ith de n ovo scoliosis at th e early st age of th e deform it y, it cou ld also occur du ring th e late course of adult idiopath ic scoliosis. At ou r cen ter, w e fou n d th at th e correct abilit y of VRS u n der t ract ion or on side-ben ding lm s cou ld be u sed to di eren t iate de n ovo scoliosis an d idiop ath ic scoliosis. In th e form er, redu ct ion of VRS u n der t ract ion or on side ben ding m ay n ot be ach ieved because of th e rigidit y from ver tebral degen erat ion at th e su blu xat ion level, in clu ding disk collap se, osteophytes, and spontaneous vertebral or facet fu sion . In con t rast , in idiop ath ic scoliosis, VRS cou ld be par t ially redu ced u n der t ract ion or on side ben ding.

Discrepancy Betw een the Cobb Angle and Rotatory Subluxation At our cen ter w e n oted th at VRS w as m ore like to occur w hen the Cobb angle increased in cases

of id iop at h ic scoliosis. How ever, in d e n ovo scoliosis, VRS m ay occur at it s early st age, an d it s on set an d severit y m ay n ot n ecessarily be correlated w ith th e Cobb angle. In oth er w ords, VRS in d e n ovo scoliosis m ay develop even in cases w ith a sm all cur ve.

The Origin of Stenosis According to th e de n it ion of de n ovo scoliosis, it s p rim ar y cau se is th e degen erat ion of sp in e, including disks, the m uscle–ligam ents com plex, an d th e facet join t . Lum bar sten osis is m ore com m on ly seen in prim ar y degen erat ive scoliosis th an in adult idiopath ic cur ves. Th erefore, radicular leg pain an d claudicat ion sh ou ld be m ore com m on in de n ovo scoliosis, even w ith sm all cu r ves. Th is is in accordan ce w ith ou r clin ical obser vat ion th at m ech an ical back p ain is th e m ost com m on com plain t in m any adu lt id iopath ic scoliosis p at ien t s du e to deform it yin du ced parasp in al m u scle fat igu e, w h ereas n eurogen ic back pain in com bin at ion w ith leg pain is th e m ost com m on com p lain t in d e n ovo scoliosis p at ien ts (Fig. 7.2).

Lumbar Lordosis In addit ion to di eren t cur ve presen tat ion s in th e coron al p lan e, sagit t al align m en t m ay also be di eren t bet w een de n ovo an d idiopath ic scoliosis, especially in th e early stages. Lu m bar lordosis m ay rem ain n orm al in id iopath ic scoliosis becau se disk h eigh t m ay be m ain tain ed for a long t im e. In de n ovo scoliosis, h ow ever, lu m bar lordosis m ay n ot be preser ved becau se of early disk collapse. Bao et al11 also dem on st rated th at de n ovo scoliosis pat ien ts w ith severe disk degeneration have lum bar hypolordosis or kyp h osis (Fig. 7.2). Moreover, osteoporot ic fracture is m ore frequently obser ved in de novo scoliosis, particularly in fem ale patients, greatly con t ribut ing to lum bar kyph osis, w h ereas in id iopath ic scoliosis, th e degen erat ive pat h ologies are n ot th e p rim ar y cau se, an d osteop orot ic fract ure m ay be less com m on .

Postoperative Coronal Decompensation in Adult Deformit y

■ Contribution of Disk

Degeneration to Spinal Imbalance and Curve Severity Sp in e im balan ce in t h e sagit t al or coron al plan e h as an im port an t im p act on th e h ealth st at u s an d t reat m en t opt ion s in p at ien t s w ith de n ovo scoliosis. Sagit t al im balan ce is closely correlated w ith p oor h ealth -related qu alit y of life (HRQOL). Im p or tan tly, it h as been w ell docu m en ted th at coron al im balan ce is also on e of th e m ain cau ses of u n sat isfactor y ap p earan ce, im paired fun ct ion , an d back pain .12 Becau se th e establish ed con sen sus in term s of th e origin of de n ovo scoliosis is t h at it is t r iggered by asym m et rical disk degen erat ion , ou r team con du cted a st udy speci cally focused on th e cor relat ion bet w een disk d egen erat ion an d sp in al im balan ce.11 We qu an t i ed disk degen erat ion u sing th e P rrm an n classi cat ion , w h ich describes ve grades of disk degen erat ion on m agn et ic reson ance im aging.13 Each grad e of disk w as scored w it h a sp eci c n u m ber to en able d oin g calcu lat ion s; for exam p le, grad e I w as given a score of 5, w h ereas grade V w as given a score of 1. Th u s, h igh er scores represen ted h ealth ier disk con dit ion s. Th e results of our st udy revealed th at disk degen erat ion at th e low er en d ver tebra (EV) w as st rongly correlated w ith sagit tal im balan ce (Fig. 7.2). We fou n d th at th e grade of th e low er EV disk reach ed a m ean degen erat ion score of 2.32, being th e secon d m ost severely degen erated disk after th e apical disk. Th ere m ay be th ree st ages of disk degen erat ion , correlated w ith st abilit y an d m ot ion : dysfu n ct ion , in st abilit y, an d st abilizat ion . W it h m oderate disk d egen erat ion , t h e d isk m igh t becom e u n st able. Also, th ere m igh t be a ten den cy for in st abilit y to lie in m oderately degen erated disks w it h w ell-p reser ved d isk h eigh t , w h ereas m obilit y m ay d ecrease an d rest abilize in t h e

collapsed disks. Th is n ding su pp or ted ou r assu m pt ion th at low er EV disk degen erat ion w as m ore resp on sible for t h e sagit t al im balan ce becau se it s st abilit y w as jeop ard ized . How ever, w e failed to n d sign i can t correlat ion bet w een coron al im balan ce an d disk degen erat ion . Cer t ain ly, degen erat ion of th e posterior elem en ts, in clu ding th e facet join t s an d th e parasp in al m u scle, is an oth er accepted factor accou n t ing for de n ovo scoliosis; th erefore, it is assum ed th at un stable posterior elem en t s in stead of disk degen erat ion m ay be th e im por t an t cau se of coron al im balan ce in lu m bar degen erat ive scoliosis. Th e degen erat ive facet join ts w ith osteoarth rit is m ay be th e prim ar y cau se, or m ay be secon dar y to th e loss of disk h eigh t , leading to ver tebral in stabilit y an d in creased segm en tal axial m obilit y, w h ich m ay con t ribu te to coron al im balan ce. Asym m et ric at rophy of p arasp in al m u scles is an oth er p ossible factor in u en cing coron al balan ce. Th e degree of in stabilit y varies in each in d ivid u al, based on th e slip in th e sagit t al plan e, t ran slat ion al dislocat ion s in th e coron al p lan e, an d th ree-dim en sion al rotat ion al su blu xat ion . Cor relat ion bet w een t h e Cobb an gle an d ap ical d isk d egen erat ion w as also n oted . Th e m ore d egen erat ion t h e ap ical d isk p resen ted , t h e larger is th e Cobb an gle. Su ch a close relat ion sh ip bet w een d egen erat ion of t h e ap ical d isk an d t h e Cobb an gle can be exp lain ed by th e path ology of degen erat ive scoliosis: asym m et ric degen erat ion in th e apical disk w ill lead to asym m et ric disk collapse, in ducing th e spin e to ben d th e apical facet join ts, w h ich in t urn exacerbates th e degen erat ion of th e con cave side. In addit ion , w e also fou n d th at region al lu m bar disk degen erat ion grade is correlated w ith sagit t al m alalign m en t , in cluding an an tever ted C7PL an d lu m bar kyp h osis (Fig. 7.2). Decreases in lu m bar lord osis in p at ien t s w ith disk d egen erat ion , as eviden ced in our st u dy, exp lain w hy d e n ovo scoliosis p at ien t s w ith severely degen erated disks h ad lu m bar hyp olordosis or kyph osis.

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■ Coronal Balance of

Adult Deformity Coronal Balance Assessment Th e con cept of balan ce of th e sp in e h as been exten sively described by th e Scoliosis Research Societ y (SRS). Th e con cept im p lies th at , in both th e coron al an d sagit t al plan es, th e h ead is p osit ioned correctly over th e sacrum an d pelvis, in both a t ran slat ion al an d an angular sen se. From th e fron t al view of th e t ru n k, balan ce im plies h orizon t al sh oulders an d th e t run k even ly dist ribu ted abou t th e ver t ical lin e p assing th rough the center sacral vertical lin e (CSVL). Spinal balan ce in th e coron al plan e can be determ in ed as th e displacem en t of th e m ost cep h alad ver tebra from th e CSVL in both a dist an ce (fron tal plane o set) and an angle (o set angle). In practice, th e de n ed cep h alad ver tebra u su ally is C7 or T1 (Fig. 7.3). Com pensation in the coronal plan e is u su ally referred to as th e t ran slat ion of

a

b

Fig. 7.3a–c Examples of the classi cation of the coronal balance pat tern in adult scoliosis. (a) Type A in a 64-year-old wom an without obvious truncal asymmetry. (b) Type B in a 63-year-old woman with

th e m idpoin t of C7 in relat ion to CSVL (m easu red in th e sam e m an n er as coron al balan ce [CB]). It prim arily describes th e p osit ion of th e h ead over th e pelvis. Decom pen sat ion occurs w h en th is align m en t st rays from th e m idlin e by m ore th an a th resh old value speci ed by th e invest igators, usually repor ted as 2 cm . Th e w ord balance im plies a stat ic align m en t in th e stan ding (or u n su pported seated) posit ion , w h ereas com pensat ion an d decom pensat ion refer to t h e resu lt of dyn am ic align m en t . In d et ail, com pensat ion sign i es t h e act ive p rocess of becom in g balan ced, w h ereas decom pensat ion in d icates a failu re to ach ieve balan ce, esp ecially after an in ter ven t ion su ch as su rger y.

Relationship Betw een Coronal Balance and Quality of Life In pat ien t s w ith adult scoliosis, th e im pact of sagit tal balan ce on clin ical h ealth stat us h as

c

the trunk shifting toward the concave side. (c) Type C in a 61-year-old wom an with the trunk shifting toward the convex side.

Postoperative Coronal Decompensation in Adult Deformit y been exten sively discussed, w h ereas th e im pact of coron al balan ce on fu n ct ion al ou tcom es is less clear. In con t rast to p at ien t s w it h id iop at h ic scoliosis, p at ien t s w it h d egen erat ive lu m bar scoliosis h ave an in creased likelih ood of im balan ce in th e coron al plan e. Because of asym m et rical degen erat ive ch anges an d ver tebral w edging in th e apical region , coron al im balan ce is frequen tly obser ved. According to th e st u dy by Daubs et al,14 13 of 85 (15%) adu lt scoliosis p at ien t s w ith preop erat ive coron al im balan ce h ad w orsen ing coron al balan ce of m ore th an 1 cm after surger y. Th is n ding suggests th at the incidence of postoperative im balan ce in th e coron al plan e is u n derest im ated . It has been found that coronal im balance correlates w ith sign i can t clin ical m an ifestat ion s su ch as p elvic obliqu it y, sit t ing or stan ding im balan ce, as w ell as severe cosm et ic t run cal deform it y. Moreover, coron al im balan ce is on e of th e m ain u n derlying cau ses of th e p rogression of deform it y, back pain , an d fu n ct ion al com prom ise. Axial p ain u su ally derives from th e convexit y of th e cu r ve, an d leads to fu r th er deterioration of coronal im balance. Radicular pain an d n eurogen ic claudicat ion m ain ly origin ate from th e com pression on th e con cavit y of th e cur ve, or from dyn am ic overst retch ing on th e convex side.1 Deteriorat ion of th ese sym ptom s r u n s in p arallel w it h t h e in crease in coron al im balan ce to som e exten t . To ad d ress t h ese p roblem s, it is im port an t to correct th e preop erat ive coron al im balan ce. To h elp elu cidate th e factors th at are m ost cru cial for im p roved ou tcom es, several st u dies h ave at tem pted to correlate rad iograp h ic n dings w ith clinical sym ptom s in adu lt scoliosis. Glassm an et al15 repor ted th at sign i can t coron al im balan ce w as associated w ith pain an d dysfu n ct ion in un operated pat ien ts, an d coron al im balan ce w as n ot as crit ical a param eter as sagit tal im balance in prediction of sym p tom s. How ever, Daubs et al14 show ed that sagittal balance is the strongest predictor of im proved fu n ct ion al ou tcom es in adu lt scoliosis p at ien ts. Th ey fou n d th at restoring sagit t al balan ce in pat ien ts w ith com bin ed coron al an d sagit tal im balan ce seem s to be th e key to im p roving th e fu n ct ion al ou tcom es. In term s of pat ien t s w ith coron al im balan ce alone, im provem en t in

coron al balan ce w as a sign i can t predictor of im proved surgical ou tcom es.14 In som e st udies, coron al im balan ce h as also been repor ted to lead to decreased HRQOL an d in creased risk of im p lan t failure in adu lt scoliosis pat ien ts.15–17 In th e st udy by Glassm an et al,15 sign i can t coron al im balan ce of greater th an 4 cm w as associated w ith m ore pain an d dysfu n ct ion for u n op erated pat ien t s bu t n ot for operated pat ien t s. Plou m is et al16 rep or ted th at pat ien ts w ith coron al im balan ce of greater th an 50 m m sh ow ed w orse p hysical fu n ct ion scores. Ch o et al17 dem on st rated th at preop erat ive coron al im balan ce led to m ore im plan t failu res, requ ir ing rem oval of t h e im p lan t . Th erefore, im p roved p ostop erat ive coron al balan ce sh ou ld be th e goal in order to im prove th e HRQOL as w ell as to reduce th e n eed for revision surger y. At our cen ter, postoperat ive coron al im balan ce w as on e of th e factors th at con t ribu ted to im plan t failure.

Decompensation in the Coronal Plane As m en t ion ed above, decom p en sat ion in th e coron al plan e im p lies dyn am ic m alalign m en t of th e spin e, com m on ly m easu red as CB (t ran slat ion of th e cen ter of C7 in relat ion to CSVL) beyon d a speci ed th resh old value. In adolescen t idiopath ic scoliosis pat ien ts, decom pen sat ion w as usually de n ed as coron al im balan ce of m ore th an 2 cm (m easured in th e sam e m an n er as CB). In adu lt scoliosis p at ien t s, th e th resh old valu e of decom p en sat ion in th e coron al plan e varied am ong st u dies. Glassm an et al15 reported th e associat ion bet w een coron al im balan ce of greater th an 4 cm an d deteriorat ion in clin ical sym ptom s in n on operated pat ient s. Daubs et al14 an d Ploum is et al16 de n ed coron al im balan ce as C7PL > 4 cm an d > 5 cm lateral to CSVL, resp ect ively. In a recent st udy, w ith em ph asis on coron al im balan ce in adult sp in al deform it y pat ien ts t reated w ith long fu sion s, Plou m is et al18 also em p loyed a criterion of 4 cm . In a st u dy by th e SRS th at classi ed adu lt scoliosis according to th e King/Moe an d Len ke classi cat ion s, coron al im balan ce w as con sidered to be one of the global balance m odi ers.19

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Chapter 7 Im balan ce w as con sidered to be presen t if th e C7PL w as located > 3 cm to th e righ t or left of th e CSVL. We recen tly su r veyed a con secu t ive series of degenerative lum bar scoliosis patients to evalu ate coron al balan ce, w ith th e balan ce th resh old set at 3 cm . We fou n d a h igh prevalen ce of p reop erat ive coron al im balan ce in adu lt s w it h d egen erat ive lu m bar scoliosis. In t h ese p at ien t s, im balan ce occu r red eith er on th e con cave sid e, n am ely C7 deviat ing tow ard th e con cave side of th e m ain cu r ve w ith referen ce to CSVL (Fig. 7.3b), or on th e convex side, w ith C7 deviat ing tow ard th e convex side (Fig. 7.3c).

Postoperative Coronal Decompensation Postoperative coronal decom pensation is a m ajor com p licat ion in adu lt scoliosis.14,18 In addit ion to th e Dau bs et al14 n ding rep or ted above (see sect ion Relat ion sh ip Bet w een Coron al Balan ce an d Qu alit y of Life), Plou m is et al,18 in a coh or t of 54 adu lt pat ien t s t reated w ith long fu sion s, found postoperative coronal decom pensation in seven p at ien t s w ith p reop erat ive coron al im balan ce an d in fou r w ith ou t , at six w eeks postoperatively. At a m inim um 2-year follow -up, four m ore pat ien t s w ith out in it ial im balan ce w ere obser ved w it h coron al d ecom p en sat ion . Th e au t h ors rep or ted t h at p ostop erat ive coron al decom pensation was found in an increased num ber of adult spine deform it y patients.18 But so far, th e un derlying factors th at predict postoperative coronal decom pensation rem ain unclear. In t h eor y, d ecreased com p en sat ion of t h e segm en t s above an d below t h e fu sion p red isp oses th e pat ien t to postoperat ive coron al d ecom p en sat ion . Mu lt ip le defor m it y- an d su rger y-related factors are p robably associated w ith th e occu rren ce of p ostop erat ive coron al d ecom p en sat ion .

Deformity-Related Factors We fou n d t h at t h e p reop erat ive coron al im balan ce pat tern plays an im portan t role in th e occurrence of postoperative coronal decom pen sat ion . A cu r ve w it h im balan ce to t h e convex sid e p red isp oses to fu r t h er d ecom p en sat ion ,

par t icu larly w h en osteotom ies of th e p osterior elem en t s, su ch as Sm it h -Petersen osteotom y (SPO), or th rough t h ree colu m n s, su ch as p ed icle subt ract ion osteotom y (PSO), are un dertaken.6,20 For cases w ith im balance to the convex side, com pression m an euvers on th e convex side at the level(s) of th e osteotom y, w h ich are perform ed to close th e osteotom y gap , m ay lead to fu r th er in clin at ion of th e t ru n k tow ard th e convex side. As in congen it al th oracolu m bar kyp h oscoliosis, w e also n ot iced t h at p at ien t s w ith preoperat ive convex im balan ce h ad a h igh er rate of postoperat ive coron al decom pen sat ion after th ree-colum n osteotom ies. At th e sam e t im e, decreased com p en sat ion above an d below th e in st r um en tat ion also play an im portan t role in th e developm en t of postop erat ive coron al d ecom p en sat ion , becau se th e com p en sat ion p oten t ial of t h e u n fu sed segm en t s com es m ain ly from t h e d isks an d p araver tebral m u scu lat u re. Hen ce, th e m ore degen erat ive ch anges t h e adjacen t ver tebrae ceph alad or caudal to th e fu sion levels m an ifest , th e w orse th e poten t ial abilit y for th ese un fu sed segm en t s to com pen sate, resu lt ing in an in creasing likelih ood of postoperat ive coron al decom p en sat ion .

Surgery-Related Factors Am ong th e surger y-related factors th at h ave im pact on th e occu rren ce of p ostop erat ive coron al decom pen sat ion , th e low er in st rum en ted ver tebra (LIV) select ion is of u p m ost im p ort an ce. En d ing LIV at a ver tebra t h at can n ot becom e h orizon tal du ring su rger y carries th e potential risk of postoperat ive decom pensat ion. If th ere is a residu al obliquit y of LIV in th e coron al plan e, an in clin at ion of th e t ru n k is boun d to occur, because th e disk below LIV provides lim ited range of m ot ion . As m en t ion ed p reviou sly, w e fou n d t h at t h e d isks of t h e low er lu m bar region sh ow ed sign i can t degen erat ive changes. The physiological function of these disks is correspondingly com prom ised. Apparently, fusion dist ally stop p ing at a ver tebra th at can n ot becom e h orizon tal places th e coron al balan ce pattern at risk of decom pensation after surgery. In addit ion , p rop er determ in at ion of t h e u pper in st rum en ted vertebra (UIV) can dim in -

Postoperative Coronal Decompensation in Adult Deformit y ish t h e in cid en ce of coron al d ecom p en sat ion . A locat ion of UIV below th e en d ver tebra of th e m ain cu r ve can resu lt in in clin at ion of th e fusion w ith referen ce to th e CSVL. If fu sion exten ds in to th e th oracic region , h ow ever, a m uch m ore ceph alad locat ion of th e UIV th an th e en d ver tebra also carries th e risk of decom pen sat ion , becau se it low ers th e n u m ber of th oracic ver tebrae w ith com p en sat ion p oten t ial. Moreover, in clin at ion of UIV to th e convex side of th e m ain cu r ve p robably im pedes balan ce in th e coron al plan e th rough th e adverse im pact on th e au to-com pen sat ion m ech an ism . An in app rop riate osteotom y algorith m m ay contribute to postoperative coronal decom pensat ion as w ell. Th ree-colu m n osteotom ies u su ally begin at t h e ap ex an d from t h e convex sid e.20 Th is is e ect ive in t h e cor rect ion of cases w it h p reop erat ive coron al im balan ce to th e con cave side. For a case w ith preexisten t im balan ce to th e convex side, h ow ever, su ch a m an euver m igh t aggravate th e im balan ce because of th e com pression forces at th e osteotom ized site from th e convex side. In pract ice, su rgeon s perform sagit t al balan ce restorat ion m ore th an in th e coron al p lan e, an d th e balan ce p at ter n an d th e com p en sat ion p oten t ial in th e coron al p lan e are som et im es ign ored. Su ch an at t it u de tow ard coron al p lan e balan ce is evid en t ly an u n d erlying r isk factor for p ostop erat ive coron al decom pensation. Multiple st udies have dem on st rated th at coron al im balan ce accom p an ied by sagit t al im balan ce is a m ore com m on clin ical scen ar io.14,16,19 Th erefore, ad equ ate at ten t ion n eeds to be paid n ot on ly to th e sagit t al plan e bu t also to th e coron al p lan e. In p at ien t s com p lain ing of sagit t al im balan ce, Br idw ell20 classi ed t h e coexisten t coron al im balan ce w it h in to t yp e A an d t yp e B. In t yp e A, t h e p at ien t ’s sh ou ld ers an d p elvis are t ilted in op posite direct ion s; t h e sh ou ld er is elevated at th e side w h ere th e pelvis is low er. Conversely, w it h t yp e B, bot h t h e sh ou ld ers an d t h e p elvis t ilt in th e sam e direct ion . An asym m et rical PSO is often u sefu l in cor rect ing t yp e A bip lan ar deform it ies.21 Th e m ore radical tech n iqu es su ch as ver tebral colu m n resect ion (VCR) are som et im es u sefu l for th e rare t yp e B d eform it ies.20

■ Prevention of

Postoperative Coronal Decompensation A Novel Classi cation of Coronal Balance Pattern A discrepan cy exist s bet w een sagit tal im balan ce, w h ich is w ell accoun ted for in th e t radit ion al t reat m en t algorith m , an d im balan ce in th e coron al p lan e, w h ich th e algorith m ign ores. Furth erm ore, postoperat ive coron al decom pen sat ion is an im port an t com plicat ion th at a ects surgical ou tcom e an d in creases th e revision rate. To address th is problem , w e h ave established a novel classi cation regarding coron al balan ce p at tern s for adult scoliosis. Th is classi cat ion is based on CB, w h ich is m easu red as th e d ist an ce of t h e m idpoin t of C7 relat ive to th e CSVL on stan ding p osteroan terior X-ray lm s (Fig. 7.3). Vertebral alignm en t in th e coron al plan e is con sidered to be balan ced if CB is less th an 3 cm at eith er side; oth er w ise, it is con sidered to be im balan ced . Pat ien ts w ith a balan ced coron al pat tern are categorized as t ype A (Fig. 7.3a). Pat ien ts w ith an im balan ced coron al p at tern (CB m ore th an 3 cm ) are categorized as t ype B if th e im balan ce is on th e con cave side of th e m ain cu r ve (Fig. 7.3b) an d t ype C if th e im balan ce is on th e convex side of th e m ain cu r ve (Fig. 7.3c).

Osteotomy Options Based on This Classi cation For a coron al p at tern of t ype A or t yp e B, th e th ree-colu m n osteotom y, if n ecessar y, sh ould be perform ed righ t at th e apex from th e convex side, so as to restore lu m bar lordosis an d to reest ablish coron al balan ce w h en th e com pression forces are app lied to close th e osteotom y gap. Th is osteotom y opt ion is ver y e ect ive in correct ing p at ien t s w ith a t ype B coron al p attern . But in t ype C pat ien ts w ith preoperat ive coron al im balan ce on th e convex side, th is osteotom y opt ion m igh t be in appropriate due to th e com pression forces at th e apex. Alth ough it is rare, in t raop erat ive dislocat ion after th reecolu m n osteotom y can occu r as a severe com -

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Chapter 7 plicat ion , du e to com p u lsively rect ifying th e im balan ced t ru n k, w h ich is accom pan ied by a relat ively rigid lu m bosacral h em icu r ve. To restore a balan ced sp in e w ith th e t r u n k cen t rally over t h e p elvis, a n ovel osteotom y st rategy h as been suggested for cases w it h t yp e C (Fig. 7.4). First , a t h ree-colu m n osteot om y n eeds to be perform ed at a m ore distal level, u su ally at th e L4 ver tebra or th e L4/5 disk from th e con cave side of th e m ain cur ve to restore th e balan ce of th e t r u n k over th e p elvis. Secon d , t h e ap ical region is t h en cor rected . In cases w it h kyp h osis, an ad d it ion al th reecolu m n osteotom y can be don e at th e ap ex. Th e opt im al st rategy of osteotom y for t yp e C begin s from t h e con cave sid e, an d conver t s th e previous im balan ce pat tern in to a t ype A pat tern . In addit ion , an asym m et rical PSO m igh t be an altern ate opt ion for pat ien ts w ith a t ype C pat tern . Toyon e et al21 described th e tech n ique of asym m et rical PSO th rough w h ich a coron al correct ion w as w ell ach ieved u p on closu re of th e osteotom y w edge on th e convex sid e.

■ Revision Surgery for

Instrumentation Failure Due to Postoperative Coronal Imbalance Long spin al in st r um en tat ion is often in dicated in adult sp in al deform it y, w h ich im m obilizes a long span of spin al segm en t s, leading to in creased m ot ion of th e adjacen t segm en t s an d th e p oten t ial for degen erat ive p ath ology. Becau se th e lu m bosacral ju n ct ion p resen t s h igh m ech an ical dem an d, a h igh rate of com plications has been well docum ented for long fusions to th e sacru m . On e of th e im plan t-related com plicat ion s is rod fract u re, w h ich is associated w ith th e use of iliac screw s or sm all-diam eter rods, op erat ing at in ap p rop riate fu sion levels, resu lt ing in p ostoperat ive coron al im balan ce, an d failing to address sagit t al im balan ce. Postop erat ive coron al im balan ce often requires addit ion al revision su rger y. In our pract ice, t h e in cid en ce of rod breakage is 15% in

adult spin al deform it y pat ien t s (9/59) w ith a m in im u m of 2-year follow -u p , p ar t icu larly in pat ien ts w ith postop erat ive residu al kyp h osis. We speculate th at rod fract ure m ay partly result from overloaded m ech an ical forces im posed on in st r um en tat ion in cases w ith postoperat ive coron al im balan ce (Fig. 7.5). Th e use of iliac screw s m igh t in crease th e risk of im p lan t failu re becau se of th e in creased st i n ess of t h e lu m bosacral con st r u ct s. Th e excessive st ress of rod con tou ring is n ecessar y to con n ect iliac screw s an d S1 pedicle screw s, but it can lead to rod fract u re.22 In part icular, w e fou n d th at , in p at ien t s w ith p ostoperat ive coronal decom pensation, the location of the rod fract u re is often close to th e level of th e iliac crest or th e osteotom y level (Fig. 7.6). Postoperative coron al im balance that is com p licated by a sym ptom at ic rod fract ure is a den it ive in dicat ion for revision surger y. Several m odalit ies h ave been em ployed to x th e fract ured rod. Traditionally, the entire incision is reopened an d the fractured rod is replaced w ith a n ew on e. Altern at ively, revision w ith a com bin at ion of in -lin e rod con n ectors an d crosslin ks can restore th e st i n ess of th e origin al con st ru ct w ith out th e n eed to replace th e en t ire con st ruct . To rein force th e local con st ruct ion of th e fract u red rod an d decrease th e risk of com plicat ions, w e use satellite rods (Fig. 7.6). Th is local d irect -rep air st rategy requ ires t h e reop en in g of on ly t h e area su rrou n d in g t h e fract u red rod rat h er th an th e en t ire op en ing along th e in st r um en t at ion . More im por t an tly, satellite rods can en able th e restorat ion of coron al balan ce t h rough local com pression at th e convex side or dist ract ion at th e con cave side. Recen tly, w e started using th e satellite rods in th e in dex surger y at th e osteotom y level or w h en th e in st ru m en t at ion bridges th e lu m bosacral ju n ct ion .

■ Chapter Summary Adult scoliosis m ay stem from the progression of scoliosis in ch ild ren or ad olescen t s (idiop at h ic t yp e), or m ay n ew ly develop in ad u lt h ood th rough d egen erat ive ch anges (d egen erat ive (text cont inues on page 93)

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a

Fig. 7.4a,b (a) A 65-year-old wom an with degenerative scoliosis and a t ype C coronal balance pat tern. Lumbar kyphosis and severe sagit tal imbalance was noted. As per the surgical algorithm , a long fusion from T6 to S1 was started with osteotomy at L4/5 to balance the spine in the coronal plane followed by a pedicle subtraction osteotomy (PSO) at L1. (b) At 2-year follow-up, the spinal balance was well maintained.

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a

e

b

f

Fig. 7.5a–h (a,b) A 56-year-old wom an with degenerative lumbar kyphoscoliosis complicated by lum bar stenosis. Posterior spinal fusion from T5 to pelvis was done together with L4-L5 decompression. (c,d) Postoperative coronal imbalance was noted.

c

g

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h

(e) Both rods were fractured at 8 m onths’ follow-up. (f) Revision surgery with a domino connector was perform ed to restore coronal balance, which was well maintained at (g,h) 2 years, follow-up.

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Fig. 7.6a–e (a,b) A 64-year-old woman with degenerative lum bar scoliosis was treated with Luque instrumentation 9 years ago in another hospital. Posterior instrumentation from T5 to S1 with an L1 PSO was performed in the revision surgery. (c) However, immediate postoperative coronal im balance toward the convex side was noted. (continued on page 92)

a

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d

e

Fig. 7.6a–e (continued ) (d) Two years later, the rod fractured at the right side of L2. (e) A second revision surgery was performed with satellite rods. Both coronal and sagit tal balance was restored at 6 m onths’ follow-up.

Postoperative Coronal Decompensation in Adult Deformit y t yp e). Su rgical in ter ven t ion s are m ain ly in d icated for p at ien t s com p lain in g of p ain an d d isabilit y. In ou r exp erien ce, several factors di eren t iate bet w een degen erat ive an d idiopath ic scoliosis. In d egen erat ive scoliosis, disk d egen erat ion con t r ibu tes to t h e occu r ren ce of sp in al im balan ce. Disk d egen erat ion at t h e low er en d ver tebra st rongly correlates w ith sagit tal im balan ce, w h ereas th at at th e apex correlates w ith cu r ve m agn it u d e. In d egen erat ive lu m bar scoliosis, im balan ce in th e coron al plan e is frequ en tly obser ved an d u su ally associated w ith deteriorat ion of sym ptom s such as back pain an d radicu lopathy. A recen t su r vey foun d a h igh rate of preoperat ive coron al im balan ce in degen erat ive lum bar scoliosis, on eith er th e con cave or th e convex side. Correct ive su rger y m igh t resu lt in coron al decom pen sat ion in ad u lt scoliosis p at ien t s, lead in g to t r u n k sh ift ing an d p ossibly im p lan t failu re. Deform it y- an d su rger y-related factors m igh t lead to th is com p licat ion . A n ovel classi cat ion system h as been devised for th e coron al balan ce p at tern in adu lt scoliosis: t ype A, balan ced; t yp e B, im balan ced on t h e con cave sid e; an d t yp e C, im balan ced on th e convex side. For a p reoperat ive coron al pat tern of t ype A or B, th e th ree-colu m n osteotom y sh ou ld be perform ed righ t at th e apex

from th e convex sid e. For t yp e C, t h e opt im al st rategy of osteotom y begin s from th e con cave side of th e m ain cu r ve, at a m ore distal level, u sually at th e L4 vertebra or L4/5 disk, follow ed by correct ion of th e apical region . For in st r u m en tat ion failure due to postoperat ive coron al decom p en sat ion , revision su rger y focu ses on rein forcing th e local con st ruct ion , using in -lin e rod con n ectors, cross-lin ks, or satellite rods.

Pearls Consult the classi cation system that has been devised for preoperative coronal balance pat tern in adult scoliosis. Identify the factors that di erentiate degenerative and idiopathic adult scoliosis. Keep in mind that disk degeneration may contribute to spinal im balance and curve severit y. Evaluate the risk factors of postoperative coronal decompensation. Be aware of revision options for instrumentation failure due to postoperative coronal im balance. Pitfalls Postoperative coronal decompensation can occur after osteotomy at the apex. Postoperative coronal decompensation may result in instrumentation failure and loss of correction.

Refere nces Five Must-Read Refe rences 1. Aebi M. Th e adult scoliosis. Eur Spin e J 2005;14: 925–948 PubMed 2. Schw ab F, Du bey A, Gam ez L, et al. Adult scoliosis: prevalen ce, SF-36, an d n ut rit ion al param eters in an elderly volun teer populat ion . Spin e 2005;30:1082– 1085 Pu bMed 3. Xu L, Su n X, Hu ang S, et al. Degen erat ive lu m bar scoliosis in Ch in ese Han p op u lat ion : p revalen ce an d relat ion sh ip to age, gen d er, bon e m in eral d en sit y, an d body m ass in dex. Eu r Sp in e J 2013;22:1326– 1331 PubMed 4. Glassm an SD, Sch w ab FJ, Bridw ell KH, On dra SL, Berven S, Len ke LG. Th e select ion of operat ive versus n on operat ive t reat m en t in pat ien t s w ith adult scoliosis. Spin e 2007;32:93–97 PubMed 5. Sm ith JS, Sha rey CI, Berven S, et al; Spinal Deform it y Study Group. Operative versus nonoperative treatm ent of leg pain in adults w ith scoliosis: a retrospec-

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tive review of a p rospect ive m u lt icen ter dat abase w ith t w o-year follow -up. Spin e 2009;34:1693–1698 PubMed Silva FE, Len ke LG. Ad u lt d egen erat ive scoliosis: evalu at ion an d m an agem en t . Neu rosu rg Focu s 2010; 28:E1 Pu bMed Bess S, Boach ie-Adjei O, Burton D, et al; In tern at ion al Spin e St udy Grou p. Pain an d disabilit y determ in e t reat m en t m odalit y for older pat ien t s w ith adu lt scoliosis, w h ile deform it y gu ides t reat m en t for you nger pat ien t s. Spin e 2009;34:2186–2190 Pu bMed Bridw ell KH, Edw ards CC II, Len ke LG. Th e pros an d cons to saving th e L5-S1 m ot ion segm en t in a long scoliosis fusion con st ruct . Spin e 2003;28(20, Sup pl):S234–S242 Pu bMed Polly DW Jr, Ham ill CL, Bridw ell KH. Debate: to fuse or n ot to fu se to th e sacr um , th e fate of th e L5-S1 disc. Spin e 2006;31(19, Su p pl):S179–S184 Pu bMed

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Chapter 7 10. Yagi M, King AB, Boach ie-Adjei O. In ciden ce, risk factors, an d n at u ral cou rse of proxim al ju n ct ion al kyph osis: su rgical ou tcom es review of ad u lt idiop ath ic scoliosis. Min im um 5 years of follow -up. Spin e 2012; 37:1479–1489 PubMed 11. Bao H, Liu Z, Zh u F, et al. Is th e sacro-fem oral-pu bic angle p redict ive for p elvic t ilt in adolescen t idiopath ic scoliosis pat ien t s? J Sp in al Disord Tech 2014; 27:E176–E180 Pu bMed 12. Mac-Th iong JM, Tran sfeldt EE, Meh bod AA, et al. Can c7 plu m blin e an d gravit y lin e predict h ealth related qu alit y of life in adu lt scoliosis? Sp in e 2009;34: E519–E527 PubMed 13. P rrm an n CW, Met zdorf A, Zan et t i M, Hodler J, Boos N. Magn et ic reson an ce classi cat ion of lu m bar in terver tebral disc degen erat ion . Spin e 2001;26:1873– 1878 Pu bMed 14. Dau bs MD, Len ke LG, Bridw ell KH, et al. Does correct ion of preoperat ive coron al im balan ce m ake a di eren ce in outcom es of ad ult pat ien t s w ith deform it y? Spin e 2013;38:476–483 PubMed 15. Glassm an SD, Ber ven S, Bridw ell K, Hor ton W, Dim ar JR. Correlat ion of radiograph ic param eters and clin ical sym ptom s in adult scoliosis. Spin e 2005;30:682– 688 Pu bMed 16. Plou m is A, Liu H, Meh bod AA, Tran sfeldt EE, Win ter RB. A correlat ion of radiograp h ic an d fu n ct ion al m easu rem en t s in adult degen erat ive scoliosis. Spin e 2009;34:1581–1584 Pu bMed

17. Ch o W, Mason JR, Sm ith JS, et al. Failure of lum bopelvic xat ion after long con st r uct fusion s in pat ient s w ith adult spin al deform it y: clin ical an d radiograph ic risk factors: clin ical ar t icle. J Neu rosu rg Spin e 2013;19:445–453 PubMed 18. Ploum is A, Sim pson AK, Cha TD, Herzog JP, Wood KB. Coron al spin al balan ce in ad u lt sp in e d eform it y p at ien t s w ith long spin al fu sion s: a m in im um 2–5 year follow -up st u dy. J Spin al Disord Tech 2013 Sep 27. [Epub ah ead of prin t] Pu bMed 19. Low e T, Ber ven SH, Sch w ab FJ, Bridw ell KH. Th e SRS classi cat ion for adult spin al deform it y: building on th e King/Moe an d Len ke classi cat ion system s. Spine 2006;31(19, Suppl):S119–S125 PubMed 20. Bridw ell KH. Decision m aking regarding Sm ith Petersen vs. pedicle subt ract ion osteotom y vs. ver tebral colum n resect ion for spin al deform it y. Spin e 2006;31(19, Su pp l):S171–S178 Pu bMed 21. Toyon e T, Sh iboi R, Ozaw a T, et al. Asym m et rical p ed icle subt ract ion osteotom y for rigid degen erat ive lum bar kyph oscoliosis. Spin e 2012;37:1847–1852 PubMed 22. Sch eer JK, Tang JA, Deviren V, et al. Biom ech anical an alysis of revision st rategies for rod fract u re in p edicle subt ract ion osteotom y. Neurosurger y 2011;69: 164–172, discussion 172 Pu bMed

8 Measuring Outcome and Value in Adult Deformity Surgery Robert Waldrop and Sigurd Berven

■ Introduction

■ Process Measures

Th e de n it ion of a h ealth -related ou tcom e varies in t h e literat ure an d m ay en com p ass a sp ect ru m of m easu res. Clin ical ou tcom e is th e en d resu lt of h ealth care delivered to p at ien ts or pop u lat ion s, an d en t ails su ch con siderat ion s as qu alit y, pat ien t-based assessm en t , an d valu e of care. Measuring outcom es is com plex, an d th ere is n o single m easu re th at su m m arizes th e pat ien t’s exp erien ce, th e h osp ital p ersp ect ive, th e p ayer p erspect ive, an d t h e t reat ing p hysician’s perspective. Therefore, outcom es m ust be con sidered broadly an d en com p ass a spect ru m of perspect ives an d m easures. Th is ch apter discusses m easures of h ealth -related qualit y of life (HRQOL), an d th e ap p licat ion of th ese m easu rem en t s in assessing ou tcom es of spin al deform it y su rger y. Ou tcom e m easurem en t is an im por tan t aspect of su rgeon accou n tabilit y an d is vital in determ in ing th e qu alit y an d valu e of h ealth care. Qu alit y m ay be evalu ated based on p rocess m easu res, object ive h ealt h ou tcom es, p at ien t-rep or ted ou tcom e m easu rem en ts, an d cost of care. Valu e is a broader m easu re th at in cor p orates an an alysis of bot h qu alit y an d cost . Th is ch apter p rovid es an over view of var ious outcom e m easures used for spin al deform it y, an d n dings from th e literat ure on ou tcom es in adu lt spin al deform it y surger y.

Process m easu res are a re ect ion of h ow care is d elivered . Exam p les in clu d e com p lian ce w it h an t ibiot ic or t h rom boem bolic p rop hyla xis gu id elin es, th e u se of su rgical “t im e-ou t s” before surger y, preoperat ive risk assessm en t s of pat ien t s, an d im plem en t ing postoperat ive care protocols for th e preven t ion of com m on postoperative com plicat ion s. Th e utilit y of process m easu res depen ds on h ow reliably th ey are lin ked to clin ical ou tcom es. For exam ple, m easu ring com p lian ce w ith preop erat ive an t ibiot ic guidelin es is u seful in th at it m ay predict a red u ct ion in t h e in ciden ce of su rgical site in fect ion s. Alth ough th ey are an in direct m easure of qualit y, the im plem en tation an d m easu rem en t of su ch gu idelin es are im p or t an t in st an dardizing care an d im proving qu alit y.

■ Physiological Outcome

Measures Physiological outcom es represent clinical h ealth m et rics th at m ay be m easu red object ively. In adu lt sp in al deform it y, th ese m ay in clude rad iograp h ic ou tcom es, im p lan t su r vival, an d fu sion rates. Cobb an gle, sagit t al ver t ical a xis (SVA), an d sp in op elvic p aram eters in clu d ing

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Chapter 8 p elvic in cid en ce (PI), p elvic t ilt (PT), sacral slope (SS), an d lu m bar lordosis (LL) are all im por t an t radiograp h ic m easu rem en ts in sp in al deform it y. Alth ough th ese ou tcom es are easy to m easu re an d in ter p ret , it is im p or t an t to evalu ate clin ical m easu rem en t s in relat ion to th eir cor relat ion w it h qu alit y m easu rem en t s (e.g., do radiograph ic outcom es predict reoperat ion rates?).

st ay, h igh er cost , an d m ore risk an d poten t ial for com p licat ion th an th e in dex su rger y. How ever, th e pat ien t repor ted a dram at ic im provem en t in h ealt h st at u s t h at is n ot capt u red by th e qu alit y m et r ics alon e. It is im p or t an t to avoid m yopic focu s on qu alit y m et rics w ith ou t givin g p riorit y to p at ien t -cen tered m easu res of clin ical ou tcom es in spin al deform it y.

■ Patient-Reported ■ Quality Measures Tradit ion al m easu rem en ts of qu alit y in clu d e outcom es such as operat ive t im e an d length of h osp ital st ay, as w ell as rates of com plicat ion s, reoperations, and readm issions. Such m easures provide im p or tan t in form at ion th at m ay be u sed to com pare th e perform an ce of in dividu al providers an d h osp itals an d to est ablish m etrics for p erform an ce an d goals for qu alit y im p rovem en t . How ever, overall qu alit y of care en com p asses m u ch m ore th an th ese t radit ion ally repor ted qualit y m et rics. Qu alit y m et rics are valu able in id en t ifying outliers, an d in im proving care processes an d path w ays. How ever, overall qu alit y m easu res are d ist in ct from p at ien t-cen tered clin ical ou tcom e m easu res. On e im p or t an t con cer n regard in g relian ce on qu alit y m easu res is t h e p ossibilit y t h at m easu r in g qu alit y alon e m ay lead to a focu s on ou tcom es t h at are n ot p at ien t-cen tered . If th e target for ou tcom e w ere on ly length of stay or avoidan ce of readm ission , th en th at goal m ay in cen t ivize sign i can t u n dert reat m en t of com p lex sp in al disorders. Fig. 8.1 provides an exam ple of a case in w h ich a pat ien t un der w en t a lim ited decom pression an d posterior-based teth ering procedure for a com plex sp in al deform it y. Measu red by on ly length of stay or com plicat ion s of care, th e lim ited decom p ression su rger y w ou ld be rated as a h igh -qualit y outcom e. How ever, th e pat ien t h ad n o im provem en t in h er h ealth st at us or in h er deform it y m easu res. Th e pat ien t un derw en t a revision surger y 3 years after th e in dex procedure an d w as treated w ith a three-colum n osteotom y for m ult iplan ar realign m en t of th e spin e. Th e revision surger y resulted in a longer

Outcomes Alth ough process m easures, physiological outcom es, an d t radit ion al qu alit y m et rics are im por t an t tools for assessing h ealth care qualit y, th ey d o n ot re ect t h e p at ien t ’s h ealt h care exp er ien ce or t h e im p act of care on HRQOL. Th ere h as been an in creasing em p h asis on pat ien t-based h ealth assessm en ts in recen t years. Pat ien t-reported outcom e m easures (PROMs) m ay in clu de a spect ru m of dom ain s to assess HRQOL. Frequ en t ly u sed dom ain s in clu d e d isabilit y/fu n ct ion al st at u s, p ain an d ot h er sym ptom s, em ot ional/psych ological w ell-being, gen eral h ealt h st at u s, an d sat isfact ion w it h h ealt h care exp er ien ce. Th e Visu al An alogu e Scale (VAS) for pain assessm ent is an other com m on ly u sed outcom e m easu re. Measurem ent tools for patient-reported outcom es in clu de both disease-sp eci c an d gen eral h ealth st at u s m easu res. Disease-sp eci c m easu res focu s on dom ain s associated w ith a par t icu lar con dit ion or pat ien t p opu lat ion , an d h ave th e advan tage of in creased respon siven ess to ch ange (th ere is a m ore reliable ch ange in ou tcom e score as th e u n derlying con dit ion ch anges) com pared w ith gen eral h ealth st at u s m easu res. Exam p les of speci c ou tcom e tools in clu de th e Scoliosis Research Societ y (SRS-22) qu est ion n aire, th e Osw est r y Disabilit y In dex (ODI), an d th e Neck Disabilit y In dex (NDI). Gen eral h ealth st at u s ou tcom es tools are advan tageous in th at th ey m ay be used in any pat ien t p opu lat ion an d allow for broad com parison s across a sp ect r u m of m ed ical an d su rgical con dit ion s. How ever, th ey are often less respon sive to ch anges in part icular con dit ion s or disease states. Exam ples of gen eric pro les

Measuring Outcom e and Value in Adult Deformit y Surgery Fig. 8.1a,b (a) A 73-year-old wom an presented with sagit tal and coronal plane deformit y, back pain, and neurogenic claudication. She was unable to live independently. The patient was treated with a limited decompression and a posterior-based tethering device. Although the length of stay was 3 days, and there was no complication or readmission within 90 days, there was also no improvement in radiographic or patient-centered clinical outcom es, and the patient remained disabled. (b) Postoperative X-rays 2 years after a revision surgery in which the patient was treated with a three-colum n osteotomy for realignment of the spine. The patient stayed in the hospital for 6 days and her perioperative course was complicated by a supraventricular tachycardia that required cardioversion. At 2-year follow-up, she was living independently and walking without lim its.

a

b

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Chapter 8 in clu de t h e Sh or t Form 36 (SF-36), Sh ort Form 6 Dom ain s (SF-6D), th e EuroQOL ve dim en sion s qu est ion n aire (EQ-5D), an d th e Health Ut ilit ies In dex (HUI). Both general health status m easures and certain disease-speci c outcom e tools m ay be used as in direct m easu res to calcu late u t ilit y scores. A ut ilit y score re ects societ al preferen ces for a h ealth state. Di eren t h ealth states are rated on a con t in uou s scale from 0 to 1, w ith th e value re ect ing a m easure of w ell years of life. Ut ilit y scores derived from p at ien t- rep or ted outcom e quest ion n aires using validated in st r u m en t s p rovide in form at ion on a p at ien t’s h ealth stat u s an d th e value th at societ y places on th at h ealth st ate. Con siderat ion of a ut ilit y score over t im e yields a qu alit y- adju sted life year (QALY), calculated as the utilit y score m ult iplied by th e n u m ber of years th at h ealth st ate is m ain t ain ed. Th u s, th e durabilit y of an ou tcom e resu lt s in in creased QALYs over t im e. A QALY is an ou tcom e m easu re th at rep resen t s a st an dardized u n it for com p arison across elds an d can be assign ed valu e by societ y.

■ Commonly Used Outcome

Measurements Th e follow ing in st r u m en t s are com m on ly u sed p at ien t -rep or ted ou tcom e m easu rem en t s in adult spin al deform it y th at h ave validated con version s to ut ilit y scores/QALYs.

Short Form 36 (SF-36) and Short Form 6 Domains (SF-6D) Th e SF-36 is a w idely u sed gen eric h ealth su rvey con sist ing of 36 qu est ion s w ith fou r physical h ealth scales (p hysical fu n ct ion ing, p hysical role lim itat ion , bod ily pain , an d gen eral h ealth ) an d fou r m en t al h ealt h scales (vit alit y, social fu n ct ion in g, em ot ion al role lim it at ion , an d m en t al h ealt h ). Th e SF-6D is an abbreviated version of th e SF-36 th at h as been est ablish ed as a preferen ce-based h ealth st ate classi cat ion th at m ay be conver ted to a u t ilit y score.1

EuroQOL Five Dimensions Questionnaire (EQ-5D) Th e EQ-5D is another validated an d w idely used gen eral h ealth quest ion n aire th at is used to establish a ut ilit y score. It in cludes ve h ealth dim ensions: m obilit y, self-care, usual activities, pain /discom for t , an d an xiet y/depression .

Scoliosis Research Society Questionnaire Th e Scoliosis Research Societ y (SRS) qu est ion n aire m easures h ow spin al deform it y a ects a pat ien t’s HRQOL based on ve d om ain s: pain , fu n ct ion , self-im age, m en tal h ealth , an d sat isfact ion . Th e 22-item quest ion n aire (SRS-22) is th e m ost w idely u sed an d validated version , alth ough several oth er version s exist (SRS-24, SRS-29, SRS-30). SRS-22 h as been validated as a reliable in st r u m en t w it h h igh in ter n al con sisten cy, resp on siven ess, rep rod u cibilit y, an d discrim in ator y cap acit y for pat ien ts w ith adu lt deform it y.2,3 A m odel h as been est ablish ed for t ran slat ing SRS-22 scores to SF-6D scores to determ in e utilit y scores.4,5

Osw estry Disability Index (ODI) Th e ODI m easu res HRQOL in pat ien t s w ith low back p ain . It rates a p at ien t ’s d isabilit y score based on 10 m easu res: p ain , p erson al care, sit t ing, stan ding, w alking, lift ing, sleeping, sex life, social life, an d t raveling. High er scores correspon d to a greater degree of disabilit y. Th e ODI is a validated and w idely used m easure that can be reliably t ran slated to a ut ilit y score.6

■ Cost and Value In our curren t h ealth care econom y, cost has becom e an increasingly im portant considerat ion in th e assessm en t of h ealth care in ter ven t ion s. Econ om ic an alyses of h ealth care in ter ven t ion s in clu de cost-m in im izat ion st u d ies, cost-e ect iven ess an alyses, an d cost-u t ilit y an alyses. An assessm en t of costs m ay in clude direct costs,

Measuring Outcom e and Value in Adult Deformit y Surgery ch arges, an d reim bu rsem en t s. In d irect cost s su ch as loss of product ivit y due to t im e o from w ork, t ran spor t at ion to h ealth care facilit ies, an d th e cost of caregivers m ay also be in clu ded in cost an alyses an d in corporate a w ider view of tot al cost s from a societ al perspect ive. Alth ough cost in it self is an im por t an t con siderat ion , th e valu e of care provid es th e m ost m ean ingfu l assessm en t of a h ealth care in terven t ion . Valu e of care en com p asses both ou tcom e an d cost an d is de n ed as th e n et ben e t of care relat ive to th e n et cost of care, or w h at w e get for w h at w e sp en d . Th e m easu rem en t of ben e t s an d cost s in sp in e su rger y is n ot u n iform an d m ay var y dep en ding on th e perspect ive of th e stakeh older in th e h ealth care econ om y. Hospitals an d oth er h ealth care facilit ies m ay em ph asize ou tcom es an d costs t h at a ect a single adm ission su ch as lengt h of h osp it al st ay, im p lan t u t ilizat ion , an d com p licat ion s. Th ird -p ar t y p ayers often focu s on outcom es an d costs in a m ediu m -term t im efram e in cluding readm ission s w ith in 90 days or th e cost of out pat ien t care. Th e value of a h ealth care in ter ven t ion to th e physician an d pat ien t is establish ed over a longer t im efram e th an a single adm ission ; it s im p act is m easu red based on HRQOL over a lifet im e. Cost-u t ilit y st u dies p rovide th e m ost u sefu l in form at ion abou t th e valu e of a h ealth care in ter ven t ion becau se a u t ilit y score is able to capture a patient’s preference for di erent health st ates over t im e. An ou tcom e m easu re th at directly re ects HRQOL an d is t ran slat able across disease states, such as QALYs, is an im portant prerequisite for estim ating the value of orthopedic care. Th e length of follow -u p is also an im portant consideration w hen m easuring value, as the cost of a single episode of care w ill be signi cantly discounted by the duration of the bene t.

■ Outcomes of Adult Spinal

Deformity Surgery Several st udies have reported various outcom es for t h e op erat ive an d n on op erat ive m an agem en t of adu lt sp in al deform it y. Est im ates of

th e prevalen ce of adu lt sp in al deform it y in th e Un ited St ates range from 2.5 to 25%7 How ever, m any of th ese pat ien t s d o n ot seek m ed ical care for t h eir con d it ion , an d of t h ose w h o do, m any m ay h ave su ccessfu l m an agem en t of t h eir sym ptom s w it h ou t su rger y. Non op erat ive care m ay in clu d e p hysical t h erapy, core st rengthening, w eight loss/aerobic activit y, pain m edicat ion s, steroid inject ion s, an d altern at ive m odalit ies su ch as acu pu n ct u re an d ch irop ract ic care. For m ost pat ien ts, a t rial of n on op erat ive care sh ou ld be in it iated before su rger y is con sid ered . Except ion s in clu d e p at ien t s w it h n eu rologic d e cit s or sign i can t in st abilit y. Su rger y m ay also be in d icated in p at ien t s w ith progressive cur ves, su bst an t ial deform it yrelated p ain , an d t h ose w h o h ave failed ap p rop r iate n on op erat ive t reat m en t . St u d ies of op erat ive an d n on op erat ive m an agem en t of adult spin al deform it y h ave dem on strated im proved pat ien t-repor ted ou tcom es w ith su rgical m an agem en t .8–12 In a review ar t icle on adu lt spin al deform it y, Youssef et al13 sum m arize th e n dings of 49 st udies report ing outcom es for various surgical st rategies in cluding decom pression alon e versus decom pression w ith fusion; an terior, posterior, or com bin ed su rgical app roach es; th e u se of ver tebral osteotom ies; an d levels of in strum ented vertebrae. A variet y of outcom e m easurem ents are reported for each technique.

Radiographic Outcomes A system atic review of adult scoliosis outcom es by Yadla et al14 fou n d a range in Cobb angle correct ion from 9.1 to 53.9 degrees (m ean 26.6 d egrees, represen t ing an average 40.7% cu r ve correct ion ) in a series of 49 ar t icles publish ed bet w een 1950 an d 2009 w ith m in im u m 2-year follow -u p. Radiographic outcom es h ave also been com pared bet ween di erent surgical approach es. Cran dall an d Revella 15 fou n d n o sign i can t differen ce in coron al cu r ve cor rect ion bet w een p at ien t s u n d ergoing p oster ior in st r u m en ted fu sion in ad d it ion to eit h er an terior lu m bar in terbody fu sion s (ALIF), w ith an average correct ion 69.5%, or t ran sforam in al lu m bar in ter-

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Chapter 8 body fusion (TLIF), w ith an average correct ion 68.7%. A literat ure review by Mu n dis et al16 reported im proved coronal and sagit tal correction w ith a lateral t ran spsoas approach com pared w ith open an terior procedures. A ret rospective rep or t by Pateder et al17 com paring pat ien ts w h o un der w en t posterior on ly surger y (n = 45) versu s com bin ed an terior-posterior su rger y (n = 35) foun d n o sign i cant di eren ce in coron al or sagit t al cur ve correct ion bet w een th e t w o grou p s. You ssef et al13 also review ed rad iograp h ic ou tcom es for di eren t t ypes of posterior osteotom ies in cluding Sm ith -Petersen osteotom y (SPO), pedicle subtraction osteotom y (PSO), an d ver tebral colum n resect ion (VCR). Th ese tech n iqu es are u sed to ach ieve var ying degrees of lordosis correct ion an d restorat ion of sagit t al balan ce. SPO p rovid es t h e sm allest d egree of cu r ve correct ion , ach ievin g u p to 10 d egrees of lordosis per vertebral level; h ow ever, m ult ilevel osteotom ies m ay ach ieve a large overall correct ion . Repor ts of PSO h ave dem on st rated an average 30 d egrees of lord ot ic correct ion p er level. In a com parison of SPO an d PSO, Ch o et al18 fou n d an average tot al correct ion of 33 d egrees for p at ien t s u n dergoing th ree or m ore SPOs an d 31.7 degrees for pat ien ts un dergoing PSO, bu t a sign i can tly low er im p rovem en t in sagit tal balan ce for th e SPO grou p th an for th e PSO grou p . VCR ach ieves th e h igh est degree of cu r ve correct ion . Su k et al19 repor ted a m ean d eform it y correct ion of 59% (109.0 degrees to 45.6 d egrees) in 16 p at ien t s w h o u n d er w en t p oster ior VCR. Pap ad op ou los et al 20 rep or ted t h at of 45 p at ien t s w h o u n d er w en t p oster ior VCR, t h e average cor rect ion of kyp h osis w as from 108 d egrees to 60 degrees w ith on e p at ien t sustain ing a com p lete spin al cord inju r y.

Complications Th e in ciden ce of com p licat ion s is an im p or t an t qualit y m easure in adu lt spin al d eform it y. Repor ted com plicat ion rates for sp in al deform it y su rger y are h igh , bu t a st an dard ized de n it ion or classi cat ion for repor t ing com plicat ion s in th e literat u re h as n ot been est ablish ed. Com plicat ion rates h ave been classi ed in variou s

w ays, in clu ding m ajor versu s m in or com plicat ion s, early versu s late com plicat ion s, an d su rgical versu s m ed ical com p licat ion s. Rep or ted com p licat ion s in d efor m it y su rger y in clu d e pseudarth rosis, adjacent segm ent disease, dural tears, su p er cial or d eep w ou n d in fect ion s, im plant com plications, n eurologic de cits, epidural hem atom a, wound hem atom a, pulm onary em bolism , deep vein throm bosis, system ic com plicat ion s, an d d eath . Th e in cid en ce of com plicat ion s m ay be in u en ced by pat ien t factors (e.g., age, com orbidities, severit y of deform it y) or surgical factors (e.g., approach t ype, n eed for osteotom y, n um ber of levels fu sed). Th e 49 ar t icles review ed by Yad la et al14 rep ort com plicat ion rates ranging from 0 to 53%, w ith a com bin ed tot al of 897 com p licat ion s am ong 2,175 p at ien t s (41.2%). Ch arosky et al31 rep or ted an overall 39% com p licat ion rate am ong 306 p at ien t s over age 50 u n d ergoin g adult deform it y surger y w ith eith er an an terior only, posterior only, or com bin ed approach . San su r et al 22 review ed a tot al of 4,980 cases of adult scoliosis from th e SRS m orbidit y an d m ort alit y database an d foun d an overall com p licat ion rate of 13.4% an d a m ort alit y rate of 0.3%. Sign i can tly h igh er com plicat ion rates resu lted from revision su rgeries, osteotom ies, an d com bin ed an terior-p osterior su rger y. Youssef et al13 su m m arized several st u dies report ing com plicat ion rates of variou s proced ures. Tran sfeld t et al23 repor t a 10% com plicat ion rate am ong adu lt deform it y p at ien ts w h o underwent decom pression alone com pared w ith 56% in pat ien t s w h o un der w en t decom pression an d fu sion . Bu rn eikien e et al24 reported a 31% in ciden ce of system ic com plicat ion s an d 49% h ardw are or su rgical tech n iqu e com plicat ion s in 29 p at ien t s u n d ergoin g TLIF. Com p licat ion s of ALIF m ay in clu de vascular injuries, ilioinguin al an d iliohypogast ric n er ve injuries, d am age to t h e blad der or u reters, p seu dart h rosis an d su bsiden ce, ileu s, lym ph ocele, an d ret rograde ejacu lat ion .13,25 Most of th ese com plicat ion s are u n com m on , alth ough rates of m ajor an d m in or com p licat ion s var y in th e lit erat u re. In a st u dy of 447 pat ien t s, McDon n ell et al26 foun d a com plicat ion rate of 11% for m ajor com plication s an d 24%for m inor com pli-

Measuring Outcom e and Value in Adult Deformit y Surgery cations. Com plicat ions of the lateral transpsoas approach are often related to m an ipulat ion of th e lu m ber p lexu s. In a p rosp ect ive m u lt icen ter evalu at ion of 107 ad u lt d egen erat ive scoliosis p at ien t s u n dergoing ext rem e lateral in terbody fu sion , Isaacs et al27 rep or ted a 12.1% m ajor com plicat ion rate.

Reoperations Sch eer et al28 an alyzed data from a prospect ive, m u lt icen ter adu lt sp in al deform it y dat abase, and exam ined the rates, indications, tim ing, and risk factors for reop erat ion as w ell as th e e ect of reoperat ion on HRQOL m easures. In a coh or t of 352 pat ients (268 w ith at least 1-year follow -u p ), th ey fou n d a total reop erat ion rate of 17%, th e m ajorit y of w h ich occurred w ith in 1 year of th e in dex operat ion . Th e m ost com m on in dicat ion s for reoperat ion in clu ded in st r u m en t at ion com p licat ion s an d radiograp h ic failure. Th ere w as a 19% reop erat ion rate for p at ien t s u n d ergoing a th ree-colu m n osteotom y an d a 16% reop erat ion rate for p at ien t s n ot requ irin g t h ree-colu m n osteotom y; h ow ever, th ree- colu m n osteotom y w as n ot sign i can t ly predict ive of reop erat ion at 1 year. Th e u p p erm ost in st r u m en ted ver tebra w as also n ot p redict ive of reoperat ion . Th ere w ere n o sign i can t di eren ces in th e Am erican Societ y of An esth esiologist s (ASA) grade, Ch arlson com orbidit y in dex rat ing, preoperat ive body m ass in dex (BMI), or sm oking h istor y bet w een pat ien ts w ho did not undergo reoperation and those w ho did. Pat ien t s w h o n eeded reop erat ion w ith in 1 year h ad w orse ODI an d SRS-22 scores at 1-year follow -u p th an did pat ien t s n ot n eeding reop erat ion . How ever, th ere w as n o sign i can t differen ce in HRQOL scores at 2 years bet w een pat ien ts w h o requ ired reop erat ion at 1 year an d th ose w ho did n ot . Other st udies have dem onst rated sim ilar reoperation rates, ranging from 10 to 21%.21,29–31 Reason s for revision su rger y in ad u lt sp in al deform it y in clude pseu darth rosis, cu r ve p rogression, infection, painful/prom inent im plants, adjacen t segm en t disease im plan t failure, an d n eurologic de cits.29,30

HRQOL Outcomes in Adult Spinal Deformity Despite h igh com plicat ion and reoperation rates in ad u lt sp in al d efor m it y su rger y, p at ien t sat isfact ion w ith th ese procedures is h igh . Both condition-speci c and general HRQOL outcom es th at can be conver ted to u t ilit y scores an d com p ared across th e literat u re are im por t an t prerequ isites for determ in ing th e valu e of sp in al deform it y su rger y. Several prospective m ulticenter studies have dem on st rated th e ben e ts of op erat ive t reatm en t of ad u lt sp in al deform it y com pared w ith n onoperative care in regard to patient-reported h ealth m easu res in cluding ODI, SRS-22, EQ-5D, an d n u m eric rat ing scale scores for leg an d back pain .8–12 Yadla et al14 repor ted th at in th e 49 st u dies in cluded in th eir system at ic review, ODI an d SRS w ere th e m ost com m on ly u sed pat ien tbased outcom e in st rum en t s, w ith 11 st udies rep ort ing pre- an d postoperat ive ODI scores an d 10 st udies repor t ing pre- an d postoperat ive SRS scores. Th ere w as an average decrease of 15.7 poin ts (range 3.1–32.3) in ODI score am ong 911 patien ts. Th is im provem en t in disabilit y ou tcom e cor relates w it h p reviou s rep or t s of sign i can t clin ical im p rovem en t of ODI scores ranging from 4 to 15 p oin t s.32 Of th e 999 p at ien t s w ith p re- an d postop erat ive SRS scores in Yadla et al’s review, th ere w as a m ean in crease in SRS scores of 23.1 p oin t s, w ell above t h e m in im al im p or t an t d i eren ce for SRS scores of 13 poin t s repor ted by Bagó et al.33 You ssef et al 13 su m m ar ized t h e resu lt s of st u d ies rep or t in g HRQOL ou tcom es for p at ien t s un dergoing various surgical approach es. Cran dall an d Revella 15 fou n d n on sign i can t di eren ces in VAS an d ODI ou tcom es bet w een pat ien ts u n dergoing posterior fu sion w ith eith er ALIF or TLIF. Mu n dis et al 16 fou n d sign i can t ly im p roved VAS an d ODI scores in a literat u re review of t h e lateral ap p roach for ad u lt sp in al d efor m it y. Var iou s st u d ies h ave repor ted im proved p at ien t -rep orted ou tcom es follow ing PLIF, in clu ding im proved ODI, SF-36, an d VAS scores.34–36 Good et al37 rep or ted sim ilar SRS an d ODI scores for both p osterior on ly

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Chapter 8 an d com bin ed fusion s, w ith both h aving im provem en ts at 2-year follow -u p.

Cost and Value in Adult Spinal Deformity Several recen t ar t icles h ave repor ted on th e costs of adu lt sp in al deform it y su rger y. McCar thy et al38 st u died th e total costs of 484 p at ien t s un dergoing operat ive t reat m en t of adult sp in al d efor m it y w it h an average follow -u p of 4.8 years, an d foun d an average tot al h ospit al cost of $120,394. Tot al cost for p rim ar y su rger y averaged $103,143, w h ich in creased to $111,807 at 1-year follow -u p an d $126,323 at 4-year follow -u p . Hosp it al readm ission s w ere requ ired in 130 p at ien t s (27%), w it h an average readm ission cost of $67,262. An oth er cost an alysis by McCar thy et al39 fou n d h igh er direct cost s w ith in creasing age, length of h ospital st ay, length of fu sion , an d fu sion s to th e pelvis. Cost -u t ilit y st u d ies of ad u lt sp in al d eform it y are lackin g in t h e literat u re. Alt h ough several recen tly pu blish ed system at ic review s rep or t on cost-u t ilit y an alyses in sp in e care,40,41 n on e of t h e review ed ar t icles in clu d e valu e assessm en t s in adu lt deform it y. On e st u dy by Glassm an et al42 exam in ed th e cost s an d ben et s of n on op erat ive care for adu lt scoliosis, an d qu est ion ed th e valu e of n on op erat ive t reatm en t given th eir n dings of a $10,815 m ean t reat m en t cost over a 2-year p eriod w ith n o sign i can t ch ange in HRQOL.

■ Improving Outcomes in

Deformity Surgery Measu rem en t of clin ical ou tcom es an d valu e is an im por t an t goal in spin e su rger y an d is crit ical in est ablish ing accou n t abilit y for th e en d resu lt of care. Ern est A. Cod m an w as a su rgeon in t h e early 20th cen t u r y an d a pion eer in advocating outcom e m easurem ent and reporting. He p rop osed an “en d resu lts system ” in w h ich pat ien ts’ sym ptom s, diagn osis, t reat m en t , an d outcom es w ou ld be t racked over t im e in an effor t to reduce com plicat ion s an d im prove qual-

it y of care. At th e t im e, Codm an’s ideas w ere seen as radical an d m et w ith st rong resistan ce, leading to h is dism issal from h is facu lt y p osit ion at Massach u set t s Gen eral Hosp it al. Alth ough great st r id es h ave been m ad e sin ce Codm an’s t im e in recogn izing th e im port an ce of outcom e m easurem en t , th ere is st ill m uch room for im provem en t in th e e ort to est ablish regu lar an d reliable system s for ou tcom e m easurem en t an d repor t ing. Th ere is a h igh variabilit y in spin e surger y w ith regard to surgical rates, surgical strategies, an d costs.43–45 High variabilit y in dicates a lack of con sen sus on th e opt im al t reat m en t st rategy an d a n eed for fur th er com parat ive e ect iven ess research . Redu cing variabilit y in spin e su rger y requ ires an eviden ce-based ap p roach to care. Th e establish m en t of large m ult icen ter procedu ral an d diagn osis-based regist ries for spin e surger y h as been an im por tan t step to im proving outcom e m easu rem en t an d reporting. Th ese regist ries provide a reliable system for th e repor t ing of com plicat ion s, clin ical ou tcom es, an d HRQOL ou tcom es, an d facilit ate th e evaluat ion of altern at ive in ter ven t ion s in com p arat ive e ect iven ess research . W it h th e accu rate m easu rem en t of com p licat ion s, qu alit y m ay be im proved th rough th e est ablish m en t of clin ical protocols based on stan dards of care in an e or t to reduce com plicat ion s. Th e w idespread use of pat ien t-repor ted ou tcom e tools th at m ay be t ran slated to a u t ilit y score is n ecessar y to address th e lack of cost-u t ilit y an alyses and value-based assessm ents in adult spinal deform it y. An increased em phasis on m easu ring an d im proving valu e in spin e care w ill resu lt in im p roved ou tcom es an d red u ced costs over t im e. Alth ough w e support an e ort to redu ce variabilit y in spin e su rger y th rough an eviden ce-based approach to care, w e also recogn ize th at care is n ot m on olith ic, an d pat ien t an d physician preferen ce m ust be con sidered to obt ain opt im al outcom es.

■ Chapter Summary Su rgical t reat m en t of adu lt sp in al d eform it y is a high-cost inter vention that consistently draw s

Measuring Outcom e and Value in Adult Deformit y Surgery th e at ten t ion of t h e lay p ress an d th e m edical profession du e to a p erceived lack of e ect . In th e evolving h ealth care econ om y, dem on st rat ion of valu e, th rough cost data cou p led w ith pat ien t-rep or ted ou tcom es, w ill be crit ical in m ain t ain ing p at ien t access to care. To best p rotect our pat ien t s’ abilit y to receive care th at can e ect ch an ge in t h eir h ealt h st at u s, it is im perat ive for spin al surgeon s to un derstan d an d collect pat ien t repor ted outcom es. Surgical t reat m en t of adu lt spin al deform it y h as been sh ow n to h ave a sign i can t e ect on pat ien t-rep or ted ou tcom es. Alth ough th e in it ial cost of spin al deform it y su rger y is h igh , th e cost per QALY decreases w ith in creasing du rabilit y of th e in ter ven t ion . Th us, it is im perat ive th at w e as a p rofession con t in u e to t rack an d rep or t secon dar y in ter ven t ion s an d com p licat ion s of care, so th at opt im al in ter ven t ion st rategies can be created . Deter m in at ion of ap propriate qualit y m et rics an d process m easu res for th e deliver y of sp in e care can h elp ach ieve im proved pat ien t outcom es an d poten t ially low er cost , th u s m a xim izing societal ret u rn on invest m en t for th e care of adu lt spin al deform it y.

Pearls In a value-based health care economy, measures of cost and clinical outcome are important to dene cost-e ective interventions. Patient-centered m easures of outcom es provide the m ost useful assessment of value of interventions in deformit y surgery. Utilit y scores are a useful m easure of general health status preference that has a de nable unit of well-years of life/year. Cost per QALY is a measure of value that is sensitive to the m agnitude of the health status change and the durabilit y of change. Selection of disease-speci c, patient-reported outcome should consider validated m etrics that can potentially be converted to a utilit y score. Pitfalls Sole focus on qualit y m etrics and process m easures creates a dissociation bet ween interventions and patient-centered outcom es. Optim izing qualit y and process m etrics in the absence of patient-centered inform ation m ay incorrectly guide evidence-based care, and provide incentives for inappropriate care. Cost-minim ization strategies or focus on cost without regard to e ect of treatment on patient reported outcom es will not be a value-optimizing strategy.

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Chapter 8 11. Sm ith JS, Sh a rey CI, Ber ven S, et al; Sp in al Deform it y St u dy Grou p. Operat ive versus n on operat ive t reat m en t of leg p ain in ad u lt s w it h scoliosis: a ret rosp ect ive review of a p rosp ect ive m u lt icen ter dat abase w ith t w o-year follow -up. Spin e 2009;34: 1693–1698 Pu bMed 12. Br idw ell KH, Glassm an S, Hor ton W, et al. Does t reat m en t (n on op erat ive an d op erat ive) im p rove t h e t w o-year qualit y of life in pat ien t s w ith adult sym ptom at ic lum bar scoliosis: a prosp ect ive m ult icen ter eviden ce-based m edicine st udy. Spin e 2009; 34:2171–2178 PubMed 13. You ssef JA, Orndor DO, Pat t y CA, et al. Curren t st at us of adult spin al deform it y. Global Spin e J 2013; 3:51–62 PubMed 14. Yadla S, Malten fort MG, Ratli JK, Harrop JS. Adu lt scoliosis su rger y ou tcom es: a system at ic review. Neurosurg Focus 2010;28:E3 Pu bMed 15. Cran dall DG, Revella J. Tran sforam in al lum bar in terbody fu sion versu s an terior lu m bar in terbody fu sion as an adju n ct to p oster ior in st r u m en ted cor rect ion of d egen erat ive lu m bar scoliosis: t h ree year clin ical an d rad iograp h ic ou tcom es. Sp in e 2009;34:2126– 2133 PubMed 16. Mun dis GM, Akbarn ia BA, Ph illips FM. Adult deform it y cor rect ion t h rough m in im ally invasive lateral ap p roach tech n iqu es. Sp in e 2010;35(26, Su p p l): S312–S321 Pu bMed 17. Pateder DB, Kebaish KM, Cascio BM, Neubaeur P, Mat usz DM, Kost uik JP. Posterior on ly versus com bin ed an terior an d posterior ap p roach es to lu m bar scoliosis in adult s: a radiograph ic an alysis. Spin e 2007;32: 1551–1554 Pu bMed 18. Ch o K-J, Bridw ell KH, Len ke LG, Berra A, Baldus C. Com parison of Sm ith -Petersen versu s pedicle su b t ract ion osteotom y for th e correct ion of xed sagit t al im balan ce. Sp in e 2005;30:2030–2037, d iscu ssion 2038 PubMed 19. Su k S-I, Ch ung E-R, Kim J-H, Kim S-S, Lee J-S, Ch oi W-K. Posterior ver tebral colum n resect ion for severe rigid scoliosis. Spine 2005;30:1682–1687 Pu bMed 20. Papadopou los EC, Boach ie-Adjei O, Hess W F, et al; Fou n dat ion of Or th op edics an d Com plex Sp in e, New York, NY. Early outcom es an d com plicat ion s of posterior vertebral colum n resect ion . Spin e J 2013 Apr 25. [Epub ah ead of prin t] Pu bMed 21. Ch arosky S, Guigui P, Blam ou t ier A, Roussouly P, Ch opin D; St udy Group on Scoliosis. Com p licat ion s an d risk factors of prim ar y adult scoliosis su rger y: a m u lt icen ter st u dy of 306 pat ient s. Spin e 2012;37:693– 700 PubMed 22. San sur CA, Sm ith JS, Coe JD, et al. Scoliosis research societ y m orbidit y an d m ort alit y of adu lt scoliosis su rger y. Spin e 2011;36:E593–E597 PubMed 23. Tran sfeldt EE, Topp R, Meh bod AA, Win ter RB. Surgical outcom es of decom pression , decom pression w ith lim ited fu sion , an d decom pression w ith fu ll cu r ve

fusion for degen erat ive scoliosis w ith radiculopathy. Spin e 2010;35:1872–1875 Pu bMed 24. Burn eikien e S, Nelson EL, Mason A, Rajpal S, Serxner B, Villavicen cio AT. Com plicat ion s in pat ien t s un dergoing com bin ed t ran sforam in al lum bar in terbody fusion an d posterior in st rum en t at ion w ith deform it y correct ion for degenerat ive scoliosis an d spin al sten osis. Surg Neurol In t 2012;3:25 Pu bMed 25. Th an KD, Wang AC, Rah m an SU, et al. Com plicat ion avoidance and m anagem ent in anterior lum bar interbody fusion . Neurosurg Focus 2011;31:E6 PubMed 26. McDon n ell MF, Glassm an SD, Dim ar JR II, Pun o RM, Joh n son JR. Periop erat ive com p licat ion s of an terior procedu res on th e spin e. J Bon e Join t Su rg Am 1996; 78:839–847 PubMed 27. Isaacs RE, Hyde J, Goodrich JA, Rodgers W B, Ph illips FM. A prospect ive, n on ran dom ized, m ult icen ter evalu at ion of ext rem e lateral in terbody fu sion for th e t reat m en t of adult degenerat ive scoliosis: perioperat ive outcom es an d com plicat ion s. Spin e 2010;35(26, Suppl):S322–S330 Pu bMed 28. Sch eer JK, Tang JA, Sm ith JS, et al; In tern at ion al Spin e St udy Group. Reoperat ion rates an d im pact on outcom e in a large, prospect ive, m ult icen ter, adult spin al deform it y dat abase: clin ical ar t icle. J Neurosurg Spin e 2013;19:464–470 Pu bMed 29. Pich elm an n MA, Len ke LG, Bridw ell KH, Good CR, O’Lear y PT, Sides BA. Revision rates follow ing prim ary adult spin al deform it y su rger y: six h un dred fort yth ree con secu t ive p at ien t s follow ed-u p to t w en t yt w o years postoperat ive. Spin e 2010;35:219–226 PubMed 30. Kelly MP, Len ke LG, Bridw ell KH, Agar w al R, Godzik J, Koester L. Fate of th e adult revision spin al deform it y pat ien t: a single in st it ut ion experien ce. Spin e 2013; 38:E1196–E1200 Pu bMed 31. Acost a FL Jr, McClen don J Jr, O’Sh augh n essy BA, et al. Morbid it y an d m or t alit y after spin al deform it y su rger y in pat ien t s 75 years an d older: com p licat ion s an d predict ive factors. J Neurosurg Spin e 2011;15: 667–674 Pu bMed 32. Fairban k JC, Pyn sen t PB. Th e Osw est r y Disabilit y In d ex. Sp in e 2000;25:2940–2952, d iscu ssion 2952 Pu bMed 33. Bagó J, Pérez- Gr u eso FJS, Les E, Her n án d ez P, Pellisé F. Min im al im p or t an t di eren ces of th e SRS-22 Pat ien t Quest ion naire follow ing su rgical t reat m en t of idiopath ic scoliosis. Eur Spin e J 2009;18:1898– 1904 PubMed 34. Wu C-H, Wong C-B, Ch en L-H, Niu C-C, Tsai T-T, Ch en W-J. In st ru m en ted p osterior lu m bar in terbody fu sion for pat ient s w ith degen erat ive lum bar scoliosis. J Spin al Disord Tech 2008;21:310–315 PubMed 35. Zim m erm an RM, Moh am ed AS, Skolasky RL, Robin son MD, Kebaish KM. Fun ct ion al outcom es an d com p licat ion s after p r im ar y sp in al su rger y for scoliosis in ad u lt s aged for t y years or old er: a p rosp ect ive

Measuring Outcom e and Value in Adult Deformit y Surgery study w ith m inim um t wo-year follow -up. Spine 2010; 35:1861–1866 PubMed 36. Tsai T-H, Huang T-Y, Lieu A-S, et al. Fun ct ion al outcom e analysis: in st rum en ted posterior lum bar in terbody fu sion for degen erat ive lu m bar scoliosis. Act a Neuroch ir (Wien ) 2011;153:547–555 PubMed 37. Good CR, Len ke LG, Bridw ell KH, et al. Can posterior-on ly surger y provide sim ilar radiograph ic an d clin ical resu lt s as com bin ed an terior (th oracotom y/ th oracoabdom in al)/posterior approach es for adult scoliosis? Spin e 2010;35:210–218 PubMed 38. McCar t hy IM, Host in RA, Am es CP, et al; In ter n at ion al Sp in e St u dy Grou p . Tot al h osp it al cost s of su rgical t reat m en t for ad u lt sp in al d efor m it y: an exten ded follow -up st udy. Spin e J 2014;14:2326– 2333 Pu bMed 39. McCarthy IM, Host in RA, O’Brien MF, et al; In tern at ion al Spin e St udy Group. An alysis of th e direct cost of su rger y for four diagn ost ic categories of adult spinal deform it y. Spin e J 2013;13:1843–1848 Pu bMed 40. In d rakan t i SS, Weber MH, Takem oto SK, Hu SS, Polly D, Ber ven SH. Valu e-based care in t h e m an -

agem en t of sp in al d isorders: a system at ic review of cost-u t ilit y an alysis. Clin Or th op Relat Res 2012;470: 1106–1123 PubMed 41. Kep ler CK, W ilkin son SM, Rad cli KE, et al. Cost u t ilit y an alysis in sp in e care: a system at ic review . Spin e J 2012;12:676–690 Pu bMed 42. Glassm an SD, Carreon LY, Sh a rey CI, et al. The cost s an d ben e t s of n on operat ive m an agem en t for adult scoliosis. Spine 2010;35:578–582 PubMed 43. Ir w in ZN, Hilibran d A, Gust avel M, et al. Variat ion in surgical decision m aking for degen erat ive spin al disorders. Par t I: lu m bar spin e. Spin e 2005;30:2208– 2213 PubMed 44. San ders JO, Hayn es R, Ligh ter D, et al. Variat ion in care am ong spin al deform it y su rgeon s: result s of a sur vey of the Shrin ers h ospit als for ch ildren . Spine 2007;32:1444–1449 Pu bMed 45. Deyo RA, Mirza SK. Tren ds an d variat ion s in th e u se of spin e surger y. Clin Or th op Relat Res 2006;443:139– 146 PubMed

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9 Junctional Issues Follow ing Adult Deformity Surgery Han Jo Kim, Sravisht Iyer, and Christopher I. Sha rey, Sr.

■ Introduction Proxim al ju n ct ion al kyp h osis (PJK) w as rst de n ed an d ch aracterized in th e literat u re by Glat tes an d colleagu es.1 Th ese au th ors p resen ted a ret rospect ive series of 81 adu lt deform it y p at ien t s an d de n ed abn orm al PJK u sing t w o criteria: (1) proxim al ju n ct ion al sagit tal Cobb angle ≥ 10 degrees (Fig. 9.1) an d (2) postop erat ive p roxim al ju n ct ion al sagit t al Cobb angle at least 10 degrees greater th an th e preoperat ive m easurem en t . Th ey repor ted an in ciden ce of PJK of 26%,1 an d h ave been suppor ted by subsequen t st udies repor t ing rates of PJK ran gin g from 17 to 61.7%.2,3 Alt h ough PJK is gen erally asym ptom at ic, t h ere is a su bset of pat ien ts (1.4–4%) w h o presen t w ith sym ptom s requ iring fur th er su rger y.4,5 Risk factors for th e developm en t of PJK in clude advan ced age, su rgical app roach , greater r igid it y of con st r u ct , greater m agn it u d e of sagit t al correct ion , th e presen ce of p reexist ing p roxim al kyp h osis, dam age to t h e p oster ior ligam en tou s com plex, dam age to th e adjacen t facet w h en in st ru m en t ing th e upper in st r um en ted ver tebra (UIV), xat ion to th e iliu m , t ype of in st ru m en tat ion (h ooks versu s p edicle screw s), an d th e presen ce of osteoporosis.1,2,6 Given th e large n u m ber of iden t i ed risk factors, th e et iology of PJK is m ost likely m u lt ifactorial in n at u re. Non eth eless, advan ced age is a factor th at seem s to be u n iform across th e m ajorit y of st u dies. In addit ion , th e curren t litera-

t u re suggests th at PJK m ay be m ore p revalen t th an th e rates in it ially repor ted 20 years ago. Th is ch apter syn t h esizes ou r cu r ren t u n d erst an ding of PJK in adults by review ing th e literat u re u n derlying th e variou s et iologies of PJK, discussing th e im pact of PJK on clin ical outcom es, exam in ing th e risk factors th at lead to revision surger y due to PJK, providing con sen sus exper t op in ion on possible m eth ods for m in im izing PJK develop m en t , an d describing in dicat ion s for surgical t reat m en t .

■ Etiology and Risk Factors

for Proximal Junctional Kyphosis Th e et iology of PJK is m ult ifactorial an d can be divided into surgical, radiographic, and pat ientrelated factors. Th ese are sum m arized in Table 9.1. We w ill closely exam ine the literat ure about th ese various causes.

Surgical Factors Disruption of the Posterior Soft Tissues In th eir classic paper, Panjabi an d W h ite 7 h igh ligh ted t h e role of t h e p oster ior sp in al ligam en t s in p reven t ing excessive m ot ion bet w een th e ver tebrae. Given th ese ligam en t s’ role as a st abilizer in th e sp in e, th e disr u pt ion of poste-

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a

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b

Fig. 9.1a,b The proximal junctional sagit tal Cobb m easurem ent (proximal junctional angle). This is de ned as the Cobb angle bet ween the inferior end plate of the upper instrumented vertebra and the superior end plate of the vertebra t wo levels above.

(a) Postoperative radiograph. (b) Radiograph at 6 months that meets both criteria of proximal junctional kyphosis (PJK): proxim al junctional angle > 10 degrees and a progression of the proximal junctional angle > 10 degrees.

rior soft t issu es h as alw ays been view ed as a potential cont ributor to th e developm en t of PJK. Th e relat ive con t ribu t ion of th e posterior soft t issu es h as been exam in ed in a cadaveric m od el.8 Th e au th ors of th is st u dy perform ed on e of several procedu res on m ot ion segm en t s obtain ed from six h um an cadavers. Th ese procedu res in cluded bilateral t ran sverse h ook site

prep arat ion , su blam in ar h ook site prep arat ion , pedicle screw p lacem en t , su p ra- an d in tersp inous ligam ent transection, and transection of all posterior structures. Follow ing these intervent ion s, th e au th ors m easu red th e torqu e n eed ed to p rodu ce 2.8 d egrees of an gu lar d isp lacem en t , an d , based on th is m easu rem en t , calculated t h e tot al exion st i n ess of t h e m ot ion

Table 9.1 A Summary of Various Risk Factors for PJK Proposed in the Literature Surgical

Radiographic

Patient-Specif c

• Disruption of posterior soft tissues • Rigidit y of instrumentation • Combined anterior-posterior approach/ fusion • Upper instrumented vertebrae in the upper thoracic spine • Fusion to the sacrum • Degree of correction ◦ Increased lumbar lordosis ◦ High SVA correction ◦ Failure to respect global sagit tal alignment

• Increased preoperative thoracic kyphosis • Increased preoperative proximal junctional angle

• Advanced age • High BMI • Osteoporosis

Abbreviations: BMI, body mass index; SVA, sagit tal vertical axis.

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Chapter 9 segm ent. Their data show ed that sectioning the su p ra- an d in terspin ou s ligam en t s led to a sign i can t (p = 0.02) loss of exion st i n ess. Th ey foun d th at th e posterior ligam en tou s com plex con t ribu ted 6.59% to th e st i n ess of th e m ot ion segm en t an d th at th e st i n ess loss cou ld rough ly double (12.62%) w ith th e exp osu re requ ired for p lacem en t of in st ru m en t at ion at th e sam e m ot ion segm en t . Sim ilarly, a biom ech an ical m odel developed by Cam m arata et al6 sh ow ed th at com plete facetectom y and posterior ligam ent resection both in dep en den tly in creased th e proxim al ju n ct ion al kyph ot ic angle; com bin ing th e t w o procedu res resu lted in an even greater in crease in th e kyp h ot ic angle. Den is et al9 p resen ted a series of 67 pat ien t s w ith Sch eu erm an n’s kyph osis t reated w ith an in st r u m en ted fu sion . Th ey h igh ligh ted th e im p or t an ce of th e p osterior ligam en tou s st ru ctures in their series. They separated their cohort of pat ien ts w ith PJK in to a group w h ere th e fusion stop ped sh ort of th e p roxim al en d ver tebra as w ell as a grou p w h ere th e p roxim al en d ver tebra w as in clu ded in th e fusion . Th e lat ter group h ad th ree pat ien ts w h o developed PJK. All th ree w ere n oted to h ave disru pt ion of th e ju n ct ion al ligam en t u m avu m w ith su blam in ar h ooks or su blam in ar w ires. In all, th e auth ors n oted that disr upt ion of th e posterior ligam en t s w as im p licated in 25% (5/20) cases of PJK obser ved in th eir series. Alth ough th e above n dings all h in t at th e im portance of th e posterior structures, the true im pact of posterior dissection h as been di cult to isolate in clin ical st u dies. Alth ough all su rgeon s w ould agree th at disrupt ion of th e m uscular, ligam entous, and bony tissue likely occurs ceph alad to the UIV, th e degree of disrupt ion is d i cu lt to quan t ify, let alon e st an dardize.2 Despite th is lim it at ion , th e spin al recon st r uct ive com m u n it y gen erally agrees t h at dam age to t h e p oster ior soft t issu es likely con t r ibu tes to th e d evelop m en t of PJK.2

Rigidity of Instrumentation In addit ion to th e posterior soft t issues, n um erou s invest igators h ave com m en ted on th e rigidit y of in st ru m en t at ion as a risk factor for

develop m en t of PJK. Th is h as been a focu s in th e eld, p ar t icularly in ligh t of th e m ore rigid, all-pedicle screw con st r ucts th at h ave gain ed in pop ularit y over th e past t w o decades. Th e biom ech an ical st u dy by Cam m arat a et al6 described in th e prior sect ion n icely h igh light s th e im pact of in creasing con st ru ct rigidit y on th e p roxim al ju n ct ion al angle. Sim ilarly, Th aw ran i et al10 u sed a p orcin e cadaver m odel to sh ow t h at t ran sverse p rocess h ooks p rovided decreased st i n ess com pared w ith an all pedicle screw construct. In the all pedicle screw grou p , t h e m ajor it y of t h e m ot ion occu r red at th e m ot ion segm en t im m ediately proxim al to th e UIV, w h ereas th is t ran sit ion w as m ore gradu al in th e t ran sverse p rocess group. How ever, clin ical st u d ies h ave n ot clearly afrm ed th e n dings of th e above biom ech an ical st u d ies.5,11,12 Y.J. Kim et al12 fou n d th at th e u se of all pedicle screw con st ructs w as associated w ith an in creased rate of PJK com pared w ith hybrid or h ook con st ru ct s (p = 0.04), bu t th is d i eren ce did n ot rem ain sign i can t w h en adju st ing for age (p = 0.33). Sim ilarly, oth er p ub lish ed series of adu lt scoliosis p at ien t s h ave n ot dem on st rated th at all pedicle screw con st ruct s w ere m ore likely to be associated w ith PJK th an w ere hybrid screw –h ook con st ru ct s.5 Hassanzadeh and colleagues 11 published a series of 47 con secu t ive adu lt p at ien t s w ith 2-year follow -u p w h o u n der w en t long sp in al fu sion w it h h ooks or screw s at t h e UIV. Th ey fou n d n o in st an ces of PJK in th e 20 pat ien t s t reated w ith a h ook at t h e UIV com pared w ith a 29.6% (8/27 p at ien t s) rate of PJK in th e screw s grou p (p = 0.01).

Surgical Approach Som e t ypes of surgical approach have also been associated w ith PJK. Y.J. Kim an d colleagues 12 foun d th at a com bin ed an terior an d posterior approach w as a risk factor for developm en t of PJK, even w h en adju sted for age (p = 0.04). Th is n ding h as been con sisten tly sh ow n to be th e case in oth er series as w ell.13,14 In a ret rospect ive series of 249 pat ien ts (adult s an d adolescen t s) w h o un der w en t surger y for idiopath ic scoliosis, H.J. Kim et al14 perform ed a m ult ivariate an alysis to iden t ify risk factors for th e d e-

Junctional Issues Following Adult Deformit y Surgery velopm ent of PJK. They found that patients w ho underwent an anterior-posterior approach were th ree t im es as likely (odds rat io [OR], 3.04; 95% con den ce in ter val [CI], 1.56–5.93) to develop PJK com pared w ith in dividuals w h o un derwent posterior-only fusion. Additionally, a com bin ed an terior an d posterior approach w as on e of th e few factors th at cou ld be con sisten tly iden t i ed as a risk in a system at ic review of th e eld.2

Upper Instrumented Vertebrae Th e contribut ion of the UIV to the developm ent of PJK w as suggested in th e in it ial descript ion of th e ph en om en on . Glat tes an d colleagu es 1 foun d a sign i can tly h igh er level of PJK w h en th e in st r u m en tat ion stopp ed at T3 (53%) w h en com p ared w ith T4 (12.5%) (p = 0.02). A su bsequ en t larger series from th e sam e in st it u t ion did sh ow t h at an u p p er t h oracic UIV (T2–6) dem on st rated a h igh er p revalen ce of PJK (33.67%, 33/98) com pared w ith low er th oracic an d upper lu m bar UIV (p = 0.036).12 How ever, th is di eren ce did n ot rem ain sign i can t w h en adjust ing for age (p = 0.65).12 Th e UIV, along w ith a com bin ed an terior-posterior ap proach , w as on ly on e of t w o in dep en den t risk factors associated w it h t h e d evelop m en t of PJK in a series of 249 p at ien t s.14 Bridwell et al15 found that patients w ith m ore advan ced PJK (PJK ≥ 20 degrees) w ere m ore likely to h ave a low er n u m ber of levels fu sed (8 versu s 11) an d w ere m ore likely to h ave a UIV in th e low er t h oracic sp in e (p < 0.001). Ha et al16 exam in ed th e di eren ce bet w een a UIV in th e low er an d upper th oracic spin e an d foun d t h at t h e m ech an ism of failu re w as d i eren t bet w een th e t w o scen arios. Failure occurred sooner (p < 0.01) an d w as m ore likely to occu r d ue to fract u re in th e low er th oracic spin e, w h ereas su blu xat ion w as m ore p revalen t in th e u pp er th oracic spin e. Oth er series, h ow ever, failed to iden t ify th e UIV as a risk factor for developm en t of PJK.5,17 A system at ic review fou n d low -level eviden ce th at th e UIV w as am ong th e risk factors associated w ith th e develop m en t of PJK.2 Th e m ech an ism of h ow th e UIV m igh t con t ribu te to th e develop m en t of PJK is in com -

pletely un derstood. Proposed th eories in clu de both dam age to th e adjacent facet joint th at can occu r m ore easily in th e upper th oracic spin e 18 as w ell as th e in terface bet w een th e m obile cer vical an d relat ively stat ic th oracic spin e.1

Instrumentation to the Sacrum/ Ilium In cases of ad u lt scoliosis, exten sion of t h e fu sion to th e sacropelvis an d th e su bsequ en t in crease in st i n ess of th e con st r u ct h as been th ough t to con t ribu te to th e develop m en t of PJK. In th eir series of adult pat ien ts, Y.J. Kim an d colleagues 12 foun d a h igh er rate of PJK in p at ien ts w h ose low er in st rum en ted ver tebra (LIV) w as S1 com p ared w ith p at ien t s w ith an LIV of L5 or above (51% vs 30%, p = 0.009). Th is rem ain ed a st rong t ren d (p = 0.059) even after adju st ing for age. Yagi et al5 obser ved a sim ilar t ren d; in th eir series, fusion to th e sacr um w as associated w ith a sign i can tly h igh er in ciden ce of PJK (an in crease of 27.6%, p = 0.02). A m ore recen t clin ical series also fou n d th at pat ien t s w ith PJK requ iring revision w ere m ore likely to h ave fu sion s exten ding to th e pelvis (74% vs 91%, p = 0.02).19 Fu sion to t h e sacru m w as also associated w ith an in creased risk of p rogression of PJK to greater th an 20 degrees.15

Magnitude of Correction More recen tly, as w e h ave begu n to un derstan d th e im port an ce of global sagit t al align m en t , in vest igators h ave sough t to determ in e if p aram eters of sagit tal align m en t correlate w ith th e in ciden ce of PJK. In gen eral, st u d ies h ave fou n d th at an in crease in sagit t al balan ce correct ion an d an in crease in lum bar lordosis correlate w ith th e developm en t of PJK.5,17,19,20 Th e m ech an ism un derlying th is in creased rate of PJK is un kn ow n . In th eir ret rospect ive series, H.J. Kim et al19 fou n d th at pat ien ts requ iring revision su rger y for PJK h ad a lu m bar lordosis (LL) th at w as closer to th e pelvic in ciden ce (PI), w h ereas th ose w ith out PJK h ad a LL m u ch low er th an PI. Th eir n dings are sim ilar to th ose of Maru o an d colleagues,17 w h o sh ow ed th at in creasing LL m ore th an 30 degrees w as associated w ith a sign i can tly h igh er in ciden ce of PJK (58% vs 28%, p = 0.003).

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110

Chapter 9 Sim ilarly, patien ts requiring revision surger y w ith PJK h ad a low er postoperat ive sagit tal ver t ical axis (SVA) (0.8 vs 4.1 cm ) an d a h igh er m agn it u de of SVA correct ion (9 vs 4 cm ) com pared w ith th ose w ith ou t PJK.19 Th ese n dings are gen erally in keeping w ith th ose of Yagi an d colleagu es,5 w h o saw th at a SVA correct ion greater th an 5 cm led to a 50% in ciden ce of PJK (p = 0.01). An oth er series of 54 p at ien t s dem on st rated th at th e risk of PJK decreases by 30%for ever y cen t im eter in crease in th e C7-plum b lin e.20 In th e sam e series, th e C7-plum blin e h ad ret urn ed closer to it s preoperat ive posit ion in all pat ien t s by n al follow -up (average 2.23 years). The interplay bet w een thoracic kyphosis and lum bar lordosis, that is, the global sagit tal alignm en t (GSA), is also becom ing an in creasingly im port an t con cept in u n derstan ding PJK. In th e sam e st udy w h ere th ey looked at sagit tal correct ion , Yagi an d colleagu es 5 sh ow ed th at a n on ideal p ostop erat ive GSA (th oracic kyph osis [TK] + LL + PI > 45°) led to a 70% rate of PJK (p < 0.001). Maru o et al17 also sh ow ed th at ideal global sagit tal align m en t p rotected again st th e d evelop m en t of PJK. Th e im port an ce of spin al balan ce is also h igh ligh ted by Men doza-Lat tes and colleagues,20 w ho found that the di erence bet w een TK an d LL w as inversely propor t ion al to th e risk of developing PJK. Taken toget h er, t h ese st u dies ad d to ou r grow ing u n derst an ding of global sagit t al balan ce. Th ey suggest th at th e goal of restoring th e SVA to 0 cm m ay n ot be opt im al for all p at ien t s. In deed, st u dies of asym ptom at ic volu n teers h ave con sisten tly sh ow n in creased age to be correlated w ith greater SVA.21,22 Th ey also h igh ligh t t h e n eed for fu r t h er st u d ies to est ablish t h e opt im al sp in op elvic param eters for surgeon s to target (i.e., to u n derstan d th e di eren ce bet w een LL + 9° an d LL – 9°).19

Radiographic Factors Preoperative Thoracic Kyphosis High p reop erat ive TK m ay p red isp ose to PJK in bot h ad u lt an d p ediat r ic p op u lat ion s. In th e adult populat ion , Maruo an d colleagues 17 sh ow ed th at preop erat ive TK greater th an 30

degrees w as a risk factor for developing PJK (62% vs 29%, p = 0.002). Sim ilarly, Men d ozaLattes and colleagues 20 found that patients w ith PJK h ad a larger d i eren ce bet w een TK an d LL at baselin e (p = 0.012). Th ese p at ien t s also p resen ted w ith low er sacral slop e an d sign s of p elvic ret roversion .

Proximal Junctional Angle Lee an d colleagues,23 on e of th e rst groups to d escribe PJK in p at ients w ith idiopath ic scoliosis, fou n d th at a preop erat ive PJ angle greater th an 5 degrees w as a risk factor for develop m en t of su bsequen t jun ct ion al kyph osis. Th is w ork h as been su p p or ted by Den is et al’s 9 series of Sch eu erm an n p at ien t s. Th e large m ajorit y of cases of PJK obser ved in th at series w ere n oted w h en th e proxim al exten t of th e fusion did n ot in clu de th e kyph ot ic proxim al en d vertebra. Mar uo an d colleagues 17 w ere able to dem on st rate th at a p roxim al jun ct ion al angle (PJA) greater th an 10 degrees (p = 0.016), in addit ion to a PI > 55° (p = 0.037), w as a risk factor for th e developm en t of PJK.17

Patient Factors Pat ien t-speci c factors such as advan ced age, h igh body m ass in d ex (BMI), t h e p resen ce of osteop orosis, sm okin g, an d t h e p resen ce of ot h er com orbid it ies are alw ays im p or t an t to con sid er p r ior to sp in e su rger y. Not su r p r isingly, m any of th ese factors h ave been lin ked to th e developm en t of PJK. In th e adu lt literat u re, in creasing age h as been associated w it h t h e in ciden ce of PJK an d PJK requiring revision in n um erou s case series.1,2,15,19,24 In terest ingly, th e lin k bet w een h igh BMI an d th e developm en t of PJK is less clear in th e literat u re. Bridw ell et al15 w ere able to sh ow th at h igh er BMI (p = 0.015) an d th e presen ce of a com orbidit y (p = 0.001) w ere associated w ith the developm ent of PJ angle > 20 degrees. How ever, ot h er ser ies from t h e sam e in st it u t ion h ave failed to show the sam e link bet ween h igh BMI an d PJK (de n ed in th e t radit ion al m an n er u sing 10 degrees as a cu to ).19,24 Given th at a large prop ort ion of PJK occu rs du e to fract u re at th e UIV,17 it is n ot surprising

Junctional Issues Following Adult Deformit y Surgery th at osteop orosis p lays a cr it ical role in t h e d evelopm en t of PJK. In on e series, osteop orot ic pat ien ts over th e age of 65 w h o u n der w en t a m in im u m ve-level fu sion w ere fou n d to h ave pedicle an d com p ression fract u res at a rate of 13%, w ith PJK occu rring in 26% of p at ien t s.25 In a sm all series of 10 adu lt p at ien t s, Wat an abe and colleagues 26 found that osteopenia and preoperative com orbidities w ere com m on am ong pat ien ts w ith proxim al ver tebral fract u re an d su blu xat ion . Case series in adu lt p at ien t s h ave fou n d t h at osteop orosis is m u ch m ore p revalen t in in d ivid u als w it h PJK th an in t h ose w ith out .24

■ Timing of Proximal

Junctional Kyphosis Th e m ajorit y of th e cases of PJK are iden t i ed w ith in th e rst year postoperat ively.5,14 Th e p at ien t s w h o do go on to develop PJK p rogress to abou t on e h alf (53%) of th eir tot al degree of PJK by 3 m on th s.5 Sim ilarly, Y.J. Kim an d colleagu es 12 rep or ted t h at 59% of p rogression of th e PJA occu rs w ith in th e rst 8 w eeks. Maru o et al17 repor ted th at 62%of cases w ith PJK w ere iden t i ed w ith in 8 w eeks, w ith fract u re being th e m ost com m on cau se.

■ Clinical Outcomes After

Proximal Junctional Kyphosis Clin ical ou tcom es after PJK are su m m arized in Table 9.2. In gen eral, m ost st udies h ave sh ow n th at m ost cases of PJK are asym ptom at ic, an d th at th is con dit ion does n ot su bst an t ially alter clin ical ou tcom e. Th ere are, h ow ever, t w o recen t series th at do sh ow th at p at ien t s w ith PJK have increased pain levels com pared w ith those pat ien ts w ith ou t PJK.19,24 Th e di eren ce in pain levels bet w een th e t w o grou p s m et th e m in im al clin ically im p or t an t d i eren ce.24 Th e in ciden ce of sym ptom at ic pain (i.e., upper back

pain reported by th e p at ien t at follow -up ) w as also m arked ly h igh er in t h e grou p w it h PJK (29.4% vs 0.9%, p < 0.001). Th ese m ore recen t result s h igh ligh t th e im port an ce of fur th ering ou r u n d erst an d ing of PJK; as w e sh all see in t h e follow ing sect ion s, th e early descript ion s of PJK as a radiograph ic n ding th at w arran t s follow -u p m igh t be u n derst at ing th e t ru e im pact of th e con dit ion . Invest igators are n ow t u r n in g a closer eye to th e con cept of sym ptom at ic PJK to see h ow th ese cases m igh t im pact clin ical outcom es. Yagi an d colleagu es 5 foun d th at th eir pat ien ts w ith sym ptom atic PJK had a signi cantly higher Osw est r y Disabilit y In dex (ODI) score com p ared w it h p at ien t s w it h ou t PJK.5 Sim ilarly, H.J. Kim et al19 fou n d low er ODI an d p ain scores in pat ien ts w ith PJK an d low er pain scores in p at ien ts un dergoing revision for PJK. Im port an tly, th ey fou n d low er ou tcom es across all d om ain s of th e Scoliosis Research Societ y (SRS) questionnaire in patients w ith PJK, though these outcom es did n ot reach stat ist ical sign i can ce.

■ Revision Surgery for

Proximal Junctional Kyphosis Th e m ajorit y of cases of PJK are asym ptom at ic an d do n ot require in ter ven t ion . Repor ted rates of revision due to PJK h ave ranged from 1.4 to 11.2% w ith pain being th e m ost com m on reason for revision .4,19,27,28 Severe cases of PJK can lead to sign i can t sagit tal im balan ce an d disabilit y. In a sm all series of 10 p at ien t s, Wat an abe et al26 rep or ted ver tebral su blu xat ion an d severe n eu rologic de cit in t w o of th eir 10 p at ien t s as a resu lt of progression of PJK. Har t et al28 repor ted on a case series from th e Invasive Species Specialist Group (ISSG) database. Th eir de n it ion of proxim al jun ct ion al failure (PJF) w as “severe PJK,” w hich w as further de n ed as a ch ange of m ore th an 10 degrees of kyph osis bet w een th e UIV an d th e ver tebra t w o levels above th e UIV (UIV +2), along w ith on e or m ore of th e follow ing: fract ure of th e

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Junctional Issues Following Adult Deformit y Surgery

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114

Chapter 9 ver tebral body of UIV or UIV +1, p oster ior osseoligam en tous disrupt ion , or pullout of in st r u m en t at ion at th e UIV. In th eir series, th ey iden t i ed 57 p at ien t s from a series of 1,218 con secu t ive adu lt pat ien t s w h o m et th is d e n it ion of PJF (4.68%). Of th e 57 cases of PJF, 27 (47.4%) un der w en t revision su rger y w ith in 6 m on th s of th eir in dex op erat ion . Of th e cau ses of PJF, fract ure w as th e m ost com m on (56%), follow ed by soft t issue failure (35%) an d screw pu llou t (9%). Of th e risk factors id en t i ed for revision surgery, a com bined anterior/posterior approach (p = 0.001) an d h igh er PJK angu lat ion (p = 0.034) w ere foun d to be sign i can t . Of th e var iou s m odes of failu re, on ly t h e p resen ce of t rau m at ic m ech an ism of failu re, w h ich occurred in six pat ien t s, w as deem ed to predispose pat ien ts to a revision (p = 0.019). A h igh er SVA also t ren ded tow ard being a sign i can t p red ictor of revision (p = 0.090) alon g w it h fem ale sex (p = 0.066). Th e overall rate of revision surger y w as 2.21%. A sim ilar st u dy w as con ducted by Yagi an d colleagu es 4 as part of th e Com plex Spin e St udy Grou p . Th ey u t ilized a con secu t ive ser ies of 1,668 p at ien t s t reated for ad u lt sp in al d eform it y an d greater th an ve levels of fu sion . Th eir series h ad longer follow -u p (2 to 12 year, m ean 4.3 years), an d th ey also focused on patients older than 50 at the tim e of surgery. They d e n ed PJF as PJK requ iring revision an d iden t i ed 23 pat ien ts (1.4%). Th e large m ajorit y of th ese 23 pat ien ts (17 pat ien t s, 74%) h ad been revision surger y cases at th e t im e of th eir long segm en t fusion an d all h ad received p osterior pedicle screw constructs. Osteopenia was prevalen t (10/23, 43%), but , in terest ingly, n on e of these patients had osteoporosis. Sixteen patients w ere revised for in tolerable p ain , an oth er six for a n eu rologic de cit , an d on e for h ead ptosis. Th e auth ors foun d th at a m ajorit y of th ese failu res occu rred early, w ith a m ean t im e to PJF (revision ) of 10.5 ± 9.3 m on th s; 87% h ad been revised w ith in 2 years of su rger y. H.J. Kim et al19 repor ted th at a h igh er lu m ber lordosis an d an in creased SVA correct ion are risk factors for revision du e to PJK. Th ey rep or ted a revision rate of 10.7%. Moving for w ard, im p or t an t w ork rem ain s to be don e regarding ou r u n derst an ding of PJF.

A classi cat ion system for PJK an d a clear de n it ion of PJF are n eed ed before w e p rogress tow ard de n ing th e risk factors for PJF. Addit ion ally, th e opt im al m agn it ude of correct ion also rem ain s to be determ in ed.

Preventing Proximal Junctional Kyphosis To date, n o d e n it ive m et h od s h ave been d escr ibed to p reven t PJK, alt h ough several ap proaches h ave been suggested. Tw o st udies h ave rep or ted on tech n ical t ricks to reduce th e in ciden ce of PJK.11,29,30 Hassan zadeh et al11 foun d n o in st an ces of PJK in 20 pat ien ts t reated w ith a h ook at th e UIV com pared w ith a 29.6%(8/27 p at ien t s) rate of PJK in p at ien t s w h o w ere t reated w it h a p ed icle screw at t h e UIV (p = 0.01). Addit ion ally, th ey fou n d th at pat ien ts w ith h ooks h ad sign i can tly h igh er fun ct ion al scores com pared w ith th ose w ith screw s (p < 0.01). Th ese dat a h ave n ot been rep licated to date. Given th at vertebral fract u res represen t a com m on et iology for PJK an d PJF, invest igators h ave also st udied th e im pact of prophylact ic on e- an d t w o-level ver tebroplast y above long fu sion s. Resu lt s rep or ted in clu d e both biom ech an ical29 an d clin ical30 dat a. In a biom ech an ical m odel u sing 18 cadaveric sp in es, Kebaish et al29 w ere able to sh ow a sign i can t redu ct ion in vertebral com pression fract ures w h en t w olevel ver tebrop last y (UIV an d UIV +1) w as com p ared w it h on e-level (UIV on ly) or n o vertebrop last y. A clin ical ser ies from t h e sam e group follow ed 38 pat ien ts w ith t w o-level vertebrop last y (UIV an d UIV +1) for 2 years.30 Th ey rep orted a low er rate of PJK or PJF (PJK 8%, PJF 5%, com bin ed 13%) th an previously publish ed rates. Th eir st u dy did n ot in clude a con t rol coh or t (i.e., pat ien ts w h o h ad n ot received ver tebroplast y), an d did n ot sh ow any sign i can t di eren ces in clin ical ou tcom es bet w een th e group s w ith an d w ith ou t PJK or PJF. Fin ally, Yan ik et al31 repor ted on a series of 60 pat ien t s t reated for Sch euerm an n kyph osis. To reduce th e st i n ess of th e proxim al con st r u ct , th ey st u died th e im pact of leaving t w o screw th reads ou t of th e p osterior cor tex w h en placing p edicle screw s at th e UIV. Th ey th eo-

Junctional Issues Following Adult Deformit y Surgery rized th at th is w ou ld redu ce th e st i n ess at t h e proxim al asp ect of th e con st ru ct . At an average of 2-year follow -up, th ey foun d th at th e screw s w ith th reads left out of th e cor tex h ad a low er PJ angle (4.44 ± 1.55 degrees vs 8.08 ± 2.96 degrees) w h en com p ared w ith st an dard pedicle screw in ser t ion (p = 0.001). Th is grou p also h ad n o cases of PJK, com pared w ith a 17.2% (5/29, p = 0.02) rate w ith th e stan dard screw tech n iqu e. Fin ally, th ey w ere also able to sh ow an im provem en t in th e physical com pon en t of th e Sh or t Form 36 score in th e grou p t reated w ith th e m odi ed screw in ser t ion .

Revision Strategies Th e ap p roach to th e p at ien t w ith PJK is sim ilar to th e approach to th e pat ien t w ith oth er sagittal plan e deform it ies. Our in dicat ion s for a revision operat ion are as follow s: 1. Progressive deform it y 2. Pain th at h as failed n on operat ive m easures for m an agem en t 3. Im p lan t p rom in en ce w it h im m in en t skin breakdow n 4. Neu rologic de cit or cord com pression Th e decision abou t th e UIV level select ion is based on several factors, but gen erally speaking, PJK cases w ith a UIV in t h e low er th oracic spin e sh ould be exten ded u p to th e u p per th oracic sp in e, an d cases w ith a UIV in th e u p p er th oracic sp in e sh ou ld be exten ded u p to T1–2 or in to th e cer vical sp in e. Osteotom ies m ay also be n ecessar y in th e t reat m en t of PJK. Osteotom y select ion is based on th e rigidit y of PJK. Flexible PJK (Fig. 9.2) can u sually be t reated w ith ou t an osteotom y, or w ith a posterior colu m n on ly osteotom y (Fig. 9.2d), w h ereas rigid deform it ies (Fig. 9.3) m ay n ecessit ate a t h ree-colu m n osteotom y (i.e., p ed icle su bt ract ion osteotom y or ver tebral colu m n resect ion ) (Fig. 9.3c). Flexibilit y can be assessed w ith hyp erexten sion or su p in e radiograph s as w ell as th e scou t im ages on som e com p u ted tom ograp hy (CT) scan s (as long as a h ead sup p or t w as n ot u sed du ring th e scan ). For cases w h ere a n eu rologic d e cit or sym ptom at ic cord com p ression is p resen t , a ver tebral colu m n resect ion m ay be n ecessar y

to decom press th e kyph ot ic area w h ere th e cord com p ression is likely to be presen t . An atom ic realign m en t is essen t ial to relieve th e cord com p ression . Th e goal for th e revision operat ion sh ould avoid th e tem pt at ion for overcorrect ion ; in stead, th e goal sh ou ld be an SVA close to 4 to 5 cm . Overcorrect ion can lead to a recurren ce of PJK and necessitate additional operations and u n n ecessar y risk for pat ien ts.

■ Chapter Summary Proxim al ju n ct ion al kyph osis is de n ed u sing t w o criteria: (1) proxim al ju n ct ion al sagit tal Cobb angle ≥ 10 degrees, an d (2) postoperat ive proxim al ju n ct ion al sagit t al Cobb angle at least 10 degrees greater th an th e preoperat ive m easu rem en t .1 PJK is gen erally an early p ostop erat ive ph en om en on , an d m ost cases t ypically are recogn ized in th e rst year after surger y.5,14 Rates of PJK rep or ted in th e literat u re range from 17 to 61.7%.2,3 Proxim al ju n ct ion al kyp h osis is likely m u lt ifactor ial in or igin . Risk factors for t h e d evelop m en t of PJK can be categorized as su rgical, radiograph ic, an d pat ien t-related factors. Advanced age appears to be th e m ost im por tan t patien t-related risk factor. Su rgical risk factors to con sid er in clu de greater m agn it u d e of sagit t al cor rect ion , dam age to t h e adjacen t facet w hen in st rum en t ing th e UIV, dam age to th e posterior ligam en tou s com p lex, a com bin ed an terior an d posterior approach , xat ion to th e iliu m , an d cer tain t ypes of in st ru m en tat ion . Of th e above, th e m agn it u de of correct ion is part icularly im por t an t , as an SVA of 0 cm m ay n ot be opt im al for all pat ien t s.21,22 A h igh er postoperat ive LL an d an SVA correct ion of greater th an 5 cm h ave both been associated w ith th e develop m en t of PJK.17,19 To date, n o d e n it ive m et h od s h ave been d escribed to p reven t PJK. Som e invest igators h ave d escribed tech n ical t r icks to redu ce th e in ciden ce of PJK.11,31 Pat ien t s w ith PJK are gen erally asym ptom at ic. How ever, recen t st u dies h ave sh ow n th at th ese pat ien t s m ay h ave in creased pain levels an d w orse fu n ct ion al ou tcom e m easu res.19,24

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Chapter 9

a

b

c

d

Fig. 9.2a–d A patient presenting with PJK who was treated with extension of the posterior fusion and posterior osteotomies only. (a) Lateral radiograph. (b) Hyperextension view, clearly showing a exible

deformit y. (c) Computed tomography (CT) scan. (d) Preoperative (left) and postoperative (right) standing radiographs.

Junctional Issues Following Adult Deformit y Surgery

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Fig. 9.3a–c A patient with a rigid deform it y. (a) Preoperative im ages of the proximal kyphotic deformit y. (b) CT scan and recumbent lm show a solid fusion extending up to the upper instrumented vertebra (UIV) with a rigid deformit y. This patient required a three-column osteotomy to correct the PJK. (c) Pre- and postrevision radiographs.

a

b

c

In t h e su bset of p at ien t s w h o are sym ptom at ic, pain is th e m ost com m on com plain t an d th e m ost com m on reason for revision . Reported rates for revision for PJK range from 1.2 to 11.4%.4,19,27,28 Patients requiring revision for PJK

are gen erally ap proach ed sim ilarly to p at ien t s w ith other sagit tal plane deform ities. Osteotom ies m ay be necessar y and are chosen based on the rigidit y of the PJK. When revising PJK, the tem ptation for overcorrection should be avoided.

118

Chapter 9 Pearls The appropriate magnitude of correction and global sagit tal alignm ent are critical to achieving successful outcomes and avoiding the development of PJK. An SVA of 4 cm is a reasonable goal, especially for those patients over 60 years of age. Proxim al junctional kyphosis is an early postoperative phenom enon, and most cases can t ypically be observed within 2 to 6 months postoperatively. Similarly, cases of junctional failure t ypically are evident within the rst year. When revising cases of PJK, it is crucial to consider the rigidit y of the deform it y, as exible PJK may be treated with instrum entation and fusion only, without an osteotomy or posterior column osteotom ies only.

Pitfalls Careful at tention must be paid to global sagit tal alignm ent; at tempting to aggressively correct all patients to an SVA of 0 cm has been shown to predispose patients to PJK. Although no consensus exists on preventing PJK, surgeons m ust pay close at tention to the integrit y of the posterior soft tissues and the rigidit y of the construct, and must select an appropriate UIV. Failure to consider these factors m ay lead to the developm ent of PJK. Although most cases of PJK are asymptomatic, these patients may have increased pain and worse functional scores. They m ust be followed regularly to ensure stable kyphosis and acceptable outcomes.

Refere nces Five Must-Read Refe rences 1. Glat tes RC, Bridw ell KH, Len ke LG, Kim YJ, Rin ella A, Edw ards C II. Proxim al jun ct ion al kyphosis in adu lt spin al deform it y follow ing long in st rum en ted posterior spin al fusion : in ciden ce, outcom es, an d risk factor an alysis. Sp in e 2005;30:1643–1649 PubMed 2. Kim HJ, Len ke LG, Sh a rey CI, Van Alst yn e EM, Skelly AC. Proxim al jun ct ion al kyph osis as a dist in ct form of adjacen t segm en t path ology after spin al deform it y surger y: a system at ic review. Spin e 2012;37(22, Su ppl):S144–S164 PubMed 3. Lee JH, Kim JU, Jang JS, Lee SH. An alysis of th e in ciden ce an d risk factors for th e p rogression of proxim al jun ct ion al kyph osis follow ing surgical t reat m en t for lum bar degen erat ive kyph osis: m in im um 2-year follow -up. Br J Neurosurg 2014;28:252–258 PubMed 4. Yagi M, Rah m M, Gain es R, et al; Com plex Spin e Study Group. Characterization and surgical outcom es of proxim al jun ct ion al failure in surgically t reated pat ien t s w ith adult spinal deform it y. Spin e 2014;39: E607–E614 Pu bMed 5. Yagi M, King AB, Boach ie-Adjei O. In ciden ce, r isk factors, an d n at ural course of proxim al jun ct ion al kyph osis: surgical outcom es review of adu lt idiopath ic scoliosis. Min im um 5 years of follow -up. Spin e 2012;37:1479–1489 PubMed 6. Cam m arat a M, Au bin CE, Wang X, Mac-Th iong JM. Biom ech an ical r isk factors for p roxim al ju n ct ion al kyp h osis: a d et ailed n u m erical an alysis of su rgical in st r u m en t at ion var iables. Sp in e 2014;39:E500– E507 PubMed 7. Panjabi MM, W h ite AA III. Basic biom ech an ics of th e spin e. Neu rosurger y 1980;7:76–93 PubMed 8. An derson AL, McI TE, Ash er MA, Bu r ton DC, Glat tes RC. Th e e ect of posterior th oracic spin e an atom ical

structures on m otion segm ent exion sti ness. Spine 2009;34:441–446 PubMed 9. Den is F, Sun EC, Win ter RB. In ciden ce an d risk factors for p roxim al an d dist al ju n ct ion al kyph osis follow ing surgical t reat m en t for Sch euerm an n kyph osis: m inim u m ve-year follow -up. Spin e 2009;34:E729–E734 PubMed 10. Th aw ran i DP, Glos DL, Coom bs MT, Bylski-Au st row DI, St u rm PF. Tran sverse process h ooks at u p p er in st ru m en ted ver tebra p rovide m ore gradu al m ot ion t ran sit ion th an pedicle screw s. Spin e 2014;39:E826– E832 PubMed 11. Hassan zadeh H, Gupt a S, Jain A, El Dafraw y M, Skolasky RL, Kebaish KM. Type of an ch or at th e proxim al fusion level h as a sign i can t e ect on th e in ciden ce of proxim al jun ct ion al kyph osis an d ou tcom e in adult s after long posterior spinal fusion . Spin e Deform it y 2013;1:299–305 12. Kim YJ, Bridw ell KH, Len ke LG, Glat tes CR, Rh im S, Ch eh G. Proxim al jun ct ion al kyph osis in adult spin al deform it y after segm en t al p osterior sp in al in st r u m entation and fusion: m inim um ve-year follow -up. Spin e 2008;33:2179–2184 Pu bMed 13. Wang J, Zh ao Y, Sh en B, Wang C, Li M. Risk factor an alysis of proxim al ju n ct ion al kyph osis after posterior fu sion in pat ien t s w ith idiopath ic scoliosis. In jur y 2010;41:415–420 PubMed 14. Kim HJ, Yagi M, Nyugen J, Cun n ingh am ME, Boach ieAdjei O. Com bin ed an terior-posterior surger y is th e m ost im por t an t risk factor for developing proxim al jun ct ion al kyph osis in idiopath ic scoliosis. Clin Orth op Relat Res 2012;470:1633–1639 Pu bMed 15. Bridw ell KH, Len ke LG, Ch o SK, et al. Proxim al jun ct ion al kyph osis in prim ar y adult deform it y surger y:

Junctional Issues Following Adult Deformit y Surgery evaluat ion of 20 degrees as a crit ical angle. Neu rosu rger y 2013;72:899–906 Pu bMed 16. Ha Y, Maruo K, Racin e L, et al. Proxim al jun ct ion al kyph osis an d clinical outcom es in adult spin al deform it y su rger y w it h fu sion from t h e t h oracic sp in e to t h e sacr u m : a com p arison of p roxim al an d d ist al up p er in st r u m en ted ver tebrae. J Neurosurg Spin e 2013;19:360–369 Pu bMed 17. Maru o K, Ha Y, In ou e S, et al. Pred ict ive factors for proxim al ju n ct ion al kyph osis in long fu sion s to th e sacr u m in adult sp inal deform it y. Spin e 2013;38: E1469–E1476 PubMed 18. Helgeson MD, Sh ah SA, New ton PO, et al; Harm s St u dy Grou p . Evalu at ion of proxim al ju n ct ion al kyph osis in adolescen t idiop ath ic scoliosis follow ing pedicle screw, hook, or hybrid instrum entation. Spine 2010;35:177–181 Pu bMed 19. Kim HJ, Bridw ell KH, Len ke LG, et al. Pat ien t s w ith proxim al ju n ct ion al kyp h osis requ iring revision su rger y h ave h igh er postoperat ive lum bar lordosis an d larger sagit t al balan ce correct ion s. Sp in e 2014;39: E576–E580 Pu bMed 20. Men d oza-Lat tes S, Ries Z, Gao Y, Wein stein SL. Proxim al ju n ct ion al kyp h osis in ad u lt recon st r u ct ive sp in e su rger y resu lt s from in com p lete restorat ion of th e lu m bar lord osis relat ive to th e m agn it u de of th e th oracic kyph osis. Iow a Or th op J 2011;31:199– 206 Pu bMed 21. Vedan t am R, Len ke LG, Keen ey JA, Bridw ell KH. Com parison of st an d ing sagit t al sp in al align m en t in asym ptom at ic adolescen t s an d adult s. Spin e 1998;23: 211–215 PubMed 22. Gelb DE, Len ke LG, Bridw ell KH, Blan ke K, McEn er y KW. An an alysis of sagit t al sp in al align m en t in 100 asym ptom at ic m id d le an d older aged volu n teers. Spin e 1995;20:1351–1358 Pu bMed 23. Lee GA, Bet z RR, Clem en t s DH III, Hu ss GK. Proxim al kyphosis after posterior spinal fusion in pat ien ts w ith idiopath ic scoliosis. Spin e 1999;24:795–799 PubMed

24. Kim HJ, Bridw ell KH, Len ke LG, et al. Proxim al jun ct ion al kyph osis resu lt s in in ferior SRS pain subscores in adu lt deform it y pat ien t s. Spin e 2013;38:896–901 PubMed 25. DeWald CJ, St an ley T. In st ru m en t at ion -related com plicat ion s of m u lt ilevel fu sion s for adu lt sp in al deform it y pat ien t s over age 65: surgical con siderat ion s an d t reat m en t opt ion s in p at ien t s w ith p oor bon e qualit y. Spine 2006;31(19, Suppl):S144–S151 PubMed 26. Wat anabe K, Len ke LG, Bridw ell KH, Kim YJ, Koester L, Hen sley M. Proxim al jun ct ion al vertebral fract ure in adult s after spin al deform it y surger y using pedicle screw con st r uct s: an alysis of m orph ological feat ures. Spin e 2010;35:138–145 PubMed 27. Ream es DL, Kasliw al MK, Sm ith JS, Ham ilton DK, Arlet V, Sha rey CI. Tim e to developm ent, clinical and radiographic ch aracterist ics, an d m an agem en t of proxim al ju n ct ion al kyp h osis follow ing adu lt th oracolum bar inst rum en ted fusion for spin al deform it y. J Spin al Disord Tech 2014 Pu bMed 28. Hart R, McCarthy I, O’Brien M, et al. Iden t i cat ion of decision criteria for revision su rger y am ong p at ien t s w ith proxim al jun ct ion al failure after su rgical t reatm en t of spin al deform it y. Spin e 2013;38:E1223– E1227 Pu bMed 29. Kebaish KM, Mar t in CT, O’Brien JR, LaMot t a IE, Voros GD, Belko SM. Use of vertebroplast y to preven t proxim al ju nct ion al fract u res in adult deform it y surger y: a biom ech an ical cadaveric st udy. Spin e J 2013; 13:1897–1903 Pu bMed 30. Mar t in CT, Skolasky RL, Moh am ed AS, Kebaish KM. Prelim in ar y resu lt s of th e e ect of prophylact ic vertebroplast y on th e in ciden ce of proxim al jun ct ion al com plicat ions after posterior spin al fusion to th e low th oracic sp in e. Sp in e Deform it y 2013;1:132–138 31. Yan ik HS, Keten ci IE, Polat A, et al. Preven t ion of proxim al jun ct ion al kyph osis after posterior surger y of Sch euerm an n kyph osis: An operat ive tech n iqu e. J Sp in al Disord Tech 2014 Ju l 29. [Ep u b ah ead of prin t] PubMed

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10 Biomechanics and Material Science for Deformity Correction Manabu Ito, Yuichiro Abe, and Remel Alingalan Salmingo

■ Introduction Th e rst ap plicat ion of a m et allic im p lan t to th e h u m an sp in e w as rep or ted by Hadra 1 in 1891. Silver w ires w ere p laced in th e th oracic sp in e for t reat m en t of a spin al fract u re. Th e m ost im portan t h istorical even t in spin al recon st ru ct ion surger y w as th e inven t ion of th e Harrington in st r um en t at ion in th e m iddle of th e 20th cen t ur y.2 Pau l Harrington develop ed th ese sp in al im plan t s, con sist ing of h ooks an d rods m ade of stainless steel, for treatm ent of severe spinal deform it y and fracture-dislocations of t h e sp in e. Sin ce t h e in t rod u ct ion of h is d evice, su rger ies to cor rect an d st abilize t h e sp in e w it h m et allic im p lan t s h ave u n d ergon e dram at ic d evelop m en t , an d su rgeries u sing m et allic im p lan t s to correct an d st abilize th e dam aged spine becam e know n as spin al in strum en tat ion su rger y. Th e Harrington in st r um en tat ion surger y w as m odi ed by h is successors, w h o added sublam in ar w ires, tapes, an d pedicle screw s.3 Sin ce 2000, p ed icle screw s an d rod s h ave been w id ely u sed for sp in al d eform it y su rger y d u e to th eir biom ech an ical su p eriorit y. Of th e biom aterials u sed for spin al deform it y su rger y, t itan iu m alloys are th e m ost p op u lar m ater ial at t h e p resen t t im e d u e to t h eir im p roved biocom p at ibilit y an d becau se they entail few er m etal-related art ifacts in m agn et ic reson an ce im aging (MRI).4 Historically, st ain less steel an d cobalt -ch rom iu m (Co- Cr)

w ere d iscovered m u ch earlier t h an t it an iu m alloys (Table 10.1). Sp in al im p lan t s m ad e of st ain less steel or Co - Cr are cu r ren t ly u sed for p at ien t s w it h r igid sp in al cu r ves d u e to t h eir su p er ior m ech an ical p rop er t ies to t it an iu m alloys. Th ere is n o con sen su s on h ow to select m etallic m aterials for spin al deform it y correct ion today, an d spin e su rgeon s depen d on th eir p erson al exp erien ce th rough th eir m edical career. Th is ch apter d iscu sses m et allic spin al im p lan t s an d th e biom ech an ics of t h e d efor m it y correct ion of th e spin e. It is im perat ive th at pract it ion ers be fam iliar w ith th ese top ics, as th ey are in dispen sable in providing pat ien ts w ith safe an d e ect ive spin al deform it y correct ion .

■ Mechanical Properties

of Metals Met als h ave a com m on p at tern of st ress–st rain cur ve consisting of the elastic deform ation zone an d th e plast ic deform at ion zon e. In th e elast ic deform at ion zon e, th e st ress–st rain relat ion sh ip is lin ear an d th e m etal deform s in p roport ion to th e app lied force (Fig. 10.1). After th e yield p oin t , th e st ress–st rain cu r ve of m etals becom es nonlinear. If increasing force is applied to a m etallic im plan t, th e im plant w ill reach the u lt im ate st rength an d n ally ru pt u re or break.

Biomechanics and Material Science for Deformit y Correction Table 10.1 History of Metallic Implants Used for Spine Surgery Year

Event

1890s

Application of sliver wires for spinal fractures Development of stainless steel Development of cobalt-chromium alloys (Vitallium ® in 1932) Development of SUS316, 317 stainless steel (Harrington instrumentation) Development of titanium alloys (Grade 1–4: commercially pure titanium, other titanium alloys: Ti-6Al-4V, Ti-6Al-7Nb, Ti-6Al-2.5Fe, Ti-13Zr-13Ta, etc.)

1910s 1920s 1940s 1960s

Abbreviation: SUS, steel use stainless.

Alth ough all m etals follow th e sam e pat tern of st ress–st rain relat ion sh ip , th ere are di eren ces in th eir yield st rength an d u lt im ate st rength an d th e slope of th e st ress–st rain cur ve. With in th e elast ic d efor m at ion zon e, m et als are able to ret u r n to t h e or igin al sh ap e after th e force is rem oved . On ce m et als w ere over-ben t to th eir plast ic deform at ion zon e, th e m et al is n ot able to ret urn to th e origin al sh ape an d perm an en t deform at ion of m etallic im plan ts occu rs. If plast ic deform at ion of th e rods occurs after scoliosis correct ion , sign i can t loss of correct ion m ay resu lt , an d t h e origin al p u rp ose of cor rect in g t h e sp in al d efor m it y w ou ld n ot be fu l lled . For t h is reason , it is im p or t an t for sp in e su rgeon s to kn ow h ow m u ch force is p u t on th e spin al im plan ts during correct ion procedu res an d m ech an ical resp on ses of th e m et allic im plan t s to th e forces created by correct ion proced ures. Th e m etals cu rren tly used for spin al deform it y su rger y in clu de st ain less steel, pu re t it an iu m , t it an iu m alloys, an d Co-Cr alloys. Th e m ech an ical p rop er t ies of each m et al are sh ow n in Fig. 10.2. Com m ercial p u re t it an iu m (cp Ti) h as fou r grades based on it s m ech an ical p rop er t ies. Grad e 1 h as t h e h igh est valu e of elon gat ion at break, bu t it h as t h e low est ten sile st ren gt h . As t h e grad e in creases, t h e ten sile strength increases, an d the capabilit y of elonga-

Fig. 10.1 The stress–strain curve of a t ypical structural m etal. Line A shows the apparent stress and line B shows the true stress. Point 1 shows the ultimate strength, and point 2 shows the yield strength. A material demonstrates rupture at point 3. The area of linear relationship bet ween the stress and strain indicates the elastic deformation region before point 2. After point 2, the stress increases up to the ultimate tensile strength (point 1) in region 4. Beyond point 1, a neck forms where the local cross-sectional area signi cantly decreases and the m aterial becomes weaker in region 5.

tion decreases. The ten sile strength of Ti alloys is m u ch h igh er th an th at of pu re t itan iu m , bu t th e elongat ion cap acit y of Ti alloys is th e low est am on g all t h e t yp es of t it an iu m . Alth ough t itan iu m rods are ben t by su rgeon s du ring su rgery to the desired contour, the m echanical sti n ess of t it an ium decreases sign i can tly aroun d th e ben ding p oin t s. Co- Cr sh ow s th e h igh est ten sile st rength an d relat ively h igh break poin t for elongat ion . Th is st i er m ech an ical proper t y of Co- Cr is favored by spin e surgeon s for t reatm en t of rigid spin al deform it ies. St ain less steel (grade, SUS316L) is a lit tle w eaker in it s ten sile st ren gt h com p ared w it h Co - Cr, bu t it sh ow s m u ch bet ter elongat ion du rabilit y. New st ain less steel m aterials w ith h igh er ten sile st rength h ave been inven ted recen tly an d w ill be available for surger y ver y soon .

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Fig. 10.2 The relationship bet ween tensile strength and elongation at the break of each metal. There are four grades for comm ercial pure titanium (cpTi), with sm all di erences in mechanical properties. Though titanium alloys show greater tensile

strength than cpTi does, the break points of titanium alloys under elongation are m uch lower than those of cpTi. Stainless steel shows the highest capabilit y for elongation and Co-Cr shows the highest tensile strength among all.

■ Changes in Mechanical

(40.3%) after three-point bending by 20 degrees.5 The yield strength of titanium alloy rods w ith a 6.0-m m diam eter is redu ced 54.1%after 20-d egree t h ree-p oin t ben d ing. Co- Cr alloy rods w ith a 6.0-m m diam eter sh ow ed th e sam e ten den cy as th e 6.0-m m t it an iu m alloy rods, w ith their yield signi cantly decreasing to 56.4% after 20-degree th ree-p oin t ben ding. If m u lt ip le rod ben ding operat ion s w ere perform ed, even th e m ech an ically st i est Co- Cr rods can exhibit a signi cant reduction in their m echan ical properties. Spin e surgeons should be aw are of th e reduct ion in m ech an ical proper t ies of each m etal to avoid m ech an ical failures of rods

Properties of Rods After Manual Bending (Table 10.2) Becau se th e m etallic rods su pp lied by m edical device com p an ies for u se du ring su rger y are st raigh t , th e su rgeon n eeds to ben d t h em by h an d to th e desired con tour ju st before perform ing th e correct ion p rocedu re. With regard to th e rods’ m ech an ical proper t ies, th e yield st rength of t it an iu m alloy rods w ith a 5.5-m m diam eter decreases from 803.9 N to 324.0 N

Table 10.2

Changes in Mechanical Properties After Rod Bending 5

Yield Strength (N) 6.0-mm Ti rod 6.0-m m Co-Cr rod Sti ness (N/mm) 6.0-m m Ti rod 6.0-mm Co-Cr rod

No Bend

Bend Back One Time

20-Degree Bend

40-Degree Bend

1,004 865

748 (74.5%) 689 (79.6%)

544 (54.1%) 488 (56.4%)

509 (50.6%) 476 (55.0%)

160 317

151 (94.6%) 278 (87.8%)

143 (89.2%) 261 (82.3%)

120 (74.9%) 208 (65.8%)

Abbreviations: Ti, titanium ; Co-Cr, cobalt-chrom ium .

Biomechanics and Material Science for Deformit y Correction during surger y and postoperative follow -up period s before solid bony fusion is obtain ed . Th e m ech an ical forces on spin al im plan t s decrease over t im e after su rger y, as biological bony fu sion m at ures an d becom es solid. Th e m a xim u m force on th e sp in al im p lan t s m ay occu r during th e correct ion procedure. Precise in -vivo forces on spin al im p lan t s du ring correct ion p rocedu res are st ill u n kn ow n . Previou s biom ech an ical st udies h ave t ried to m easure in -vivo forces on rods by variou s engin eering m eth od s.6,7 It is di cult to obt ain in -vivo data d uring op erat ive p rocedures du e to eth ical restrictions, and reliable in-vivo data in spinal deform it y correction are lacking. Medical devices such as m et allic rods an d screw s for sp in al deform it y sh ou ld be design ed an d m an u fact u red based on th e biom ech an ical an d biological en viron m en t in w h ich th ey w ill be used in th e h um an body. Reliable in -vivo biom ech an ical in form at ion regarding th e force on spin al im p lan t s du ring spin al deform it y correct ion m ay advan ce th e safet y an d e ect iven ess of d eform it y surger y in th e fu t ure.

■ Viscoelasticity of the Spine Th e sp in al colu m n , con sist in g of bon e, ligam en t s, an d in ter ver tebral disks, is a com p osite m ater ial w it h sign i can t viscoelast icit y. Viscoelast ic m ater ials sh ow t w o biom ech an ical ch aracterist ics: creep p h en om en on an d st ress relaxat ion . Th e creep p h en om en on states th at w h en st ress is h eld con st an t , th e st rain on th e m aterial in creases w ith t im e. St ress rela xat ion st ates th at w h en t h e st rain is h eld con st an t , th e st ress decreases w ith t im e. Con sidering th e viscoelast ic p rop er t y of th e spine, rapid correction procedures such as quick rod rot at ion m an euvers m ay m ake t h e sp in e m u ch st i er an d m ay h in d er e cien t sp in al correct ion , resu lt ing in a low er correct ion rate th an th e surgeon an t icipated p reoperat ively. Th u s, dest abilizat ion p rocedu res, su ch as bilateral facetectom ies, diskectom ies, an d release of costot ran sverse ligam en t s, are ver y im p or t an t in obt ain ing bet ter cor rect ion . Besides th ese tech n ical issues, th e biom ech an ical prin ciples

in dicate th at slow rod rot at ion an d t ran slat ion procedu res can obtain bet ter n al correct ion rates. After th e correct ion p rocedu re is com pleted, th e rod w ith in an elast ic deform at ion range w ill ten d to spring back to th e origin al sh ap e du e to th e st ress relaxat ion e ect after cor rect ion p roced u res (Fig. 10.3). Fast rod ro t at ion m ay cau se sign i can t in crease of m ech an ical loads on th e im plan t s an d resu lt in dram at ic ch anges in th e sh ap e of th e rods. If th e forces on th e rods w ere w ith in th e elast ic deform at ion zon e of m etal, th e rods w ou ld st ill h ave a poten t ial to ret urn to th e origin al sh ape. Spine surgeons should be fam iliar w ith the m echanical characteristics of m etals and the sp in al colu m n to obt ain bet ter correct ion rates an d provide pat ien ts w ith safe su rger y.

■ Correction Procedures for

Adolescent Idiopathic Scoliosis Th ere are m any su rgical procedu res to correct adolescen t idiopath ic scoliosis (AIS) repor ted after th e in t roduct ion of th e Harrington in st ru m en t at ion . Th e Cobb angle correct ion on an teroposterior (AP) radiograph s w as 40% w ith Harrington rod s, 55% w ith th e du al-rod m u lt ihook system (CD, Cotrl-Dubousset instrum en t), an d 65% w ith t h e d u al-rod m u lt ip le p ed icle screw con st r u ct s in t h e coron al p lan e. Recen t st u dies repor ted th at p ed icle screw con st r u ct s in th e sagit tal plan e in creased th e lordosis of th e th oracic sp in e.8 W h ile th e surgeon is perform ing th e direct ver tebral rot at ion tech n ique to d ecrease rot at ion al d efor m it y arou n d t h e ap ex of t h e t h oracic cu r ve, t h e m ajor force on th e sp in e p u sh es th e th oracic rib h u m p dow n to lessen th e rot at ion al deform it y of th e spin e, w hich eventually causes dekyphosis in the thoracic spin e.9 Th ere h ave been several at tem pt s to create th oracic kyph osis by p osterior sp in al in st r u m en tat ion surger y. Becau se a t itan iu m rod is m ech an ically w eaker th an a st ain less steel or Co-Cr rod, som e surgeons utilized stain less steel or Co - Cr rod s rat h er t h an t it an iu m rod s so as

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Fig. 10.3 The shape changes of the t wo rods on both sides of the curve before (red) and just after (blue) rod rotation and 1 week after surgery (white). The original contours of the t wo rods showed signi cant reduction just after the rod rotation procedure. The rods, however, tended to spring

back to their original shapes as long as the forces were within the elastic deformation zone of the metal (titanium alloy). The mechanical stress on rods tends to decrease with tim e due to the stress-relaxation e ect of the spine.

n ot to yield to t h e force on t h e rod s. An ot h er m eth od w as to u se an in -sit u rod ben ding tech n ique after a single rod-rotat ion to create th oracic kyphosis. One of the problem s of an in-situ rod-ben ding procedu re is th at a m uch greater load w ou ld be app lied to th e p ed icle screw s arou n d t h e area of rod ben ding, w h ich m ay in crease th e possibilit y of ver tebral fract u res or screw loosen ing due to a h igh er con cen t rat ion of m ech an ical force on th e screw s. Also, m u lt ip le rod-ben ding p rocedu res w ill redu ce th e origin al m ech an ical st rength of th e m et allic im plan t . Th ere h ave been n ew su rgical tech n iqu es for correct ing spin al deform it y to m ain tain or create th oracic kyph osis. On e tech n ique is th e ver tebral coplan ar align m en t (VCA) rep or ted by Vallespir et al.10 Th is tech n iqu e u ses slot ted t ubes at tach ed to each pedicle screw on th e convex side of th e th oracic cu r ve. Tw o longit ud in al rods are in serted an d separated along th e slot s, driving th e t ubes in to on e plan e, m aking the axis of the vertebrae coplan ar, thus correct-

ing transverse rotation and coronal translat ion . For creat in g t h oracic kyp h osis, t h e en d s of t h e t u bes are sp read in t h e t h oracic sp in e. After lockin g a d e n it ive rod on t h e con cave sid e an d ret rieving t u bes on t h e con cave side, th e convex-side rod is in ser ted an d t igh ten ed. Th e cur ve correct ion rate in the m ain thoracic cur ve w as 73%on average, an d th e average p reop erat ive th oracic kyph osis of 18 degrees rem ain ed u n ch anged after su rger y. An oth er tech n ique is th e sim ultan eou s t ran slat ion tech n iqu e using t w o rods as reported by Clem en t et al.11 Th is tech n iqu e u ses p olya xial p edicle screw s an d polyaxial claw s consisting of a pedicle hook and an op p osin g t ran sverse cou n ter-h ook p laced at th e m ost ceph alad en d of th e rod . Th e t w o 6.0-m m t it an iu m rods are ben t rst an d are in ser ted p re-orien ted. Redu ct ion of th e deform it y is obtain ed by gradu al an d altern ate t igh ten ing of all n u t s on both rods, allow ing th e ver tebrae to gradu ally ap p roach th e rods. An ot h er tech n iqu e u ses a Un iversal clam p con sist ing of a w oven p olyester ban d, a t it an iu m alloy clam p ,

Biomechanics and Material Science for Deformit y Correction an d a locking screw as w ell as pedicle screw s.12 Pedicle screw s w ere placed in t w o or m ore vertebrae at th e distal ext rem it y of th e cur ve w ith m on axial screw s on th e convex sid e an d p olyaxial screw s on the concave side. Thoracic levels w ere in st rum en ted w ith th ree to seven sub lam in ar Un iversal clam p s (UCs) on th e con cave side an d on e su blam in ar UC at th e apex on th e con cave side. Correct ion of th e th oracic cu r ve w as perform ed using posterom edial translat ion by t igh ten ing th e UCs for th e spin e to approach th e pre-ben t dou ble rods. Th e kin em at ic con cept of h ow to correct th e deform it y w ith p edicle screw s is sh ow n in Fig. 10.4. Th e ap ex ver tebra sh ou ld be m oved from an terior to posterior an d from lateral to m edial

w ith t w o an ch or poin t s correspon ding to th e t ips of p edicle screw s. Th e screw t ip on th e con cave sid e sh ou ld be m oved m ore p osteriorly th an th at of th e convex side. By providing a bigger ben d to th e con cave side rod th an to th e convex side rod an d rot at ing th e t w o rods sim u ltan eously, th e screw t ip of th e con cave side at th e ap ex of th e cu r ve m oves m ore p osteriorly th an th at of th e convex side does. Th is technique w as reported by Ito et al13 and nam ed th e sim ultan eou s double rod rot at ion tech n iqu e, w h ich allow s sim u lt an eou s correct ion of th e coron al p lan e deform it y an d restorat ion of th e th oracic kyph osis. Th e biom ech an ically st rongest correct ion procedure, w hich u t ilized a solid fram e bet w een th e p edicle screw s on

Fig. 10.4 The locations of the apex vertebra in the axial plane. The apex vertebra is located anterolaterally before surgery and the vertebra is to be relocated posteromedially during surgery. The pedicle screw at the apex vertebra on the concave side of the curve should be moved more toward the back (red line) than that on the convex side (blue

line) to relocate the apex vertebra to the normal position. In the simultaneous double rod rotation technique,13 the concave side rod should be bent more than the convex side rod, which allows the head of the pedicle screw on the concave side to move m ore toward the back than that on the convex side.

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Chapter 10 both th e convex an d con cave side of th e cu r ve, w as reported by Ch ang an d Len ke.14 By con n ect ing th e t w o rods w ith a solid m etal fram e, th e sp in al im p lan t is able to produ ce th e m ost pow erfu l force on th e spin e, bu t th e st ress con cen t rat ion m ay n ot occu r on sp eci c p ed icle screw s.

■ Intraoperative Mechanical

Forces on Rods During Rod Rotation Maneuvers During rod rot at ion procedures to correct th e deform ed sp in e th ree dim en sion ally, th e in ser ted rods frequ en tly sh ow d ram at ic con tou r ch an ges d u e to sign i can t m ech an ical load s on t h e rod s an d screw s. A recen t biom ech an ical st u dy h as u sed n ite elem en t an alysis of th e m ech an ical p rop er t ies of m et als an d t h e geom et r ical ch an ges of m et allic rod s before

Fig. 10.5 The force on each pedicle screw during rod rotation procedure in an adolescent idiopathic scoliosis (AIS) patient. The contour of the concave side rod shows signi cant reduction, and pullout forces around the apex of the curve have reached about 200 N according to the calculation. At both

an d after su rger y.15–17 Th ese au th ors m easured th ree- dim en sion al (3D) con tou r ch anges of th e rods before an d after surger y using postop erat ive 3D com pu ted tom ograp hy (CT) im ages. Speci c m athem atical assum pt ions and boun dar y conditions w ere put into the com puter sim ulat ion . In th eir n ite elem en t an alysis (FEA) m od el, th e dist al en d of th e rod w as xed com pletely, an d th e upp erm ost en d w as able to m ove p arallel to th e axis of th e t r u n k. By calcu lat ing th e forces on rods in AIS pat ien ts w ith a single th oracic cu r ve, p u llou t forces of abou t 150 N w ere exer ted on th e con cave side screw s aroun d th e apex of the cu r ve if pedicle screw s w ere in serted at all the fusion levels (im plan t den sit y 100%) (Fig. 10.5). At both en ds of th e rods, p ush -in forces of abou t 200 N w ere on t h e pedicle screw s on th e con cave side of th e cu r ve. Push-in forces on pedicle screw s rarely result in clin ical p roblem s, bu t p u llou t forces on screw s can lead to screw loosen ing or bony fract u res, w h ich can create serious com plicat ion s for th e

ends of the concave side rod, maximum pushing-in force was exerted on the pedicle screws. The m inus sign indicates pull-out force on each screw. The total amount of the force acted on the concave side rod has topped 1,400 N.

Biomechanics and Material Science for Deformit y Correction spin al cord or great vessels. According to th e FEA m odel, th e pullout forces on pedicle screw s around the apex of the cur ve m ay exceed 500 N if th e n u m ber of pedicle screw s w ere redu ced . Maxim u m pu llou t forces of th oracic p edicle screw s in cadaveric sp in es are abou t 600 N, so th at th ere m ay be an in creasing risk of screw pu llou t s arou n d th e ap ex in p at ien t s w ith rigid cu r ves an d few er p edicle screw s. On e of th e e ect ive solu t ion s to redu ce m ech an ical forces on p edicle screw s is to p lace cross-lin ks or a fram e over th e t w o rods. Many rod rot at ion procedu res u t ilize on ly th e con cave-side rod for correct ion of scoliosis, an d th e convex-side rod is p laced after com p let ion of rod rotat ion of th e con cave side. In th ese correct ion p roced u res, th e force on th e concave side rod is m u ch h igh er th an th at on th e convex side rod. Th e resu lt s sh ow ed th at 50%of th e rod con tou r on th e con cave side w as lost after rod rotat ion m an euvers an d th e opposite side rod sh ow ed alm ost n o ch ange in its sh ape. If a cross-lin k w as placed bet w een th e t w o rods, 15% of t h e tot al load w as sh ared by th e convex sid e rod, w h ich sh ow ed som e con tou r ch an ges. Th e biom ech an ically st ron gest con st r u ct w it h p ed icle screw s is bilateral screw p lacem en t w it h a cross-lin k, w h ich for m s a t r iangular sh ape in each vertebra. From th is biom ech an ical poin t of view, ver tebral colum n m an ipu lat ion w ith a rigid fram e cross-lin king th e t w o rods an d p edicle screw s is th e m ost pow erfu l correct ion p rocedu re in spin al deform it y su rger y.14

■ Implant Density and

Correction Rate According to th e presen t con sen sus am ong spin e exper t s w orldw ide, AIS cu r ves of less th an 70 degrees w ith exibilit y n eed less th an 80% of screw den sit y.18 From a biom ech an ical st an dp oin t , a sm all n u m ber of an ch ors w ith less rigid m etallic rods are n ot able to correct th e spin al deform it y su cien tly becau se th ey can su st ain on ly sm all am ou n t s of m ech an ical load. It seem s reason able to assu m e th at m ore im plan t den sit y an d m ore rigid rods w ill p ro-

vide bet ter correct ion rates an d n al outcom es. Several recen t st u dies, h ow ever, fou n d th at th e n al ou tcom e of t h e su rgical cor rect ion d id n ot sh ow any sign i can t im provem en t even if su rgeon s u sed m ore rigid an d th icker rods w ith a h igh er im p lan t den sit y.19,20 Im p lan t den sit y an d m ech an ical st i n ess of t h e rod s are of som e im p or t an ce to obt ain bet ter cor rect ion rates. Th e m ore im p or t an t step s to a ect t h e n al ou tcom e of deform it y correct ion m ay be perform ing p reoperat ive cu r ve exibilit y an d destabilizat ion proced u res, su ch as Pon te osteotom ies, before perform ing correct ion procedures in cluding rod rot at ion an d t ran slat ion .

■ Chapter Summary Harrington st ar ted to u se h is spin al im p lan t s, con sist ing of h ooks an d rod s m ade of st ain less steel, for t reat m en t of spin al deform it y alm ost 50 years ago. Sin ce th e in t roduct ion of h is device, surgeries to correct an d st abilize th e spin e w ith m etallic im plants have show n dram atic im provem en t in th ree-dim en sion al correct ion of the curves; an excellent correction rate has been obtained in recent years by using pedicle screw s and rigid rods. Titanium alloys are the m ost pop u lar m aterial for recen t spin al surger y due to th eir biocom pat ibilit y an d few er m et al-related ar t ifacts on MRI. How ever, ben ding a t itan ium rod m u lt ip le t im es m ay lead t h e m ater ial to p last ic d efor m at ion , w h ich m akes it sign i can tly w eaker m ech an ically. Surgeon s sh ou ld be fam iliar w ith th e m ech an ical ch aracterist ics of each m aterial used for deform it y surger y and refrain from excessive m an u al ben ding of th e rods to m ain t ain th e origin al m ech an ical prop er t y of each m et al. Sp in al im p lan t s m ad e of st ain less steel or Co- Cr are com m on ly u sed for correct ion of rigid sp in al deform it ies, su ch as severe scoliosis an d rigid kyph osis, becau se of th eir su perior m ech an ical st i n ess an d abilit y to obtain bet ter correct ion rates. Surgical t reatm en t of sp in al d efor m it y requ ires fam iliar it y w it h sp in al biom ech an ics an d t h e m ech an ical ch aracterist ics of each biom aterial. Th is ch ap ter discussed th e fun dam en tals of biom ech an ics of spin al deform it y correct ion , m ech an ical

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Chapter 10 behaviors of m etallic im plants, in-vivo forces on rods an d pedicle screw s, biom ech an ical ben ets of destabilization procedures for rigid curves, and viscoelastic properties of the spine. Readers can ap p ly t h e con cept s of spin al biom ech an ics an d m aterial scien ce to th eir ow n correct ion procedures to provide their patients w ith a safe an d e ect ive surgical procedure an d excellen t clin ical ou tcom es. Pearls Spinal deform it y correction relies on m etallic im plants such as screws, hooks, and rods. Popular metals used for spinal implants are titanium alloys, stainless steel, and cobalt-chromium.

Each metallic m aterial has di erent m echanical behaviors for the stress–strain relationship and repetitive loading. The viscoelastic propert y of the spine should be considered when operating on cases with rigid large spinal deform it y. Pitfalls Mechanical loads on spinal im plant s during correction procedures often exceed the lim it of bone sti ness, which may lead to surgery-related complications. Di erent deform it y correction procedures have bene ts and limitations. Rapid rod rotation for rigid deform it y correction will signi cantly increase mechanical loads on the spinal implant.

Refere nces. Five Must-Read Refe rences 1. Hadra BE. W ir ing of t h e ver tebrae as a m ean s of im m obilizat ion in fract u re an d Pot t ’s d isease. Th e Tim es an d Register, Med ical Press, Ph ilad elp h ia, 1891:1–8 2. Harrington PR. Treat m en t of scoliosis. Correct ion and intern al xat ion by spin e in st rum en t at ion . J Bon e Join t Surg Am 1962;44-A:591–610 Pu bMed 3. Su k SI, Lee CK, Kim W J, Ch u ng YJ, Park YB. Segm en t al p ed icle screw xat ion in t h e t reat m en t of t h oracic id iop at h ic scoliosis. Sp in e 1995;20:1399– 1405 Pu bMed 4. Uh th o HK, Bardos DI, Liskova-Kiar M. Th e advan t ages of t it an ium alloy over st ain less steel plates for th e in tern al xat ion of fract u res. An exp erim en tal st u dy in dogs. J Bon e Join t Surg Br 1981;63-B:427– 484 Pu bMed 5. Dem u ra S, Murakam i H, Hayash i H, et al. Th e in uen ce of rod con touring of di eren t spin al con st ruct s on st rength an d st i n ess. Orth opedics, in press 6. Wang X, Au bin CE, Cran dall D, Labelle H. Biom ech an ical m odeling and an alysis of a direct in crem en t al segm en t al t ran slat ion system for the in st ru m ent at ion of scoliot ic deform it ies. Clin Biom ech (Bristol, Avon ) 2011;26:548–555 Pu bMed 7. Au bin CE, Labelle H, Ch evre ls C, Desroch es G, Clin J, En g AB. Preop erat ive p lan n in g sim u lator for sp in al d efor m it y su rger ies. Sp in e 2008;33:2143–2152 Pu bMed 8. Sucato DJ, Agraw al S, O’Brien MF, Low e TG, Rich ard s SB, Len ke L. Restorat ion of th oracic kyph osis after operat ive t reat m en t of adolescen t id iopath ic scoliosis: a m ult icen ter com parison of th ree surgical ap proaches. Spin e 2008;33:2630–2636 Pu bMed

9. Lee SM, Suk SI, Ch ung ER. Direct ver tebral rot at ion : a n ew tech n iqu e of th ree-dim en sion al d eform it y correct ion w ith segm en t al pedicle screw xat ion in adolescen t idiop ath ic scoliosis. Spin e 2004;29:343– 349 Pu bMed 10. Vallespir GP, Flores JB, Trigueros IS, et al. Vertebral coplanar alignm ent: a standardized technique for three dim en sion al correct ion in scoliosis su rger y: tech n ical descript ion an d prelim in ar y result s in Len ke t ype 1 cu r ves. Sp in e 2008;33:1588–1597 Pu bMed 11. Clem en t JL, Ch au E, Geo ray A, Vallade MJ. Sim ult aneou s t ran slat ion on t w o rods to t reat adolescent idiopath ic scoliosis: radiograph ic result s in coron al, sagit t al, an d t ran sverse plan e of a series of 62 pat ien t s w ith a m in im um follow -up of t w o years. Spin e 2012;37:184–192 PubMed 12. Mazda K, Ilh arreborde B, Even J, Lefevre Y, Fitou ssi F, Pen n eçot GF. E cacy and safet y of posterom edial t ran slat ion for correct ion of th oracic cur ves in adolescen t idiopath ic scoliosis using a n ew con n ect ion to th e spin e: th e Universal Clam p. Eur Spine J 2009; 18:158–169 PubMed 13. Ito M, Abum i K, Kot an i Y, et al. Sim u lt an eous dou blerod rot at ion tech n ique in posterior in st ru m en t at ion su rger y for correct ion of adolescen t idiopath ic scoliosis. J Neu rosu rg Spin e 2010;12:293–300 Pu bMed 14. Ch ang MS, Len ke LG. Vertebral derot at ion in adolescen t idiopath ic scoliosis. Op er Tech Or th op 2009; 19:19–23 15. Salm ingo R, Tadan o S, Fujisaki K, Abe Y, Ito M. Correct ive force an alysis for scoliosis from im p lan t rod deform at ion . Clin Biom ech (Bristol, Avon ) 2012;27: 545–550 Pu bMed

Biomechanics and Material Science for Deformit y Correction 16. Salm ingo RA, Tadano S, Fujisaki K, Abe Y, Ito M. Relat ion sh ip of forces act ing on im plan t rods an d degree of scoliosis correct ion . Clin Biom ech (Bristol, Avon ) 2013;28:122–128 PubMed 17. Salm ingo RA, Tadan o S, Abe Y, Ito M. In u en ce of im plan t rod cur vat u re on sagit t al correct ion of scoliosis deform it y. Spin e J 2014;14:1432–1439 Pu bMed 18. de Kleuver M, Lew is SJ, Germ sch eid NM, et al. Opt im al surgical care for adolescen t idiopath ic scoliosis: an in ter n at ion al con sen su s. Eu r Sp in e J 2014;23: 2603–2618 Pu bMed

19. Prin ce DE, Mat su m oto H, Ch an CM, et al. Th e e ect of rod diam eter on correct ion of adolescen t idiopath ic scoliosis at t w o years follow -up. J Pediat r Or th op 2014;34:22–28 PubMed 20. Ch en J, Yang C, Ran B, et al. Cor rect ion of Len ke 5 adolescen t idiopath ic scoliosis u sing pedicle screw inst rum en t at ion : does im plan t den sit y in uen ce th e correct ion? Spin e 2013;38:E946–E951 Pu bMed

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11 Pseudarthrosis and Infection Michael P. Kelly and Sigurd Berven

■ Introduction Adu lt spin al deform it y (ASD) is am ong th e m ost ch allenging p ath ologies t reated by sp in e su rgeon s. Preoperat ive p rep arat ion to correct n eural elem en t com pression as w ell as coron al an d sagit t al m alalign m en t requ ires st rict atten t ion to detail an d n ear-perfect tech n ical execu t ion . Su rger y to t reat ASD can be fru st rat ing, h ow ever, as a seem ingly “p erfect” su rger y m ay st ill be com plicated in th e both n ear- an d longterm periods by com plicat ion s requiring un an t icipated revision su rger y. Tw o su ch com m on com plications are pseudarth rosis and infection. Ou r grou p h as repor ted a 9% rate of u n an t icipated secon d procedu res in adu lt s u n d ergoing prim ar y surgery for ASD, w here pseudarthrosis (4%) an d in fect ion (1%) w ere com m on causes for revision.1 Even m ore troublesom e w as a 21% rate of repeat revision surger y, w h ere pseu darth rosis (5%) an d in fect ion (2%) w ere again t w o com m on causes.2 These num bers are in line w ith repor t s from oth er coh or t s; th u s, pseu darth rosis rem ain s a com m on cause of revision su rger y in prim ar y an d revision ASD.3,4

■ Pseudarthrosis Su ccessfu l fu sion requ ires opt im al biological and biom echanical environm ents, w hich rely on both pat ien t select ion an d surgical tech n ique.

Alth ough advan ces in im plan t tech n ology an d osteobiologics have im proved union rates, pseudart h roses p ersist in as m any as 16% of th reecolu m n osteotom y p at ien t s.5,6 Th is is a resu lt of th e risk factors for p seu dar th rosis th at exist by th e n at u re of ASD surgeries. Long-segm en t fu sion s are at a h igh er risk for p seu darth rosis because of th e large surface area of bon e th at m ust heal. In addition, the com m only em ployed m id lin e ap p roach is associated w it h a d en ervat ion of th e paraspin al m u sculat ure, w ith an associated decrease in vascularit y to th is m usculat ure. Th is is an in sult to the local h ealing environ m en t . ASD su rger ies are n ot u n com m on ly associated w ith sp in al sten osis, requ iring decom pression , or rigid coron al an d sagit t al plan e deform it ies, requ iring posterior colu m n osteotom ies. Th e greater th e am oun t of bon e resected, th e greater th e th eoret ical risk of a pseudarth rosis developing. Despite m odern im plants, a long segm ent fusion w ill rem ain som ew h at m obile, th rough elast ic deform at ion of the const ruct . Th is m icrom otion, in som e cases, m ay be excessive, w ith ou t th e rigid it y requ ired to prom ote fusion . In th e absen ce of a fusion m ass, im plan t s w ill alm ost cert ain ly fract u re. Th is m ay occu r as early as 6 m on th s to 1 year, th ough w e h ave en cou n tered p seu dar t h rosis th at p resen ted a late as 7 years postop erat ively (Fig. 11.1). Fin ally, ASD often involves fu sion of ju n ct ion al segm en t s (e.g., lu m bosacral ju n ct ion , t h oracolu m bar ju n ct ion ), w h ich are at a h igh er r isk of n on u n ion .6 In som e cases, an te-

Pseudarthrosis and Infection

Fig. 11.1 A 50-year-old woman presented 8 years after L3 pedicle subtraction osteotomy with broken implants and pseudarthrosis causing xed sagit tal

plane m alalignm ent. She was treated with revision posterior spinal fusion; note the four rods spanning the level of the pedicle subtraction.

rior colu m n su p p or t , th rough eith er a t ran sforam in al lum bar in terbody fusion (TLIF) or an anterior lum bar interbody fusion (ALIF), m ay assist w ith im proving un ion rates. Appropriate u se of recom bin an t h u m an bon e m or p h ogen et ic p rotein -2 (rh -BMP2) at t h e lu m bosacral ju n ct ion m ay obviate t h e u se of TLIF/ALIF at L5-S1. Nicot in e exp osu re is associated w it h d ecreased fu sion rates in sp in e su rger y. In t h e case of ASD, th e risk of n on u n ion w ith m u lt ilevel su rger y is great an d, in ou r p ract ice, su rger y is n ot o ered to pat ien ts w h o are un able to cease n icot in e u se. To test for n icot in e u se, w e rou t in ely ch eck urin e cot in in e levels. Th is m et abolite of n icot in e is excreted in th e u rin e an d o ers reliable values for act ive an d passive exp osu re to cigaret te sm oke, m aking it a su itable screen ing test for th is pat ien t populat ion . Nicot in e h as proven an t iangiogen ic e ect s on fusion m asses, increasing the likelihood of nonunion. Furtherm ore, nicotine has been show n to have an adverse in uence on patient-reported ou tcom es in several areas of sp in e su rger y, in depen den t of oth er risk factors, fu r th er d ecreasing th e p oten t ial for su ccess w ith surger y.

Given th e cost s an d risks associated w ith sp in al deform it y su rger y, n icot in e cessat ion is n ecessar y. In m ost cases, w e requ ire 3 m on t h s of preop erat ive abst in en ce, to p rove th at th e cessat ion is last ing. Osteoporosis is increasingly com m on in ASD pat ien ts, as th e age of pat ien t s seeking surger y rises. Perh aps even m ore com m on is hyp ovit am in osis D, w h ich h as been sh ow n to be com m on in gen eral ort h opedic su rger y pract ices an d in spin e surger y–speci c pract ices.7 Vitam in D plays an essen t ial role in bon e m etabolism an d h om eost asis, an d low vit am in D levels are associated w ith osteom alacia (hyp om in eralized bon e). We rou t in ely ch eck ser u m 25hydroxyvit am in D levels at p reop erat ive visit s, an d w e p rescr ibe su p p lem en t at ion w it h oral vit am in D as n eeded . In m ost cases, 50,000 In ter n at ion Un it s (IU) w eekly for 6 w eeks, follow ed by 1,000 IU daily. In ad d it ion , w e recom m en d su pplem en tat ion w ith 1,000 m g of calciu m daily. In som e cases, hypovit am in osis D exists du e to som e oth er system ic path ology, rat h er t h an m aln u t r it ion . For t h ese p at ien t s, w e con su lt en d ocr in ologist s w it h a p ar t icu lar in terest in bon e m etabolism .

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Chapter 11 As p reviou sly m en t ion ed, h ow ever, osteoporosis is a com m on com orbidit y en cou n tered by sp in e su rgeon s. Th is is of con cer n to su rgeon s, as bon e m in eral d en sit y (BMD) is d irect ly cor related w it h in ser t ion al torqu e an d p u llou t st rengt h . St ren gt h of screw p u rch ase, in t urn , a ect s fusion rates by determ in ing th e du rabilit y an d rigidit y of th e con st r u ct an d its st abilit y w h ile th e fu sion m ass m at u res. We rout in ely obt ain bon e den sitom et r y tests su ch as dual-en ergy X-ray absorpt iom et r y (DEXA) scan s preop erat ively. Th ese tests provide th e t r u e valu e of t h e BMD an d t h e T-score, w h ich is t h e n u m ber of st an dard d eviat ion s above or below th e m ean for you ng-adu lt referen ce st an dards. Osteop orosis is de n ed as a T-score of –2.5 or low er. Osteopen ia exists at bet w een –1 an d –2.5 stan dard deviat ion s. W h en orderin g a DEXA scan , on e m u st rem em ber t h at in m any cases th e lum bar spin e BMD m ay be falsely elevated due to spon dylosis, w ith en dplate sclerosis an d osteop hyte form at ion (Fig. 11.2). Th e DEXA scan sh ould in clude den sit ies at t h e h ip an d d ist al rad iu s. We h ave fou n d t h e d ist al radiu s par t icu larly u sefu l for m aking

Fig. 11.2 Upright and supine radiographs of a 65-year-old woman with degenerative lumbar scoliosis. Note the hypertrophic osteoarthritis through the apex of the deformit y, which would cause a falsely elevated bone m ineral densit y.

th e diagn osis of osteoporosis, w h ich facilit ates ph arm acological m an agem en t of th e disorder. Alt h ough a m u lt it u d e of opt ion s exist for t h e m an agem en t of osteop orosis, on ly on e an abolic th erapy exist s, terip arat ide (For teo, Eli Lilly, In dian ap olis, IN).8 Teriparat ide is a recom bin an t form of a p or t ion of th e p arathyroid h orm on e (PTH). Alth ough PTH in creases osteoclast ic act ivit y, via osteoblast sign aling, pulsat ile adm in ist rat ion of terip arat ide in creases osteoblast ic act ivit y to a greater degree, in creasing bon e form at ion . An adverse e ect of teriparatide obser ved in anim al m odels w as osteosarcom a form ation , h ow ever, an d patien ts w ith risk factors for osteosarcom a, in clu ding Paget’s disease an d p rior radiat ion th erapy, sh ou ld avoid ter ip arat id e exp osu re. In cases of a con t rain d icat ion to ter ip arat id e, w e often em ploy denosum ab, a m onoclonal antibody that bin ds receptor act ivator of n u clear-κB (RANK) ligand (RANKL). The binding of RANKL prevents RANK act ivat ion s, th ereby su p p ressing osteoclast activation. This is an “anti-catabolic” m echan ism of osteoporosis m anagem en t , h ow ever, sim ilar to bisp h osph on ates. Both den osu m ab an d bisph osph on ates delay callu s m at urat ion in fract u re m odels, w h ich likely beh ave sim ilarly to a fu sion m odel, but th ere is n o h u m an eviden ce to suppor t a correlat ion bet w een exposu re to th ese an t i-cat abolic m edicat ion s an d p seu dar t h rosis.8 Non et h eless, w e at tem pt to avoid bisp h osp h on ate exp osu re early in t h e spin e fusion process, as th ere are an im al data to su p p or t a n egat ive e ect of bisp h osp h on ates. Th ere is som e eviden ce, h ow ever, th at a com bin at ion of terip arat id e an d bisp h osp h on ate th erapy m ay be ideal to m axim ize callus form at ion an d rigidit y, w ith early teriparat ide adm in ist rat ion follow ed by conversion to bisph osph on ate th erapy. Surgical techniques m ay play a role in instrum en t ing th e osteop orot ic sp in e as w ell. Sp ecially design ed screw th reads h ave been sh ow n to in crease in sert ion al torque, w h ich m ay ben e t t h e du rabilit y of a con st ru ct in osteop orot ic bon e. Hydroxyap at ite coat ing h as also been sh ow n to increase screw purch ase. As th e p ed icle is often p at u lou s in t h e osteop orot ic sp in e, on e m ay ch oose to avoid t ap p in g t h e ch an n el of th e p edicle screw. If t app ing is p er-

Pseudarthrosis and Infection for m ed , it sh ou ld u n dersize t h e an t icip ated screw d iam eter by 1 m m or m ore. Screw d iam eters sh ould be m axim ized, at least 70% of pedicle diam eter, to en su re an ap propriate in terferen ce t w ith in th e pedicle. Screw length sh ou ld be m axim ized an d , in ext rem e cases, on e m ay ch oose to t ap th e an terior cor tex an d ach ieve bicor t ical purch ase of th e screw, as th is w ill signi cantly im prove pullout strength. One sh ou ld at tem pt to leave th e dorsal cor tex in tact as w ell, as th is m ay m in im ize screw toggling an d loosen ing. Im p lan t m ater ials are a m at ter of p referen ce an d are d ebated am on g sp in al d efor m it y su rgeon s. We p refer to u se 5.5-m m cobalt ch rom iu m (Co- Cr) rods in cases of degen erat ive scoliosis w ith poor bon e qu alit y. In larger, st i er recon st ru ct ion s, w e com m on ly u se a 6.0-m m Co- Cr rod on th e “w orking side,” an d place a 5.5-m m Co- Cr on th e con t ralateral side. Som e su rgeon s p refer com m ercially p u re t it an ium rods, w h ich are a bit less st i th an Co- Cr, believing th at th is w ill st ress th e bon e–im plan t in terface less, th ereby decreasing th e in ciden ce of adjacent segm ent problem s. Conversely, som e su rgeon s prefer 6.35-m m stain less steel (SS) rods, believing th is is th e m ost du rable m etal for spin al deform it y su rger y. In a series of sp in al deform it y pat ien ts, im plan t fract ure w as less com m on am ong th ose xed w ith Co- Cr rods.9 In cases of th ree-colum n osteotom y (i.e., pedicle su bt ract ion osteotom y, ver tebral colum n resect ion ), dom in oes are u sed to sp an th e osteotom y level w ith m ore th an t w o rods, in creasing th e rigidit y of th e con st r uct at th e osteotom y site an d decreasing m icrom ot ion . In any case, secu re xat ion , w ith accurate screw placem en t , is requ ired along th e length of th e deform it y. Th is in creases th e rigidit y of th e con st ru ct , decreasing n on u n ion rates. We p erform high -densit y in strum entation (1.8 screw s/ level) in th e vast m ajorit y of ASD su rgeries. Alth ough th is issu e is debated regarding adolescen t idiopath ic scoliosis, w e feel st rongly th at high -densit y instrum entation is n eeded in ASD. In all cases in st r u m en ted to S1, w e p lace dist al su p p or t in g screw s, often S2-alar-iliac (S2AI) or iliac screw s.10 Iliac screw s distal to S1 d ecrease st rain on S1 xat ion in exion , m in im izing m icrom ot ion at th e lum bosacral jun c-

t ion . S2AI screw s h ave been proposed as an altern at ive to iliac screw s, w ith a m ore ven t ral st ar t ing p oin t an d “in -lin e” t u lip h eads, facilitat ing rod placem en t . Midterm result s of S2AI screw s are en cou raging, an d w e em p loy th is tech n iqu e frequ en tly. A th ird opt ion for dist al xat ion is S2-alar screw s. Th ese screw s o er su p por t to S1 pu llou t , w ith ou t crossing or im m obilizing th e sacroiliac join t . If on e ch ooses to use th is m eth od, at ten t ion m ust be paid to th e cou rse of th e L5 root , as it cou rses over th e fron t of t h e sacral ala. Bon e graft m ater ials sh ou ld con sist of locally obt ain ed au tograft , allograft , an d iliac crest bon e graft (ICBG) or rbBMP-2. We rout in ely use fresh -frozen can cellous allograft , as it s osteoin duct ive propert ies are likely bet ter t h an t h ose of cor t ical ch ip s. In long fu sion s, in adequ ate volu m es of ICBG m ay in dicate th e use of rh -BMP2 in an o -label fash ion . We h ave sh ow n th is to be an e ect ive m eth od of im p roving fu sion rates. We n eith er u se n or advocate oth er so-called osteobiologic product s, as th e eviden ce to support th eir u se is w eak. Th e dorsal elem en t s sh ou ld be decor t icated, using gauges or burs, to fresh bleeding bon e. Bleeding bon e is a requisite for com petit ive fusion rates. If using m ore than t w o rods or cross-lin ks, th ey are xed after bon e graft placem en t , to m in im ize disru pt ion an d in terferen ce w ith con t igu ous graft ing. In th e vast m ajorit y of cases, th e diagn osis of pseu dar th rosis is m ade w ith th e presen ce of loose or fractured im plants. We intervene w hen th ere is a progression of deform it y or p ain . In th e absen ce of p rogression , w e often obser ve u n ilateral rod fract u res. W h en both rods h ave fract ured, w e usually recom m en d revision surger y. In a sm all n u m ber of cases, a pseudarth rosis m ay p resen t as sym ptom s con sisten t w ith n eural elem en t com pression (e.g., radiculopathy, claudication) due to scar tissue/ brous callu s accu m u lat ion (Fig. 11.3). Com puted tom ograp hy (CT), w ith n e cu t s an d m et al su b t ract ion , is th e preferred im aging m odalit y for diagnosing pseudarth rosis.11 Flexion/extension radiograph s h ave been used, th ough th ey are n ot as sen sit ive as CT scan n ing. Man agem en t of pseu darth rosis con sists of revision su rger y. Th e u se of rh -BMP2 in posterolateral fu sion revision s h as received Food

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Fig. 11.3 A 61-year-old man presented with a sagit tal plane malalignment and L4 radiculopathy due to pseudarthrosis. Note the vacuum disk within the instrumented levels, indicative of a pseudarthrosis.

and Drug Adm inistration (FDA) approval. W hen revising a pseu dar th rosis case, in sp ect ion of th e en t ire fu sion m ass is recom m en ded, as on e p seu dar t h rosis m ay beget an ot h er.12 In ou r exp er ien ce, m ost p seu dar t h rosis p resen t s at L5-S1, L4-L5, an d at th e th oracolu m bar ju n ct ion , in th at order. Revision su rger y often con sist s of an terior colu m n su pp or t , if n ot already don e, in th e form of a TLIF, ALIF, or t ran sp soas in terbody fu sion . Opt ion s for graft m ater ial in clu de t itan ium , polyeth ereth erketon e (PEEK), an d allograft . Our preferen ce is to use t itan ium , as it bon ds to bon e, in creasing th e st abilit y of th e con st r u ct an d likely im proving fu sion rates. Th e pseu dar th rosis t issu e sh ou ld be debrid ed, as th ese t issu es are un able to un dergo m in eralizat ion an d m u st be rem oved to ach ieve u n ion . In the lum bar spine, we often perform a posterior colum n osteotomy through the pseudarthrosis tissue and com press through the pseudarthrosis. In addit ion to en cou raging fusion by exposu re of bleeding cancellous bone, the osteotom y aids in restoration of lordosis, taking tension o of th e fu sion m ass an d prom ot ing com p ression at

the pseudarthrosis level. If rh -BMP2 is not used, w e use au togen ous iliac crest graft , as th e biologic act ivit y of allograft is n ot su cien t to create a com pet it ive environ m en t for fu sion in th e set t ing of a p reviou s pseu dar th rosis. For cases of lu m bosacral ju n ct ion p seu dar t h rosis, w e en su re t h at w e h ave ad equ ate d ist al xat ion , con sist ing of p ed icle screw s at t h e rst sacral vertebra an d iliac screw s below th at . In th e case of p at u lou s, eroded S1 p ed icles, w e place m u lt iple iliac screw s on each side. Th e postoperat ive rou t in e is un ch anged in th e m an agem en t of pseu dar th rosis. No bracing is u sed an d th e pat ien ts are m obilized on postop erat ive day 1. St r ict act ivit y p recau t ion s are establish ed, h ow ever, an d pat ien t s are in st r u cted on h ow to safely r ise from bed an d are given a fron t-w h eeled w alker to use for 6 w eeks to en courage an uprigh t post ure, discou raging exion th rough th e revision fu sion m ass. Terip arat ide th erapy is con t in u ed for a m in im um of 3 m on th s after surger y. We do n ot perform CT scan n ing for evalu at ion of fu sion m asses, as th e exp osu re to radiat ion is excessive, and ndings are unlikely to a ect our m anagem en t of th e pat ien t. Carefu l at ten t ion to det ail in preoperat ive planning, intraoperative perform ance, and postoperat ive reh abilitat ion h elps surgeon s m in im ize pseu dar th rosis in th eir p ract ice. Sm oking cessat ion is absolutely m an dator y to en sure com p et it ive resu lt s. Ap propriate ch oices of biologics an d in st rum en tat ion h elp in crease fusion rates. How ever, a n on u n ion rate of 0% is not realistic, and the inform ed decision -m aking process sh ou ld in clu de discu ssion of th e risk of reop erat ion for n on un ion in ASD surger y.

■ Infection Perioperat ive su rgical-site in fect ion (SSI) is a sign i can t cau se of m orbidit y in ASD su rger y, w it h rep or ted rates ran gin g from 0.3% to 20%.1,2,13 Th ese rates in clu d e bot h su p er cial and deep w ound infect ions; th e treatm en ts an d im plicat ion s for each di er. In m any in st an ces, a su p er cial in fect ion can be m an aged on an ou t p at ien t basis, w it h oral an t ibiot ics alon e.

Pseudarthrosis and Infection Conversely, a d eep w ou n d in fect ion is a cat ast rop h e, n early u n iversally m an aged w it h reh osp it alizat ion , revision su rger y, an d p rolonged in t raven ou s an t ibiot ics follow ed by oral an t ibiot ics. A review of th e Scoliosis Research Societ y (SRS) Morbidit y an d Mor talit y database revealed an overall in fect ion rate of 2.1% in cases perform ed by par t icipat ing m em bers.13 Th is coh or t in clu ded a h eterogen eou s m ix of procedures, including n onin strum ented degenerative lu m bar su rgeries, in addit ion to in st r u m en ted ASD p rocedu res. Not su rp risingly, less exten sive su rgeries, in clu ding lu m bar d iskectom ies an d m in im ally invasive TLIF procedures w ere associated w ith low er rates of in fect ion . Th ose cases th at w ere associated w ith in st ru m en ted sp in al fu sion s h ad h igh er rates of in fect ion . Neu rom u scu lar scoliosis (14%) an d p ost lam in ectom y kyph osis (5.1%) h ad th e h igh est rates of postoperative w ound infection. Revision surgeries w ere m ore com m on ly a ected by in fect ion s (3.3% vs 2.0%), an d deep in fect ion s w ere m ore com m on in th is sit u at ion as w ell. Alth ough th e SRS dat abase provides good ep idem iological dat a regard ing rates of in fect ion s, it does n ot p rovide th e gran u lar data th at allow for n er con clusion s regarding postoperat ive in fect ion s in th e ASD pop u lat ion . Several sm aller ser ies h ave review ed t h e rates of reop erat ion for pat ien t s u n dergoing ASD recon st r u ct ion s. Pich elm an n et al1 p u blish ed ou r group ’s exp erien ce w ith p rim ar y ASD su rgeries, n ot ing a rate of reoperat ion for in fect ion of 1.4% an d accoun t ing for 15.5% of revision surgeries. On e m ust n ote th at this rate is likely low er th an th e t ru e valu e, as sup er cial in fect ion s are u n likely to h ave u n dergon e reop erat ion . As a follow -u p st u dy, w e review ed th e rates of u n an t icip ated reoperation for revision ASD procedures, n ot ing in fect ion in 14% of revision su rger ies p er for m ed .2 Th ese rates are sim ilar to t h ose p resen ted by ot h ers, w it h in fect ion accou n t ing for 15%of revision su rgeries in ASD.3 Adult spinal deform it y surgeries are at higher risk for p eriop erat ive in fect ion th an oth er orthopedic or n eurologic surgeries because of the long duration, high estim ated blood losses, large su rface areas, an d exten sive u se of im p lan t s. It

st an ds to reason th at th e longer a w ou n d is exposed to air, th e m ore likely som e con tam in at ion m ay occu r. High est im ated blood losses are often associated w ith th e n eed for periop erat ive allogen eic t ran sfu sion s. Alth ough allogen eic t ran sfusion s are associated w ith m ajor com plications, such as transfusion-related acute lu ng injur y (TRALI), m ore com m on are periop erat ive in fect ion s, in clu ding SSI, u rin ar y t ract in fect ion s, an d respirator y t ract in fect ion s.14 Th e exposu re to allogen eic blood an d p rotein s is associated w it h an im m u n om od u lator y effect t h at m ay d ep ress t h e im m u n e resp on se to path ogen s, m aking th e pat ien t suscept ible to SSI. Th is relat ion sh ip h as been sh ow n in less exten sive lu m bar d egen erat ive fu sion p rocedures an d th e sam e is likely t rue in ASD. Im plants ren der patients susceptible to deep w ou n d in fect ion s, as th ere is a race bet w een n at ive cells an d bacteria to th e im plan t su rface. Bacteria form a glycocalyx on im plan ts, w h ich h elp s t h em ad h ere to t h e su r face. Th e glycocalyx “protects” th e bacteria from an t ibiot ics, du e to p oor p en et ran ce by an t ibiot ics, an d also decreases th e valu e of w ou n d cu lt u re, as bacteria becom e adh eren t to th e glycocalyx an d are n ot easily sh ed in to th e w oun d bed. Th ere is eviden ce th at t it an ium an d cobalt ch rom ium im plan t s are less suscept ible to glycocalyx form at ion t h an st ain less steel. Ou r p referen ce is to u se Co- Cr rods for th eir m aterial proper t ies in ASD. Pat ien t dem ograph ics cer t ain ly h elp iden t ify th ose at risk for develop ing SSI. Th u s, as w ith pseudar th rosis, it is im perat ive th at th ese p at ien t s are id en t i ed an d t h at ap p rop r iate step s are t aken to m in im ize th e r isk of SSI. A com p reh en sive review of p at ien t s t reated at our in st it u t ion , w ith an overall deep in fect ion rate of 2.0%, foun d th at a con com itan t diagn osis of diabetes h ad th e st rongest associat ion w ith a perioperat ive in fect ion (odds rat io [OR], 3.5).15 Th e im por tan ce of con t rolled blood glu cose levels w as em p h asized, as even p at ien t s w ith out a diagn osis of diabetes bu t w ith episodes of hyp erglycem ia sh ow ed a h igh er rate of in fect ion . Th ese n dings w ere later su pp or ted by Richards et al,16 w h o foun d an increased rate of infection in orthopedic traum a patients w ith poorly con t rolled p eriop erat ive blood glu cose

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Chapter 11 levels. Obesit y (body m ass in dex 30–35 kg/m 2 ) w as also associated w ith an in creased risk of in fect ion (OR, 2/2). Prein cision an t ibiot ic p rop hyla xis is m an dator y, an d an t ibiot ics m u st be given at t h e ap propriate t im e. We h ave sh ow n a 3.4-fold increased risk of infection in those patients w ho did n ot receive in t raven ou s cefazolin w ith in 1 h our of in cision . In a st udy of pediat ric spin al deform it y su rgeries, Milston e et al17 fou n d a sim ilar relat ion sh ip bet w een in fect ion s an d in appropriate an t ibiot ic adm in ist rat ion t im ing. Th e ch oice of p rop hylact ic an t ibiot ics m ay var y by in st it ut ion , but it sh ould con sist of an an t ibiot ic w ith broad-spect rum gram -posit ive coverage of com m on skin ora. At ou r in st it u t ion , p rop hylaxis is p rovided w ith cefazolin an d van com ycin . In th e case of penicillin or cep h alosporin allergy, w e u se azt reon am . Both an t ibiot ics are given w ith in 1 h our of th e skin in cision , w ith van com ycin started earlier to provide an ap prop riate rate of adm in ist rat ion an d to m in im ize th e risk of red m an syn drom e. During su rger y, w e re-dose an t ibiot ics at h alf th e t im e of n orm al adm in ist rat ion . For exam ple, cefazolin is given ever y 4 h ou rs, as it is n orm ally given ever y 8 h ou rs. In t ra-site an t ibiot ics, com m on ly in th e form of lyoph ilized van com ycin pow der, adm in istered at th e t im e of w oun d closure are becom ing in creasingly com m on . Several ret rospect ive an alyses h ave sh ow n d ecreased rates of SSI w ith th e in st it u t ion of th is tech n iqu e. Sw eet et al18 pu blish ed th e rst repor t on th is m eth od, n ot ing a decreased prevalen ce from 2.6% to 0.2% w ith th e use of in t ra-site van com ycin in adult sp in e p at ien t s. Th is ben e t h as been su p p orted by several oth er st u dies in adult an d p ediat ric spin e su rgeries. Th ere h ave been n o com plicat ion s de n it ively lin ked to th e use of in t ra-site van com ycin p ow der, th ough th ere are concerns about pseudarthrosis, anaphylaxis, and “super-in fect ion.” Vancom ycin is acidic and ch anges th e environ m en t w ith in th e w oun d bed, th ough n o e ect on u n ion rates h as been obser ved . Van com ycin p ow der is e ect ive in elim in at ing gram -p osit ive con tam in an ts, bu t som e con cern over an in crease in gram -n egat ive an d polym icrobial in fect ion s exists. A sin -

gle ran dom ized con t rolled t rial did n ot su p por t t h e e ect iven ess of lyop h ilized van com ycin p ow der.19 Non eth eless, ou r exp erien ce m irrors th ose of oth ers, an d w e con t in ue to em ploy th is pract ice. We p lace both su per cial an d deep d rain s at the tim e of w ound closure. There is lim ited but n ot strong evidence supporting their use in spin al deform it y surgery. Blank et al20 perform ed a ran dom ized t rial of su rgical drains in p at ien t s un dergoing surger y for adolescent idiopat h ic scoliosis. Th ey fou n d in creased rates of w ou n d drain age in th ose p at ien ts t reated w ith ou t a drain . Th e st u dy w as u n d erp ow ered an d th u s cou ld n ot detect a di eren ce in in fect ion rates, h ow ever. It st an ds to reason th at an adequately pow ered st u dy w ou ld su p por t a decreased rate of postoperative infection w ith decreased wound drain age. Postoperat ive drain s h ave been associated w ith in creased rates of perioperat ive blood t ran sfusion s, an d th is m ust be balan ced w ith th e p oten t ial ben e t of w ou n d drain age. Diagn osis of sp in e in fect ion s can often be m ade w ith a h istor y an d physical exam in at ion . Fevers an d ch ills as w ell as leth argy/m alaise are com m on —th e form er are m ore frequ en t w ith acu te in fect ion s, an d th e lat ter are m ore com m on w ith ch ron ic, deep in fect ion s. In th e case of acute infections, som e m ay show w ound er yt h em a, u ct u an ce, an d w ou n d d rain age. Th ese sign s are n ot u biqu itou s, h ow ever, an d th e clin ician m u st h ave som e level of su sp icion . In ch ron ic in fect ion s, a sm all drain ing sin us is com m on , or a n ew an d en larging uct uan t m ass m ay be presen t . Upon p resen t at ion , on e should draw a com plete blood count an d serum C-react ive protein (CRP). We h ave fou n d CRP to be m ore u seful th an th e er yth rocyte sedim en tat ion rate (ESR) in diagn osing postoperat ive in fect ion s. In th e im m ediate postoperat ive period, th e h alf-life of CRP is ~ 2.5 days, w h ereas th e kin et ics of ESR are of lit tle u t ilit y. Im aging of t h e sp in e sh ou ld begin w it h p lain rad io grap h s, w h ich m ay sh ow evid en ce of screw loosen ing, w it h h alos, in cases of ch ron ic in fect ion (Fig. 11.4). Follow ing plain radiograp h s, CT or m agn et ic reson an ce im aging are of lim ited u t ilit y, as a serom a form s in all cases, regardless of bacterial con tam in at ion. Aspirat ion

Pseudarthrosis and Infection

Fig. 11.4 An 11-year-old girl with neuromuscular scoliosis presented with pain 11 months after posterior spinal fusion. Exploration revealed a deep wound infection. Note the lucencies (arrows) surrounding the m idthoracic pedicle screws.

versu s d elayed p rim ar y closu re. A ch ron ic, d elayed deep wound infection is treated di eren tly, h ow ever. Th ese in fect ion s are m ore com m on ly associated w ith less viru len t bacteria, such as Propionibacterium acnes or Staphylococcus epiderm idis. As th ese bacteria are less viru len t , an d grow m ore slow ly, in t raop erat ive cu lt ures sh ou ld be t aken an d in cu bated for a longer p eriod th an n orm al, 14 to 28 days. In cases of ch ron ic, delayed in fect ion , w e rem ove im plan t s an d con r m t h e ar t h rod esis an d t h e absen ce of p seudar th rosis. Pat ien ts are follow ed for evid en ce of cu r ve progression or p seu dar th rosis in follow -u p an d are re-in st r u m en ted on ly w h en n eeded for deform it y progression . W h en su ccessfu lly t reated , p at ien t s w it h d eep w ou n d in fect ion follow ing ASD su rger y can exp ect good ou tcom es, equ ivalen t to th ose of p at ien t s w h o d id n ot en cou n ter th is com p licat ion .21

■ Chapter Summary of a serom a an d u id an alysis m ay be p erform ed w h en there is uncertaint y regarding th e presen ce of an in fect ion . Physician su sp icion an d con cern sh ould drive th e decision to in terven e for a su sp ected in fect ion . Man agem en t of a su per cial in fect ion is often successful w ith antibiotics alone, as this is usually a cellulitis related to the surgical wound. Acute, deep w oun d in fect ion s are t reated aggressively in ou r pract ice. Th e stan dard of care is irrigat ion an d debridem en t . In th e w ou n d is grossly con t am in ated, w e m ay rem ove loose graft . In th e absen ce of gross con t am in at ion , graft an d im p lan t s are ret ain ed. E or t sh ould be m ade to ach ieve good decon tam in at ion of th e w ou n d, so th at im p lan t s can be ret ain ed. Although their presence as a foreign body m igh t con cer n su rgeon s, t h e in st abilit y cau sed by im plan t rem oval w ill m ake eradicat ion of th e in fect ion m ore d i cu lt . If t h ere is any qu est ion regarding th e level of con tam in at ion of th e w ou n d, w e place a w ou n d vacu u m -assisted closu re (W VAC) d ressing an d ret u rn to th e op erat ing room in 72 h ou rs for rep eat irrigat ion an d debridem en t , w ith possible W VAC ch ange

Pseu dar th rosis an d in fect ion are t w o com m on reason s for revision su rger y in ad u lt sp in al d eform it y. Both of th ese path ologies h ave risk factors th at are m odi able by both th e pat ien t an d t h e su rgeon . Nicot in e avoidan ce is m an dator y in ASD, given t h e already h igh rate of p er iop erat ive com p licat ion s associated w it h these surgeries. Evaluation of bone health, w ith bon e m in eral den sit y test ing, an d t reat m en t of osteoporosis sh ould be rout in e. Appropriate m an agem en t of d iabetes m ellit u s, in clu d in g t igh t con t rol of p eriop erat ive blood glu cose levels, w ill h elp m in im ize risks of p erioperat ive in fect ion . An t ibiot ic prophyla xis sh ou ld be given w ith in an h our of in cision an d be tailored to p rop hyla xis again st com m on ora in t h e com m un it y. As tech n iques evolve, w ith con com itan t im provem en ts in im plan t s an d biologic th erapies, th e rates of th ese t w o com p licat ion s w ill fall. Ult im ately, m et icu lou s at ten t ion to d et ail before, d u r ing, an d after su rger y w ill m a xim ize th e likelih ood of su ccess an d m in im ize com p licat ion s in th ese pat ien t s.

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Chapter 11 Pearls Smoking cessation is necessary in adult spinal deformit y surgery. Evaluation for osteoporosis, with bone mineral densit y testing, and appropriate pharm acological intervention should be perform ed in ASD patients. Teriparatide is an anabolic agent available for management of osteoporosis and may have some bene t in achieving arthrodesis. Facetectomies m ust be performed, and decortication of dorsal elements is necessary. Recom binant hum an bone m orphogenetic protein-2 decreases rates of reoperation for pseudarthrosis in ASD. Inform ed consent speci cally tailored to the use of rh-BMP2 in both on-label and o -label applications (addressing risks of pain, serom a, ectopic bone, and potential for malignancy) should be sought from the patient. Iliac or S2-alar-iliac screws should be placed routinely, when fusing to S1. High-densit y (≥ 1.8 screws/level) constructs are recomm ended in ASD. Patient factors associated with surgical-site infections in ASD include high body mass index and poorly controlled diabetes m ellitus. Prophylactic, intravenous antibiotics must be administered within 1 hour of incision.

Prophylactic, intra-site, lyophilized vancomycin powder m ay decrease rates of surgical-site infection. Aggressive m anagem ent of acute, deep wound infections o ers patients a chance for equivalent outcomes once the complication has resolved. Pitfalls Nicotine exposure increases rates of pseudarthrosis. One m ust resist the desire to operate on patient s who are using nicotine product s and insist that they be com pliant with sm oking cessation prior to surgery. Implants and osteobiologics do not compensate for poor planning and execution of technique in ASD. Poor planning and performance increase rates of pseudarthrosis and surgical-site infection. The use of rh-BMP2 without informed consent from the patient is ill-advised. Inadequate debridem ent of pseudarthrosis tissue increases the likelihood of recurrent pseudarthrosis. Prophylactic antibiotics must be adm inistered within 1 hour of incision. Cefazolin should be given every 4 hours during surgery. Poorly controlled postoperative blood glucose levels increase the risk of infection.

Refere nces Five Must-Read Refe rences 1. Pich elm an n MA, Len ke LG, Bridw ell KH, Good CR, O’Lear y PT, Sides BA. Revision rates follow ing prim ar y adult spin al deform it y surger y: six h un dred for t y-t h ree con secu t ive p at ien t s follow ed -u p to t w en t y-t w o years p ostop erat ive. Sp in e 2010;35: 219–226 PubMed 2. Kelly MP, Len ke LG, Bridw ell KH, Agar w al R, Godzik J, Koester L. Fate of th e adu lt revision sp in al deform it y pat ien t: a single in st it u t ion exp erien ce. Sp in e 2013;38:E1196–E1200 Pu bMed 3. Rich ards M. Un an t icipated revision surger y in adult spin al deform it y: an experien ce w ith 815 cases at one in st it ut ion . Spin e 2014;39(26, Suppl 1):S174– 182 PubMed 4. Mok JM, Cloyd JM, Bradford DS, et al. Reoperat ion after p rim ar y fu sion for adu lt sp in al d eform it y: rate, reason, an d t im ing. Spin e 2009;34:832–839 PubMed 5. Kim HJ, Bu ch ow ski JM, Zebala LP, Dickson DD, Koester L, Bridw ell KH. RhBMP-2 is superior to iliac crest bon e graft for long fu sion s to th e sacr u m in adult spinal deform it y: 4- to 14-year follow -up. Spine 2013;38:1209–1215 Pu bMed

6. Kim YJ, Bridw ell KH, Len ke LG, Rh im S, Ch eh G. Pseu dar th rosis in long adult spin al deform it y in st ru m en t at ion an d fusion to th e sacrum : prevalen ce an d risk factor an alysis of 144 cases. Spin e 2006;31:2329– 2336 PubMed 7. Stoker GE, Buch ow ski JM, Bridw ell KH, Len ke LG, Riew KD, Zebala LP. Preop erat ive vit am in D st at u s of adult s un dergoing surgical spin al fusion . Spin e 2013; 38:507–515 Pu bMed 8. Hirsch BP, Unn an un t an a A, Cun n ingh am ME, Lan e JM. Th e e ect of th erap ies for osteop orosis on spin e fusion : a system at ic review. Spin e J 2013;13:190– 199 PubMed 9. Sm ith JS, Sh a rey CI, Am es CP, et al; In tern at ion al Spine St udy Group. Assessm en t of sym ptom at ic rod fract u re after p osterior in st r u m en ted fu sion for adult spin al deform it y. Neurosurger y 2012;71:862– 867 Pu bMed 10. Kebaish KM. Sacrop elvic xat ion : tech n iqu es an d com plicat ion s. Spine 2010;35:2245–2251 PubMed 11. Carreon LY, Djurasovic M, Glassm an SD, Sailer P. Diagn ost ic accu racy an d reliabilit y of n e-cu t CT scan s

Pseudarthrosis and Infection w ith recon st r uct ion s to determ in e th e st at u s of an inst rum en ted posterolateral fusion w ith surgical explorat ion as referen ce st an dard. Sp in e 2007;32:892– 895 Pu bMed 12. Pateder DB, Park YS, Kebaish KM, et al. Sp in al fu sion after revision su rger y for p seu dar th rosis in ad u lt scoliosis. Spin e 2006;31:E314–E319 Pu bMed 13. Sm ith JS, Sh a rey CI, San su r CA, et al; Scoliosis Research Societ y Morbidit y an d Mor t alit y Com m it tee. Rates of in fect ion after sp in e su rger y based on 108,419 procedures: a report from th e Scoliosis Research Societ y Morbidit y an d Mor t alit y Com m it tee. Spin e 2011;36:556–563 PubMed 14. Woods BI, Rosario BL, Ch en A, et al. Th e associat ion bet ween perioperative allogeneic transfusion volum e an d postoperat ive in fect ion in pat ien t s follow ing lum bar spin e surger y. J Bon e Join t Su rg Am 2013;95: 2105–2110 Pu bMed 15. Olsen MA, Nepple JJ, Riew KD, et al. Risk factors for su rgical site in fect ion follow in g or t h op aed ic sp in al op erat ion s. J Bon e Join t Su rg Am 2008;90:62–69 PubMed 16. Rich ards JE, Kau m an n RM, Zu ckerm an SL, Obrem skey W T, May AK. Relat ion sh ip of hyperglycem ia an d su rgical-site in fect ion in or thopaedic surger y. J Bon e Join t Su rg Am 2012;94:1181–1186 Pu bMed

17. Milston e AM, Maragakis LL, Tow n sen d T, et al. Tim ing of preoperat ive an t ibiot ic prophylaxis: a m odi able risk factor for deep surgical site in fect ion s after pediat ric spin al fu sion . Pediat r In fect Dis J 2008;27:704– 708 PubMed 18. Sw eet FA, Roh M, Sliva C. In t raw oun d applicat ion of van com ycin for p rop hylaxis in in st ru m en ted th oracolum bar fusion s: e cacy, dr ug levels, an d pat ien t outcom es. Spin e 2011;36:2084–2088 Pu bMed 19. Tubaki VR, Rajasekaran S, Sh et t y AP. E ect s of using in t raven ou s an t ibiot ic on ly versus local in t raw oun d van com ycin an t ibiot ic pow der applicat ion in addit ion to in t raven ous ant ibiot ics on postoperat ive in fect ion in spin e su rger y in 907 p at ien t s. Spin e 2013; 38:2149–2155 PubMed 20. Blan k J, Flyn n JM, Bron son W. Th e use of postoperat ive subcut an eous closed su ct ion drainage after poster ior sp in al fu sion in ad olescen t s w it h idiop at h ic scoliosis. J Spin al Disord Tech 2003;16(6):508–512 21. Mok JM, Gu illau m e TJ, Talu U, et al. Clin ical ou tcom e of deep w oun d in fect ion after in st r um en ted posterior spin al fusion : a m atch ed coh ort an alysis. Spin e 2009;34:578–583 PubMed

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Index

Note: Page referen ces follow ed by f or t in dicate pages or tables, resp ect ively. A Acetabulum , iliac screw xat ion -related injur y to, 53, 54 Adjacen t segm en t disease/failu re, 24, 56–57, 65–66 proxim al, 25 Ad olescen t idiopath ic scoliosis correct ive procedu res for, 123–127, 125f, 126f fusion levels in , 23 progression to adult scoliosis, 78, 79f u n t reated, 1 Ad ult degen erat ive spin al deform it ies, 1. See also Adult scoliosis, degen erat ive (de n ovo) clin ical evalu at ion of, 2–4 epidem iology of, 1–2 preop erat ive evaluat ion of, 2–4 progression rate of, 2 Ad ult scoliosis, 1–11 classi cat ion of, 79, 81 de n it ion of, 78 degen erat ive (de n ovo), 80f apical disk h eigh t in , 80f, 81 coronal im balan ce in , 81–82 de n it ion of, 78 di eren t iated from adult idiop ath ic scoliosis, 79, 81–82, 93 lum bar kyph osis associated w ith , 80f, 83 path ology of, 83 spin al cu r ve pat tern s in, 81 sten osis-related, 82 surgical opt ion s for, 78–79 t run k sh ift ing in , 81–82 fusion levels for, 18 idiopath ic as back pain cause, 82 de n it ion of, 78

di eren t iated from adult degen erat ive scoliosis, 79, 81–82, 93 proxim al ju n ct ion al kyp hosis in , 110 n on op erat ive m an agem en t of, 78 surgical t reat m en t of, in d icat ion s for, 78 t reat m en t decision m aking abou t , 12–27 Ad ult sp in al deform it ies. See also Adu lt scoliosis de n it ion of, 1 n on op erat ive m an agem en t of, 4, 17, 99 path ogen esis of, 1 presen t ing age of, 2, 5 prevalen ce of, 99 progression of, 2, 4, 17 t ypes of, 1 Ad ult sp in al deform it y surger y ind icat ion s for, 4–5, 78, 99 levels of, 8–9 ou tcom es m easu res for. See Health -related qu alit y of life (HRQOL) m easu res Albu m in levels, preoperat ive assessm en t of, 5 Am erican Sp in al Inju r y Associat ion (ASIA) scoring system , for spin al cord inju r y, 68, 69f, 70 An kylosing sp on dylit is, osteotom y plan n ing for, 31–32, 31f An terior ap proach . See also Com bin ed an terior/ posterior app roach in ad u lt scoliosis, 78 in rigid spin al deform it y surger y, 24 An terior colu m n su p port e ect on u n ion rates, 130–131 in osteop orot ic sp in e, 62 in p seu doarth rosis revision su rger y, 134 An terior xat ion , in osteop orot ic sp in e, 63 An terior lu m bar in terbody fusion (ALIF), 130–131, 134 Arter y of Adam kiew icz, in osteotom y, 29–30, 29f, 31

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Index B Back pain , adult spin al deform it y-related , 2, 9, 78 axial, 12, 85 clin ical evalu at ion of, 2 diagn osis of, 12–16, 13f, 14f, 15f, 16f as in dicat ion for su rger y, 17 m ech an ical, 82 neurogen ic, 82 radiologic assessm en t of, 13–16, 13f, 14f, 15f Biom ech an ics, of spin al deform it y correct ion , 120–129 im plan t m aterials, 133 int raoperat ive m ech an ical forces, 126–127, 126f m ech an ical p ropert ies of im plan t s, 120–121 after m an u al ben ding, 122–123, 122t spin al viscoelast icit y, 123, 124f, 128 st ress-st rain cu r ves, 120–121, 121f Bisph osph on ates, 132 Blood m an agem en t , p erioperat ive, 5–6 Blood t ran sfusion s, com p licat ion s an d risks of, 6, 135 Bon e grafts, 133, 134 Bon e m in eral den sit y (BMD) correlat ion w ith im plan t pu llou t st rength , 58, 132 insert ion al torque, 132 falsely elevated, 132, 132f low, as spin al im plan t failu re cau se, 56 in osteoporot ic sp in e, 56, 58, 132, 138 preoperat ive m easurem en t of, 7, 57 Bracing con t rain dicat ion to, 4 postoperat ive, of osteoporot ic spin e, 65, 66 Bu t tock pain , 13, 16 C Cages, for osteoporot ic spin e, 63 Cen t ral sacral ver t ical lin e (CSVL), 14–15, 15f, 84 Claudicat ion n eurogen ic, 2, 78, 82 di eren t iated from vascu lar clau dicat ion , 16 level of surgical t reat m en t for, 8 n er ve root com pression -related , 16 ph arm acoth erapy for, 4 relat ionsh ip to coron al im balan ce, 85 vascular, di eren t iated from n eu rogenic claudicat ion , 16 Cobb angle, in adu lt spin al deform it ies, 2, 82 correlat ion w ith apical disk degen erat ion , 83 discrepan cy w ith rot ator y su blu xat ion , 82 less th an 30°, 18, 19f, 25 preoperat ive m easurem en t of, 3 in proxim al jun ct ion al kyp hosis, 106, 107t, 115 in spin al cu r ve p rogression , 17 as surger y outcom e m easu re, 95–96 Codm an , Ern est A., 102 Com bin ed an terior/posterior ap proach in adult scoliosis, 78

as proxim al ju n ct ion al kyp h osis cau se, 107t, 108–109, 114 as respirator y system injur y cau se, 6 Com orbidit ies, in adu lt sp in al deform it y pat ien t s, 5, 7, 56 Com p en sator y spin al cu r ves, 81–82 Com p licat ion s, of ad u lt sp in al deform it y su rger y, 3, 24–25, 100–101. See also Neu rologic com plicat ions, of adu lt spin al deform it y surger y; Pseu doar th rosis; Su rgical-site infect ion s cau ses of, 24–25 preoperat ive assessm en t for, 5 preven t ion of, 7–8 rate of, 17, 24 Com p u ted tom ograp hy (CT) postoperat ive, 74, 76 preoperat ive, 3, 57 of pseu doarth rosis, 133 Com p u ted tom ograp hy m yelograp hy for back p ain assessm en t , 13 int raoperat ive, 74 “Con e of econ om y,” 13 Con t ract u res, of h ip or kn ee, 3 Coron al balan ce in ad u lt scoliosis, 84, 84f assessm en t of, 14–15, 15f, 84 Coron al com p en sat ion , de n it ion of, 84 Coron al decom p en sat ion . See also Coron al im balan ce de n it ion of, 84, 85 postoperat ive, p reven t ion of, 87–88 Coron al im balan ce in ad olescen t idiop ath ic scoliosis, 79f, 81 in ad u lt scoliosis in ad u lt degen erat ive scoliosis, 81–82 correlat ion w ith qu alit y of life, 84–85 de n it ion of, 85–86 w ith associated sagit t al im balan ce, 87 e ect s of, 13 greater th an 4 cm , 8 postoperat ive, 85 as in st ru m en t at ion failu re cau se, 88, 90f–92f, 93 revision su rger y for, 88, 90f–92f, 93 preoperat ive, 85 t ypes of, 24 t ype A, 84f, 87, 93 t ype B, 84f, 87, 93 t yp e C, 84f, 87, 88, 89f, 93 Cor t icosteroid ep idu ral inject ion s, diagn ost ic, 4 Cost , of adult spin al deform it y su rger y, 95, 98–99 Cross-lin ks in osteop orot ic spin e, 61, 66 in p edicle screw xat ion , 127 C7 p lu m b lin e, 14–15, 15f, 110 D Decom pression , 8 e cacy of, 17

Index w ith fu sion an terior an d posterior fu sion , 8, 78 com plicat ion rate of, 100 lim ited posterior fu sion , 8, 78 lum bar cur ve in st ru m en ted fu sion , 8, 78 w ith pedicle subt ract ion osteotom y, 34–35 Decom pression -on ly su rger y for adu lt degen erat ive scoliosis, 78 com plicat ion rate of, 100 in dicat ion s for, 18, 25 versus sh or t or long fusion , 26t Degen erat ive cascade, of adu lt spin al deform it ies, 12 Degree of slip , radiologic m easurem en t of, 13–14, 13f, 14f Den osum ab, 132 Diabetes m ellit us, as surgical-site in fect ion risk factor, 135–136, 138 Disk degen erat ion correlat ion w ith spin al im balan ce, 83 im aging of, 16 lu m bar, 17 Disk h eigh t , m easu rem en t of, 14 Dual-en ergy X-ray absorpt iom et r y (DEXA), preoperat ive, 7, 57–58, 66, 132 E Elderly pat ien t s ad ult spin al deform it y on set in , 2, 5 spin al surger y-related com p licat ion s in , 24 Elect rom yograp hy spon t an eous, 72 t riggered, 72 EuroQOL Five Dim en sion s (EQ-5D) qu est ion n aire, 96, 98 F Facet n er ve blocks, 4 Fen est rat ion , posterior, 18 Fibu lar st rut graft ing, 48 Flat-back syn drom e, w ith lum bar lordosis, 8 Fract u res of im p lan t s, 130, 133 osteoporot ic, 7, 56, 65, 81, 82 as proxim al jun ct ion al kyp h osis cause, 110–111 114 Fusion . See also In terbody fusion /su pp or t in adu lt degen erat ive scoliosis, 78–79 an terior, 24 w ith decom pression , 8, 78, 100 in dicat ion s for, 18–19 lim ited, 17 local, w ith pedicle screw xat ion , 18 long-segm en t , 18–19, 20f–22f, 23 com plicat ion s of, 25, 130 versus decom pression -on ly surger y, 26t indicat ion s for, 26, 26t w ith low er in st rum en ted ver tebra (LIV), 23–24, 25–26

as pseu doarth rosis risk factor, 130 w ith u p per in st ru m en ted ver tebra (UIV), 19, 23 in osteop orot ic sp in e, 65, 132 to th e p elvis, as proxim al ju n ct ion al kyp h osis risk factor, 109 to th e sacru m , 23–24, 25, 26, 79 as proxim al ju n ct ion al kyp h osis risk factor, 107t, 109 sh ort-segm en t , 18, 19f–20f ind icat ion s for, 26, 26t G Gait assessm en t , 3, 13 Galveston tech n iqu e, 49 Groin p ain , 13 H Harrington , Pau l, 120, 127 Harrington in st ru m en t at ion system develop m en t of, 120, 127 w ith sacral h ooks, 48 Harrington th readed sacral rods, 48–49 Health -related qualit y of life (HRQOL) m easu res, 95–105 com m on ly u sed m easu res, 98 correlat ion w ith coron al im balan ce, 83, 85 sagit t al im balan ce, 83 cost an d valu e-related m easu res, 95, 98–99 de n it ion of, 95 n eed for im provem en t in , 102 pat ien t-rep or ted m easu res (PROMs), 96, 98, 103 physiological m easures, 95–96 process m easu res, 95 qu alit y m easu res, 96 radiograp h ic ou tcom es, 99–100 u t ilit y scores, 96, 98, 103 Health Ut ilit ies In dex (HUI), 96, 98 Hem oglobin levels, preop erat ive, 5–6 Hem ost asis, in t raoperat ive, 6 High -risk pat ien ts decom p ression -on ly su rger y for, 18 protocol for, 5 Hydroxyap at ite, as p ed icle screw coat ing, 59–60, 132 Hyp erglycem ia, as su rgical-site in fect ion risk factor, 135–136, 138 Hyp ovitam in osis D, 6–7, 9, 131 I Iliac screw xat ion , 48–51, 50f, 53–54 asym ptom at ic h aloing of, 53f, 54 com plicat ion s of, 53, 54 im p lan t at ion p roblem s w ith , 25, 26 in p ostoperat ive coron al im balan ce revision surger y, 88 S2-alar-iliac, 51, 52f, 53, 54 in fu sion s to S1, 133, 138

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Index Ilium , fusion to, as proxim al ju n ct ion al kyp h osis risk factor, 106, 109 In fect ion s. See Surgical-site in fect ion s “In st abilit y catch ,” 12–13 In st rum en t at ion , spin al. See also Osteoporot ic sp in e, inst rum en t at ion st rategies for im plicat ion for m agn et ic resonan ce im aging, 3 levels of, 18 rigidit y of, as proxim al ju n ct ion al kyph osis risk factor, 108 th oracic, w ith fusion exten sion , 8 In terbody fusion /su pp or t an terior lu m bar (ALIF), 130–131, 134 com plicat ion rate of, 100–101 in osteoporot ic sp in e, 62–63, 64f in sacral-pelvic xat ion , 51 t ran sforam in al lu m bar (TLIF), 130–131 In t raoperat ive m on itoring. See Neu rom on itoring, int raoperat ive Isch em ia, sp in al, 75 J Jackson in t rasacral rod tech n iqu e, 48 K Kost uik t ran siliac bar, 49 Kyph osis lum bar, adult degen erative scoliosis-related, 80f, 83 osteotom y for, 30, 34–36, 35f postlam in ectom y, 135 proxim al jun ct ion al, 79, 106–119 clin ical ou tcom es after, 111, 112t–113t et iology of, 106–111, 115 preven t ion of, 114–115 revision surger y for, 111, 114–115, 116f–117f, 117, 118 risk factors for, 106–111, 107t, 115 t im ing of, 111 Sch eu erm an n’s, 108, 114–115 th oracic osteotom y for, 31–32, 31f posterior spin al in st ru m en tat ion -related, 123–124 postop erat ive, 110, 123–124 preop erat ive, 107t, 110 tech n iques for creat ion of, 123–125 L Lam in ectom y in d ecom pression -on ly surger y, 18 as kyphosis cause, 135 Leg-length d iscrepan cy, 2–3, 79, 81 Leg pain , 16, 18, 82 Lidocain e, as spin al cord isch em ia t reat m en t , 75 Listh esis. See also Spon dylolisth esis an teroposterior, 3 lateral, 3, 16 Lordosis xed, osteotom y for, 40, 42f, 43

lu m bar adu lt degen erat ive scoliosis-related, 80f, 82 adu lt idiop ath ic scoliosis-related, 82 an terior fu sion app roach to, 8 w ith at-back syn d rom e, 8 as proxim al jun ct ion al kyph osis risk factor, 107t, 109, 110, 115 radiological m easu rem ent of, 15 as sp in al su rger y outcom e m easu re, 95–96 Low er in st ru m en ted vertebrae (LIV) in long-segm en t fu sion , 23–24, 25–26 in p roxim al ju n ct ion al kyph osis, 109 Lu m bar spin e. See also Lordosis, lu m bar d egen erat ive ad ult scoliosis of, 81 p edicle screw xat ion in , 60 Lu m bosacral xat ion , in osteop orot ic spin e, 61 Lu m bosacral ju n ct ion biom ech an ics of, 45 sacral-p elvic xat ion of, 45–55 Lu m bosacral p ivot p oin t , 45 Lu que in st ru m en tat ion , 91f Lu que L- xat ion , 49 M Magn et ic reson an ce im aging (MRI) of disk degen erat ion , 16 lu m bar, for back p ain assessm en t , 13 p ostop erat ive, 74, 76 p reop erat ive, 3, 70 of sp in al sten osis, 16 Mean arterial p ressu re (MAP), in t raoperat ive m on itoring of, 71, 73, 74, 75 Met abolic bon e d isease, as adu lt scoliosis cau se, 1, 79 Met allic im p lan ts, for spin al deform it y correct ion , 120–129 for adolescen t idiopath ic scoliosis, 123–127, 125f, 126f n ite elem en t an alysis of, 126–127 fract u res of, 130, 133 h istor y of, 120, 121t im p lan t d en sit y, 133 relat ion sh ip w ith correct ion rate, 127 in fect ion of, 135 in t raop erat ive m ech an ical forces on , 126–127, 126f m aterials for, 133 m ech an ical p roper t ies of, 120–121 after m an u al ben ding, 122–123, 122t sp in al viscoelast icit y an d, 123, 124f, 128 st ress-st rain cu r ves of, 120–121, 121t Methylp redn isolon e, 75 Microden sitom et r y, p reoperat ive, 57 Motor evoked p oten t ial (MEP) in t raop erat ive m on itoring, 29–30, 43, 71, 72, 73, 74 N Narcot ics p ain m edicat ion s, 4, 10 Neck Disabilit y In dex (NDI), 96

Index Ner ve root com pression , sym ptom s of, 16 Ner ve root/t ran sforam in al inject ions, diagn ost ic, 3–4 Neu rologic com plicat ion s, of adu lt sp in al d eform it y surger y, 68–77 delayed postoperat ive, 75–76 in t raoperat ive m an agem en t of, 71 in t raoperat ive n eu rom on itoring for, 29–30, 43, 71–73, 74, 75 m ech an ism s of, 70 postoperat ive m an agem en t of, 75 preop erat ive risk assessm en t for, 70 prevalen ce of, 68–70, 68f steroid protocol for, 75 Neu rologic de cits, preoperat ive evalu at ion of, 2 Neu rom on itoring, in t raoperat ive, 74, 75 m otor evoked poten t ial (MEP) m on itoring, 29–30, 43, 71, 72, 73, 74 som atosen sor y evoked poten t ial (SSEP) m on itoring, 71–72, 73, 74 Neu rovascular exam in at ion , preoperat ive, 3 Nicot in e. See also Sm oking cessat ion e ect on pat ien t ou tcom es, 131 Non steroidal an t i-in am m ator y d rugs (NSAIDs), 4 Non un ion . See also Pseu doarth rosis n icot in e-related, 131 rates of, 133, 134 reoperat ion risk of, 134 Nut rit ion al st at us, preop erat ive assessm en t of, 5, 10 Nut rit ion al supp or t , in sp in al su rger y p at ien t s, 5 O Obesit y as proxim al jun ct ion al kyp h osis risk factor, 110 as su rgical-site in fect ion risk factor, 136, 138 Open an terior surger y, p ulm on ar y fu n ct ion e ect s of, 6 Osteopen ia, 56, 111, 114, 132 Osteophytosis, preoperat ive evalu at ion of, 3 Osteoporosis, in adu lt sp in al deform it y p at ien t s, 138. See also Osteoporot ic spin e, in st rum en tat ion st rategies for bon e m in eral den sit y in , 56, 58, 132, 138 diagn osis of, 132 m an agem en t of, 132, 138 preop erat ive m edical t reat m en t for, 58 as proxim al jun ct ion al kyp h osis risk factor, 106, 110–111 in sp in al surger y pat ien t s, 7, 10 Osteoporot ic spin e, in st rum en t at ion st rategies for, 56–67 adjacen t segm en t failure in , 56–57, 65–66 an ch or poin t s en h an cem en t , 61 an terior xat ion , 63 bon e-im plan t in terface protect ion , 63, 65 xat ion failure in , 56–57, 65–66 fusion , 132 for in st ru m en t at ion failu re preven t ion int raoperat ive m easu res, 58–65

postoperat ive m easu res, 65 preoperat ive m easu res, 57–58, 66 interbody su p port , 62–63, 64f n on un ion an d, 57 ped icle screw xat ion , 58–61 insert ion tech n iqu e an d in sert ion torqu e in , 60–61 t ract augm en tat ion in , 59–60 prop hylact ic vertebroplast y, 61–62, 66 pseudoarth rosis an d, 56–57, 65–66 sem i-rigid xat ion , 63 Osteotom y, 8. See also Ver tebral colu m n resect ion (VCR) closure of, 30, 35–36, 36f for xed lordosis, 40, 42f, 43 w ith long-segm en t fu sion , 24 ped icle subt ract ion closure of, 35–36, 36f com parison w ith Sm ith -Petersen osteotom y, 36f com plicat ions of, 34 for coron al im balan ce correct ion , 88, 91f ou tcom es, 100 w ith previou s an terior im p lan t s, 36–37, 38f revision su rger y of, 131f for rigid spin al deform it ies, 30, 31–32, 31f, 33f, 34–36, 35f, 36f tech n iqu e of, 34–36, 35f for t ype A coron al im balan ce correct ion , 87 posterior ou tcom es of, 100 in pseu doarth rosis revision su rger y, 134 Sm ith -Petersen , 36f, 100 as spin al cord in farct ion cau se, 29–30 for p roxim al jun ct ion al kyph osis, 115, 116f, 117 for rigid sp in al deform it ies, 28–44 an terior ap p roach in , 28 closu re of, 30 xat ion in , 30 fu sion across, 32 level of osteotom y, 30–31 m ult i-level vertebrectom y, 32, 33f, 40, 41f n u m ber of osteotom ies requ ired, 30 pedicle subt ract ion osteotom y, 30, 31–32, 31f, 33f, 34–36, 35f, 36f plan n ing of, 28–32 posterior ap proach in , 28 posterior colu m n osteotom y, 33–34, 33f, 34f as single procedu re, 32 as st aged p rocedu re, 32 t ran sdiskal ped icle su bt ract ion osteotom y, 32, 33f, 36–37, 37f t ypes of, 32–40 th ree-colum n , 8–9, 10 for coron al im balan ce correct ion , 87–88, 89f deform it y exibilit y determ in at ion in , 28–29 in dicat ion s for, 28–29 level of, 31 versus m u lt ip le posterior colu m n releases, 28, 29

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Index Osteotom y (cont inued ) for proxim al ju n ct ion al kyph osis, 117f reoperat ion rate for, 101 spin al cord blood ow in , 29–30 spin al cord p rotect ion in , 43 surgical exposure in , 29 th oracolum bar, 29, 29f Osw est r y Disabilit y In dex (ODI), 8, 96, 98, 101–102, 111 Outcom e m easures, in spin al deform it y su rger y. See Health -related qualit y of life (HRQOL) m easu res P “Pain fu l catch ,” 12–13 Pain m an agem en t , in adu lt sp in al d eform it ies, 4, 10 Parathyroid h orm on e, 132 Pat ien t-reported outcom e m easu res (PROMs), 96, 98, 103 Pedicle rods, biom ech an ical p ropert ies of, 120 Pedicle screw xat ion altern at ives to, 30, 43 int raoperat ive assessm en t of, 74 w ith local fusion , 18 in osteoporot ic sp in e, 58–61, 132–133 as proxim al jun ct ion al kyp h osis risk factor, 108 sacral, 46–48, 47f m edial in sert ion t rajector y for, 51, 53, 53f Pedicle screw s biom ech an ical prop ert ies of, 120 hydroxyap at ite-coated, 59–60, 132 m ech an ical forces on , 126–127, 126f Pediculolam in ar in st ru m en t at ion , for osteoporot ic spin e, 61 Pelvic in ciden ce (PI), as spin al deform it y su rger y ou tcom e m easu re, 95–96 Pelvic obliqu it y, 2–3 Pelvis fu sion to, as proxim al ju n ct ion al kyph osis risk factor, 109 ped icle screw xat ion in , 60 Periap ical reduct ion screw s, 30 Physical exam in at ion , p reoperat ive, 70 Physiological ou tcom e m easu res, 95–96 Polym ethylm eth acr ylate (PMMA) bon e cem en t , 59 Posterior approach , 9. See also Com bin ed an terior/ posterior approach in adult scoliosis, 78 in severe adult spin al deform it ies, 6 Posterior colu m n release, m ult iple p eriapical osteotom ies for, 30–31 Posterior spin al ligam en t s, surger y-related disrupt ion of, 106–108, 107t, 115 Post m en opau sal w om en , bon e m in eral den sit y screen ing in , 7 Post ural im balan ce, as back pain cause, 13 Prealbum in levels, p reop erat ive assessm en t of, 5 Preoperat ive evaluat ion , of adult degen erat ive spin al deform it ies, 1–4

Preoperat ive plan n ing, of ad u lt sp in al deform it y surger y, 8–9 Process m easu res, 95 Provocat ive test ing, preop erat ive, 3–4 Proxim al ju n ct ion al angle, in p roxim al ju n ct ion al kyph osis, 107t, 110 Pseu doar th rosis, 130–134, 131f, 133f, 134f diagn osis of, 133 Harrington th readed sacral rod-related, 48–49 L5-S1, fu sion -related, 25 long-segm en t fu sion -related, 24 m an agem en t of, 133–134 rate of, 130 as revision su rger y cau se, 130, 133–134 risk factors for, 130–133 sacral h ook-related, 48 Psych ological d isord ers, in adult spin al deform it y pat ien t s, 7 Pu lm on ar y disorders, p ostoperat ive, 8 Pu lm on ar y fun ct ion test ing, p reop erat ive, 6, 9 Q Qu alit y-adju sted life years (QALYs), 98, 99, 103 R Radicular p ain , 4, 16, 82, 85 Radiculop athy, 2, 78 Radiograp h ic m easu rem en t s, of spin al deform it y, 95–96 Radiograp h ic ou tcom es, of adu lt spin al deform it y surger y, 99–100 Radiological im aging, preop erat ive, 3, 9, 70 Radiological in st abilit y, 13–14, 13f Recom bin an t h u m an bon e m orph ogen et ic protein -2 (rh -BMP2), 133–134, 138 Recom bin an t h u m an er yth ropoiet in (rEPO), 6 Reop erat ion /revision su rger y, 101 for osteotom y, 101 for p edicle xat ion osteotom y, 131f for p ostop erat ive coron al im balan ce, 88, 90f–92f, 93 for p seu doar th rosis, 130, 133–134 for su rgical com p licat ion s correct ion , 24 surgical-site in fect ion -related , 135 Rigid spin al deform it ies com bin ed an terior/p osterior ap p roach to, 8–9 osteotom y for. See Osteotom y, for rigid sp in al deform it ies proxim al ju n ct ion al kyp hosis-related, 117f, 118 Rod rot at ion m an euvers, in t raop erat ive m ech an ical forces in , 126–127, 126f S Sacral-pelvic xat ion , 45–55 adju n ct ive an terior in terbody su p p ort in , 51 an atom ic an d biom ech an ical con siderat ion s in , 45–46

Index in dicat ion s for, 46 in st rum en t at ion select ion an d tech n iques for, 46–51 iliac xat ion , 48–51, 50f, 52f sacral xat ion , 46–48, 47f operat ive tech n iques in , 51, 53, 53f pat ien t posit ion ing for, 51 Sacral slope, 95–96 Sacru m bon e m in eral den sit y of, 58 fusion to, 23–24, 25, 26, 79 as proxim al jun ct ion al kyp h osis risk factor, 107t, 109 pedicle screw xat ion in , 60 Sagit t al align m en t , global, 107t, 109–110, 118 Sagit t al balan ce preop erat ive assessm ent of, 8 radiological assessm en t of, 14–15, 15f as su rgical outcom e pred ictor, 85 Sagit t al im balan ce ad ult degen erat ive scoliosis-related, 83 w ith associated coron al im balan ce, 87 correlat ion w ith disk degen erat ion , 80f, 83 in osteop orot ic spin e, 65 preop erat ive evaluat ion of, 10 proxim al jun ct ion al kyph osis-related, 111 su rgical correct ion of, 87 t yp es of, 24 Sagit t al plan e deform it ies, 13 Sagit t al plu m b lin e, C7, 14–15, 15f, 110 Sagit t al vert ical axis (SVA), in p roxim al ju n ct ion al kyph osis, 107t, 110, 114, 115 Sciat ic n er ve, iliac screw xat ion -related inju r y to, 53, 54 Scoliosis, 1. See also Adolescen t idiop ath ic scoliosis; Adult scoliosis n eurom uscu lar, as su rgical-site in fect ion risk factor, 135, 137f prim ar y degen erat ive, 1 secon dar y, 1 su rger y-related, 1 Scoliosis Research Societ y, 84 Morbidit y an d Mort alit y dat abase, 135 SRS-22 qu est ion n aire, 8, 11, 96, 98, 101–102 Sem i-rigid xat ion , in osteoporot ic spin e, 63 Severe adu lt spin al deform it ies, su rgical decision m aking regarding, 17–26 Sh ort Form 6 Dom ain s (SF-6D), 96, 98 Sh ort Form -36 (SF-36), 96, 98 Slip angle, radiological m easu rem en t of, 13–14, 13f, 14f Sm oking cessat ion , preoperat ive, 6, 8, 131, 138 Som atosen sor y evoked p oten t ial (SSEP) int raoperat ive m on itoring, 71–72, 73, 74 Speed tech n ique, of bular st ru t graft ing, 48 Spin al cord injur y acute, m edical t reat m ent for, 75 delayed in t raoperat ive, 75–76 Spin al cord perfu sion , in t raoperat ive, 73

Spin al cu r ves com pen sator y, 81–82 progression of, 16–17 Spin al in st abilit y, d iagn osis of, 12–13 Spin al su rger y decision m aking for, 17–26 h igh -risk protocol for, 5 ind icat ion s for, 17 as scoliosis cau se, 1 Spin e, viscoelast icit y of, 123, 124f, 128 Spin op elvic im balan ce, radiograp h ic d eterm in at ion of, 3 Spin op elvic p aram eters, as spin al deform it y surger y ou tcom e m easu res, 95–96 Spon dylolisth esis degen erat ive, 12 L5-S1 fu sion su rger y for, 25 slip angle m easu rem en t in , 14 lateral, 17 St agn ara Wake-Up Test , 71, 73–74 Sten osis, sp in al im aging of, 16 lu m bar as adu lt d egen erat ive scoliosis cause, 82 at L5-S1, 23 as pseu doarth rosis risk factor, 130 Su blam in ar in st ru m en tat ion , 48, 61 Su blu xat ion , rotator y, 15–16, 16f, 82 de n it ion of, 82 discrep an cy w ith Cobb angle, 82 w ith in fu sion block, 26 preoperat ive evalu at ion of, 3 as spin al cu r ve progression risk factor, 17 Su p erior gluteal arter y, iliac screw xat ion -related inju r y to, 53 Su rgical-site in fect ion s, 134–137 an t ibiot ic prop hylaxis/t reat m en t for, 134–135, 136, 137, 138 diagn osis of, 136–137, 137f m an agem en t of, 137 as revision su rger y cau se, 130 risk factors for, 135–136, 138 T Teriparat ide, 132, 134, 138 Th oracic in st ru m en tat ion , w ith fu sion exten sion , 8 Th oracic sp in e, ped icle screw xat ion in , 60 Th oracolum bar sp in e, adu lt degen erat ive scoliosis of, 81 Th oracolum bar/th oracolu m bosacral orth oses (TLO/TLSO), 4 Tran sforam in al lum bar in terbody fu sion (TLIF), 130–131 Tran siliac xat ion , 48–49 Tran ssacral iliac xat ion , 51, 52f Tran svertebral bu lar st ru t graft ing, 48 Tricor t ical xat ion , of sacral p edicle screw s, 46, 47f

147

148

Index U Un iversal clam p tech n iqu e, 124–125 Upp er in st rum en ted vertebrae (UIV) in long-segm en t fu sion , 19, 23 in proxim al jun ct ion al kyp hosis, 107t, 108, 109, 110–111, 114, 118 Urinar y t ract in fect ion s, p erioperat ive, 7–8, 135 V Value, of h ealth care, 95, 98–99 of adult sp in al deform it y surger y, 102, 103 Vertebrae apex/apical in adu lt degen erat ive scoliosis, 81 in p ed icle screw xat ion , 125, 125f osteoporot ic, p ath om orph ology of, 58 proxim al n eut ral, 15

Vertebral colu m n resect ion (VCR) ou tcom es of, 100 of proxim al ju n ct ion al kyp h osis, 115 of rigid sp in al d eform it ies, 32, 33f, 37–40, 39f of severe adult spin al deform it ies, 6 for t ype B coron al im balan ce correct ion , 87 Vertebral cop lan ar align m en t (VCA), 124 Vertebrectom y, m u lt i-level, 32, 33f, 40, 41f Vertebroplast y, prop hylact ic, in osteoporot ic sp in e, 61–62, 66 Visual An alogu e Scale (VAS), 96, 101 Vit am in D de cien cy, 6–7, 9, 131 W Wou n d in fect ion s, postoperat ive. See Su rgical-site in fect ion s