Tissue Grafts / orthodontic courses by Indian dental academy
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GITAM DENTAL COLLEGE & HOSPITAL
ORAL & MAXILLOFACIAL SURGERY
TISSUE GRAFTING- BIOLOGICAL CONSIDERATIONS OF AUTOGENOUS & HETEROGENOUS GRAFTS
Dr. Sambhav K Vora I MDS
1. Introduction 2. Types of bone grafts 3. Bone harvesting procedures 4. Embryological aspect of bone grafts 5. Vascularized. Vs. non vascularized grafts 6. Mechanisms of bone regeneration 7. Bone morphogenetic protein 8. Growth factors 9. Factors affecting bone regeneration 10. Factors causing rejection of graft material 11. Graft survival 12. Skin grafting 13. Mechanism of healing of skin grafting 14. References
A tissue graft is a procedure in which tissue from a donor is used to replace missing or damaged tissue on a patient. Tissue grafts can be classified as Hard tissue grafts • Bone & bone substitutes.. Soft tissue grafts • Skin grafts • Gingival grafts • Connective tissue grafts BONE GRAFT MATERIAL A bone graft is defined as the transplantation of living bone from one location to another. Transplantation implies the transfer of living cells, whereas implantation refers to the transfer of nonliving cells.16 There are three primary types of graft material – Autogenous bone grafts Allografts Alloplasts, Xenografts are considered as subgroup. All the graft material work by either of the mechanismAutogenous graft material work on all the three mechanism i.e osteogenesis , osteoconductive & osteoinduction Allografts work on mechanism of osteoconductive & osteoinductive Alloplast work on osteoconductive mechanism. Normally for larger defect autogenous graft are used & for smaller defect either alloplast or allograft or a combination of both can be used.
Autologous bone grafts:
Autologous bone grafts are the grafts in the form of the bone which are collected from the body of the same person .This graft material collected can be used either as block form or in the particulate form. There are various types of autologous bone grafts available which can be harvested from either intraoral sites or extraoral sites. Extra oral sites of harvesting bone are: 1. Anterior ileum 2. Posterior ileum 3. Tibia 4. Calvarium 5. Ribs
Intra oral sites of harvesting bone are: 1. Maxillary tuberosity 2. Zygomaticomaxillary buttress 3. Zygoma 4. Mandibular symphysis 5. Mandibular ramus 6. Mandibular body The optimal donor site depends on the volume & type of regenerated bone needed for specific cases. MAXIMUM VOLUME AVAILABLE FROM AUTOGENOUS BONE DONOR SITESPosterior iliac crest -140ml Anterior iliac crest – 70ml Tibia-20mto 40 ml Cranium- 40ml Ascending ramus -5 to 10 ml Anterior mandible -5 ml
Tuberosity- 2 ml Miscellaneous (eg, bone scrapings , suction tips)-varies
Advantages of autologous bone: 1. They contain viable cell that proliferate & contribute to the new bone growth 2. They contain bmps, capable of inducing osteogenesis to produce bone 3. Healing is faster compared to other grafts (autologous bone heals as fast as 3 to 4 months compared to 8 to 10 months with other graft material)
Disadvantages : 1. Need for second operative site 2. Resultant patient morbidity 3. Difficulty of obtaining a sufficient amount of graft material These limitations led to the development of allografts & alloplast as alternative grafting material. Risk associated with autogenous bone is morbidity at the bone harvest site.
ALLOGRAFTS: These are obtained from the cadavers or from the patients living relatives or non relatives, those obtained from cadavers are available through tissue banks stored under complete sterilization.
Advantages of allografts1. Ready availability 2. Elimination of donor site 3. Reduced anesthesia & surgical time
4. Decreased blood loss
Disadvantages1. Antigenicity of tissue harvested & concerns of transmission of hiv or other infections. 2. Transplanted bone may induce a host immune response 3 .Cadaveric bones may be rejected Fresh allografts are the most antigenic, freezing or freeze-drying the bone significantly reduces the antigenicity
Commonly used allografts are frozen, freeze-dried (lypophilized), demineralized freeze dried & irradiated. FDBA can be used as either mineralized or demineralised form. Demineralization removes the mineral phase of the graft material & purportedly exposes the underlying bone collagen,possibly some growth factors ,particularly bmp which may increase its osteoinductive capabilities. & also causes inadequate preservation of the osteoinductive proteins Mineralized FDBA is not osteoinductive but does have osteoconductive properties FDBA is more effective than DFDBA in following situation1. Repair & restoration of fenestrations 2. Minor ridge augmentation 3. Fresh extraction sites 4. Sinus lift cases 5. Repair of dehiscences & failing implants. Puros is an allogenic material which is solvent preserved ( as opposed to freeze drying to extract the water component ), has been shown to ossseointegrate as effectively as cryopreserved material & to be equally biotolerable. It is generally believed that bmp & other noncollagenous proteins in the exposed matrix are responsible for the osteoinductivity of the DFDBA Fresh frozen bone is an alternative to FDBA & autogenous bone. It can be obtained as either corticocancellous bone or as cancellous bone.
Major disadvantage of this is the small risk of disease transmission.
Irradiated cancellous bone has also been used as a substitute material for autogenous material. This is trabecular bone obtained from the spinal column & treated with between 2.5 & 3.8 megarads of radiation, irraradiated bone is most similar to the autogenous bone in terms of demonstrating rapid replacement & consistent establishment of a reasonable ratio of the new bone with less expense & morbidity than that associated with autogenous material.
ALLOPLASTS, XENOGRAFTS & TISSUE ENGINEERED MATERIALThese include – 1. Deorganified bovine bone 2. Synthetic calcium phosphate ceramics (eg-hydroxyapetite,tcp) 3. Calcium carbonate (eg-coralline) Mechanism of action in these materials is strictly osteoconduction with new bone formation taking place along their surfaces.
HYDROXYAPETITE: Is readily biocompatible & bonds readily to the adjacent hard & soft tissues. The greater the material porosity the more scaffolding it provides for new bone growth & more quickly it is resorbed,the more crystalline the graft the slower its resorption.. hence amorphous graft s resorb more quickly than the crystalline grafts.
BOVINE DERIVED ANORGANIC BONE MATRIX MATERIAL: Bio-oss is anorganic bovine bone which is osteoconductive & undergoes physiologic remodeling & becomes incorporated with the surrounding bone. In large alveolar ridge deficiencies, this anorganic bone can be combined with autogenous bone for successful augmentation. Osteograf is a microporous hydroxyapetite particulate material derived from bovine bone. It is available in both small particle (250-420microm& large particle (4201000microm)sizes. This material has been widely used in combination with DFDBA for sinus augmentation.
Pepgen p-15 is an enhanced form of bovine derived hyroxyapetite that contains an added synthetic short chain peptide, p-15. This component mimcs like type I collagen which is responsible in natural bone for cell migration, differentiation & proliferation. It has been studied that this material provides enhanced bone formation in a shorter time compared with the bovine derived hydroxyapetite+ dfdba graft material used for sinus augmentation.
SYNTHETIC BONE MATERIAL: It is a synthetic bioactive resorbable graft, osteoconductive non ceramic graft material indicated for contouring & improving alveolar ridge deformities, filling extraction sockets, dental implants, sinus grafts & repairing marginal periapical & periodontal alveolar bony defects. This material is highly porous crystalline clusters which act as a physical matrix to permit the infiltration of bone forming cells & its subsequent deposition of host bone. As new bone is deposited the material progressively resorbs over 6-8 months period.
TRICALCIUM PHOSPHATE: TCP is osteoconductive & is indented to provide a physical matrix that is suitable for the deposition of new bone. It s often used for repairing nonpathological sites where resorption of the grafts where concurrent bone replacement might be expected. Both hydroxyapetite & TCP are safe & well tolerated. Cerasorb is a beta-tricalcium phosphate which is used in bone defect regeneration in the entire skeletal system. It is completely resorbed & replaced by natural bone in 3-4 month period depending on the type of bone.
CALCIUM CARBONATE MATERIALS: Coralline is a ceramic graft material synthesized from the calcium carbonate. Advantage: It s three dimensional structure is similar to that of bone.
Interpore 200 is composed of pure hydroxyapatite & TCP, works on osteoconduction. Resoprtion of this material was very slow both in bone & soft tissue compared to other materials.
HARD TISSUE REPLACEMENT POLYMER: Bioplant HTR polymer is a microporous composite with a calcium hydroxide graft surface. This polymer resorbs slowly & is replaced by bone after approximately 4-5yrs. It is useful in: 1) bone ridge maintenance by preventing the anticipated loss of alveolar bone following extraction, preserving the height & width of the alveolar ridge. 2) Ridge augmentation 3) Delayed augmentation, in which the dimensions of the alveolar ridge are increased& bony defects are corrected. 4) Repair of periodontal & other defects.
BIOACTIVE GLASS CERAMICS: It is composed of calcium salts & phosphate in a proportion similar to that found in bone & teeth, as well as sodium salts & silicon which is essential for bone to mineralize. It has two properties that contribute to the successful results: 1) relatively quick rate of reaction with host cells, 2) An ability to bond with the collagen formed in the connective tissue. It produces osteogenic cells in the implantation site which will colonize the surface of the particles & produce collagen on these surfaces. Osteoblasts then lay down bone material on the top of the collagen & this latter action may supplement that grows by osteoconduction from the alveolus. This material bonds not only to the bone but also soft connective tissues. Perioglas is a particulate form of bioglass that bonds to both bone & certain soft connective tissues. It is composed of calcium, phosphorus, silicon & sodium. Criteria for successful perioglas include pre treatment planning, debridement of the defect, preservation of soft tissue vascularity & infection control. This material has two favourable characteristics: 1) ease of compactibility, 2) ability to promote hemostasis. Hemostasis is most likely related to the compactibility & adhesiveness of the material.
CRITERIA FOR SELECTING A GRAFT MATERIAL: • Individual’s systemic healing ability ( eg: age, systemic illness affecting healing such as diabetes or autoimmune disorders like scleroderma, lupus, previous surgeries to the area, previous treatment with radiation or chemotherapy, irradiated tissue bed. • Local osteogenic potential of the defect • Osteogenic potential of the graft site • Surgeon’s skill • Time available for graft maturation
Bone harvesting procedures:
Intra oral sites:- Maxillary tuberosity: Anatomical limits of tuberosity are maxillary sinus, the pterygoid plates, the molar teeth,& the greater palatine canal. An incision is made along the ridge crest in the posterior maxilla & continued posteriorly over the tuberosity& a vertical releasing incision is made laterally, this exposes the tuberosity,ridge crest & lateral maxilla.tuberosity bone is usually removed following reflection of the antral mucosa which allows for more aggressive bone harvesting without concern for membrane perforation. With the help of either chisel , ronguer or bone scraper bone is removed
Zygoma: The mucoperiosteal flap used to gain access to the sinus is reflected higher to expose the inferior aspect of the zygoma, just above the inferior border of the zygomatic rim lateral from the maxillary sinus, cores or small bundles of bone are removed using a trephine bur or carbide bur .The drill is kept parallel to the lateral maxilla & penetration is limited to 12 to14 mm to avoid infra temporal fossa &orbital floor.
Mandibular symphysis: symymphysis is a good source for procuring smaller grafts either in a block form or in the particulate form. This graft material yields more of coticocancellous graft material, compared to ramus Advantages: 1. Relatively low morbidity 2. Minimal graft resorption. Indications: Class 3 ridge defects( both vertical & buccal bone loss) In the anterior maxilla ( as block form) For sinus elevations (particulate form)
Exposure of the symphysis can be obtained through a vestibular, sulcular incision or attached gingiva method.each incision has its own advantages & disadvantages. Sulcular methodAdvantages:minimized bleeding & trauma &facilitated flap retraction Disadvantages:difficulty in suturing, recession & loss of bone at the alveolar crest. Vestibular methodAdvantages;no interferences with the gingiva surrounding the anterior teeth,no mentalis muscle detachment, reduced risk of facial ptosis,ability to use two step suturing technique Disadvantages:more bleeding & edema & invisible scarring.
The vestibular incision is made in the mucosa distal to the canine teeth approximately 1cm from the mucogingival junction . a mucoperiosteal flap,is reflected inferiorly to the
inferior border of the mandible , osteotomies should be carried at least 5mm from the root apices & the mental foramina. The facial cortex is thick & the underlying cancellous bone is usually dense. Bone can be harvested for either particulate grafting or block grafting. Particulate grafting – incision is given& the area is exposed , 4 mm trephine burs provides both cortical & cancellous bone . The cores of bone are harvested with the trephine bur. The osteotomies can connect or can be made with the bone inbetween them. The core from the donor site can be removed with a small hemostat, cotton pliers or tissue forceps. If more material is required then septal bone from inbetween the trephined osteotomies can be removed with the ronguers, but can leave a large defect at the donor site.
Block bone may be harvested depending on the size of the recipient defect using carbide bur or sagittal saw& finally it is removed with the help of osteotome. Bone blocks are deposited in the container filled with the sterile saline solution. Donor site can be filled with the microfibrillar collagen to provide hemostasis.Perforations are made on the recipients site for new vascularisation at the bone graft. Harvested block is shaped & placed with the help of the screws. Complications-
Damaged submental & sublingual arteries Potential damage to mandibular roots Mental nerve paraesthesia Incision dehiscence in donor area Temporary altered sensation of the lower teeth Chin ptosis
MANDIBULAR RAMUS: Ramus is one of the ares in the oral cavity that serves as a donor site for harvesting cortical bone. If larger amount of bone is required then along with it anterior mandible is also used.recipient site should be properly checked for the amount of bone that needs to be harvested from the ramus.
Bone harvested from the ramus is usually cortical in nature &therefore it is useful in areas that require block grafts for structural support rather than particulated graft material from cancellous marrow harvests. Ramus yields around 4mm thick, 3 cm or more in length, & up to 1 cm in height of bone. Ramus grafts are useful in • Bone augmentation before implant placement • Sinus grafting • Facial augmentation • Orthognathic surgery • Immediate reconstruction following tumour resection. Procedure: incision started at the oclusal level of the maxillary posterior molars & brought anteriorly ,always touching the bone medial to the external oblique ridge & lateral to the retromolar pad. The lingual tissue is also dissected from the bone for proper visualization of the thickness of the bone. Retraction is done by Minnesota retractor. Small perforations are made to give the clinician an idea of the potential extension of the cut & this perforations are then connected which should cut completely through the cortical bone & into the cancellous bone. Final separation of the bone is done by chisel. As only cortical bone is removed inferior alveolar nerve is not damaged .the block of the bone is ready to be cut &shaped to fit the recipient size, but each piece must be long enough to hold at least two screws. A simple resorbable collagen membrane which resorbs in 2 weeks , is placed over the grafted bone to retard fibrous down growth during initial healing. Before placing the bone harvested from the ramus graft, the cortex of the recipient site should be perforated to enhance revascularization, & the graft should have intimate contact with the host bone. Complications of bone harvesting from the ramus• Potential damage to the inferior alveolar nerve • Limitation of graft size & shape • Incision dehiscence in donor area • Postoperative trismus • Potential damage to lingual nerve during flap incision
HARVESTING BONE FROM TIBIA: Bone obtained from tibia contains osteocomponent cells, an island of mineralized cancellous bone, fibrin from blood clotting & platelets from within the clot. Within hours of graft placement the clots platelet degranulte releasing platelet derived growth factors, transforming growth factor & other growth factorsto initiate the process of bone regeneration. Advantages: • Almost 20 to 40 cm cube of non compressed bone can be harvested from the marrow spaces. • The procedure is straight forward & can be performed using in office conscious sedation or general anesthesia • Total procedure time avg only 20 to 40 min • Blood loss is minimal & drainage is not required • Patients report minimal postoperative pain & dysfunction • Procedure allows immediate post operative weight bearing • Complication s & morbidity rates are less compared to other materials . studies have shown that complication rates with tibia ranges from 1.3% to 3.8% compared to 8.6% to 9.2% with iliac crest grafting.
Contrindications: • Need for block bone(provides only cancellous bone i.e particulate form of bone) • Patient s18 years of age or younger • Patients with history of knee injury or knee surgery • Patients with advanced rheumatoid or degenerative arthritis • Patients with metabolic bone disease.
Surgical approach & technique of harvesting:
The skin is disinfected with betadine applicators to remove surface bacteria. Then a sterile surgical marker will be needed to draw the anatomic landmarks on the skin, the location of patella , head of the tibia& the gerdy tubercle is marked on the skin. Local anesthesia with vasoconstrictor is first given subcutaneously & then deep into the periosteum. And 15 blade is used to make a 2 to 3 cm incision in layers through the skin, subcutaneous tissue, muscle fibre& periosteum, sharp periosteal elevator is then used to reflect the periosteum which is firmly attached to the bone. The osteotomy begins as a series of holes forming a circle with a circumference not larger than 1 cm , these perforations are then connected with the same bur& the central cortical bone is then removed with the help of molt curette. Postoperative wound managementIncludes hemostatic agents, suturing & anti bacterial ointment. The wound does not need to be drained.before closing the donor site haemostatic agent is applied & closure of the soft tissues with resorbable suture is performed in layers starting with the periosteum. The muscle is sutured with 4-0 chromic gut, followed by skin by 5-0 prolene suture. Complications: • Potential entrance into the joint space • Limited size & shape of the graft • Entrance into the fibula head instead of tibia • Postoperative edema or ecchymosis • Large & unsightly scar.
ILIAC CREST BONE GRAFT: Anterior approachThe patient is prepared with povidone iodine soap& paint & draped in an a standard sterile fashion. Local infiltration of 1% lidocaine with epinephrine is given. A no 15 blade is used to make the incision extending to the subcutaneous tissue. Electro cautery can be used to gain hemostatic control, sharp dissection is completed through the external & internal oblique musculature& periosteal layers to gain access to the bony crest. A sub periosteal reflection of the iliac crest in the medial direction is preferred to avoid dissection of the tensor fascialata muscles laterally creating gait disturbance. Several osteotomy approaches, with either conventional mallet & osteotomies or air or electrical driven saw blades can be used to gain access to the
cancellous bone. Tessiers approach (particulate cancellous bone) attempts to maintain the contour of the crest by performing oblique osteotomies off the lateral & medial aspects & retrieving the bone deep to the crest itself. If a corticocancellous block is desired, full thickness osteotomies are completed on the medial aspect ,detaching the block at the most medial aspect.
Posterior approach: Advantages• More bone is available i.e more than 2 to 2.5 times the quantity taken from the anterior site. • Less morbidity • Less complication. • Less associated bleeding • Less gait pain & disturbance
Disadvantages• Overall operative time is increased • Inability to operate simultaneously on both the facial & ilium regions
Procedure: Incision is made at the well defined bony prominence laterally where the gluteus maximus inserts. The curvilinear incision courses medially about 3 cm lateral to the midline entering at the length of about 10 cm.This direct approach minimizes damage to the vital neural & vascular structures.. subperiosteal reflection allows easy access to the desired site. Osteotomy of around 5 cm removes the cortical plate to gain access to the cancellous marrow. In both the approaches once the cancellous bone is reached, bone can be harvested using bone gouge or curets.Any sharp edges are smoothened, hemostasis achieved & closure is done in layers. A drain is usually required, exiting at a site away from the incision & suctioned at the low intermittent strength to avoid continuous aspiration of the marrow blood..
Comparision between iliac crest & tibia: Autologous grafts are considered as the gold standard for bone substitution, & iliac crest is considered as the choice of material. But bone harvesting from the iliac crest is associated with 49% of postoperative complications compared to tibia which is associated with only 2 % of complications. i.e lower donor site morbidity, accessibility, easier and faster harvesting, less blood loss, fewer postoperative analgesic requirements, and less gait disturbance6 But the volume of bone harvested is more from iliac crest compared to the tibial grafts.
Cancellous iliac bone measuring around 1 mm is trimmed & used for orbital reconstruction without rigid fixation.1
Bone harvesting from the ribs: Depending on the size & contour, 4 th , 5th & 6 th ribs are best. The sixth rib is most widely used because it can be accessed through an inframammary crease incision. With the patient in the supine position , an infrmammary incision is made through the skin & sub cutaneous tissue until the fibres from the pectoralis major muscle & rectus abdominis muscle are seen attaching to the sixth rib. A periostael incision is placed at the greatest convexity on the lateral aspect of the rib & with the help of periosteal elevators, the rib is exposed from its costrocondral junction anteriorly to a posterior length as much as 18 cm. careful elevation of the periosteum has to be done or else it may perforate the pleura & cause small tears. Once reflection is completed , the resection is begun at the cartilage site ,taking only 3mm of cartilage medially. More than 3 mm increases the chance of cartilage separation from the bone, especially in children. Once the anterior end is separated from the sternum , the rib can be elevated by placing an instrument on the undersurface of the rib, protecting the parietal pleura. Closure is then done in layers. , in children full morphologically normal rib will regenerate within 1 year , whereas in adults an incomplete bone ossicles resembling a rib slowly forms over 1 to 3 years.
CALVARIAL BONE GRAFTING:
It has a unique characteristic of early revascularization which is directly related to the numerous vascular systems, as a result the graft survives with little dimensional change.the site o harvesting bone is paramedian portion of the parietal bone as it is the thickest & is away from the vital structures (egsuperior sagittal sinus) & also less chance of scar being visible in male pattern baldness.. approach to this area is through the hemicoronal or bicoronal incision , posterior to the ear& is carried through the five scalp layers. The exposed cranium can then be prepared for either split thickness or full thickness graft. Split thickness grfat is most common in oral & maxillofacial surgery,a bur is used to create the shape of the desired graft in the outer cortex to the level of the cancellous marrow. Then with the help of curved ostetome the outer table can be cleaved from the inner table in the plane of the interposed cancellous marrow. Full thickness grafts are approached from a similar scalp incision; large full thickness bur holes are created at the periphery of the desired graft design.The Dura is then reflected from the undersurface of the inner table, allowing a bur or saw to connect the bur holes without dural perforation. The defect created from this graft harvested is usually repaired by split thickness graft harvested from the contra lateral side. This aids in protecting the brain & restores scalp contour. Drains are usually placed to reduce the dead space as well as to prevent hematoma formation. Once the graft is placed it is has to be properly stabilized, if not will result in resorption of the graft. Different forms of bone grafts: There are 2 types of bone graft material 1. vascularised graft 2 .Non-vascularised grafts. The non vascularized bone grafts are usually of two different types – cortical & cancellous. Corticocancellous bone grafts have characteristics of each of these two biological types. The easier the penetration of the blood vessel into the graft to revascularise it, the less mechanical strength the graft can take up. The more solid the bone graft is in its form to withstand mechanical stress, the harder it is to revascularise it, to be incorporated & to become a viable bone. Cortical bone: they are primarily used in an area where there is great mechanical stress, proper fixation has to be used to allow this graft to produce the function needed. This form of graft is useful in long bones but it’s not very effective when used in membranous bone sites such as facial skeleton. They are used in discontinuity defects to study mechanical
strength in response to shear stress & to evaluate stress shielding. To achieve an exact fit in the cortical bone application, a plentiful supply of autologous bone is needed. This is one of the main reasons why such cortical graft incorporating structures are used in allograft variety of bone grafting.
Cancellous bone: it is used because of its extensive ease of application for achieving fusion & for correcting discontinuity defects. It can be used in clean contaminated & grossly contaminated bones. The supply site mainly is the iliac or iliac crest graft. They usually do not have mechanical strength desired for such reconstruction for application in large defects. Because of this large open areas in this graft, revascularization takes place very well, thereby bringing new cellular regeneration, remodeling & substitution with new bone forming as old bone is removed. Corticoncancellous bone : it usually produces the best results because it enables good vascularization to help the incorporation of the bone graft with the surrounding structures & it also gives good mechanical strength. A rigid fixation apparatus can be used to produce the desired contour particularly in a discontinuity defect application.
Bone grafts can be obtained either block or particulate form. The block form can be reshaped before application. Unfortunately when larger blocks are needed the supply is limited. Particularly because the ideal material for bone grafting is autogenous bone. The larger pieces of bone graft cannot be supplied from autogenous components, particularly for repair of large continuity defects. This is the main reason why it has been necessary in certain clinical applications particularly in orthopedic surgeries to use allograft. Particulate bone is composed of small chips of bone is usually applied in an area where there is no need for mechanical strength. It is used for discontinuity defects where the defect is also bridged with mechanical device, internal or external & the defect is filled with this particulate bone. With the advent of improved mechanical unities an internal rigid fixation structures particularly vitallium & titanium, internal fixation is preferred so the patient can have near normal function during the healing phase which will take as long as 2 years. EMBRYOLOGICAL ASPECTS OF BONE GRAFTS: Bone is either of membranous or endochondral type. Membranous bone: It is a bone in which trabecular ossification was formed denovo in the embryo the primitive mesenchymal cells form a sheet of mesoderm with a rich vascular supply. Intercellular deposition of collagen follows cellular differentiation. As ossification centres develop osteoblasts can be identified within closely packed small bundles of collagen fibres, finally calcium salts are deposited in the intercellular spaces & within the adjacent
osteoid. Thus the direct bone formation occurs without an intermediate process. Examples of membranous bones includes vault of the skull, facial skeleton, much of the mandible & most of the clavicle. Endochondral ossification: it is a process of bone formation in which a primitive cartilage is required before osteoid deposition. Ex: most of the cranial base, portion of the mandible & majority of bones of the axial skeleton which are preceded by primitive hyaline cartilage, which differentiates from the mesenchyme early in embryonic life. This cartilage matrix is later invaded by blood vessels & bone forming cells which is then resorbed & replaced by osteoid. Peer empirically noted that fresh human autogenous endochondral bone ( rib,tibia ,iliac crest)when orthotopically or heterotopically transplanted ,the majority of the grafted bone was replaced with the fibrous tissue. In contrast when bone of membranous origin (vomer ) was grafted it retained its bony mass & showed no evidence of fibrous replacement even when transplanted to distant heterotopic sites. It was also studied that host maturation at membranous bone site was significant in both matured & immature animal study compared to endochondral site where it was not significant in immature animals. Membranous bone consistently outperformed endochondral bone with respect to resorption, graft orientation, host stages of maturation, morphologic designs, & fixation techniques.
Mechanism of bone regeneration & augmentation:4 Three different processes are associated with successful bone grafting-
Osteogenesis is the process that occurs when surviving osteogenic cells from within the graft produce new bone. This mechanism of graft healing relies on viable post transplant osteogenic cells to become the source of new bone formation. Although most cells within the graft die soon after transplantation some surviving cells are believed to take part in osteogenesis. The superior revascularization qualities of cancellous bone grafts are thought to result in a greater proportion of post transplant osteogenic cell survival and, consequently, a greater degree of osteogenesis than in cortical bonegrafts. The local sources of cells partaking in osteogenesis are believed to be the periosteum, endosteum, marrow, and intracortical elements. The role of osteogenesis as a mechanism of new bone formation during nonvascularized bone graft healing is thought to be of lesser significance than that of
osteoconduction. Although osteogenesis has a secondary role in the healing of nonvascularized bone graft, it constitutes the primary mechanism of vascularized bone graft healing. Cells within these grafts maintain their blood supply and remain viable after transplantation Osteoinduction is the process by which active factors released from the graft matrix stimulates cells from the host to form new bone. Osteoinduction has been studied extensively; however, there is significantly less research within the specific context of bone graft healing. Three phases of osteoinduction— chemo taxis, mitosis, and differentiation—have been described. In response to a chemical gradient during chemotaxis, bone induction factors direct the migration of cells to the area in which they are to be utilized. Following chemotaxis, these factors stimulate intense mitogenic and proliferative activity in these cells; the cells differentiate into cartilage and become revascularized by invading blood vessels to form new bone. Research on osteoinduction during graft healing has demonstrated that chemical and Physical alterations to the graft, such as hydrochloric acid decalcification and freezing, will decrease its osteoinductive properties . These Findings suggest that osteoinduction is most significant when freshly harvested bone grafts are utilized. Burwell suggested that osteoinductive factors within a bone graft are released by the necrotic bone and marrow components of the graft .The true mechanisms of osteoinduction during bone graft healing are still unknown and may provide a fertile ground for new research endeavors. Osteoinductive factors have been shown to be powerful stimulators de novo bone production in bony defect healing of animal models; their potential applications in bone graft healing and incorporation have yet to be exploited. Although the roles of osteoinduction and osteogenesis are thought to be of lesser significance than osteoconduction in nonvascularized bone graft healing, these three processes are thought to be intimately connected. Osteogenic stimulation or bone induction: Bone induction systems are autogenous.the cancellous bone matrix apparently has the ability to stimulate the autogenous marrow to become markedly ostegenic & to form new bone. This graft matrix &marrow substrate is the primary model for bone induction . How the induction takes palce-In the particulate cancellous bone graft there are various vascular marrow spaces which contains cells of pluripotent origin as vascular lining cells. The host bed also contains the same types of cells, so there are two possible approaches to stimulate the osteoblastic potential of pluripotent cells 1. The effect of graft on the itself. When the graft is properly immobilized & properly vascularized, its own pluripotent cells can be stimulated to form bone.
2. The effect of the graft on the host bed (i.e on the pluripotent cells of the marrow vascular spaces of the recipient site).these host pluripotent cells also need to be activated in the bone inductive process.. In the live autograft,there are also surviving osteoblasts &preosteoblasts,which have already been committed to becoming bone forming cells in the graft itself.such bone formation from existing osteoblast &committed osteoblasts is a short lived part of the bone inductive process.so induction can come from the 1. The graft material & its own surviving osteoblasts 2. The induction of the graft s own pluripotent cells & 3. Induction of the primitive cells of the recipient site s marrow vascular bed. The bone graft if properly vascularized, Can stimulate its own pluripotent cells to form bone at the graft site.this graft can also initiate the pluripotent cells in the host bed which either differentiate into cartilage or bone. However in clinical situation of osseous repair in bone grafting, most of the bone induction results when the pluripotent cells from the osteoblast &bone directly, & the cartilaginous pathway becomes a minor one in maxillofacial osseous reconstruction.
BONE MORPHOGENETIC PROTEIN: One group of cytokines, bone morphogenetic proteins (BMPs), has been demonstrated to have true osteoinductive properties. BMPs have been proven to stimulate new bone formation in vitro and in vivo. In addition, they play critical roles in regulating cell growth, differentiation, and apoptosis a variety of cells during development, particularly in osteoblasts and chondrocytes. There are currently 16 identified BMPs, although only a subset have been found to be expressed in fracture healing. BMPs were initially characterized by Urist; their identification was based on the capacity of demineralized bone powder to induce de novo bone formation in an intramuscular pouch, demonstrating the ability to directly induce mesenchymal connective tissue to become bone-forming osteoprogenitor cell. During fracture repair & graft healing, BMP-2, BMP-3 (also known as osteogenin), BMP-4, and BMP-7 (OP-1) have been found to be expressed to varying degrees. BMPs are initially released in low levels from the extracellular matrix (ECM) of fractured bone. Osteoprogenitor cells in the cambium layer of the periosteum may respond to this initial BMP presence by differentiating into osteoblast. Immunolocalization demonstrates an increase in detectable BMP-2=4 in the cambium region of the periosteum. BMP receptor IA and IB expression is dramatically increased in osteogenic cells of the periosteum near the ends of the fracture in the early postfracture period or post grafting period. Approximately 1– 2 weeks postfracture or graft placement, BMP-2=4 expression is maximal in chondroid precursors, while hypertrophic chondrocytes and osteoblasts show moderate levels of
expression. It is hypothesized that the role of BMPs in fracture repair is to stimulate differentiation in osteoprogenitor and mesenchymal cells that will result in osteoblasts and chondrocyte. As these primitive cells mature, BMP expression decreases rapidly. BMP expression temporarily recurs in chondrocytes and osteoblasts during matrix formation, and eventually decreases during callus remodeling. TYPES OF BMPs THEIR PROPERTIES, LOCATION & ROLES: BMP-1: functions as procollagen C- proteinase responsible for removing carboxyl propeptides from procollagen I, 2 ,3 . It activates bmp but not osteoinductive BMP-2: osteoinductive , embryogenesis, differentiation of osteoblasts , adipocytes, chondrocytes & also may influence osteoclast activity , may inhibit bone healing It is located in the bone, spleen, liver, brain, kidney, heart, placenta. BMP-3:(osteogenin)- osteoinductive , promotes chondrogenic phenotype It is located in the lung, kidney, brain, intestine. BMP-4: osteoinductive, embryogenesis, fracture repair, gastrulation & mesoderm formation (mouse). It is located in the apical ectodermal ridge, meninges, lung, kidney, liver. BMP-5:-osteoinductive, embryogenesis. It is located in lung, kidney, and liver. BMP-6:- not osteoinductive, embryogenesis, neuronal maturation, regulates chondrocyte differentiation. It is located in the lung, brain, kidney, uterus, muscle, skin. BMP-7:-(osteogenic protein-1) osteoinductive, embryogenesis, repair of long bones, alveolar bone, differentiation of osteoblasts,chondroblasts & adipocytes. It is located in the adrenal glands, bladder, brain, eye, heart, kidney, lung, placenta, spleen & skeletal muscles. BMP-8(osteogenic protein-2) osteoinductive, embrogenesis, spermatogenesis(mouse). BMP-8B(osteogenic protein-3)initiation & maintainance of spermatogenesis(mouse). BMP-9:-osteoinductive, stimulates hepatocyte proliferation, hepatocyte growth & function. BMP-12 & BMP-13:-inhibition of terminal differentiation of myoblasts.
Osteoconduction- it is a physical effect by which the matrix of the graft forms a scaffold that favors outside cells to penetrate the graft & form the bone. Bone conduction implies that a
surgical system has the ability to influence cells that are already programmed to become osteoblast to differentiate more efficiently and more expeditiously in bringing about bone formation. Therefore effective bone conduction takes place only in already predetermined or preprogrammed cells and not in pleuripotent cells. This is best seen in the apparent effect of the graft in leading bone repair from the surface of recipient site to produce an overgrowth of the bone. The bone repair in these cases is extremely limited and could not usually be used. All bone graft material possesses at least one of the three modes of action.
VASCULARIZED VERSUS NON VASCULARIZED GRAFTS At the cellular level one of the two outcomes is possible either the osteocytes in the graft can live or die. But the most important factor which is of concern is blood supply. In the non vascularized bone graft the bone fragments are laid across the defect. Only nutritional support available is via diffusion from the surrounding tissue bed. If the tissue bed is also compromised the graft is in further danger. The first event to occur is death of the osteocytes farthest from the nutritional supply and it is said that with the death these cells secrete a substance that promotes neovascularization. Osteoclast breakdown the necrotic bone and the vesssels begin to migrate into this region. These new vessels bring osteoprogenitor cells which initiate new bone formation along the path of a new vessel. This leads to an advancing front for new bone formation via the breakdown of donor bone (creeping substitution). It occurs more rapid in cancellous bone than cortical bone. Creeping substitution refers to the movement of new tissue through channels made by blood vessels invading a transplanted bone. This term was first used by Axhausen in 1907. To describe the dynamic healing and reconstructive process of bone transplantation. Axhausen determined that bone transplants undergo necrosis, and that necrotic bone is replaced by new bone via creeping substitution Two things to be considered: 1. As they are dependent upon nutritional support, they cannot be transplanted into small defects. 2. They depend on the condition of tissue bed at the recipient site. If the bed has a poor blood supply the osteocytes die too quickly and the graft does not survive long enough to generate a good osteoblastic response. VASCULARIZED BONE GRAFT This graft carries its own blood supply so bone healing occurs without bony resorption and creeping substitution. This leads to greater strength in the graft much sooner after the repair, which decreases the risk of fracture and enables quick repair of the defect. The graft is not dependent on the state of the surrounding tissue of the defect. So it can be transplanted into
more hostile environments. The increase blood supply also decreases the incidence of graft rejection. These free vascularized bone grafts can be transplanted into larger defects. Free vascularized grafts could also be transplanted as a composite graft with skin or muscle attachment and this would be useful for reconstruction involving both bony and soft tissue defects.
Nonvascularized Bone Graft Physiology Healing and incorporation involve the processes of inflammation, Revascularization, osteoconduction, osteoinduction, osteogenesis, and remodeling. An important aspect in (nonvascularized) bone graft healing is that a Substantial portion of the biological activity originates from the host. Most Viable osteocytes within the graft itself die quickly after transplantation, rendering the graft comparatively inert versus the host. Despite this substantial biological interactions occur between the graft and the host, and the graft has a fundamental role in determining its own fate. This biological interplay between graft and host establishes the final result. AXHAUSEN noted that bone grafts initially undergo partial necrosis, followed by an inflammatory stage, in which the existing bone is replaced with new bone by osteoblasts that are brought in through the invading blood vessels. Axhausen coined the term ‘‘creeping substitution’’ to describe the slow process of vessel invasion and bony replacement. More recently, These events have been referred to as osteoconduction, and both terms are used interchangeably. Hematoma formation around the bone graft is the first event that occurs after graft transplantation, usually caused by bleeding from the surgical disruption of host soft tissues and the recipient bony bed. During this early stage, only a small minority of the cells within the bone graft are still viable, located at the graft’s peripheral surface. These surface cells survive, owing to early revascularization or by plasmatic imbibition An inflammatory reaction around the graft ensues and lasts for 5–7 days. The inflammatory tissue becomes reorganized into a dense fibrovascular stroma around the graft, and the onset of vascular invasion occurs at 10–14 days bringing cells with osteogenic potential into the graft . These cells (osteoblasts and osteoclasts) begin to replace the graft, while the interstices of the old bone act as a scaffold for the deposition of new bone. As the deposition takes place through osteoblast activity, resorption of necrotic bone occurs through osteoclastic activity, and the bone graft is slowly penetrated by vascular tissue. These processes continue to occur until revascularization and deposition are complete.13 Important factors for graft survival: 1. Mechanical stress(onlay or inlay graft) 2. Microarchitecture of the graft material.(cancellous or cortical bone) 3. Revascularization
After transplantation, loss of this stress led to resorption and poor volume maintenance when compared to grafts from non-stress-bearing donor sites, such as the calvarium,that is the reason why iliac bone resorbs faster than the calvarial bone because it requires more of stress & without which it resorbs. Onlay bone grafts are subjected to more forces even from the soft tissue ,which causes it to resorb faster, when compared to inlay which has no force from soft tissue ,so less resorption. Iliac bone also had more of cancellous bone, which causes more of its resorption compaped to calvarial bone
Factors affecting revascularization at the recipient site: • Recipient bed environment • Graft position (inlay or onlay) • Graft microarchitecture( cancellous or cortical) • Presence of rigid fixation • Presence of periosteum. Cancellous bone graft revascularization & healing Occurs due to the large spaces between the trabeculae that permit unobstructed invasion of Vascular tissue. Autogeneic cancellous bone graft healing is dividedinto early and late phases .The early phase, occurring within the first 4 weeks, is characterized by inflammation,revascularization, and osteoinduction.Osteocyte precursors and osteocytesthat survive transplantation begin producing new bone. Bone marrow necrosis occurs, followed by invasion of host granulation tissue. Revascularization, which may begin as early as 2days after transplantation, rapidly progresses. Bone morphogenetic proteins and other growth factors induce migration of osteoblast precursor cells to the graft. These stem cells differentiate into osteoblasts and new bone forms by the end of the early phase. At 4 weeks, active bone resorption and new bone formation occurs throughout the graft's interior. The late phase is a continuum, proceeding through osteoconduction and eventual graft incorporation. Active graft resorption with new capillary ingrowth continues. Mature osteoblasts line the edges of the dead trabeculae as osteoid is deposited around the necrotic core. Remodeling proceeds and the graft is eventually replaced with live host bone. Skeletal strength is restored as the trabeculae gradually return to normal. The end of the late phase is characterized by replacement of the cancellous autograft with the host skeleton. This occurs approximately 6 months after transplantation and is usually complete by 1 year . Peripheral bone callus remodels and consolidates into new cortex16
Cortical bone graft revascularization & bone deposition: Vascular invasion of cortical bone graft is thought to be limited, due primarily to its dense lamellar structure that constrains vessels to invading the graft along the preexisting haversian and Volkmann’s canals. While cancellous bone grafts precede with initial Osteoblastic activity, revascularization of cortical bone grafts proceeds with
Initial Osteoclastic activity. Osteoclastic enlargement of the haversian and Volkmann’s canals must occur before vessels are able to penetrate the graft. The course of revascularization begins at the graft periphery. In cancellous grafts, vessel invasion may begin within a few hours post transplantation, and the process is completed in a few days. In cortical grafts, the earliest vessels enter the graft at 6 days, and the process of revascularization may take months, often resulting in incomplete graft revascularization (120,124). incompletely revascularized regions of necrotic graft may persist indefinitely, sealed off from the viable regions of the graft. The final appearance of a cortical bone graft is often a patchwork of necrotic bone, interspersed by areas of new bone. Healing of allograft & alloplastic material: Depending on the genetic differences between host and donor, three types of responses are observed: Acceptance (type 1), Partial Acceptance (type 2), or Rejection (type 3) In a Type 1 response, there is no apparent genetic disparity and the host accepts the allogeneic bone. Inflammation decreases, incorporation proceeds in a manner similar to autograft, and the allogeneic bone fully incorporates. Radiographic union, remodeling, and incorporation are identical to autografts. Histologic data regarding cumulative bone formation, porosity, and rate of resorption matches that for autografts A Type 2 response indicates a greater genetic difference between host and donor, allowing partial incorporation without provoking complete resorption . Despite this lack of histocompatibility, these allografts and alloimplants generally proceed to a satisfactory clinical result although at a slower rate .Under these conditions, ingrowing vessels become occluded due to a heightened inflammatory reaction . Vascular penetration and new bone formation are less extensive, leading to varying amounts of necrosis . A type 2 response may be characterized by a viable graft perimeter (several millimeters)with a necrotic central portion, limited creeping substitution, delayed/nonunion of the host allograft/implant interface, bone callus bridging of the allograft/implant segment, limited bony remodeling, increased frequency of fatigue fracture, loss of allograft/ implant size, decrease in mechanical strength, and tenuous soft tissue attachment to allograft/implant . A type 3 response occurs when significant genetic differences exist between host and donor . These allografts are rapidly and completely resorbed. This vigorous rejection occurs by continuous, unremitting peripheral resorption. There is no histologic or radiographic evidence of incorporation.16 Immunogenicity Sources of allogeneic bone immunogenicity have been studied in detail . The most critical aspect is whether the host recognizes the donor bone as foreign or self . Allogeneic bone, like other allogeneic tissues, induces an immune response, and follows the same immunologic rules as other grafting tissues . Its biologic fate is determined by the aggressiveness of the host's response .Allografts and alloimplants are attacked primarily by
the cellular limb of the immune system, rather than the humeral . The initial response involves a cellular influx of macrophages and neutrophils followed by T and B lymphocytes . T- and B-cells have antigen-specific receptors that recognize alloantigens. T-cells are further separated into CD4+ helper cells andCD8+ cytotoxicsuppressor cells.' which are involved in antigen recognition . A specific immune response is triggered when the T-cells recognize alloantigens as "nonself." This recognition activates Tcells to secrete cytokines that, in turn, stimulate osteoclastic activity. This results in excessive resorption and failure of incorporation16
Rigid fixation in bone grafts: Rigid fixation improves onlay graft survival when compared to graft without fixation or with wiring. The reasons believed responsible for improved survival with rigid fixation included increased primary bone healing and more rapid revascularization by virtue of graft immobility. rigid fixation of onlay bone grafts is thought to prevent resorption, loss of volume, and loss of projection periosteum: Preserving the periosteum on a bone graft during transplantation has been Shown to improve graft survival in the craniofacial region .the importance for early revascularization of the graft material was thought to be increased due to presence of periosteum. Three layers of the periosteum were described—an outer vascular network, with communications to the internal portions of the bone, a middle layer of osteogenic reserve cells, and the inner cambial layer. They proposed that bone graft revascularization was enhanced by means of the outer periosteal layer and its direct connections to the interior of the graft
Bone graft recipient site: Factors affecting graft survival at the recipient site1. Avascular bed 2. Irradiated area 3. Infection 4. Tissue scarring. A bonegraft placed in a defect normally occupied by bone is known as orthotopically transplanted; a graft placed in a site normally not occupied by bone is heterotopically transplanted. Whitaker introduced the concept of the biological boundary which is an extension of Wolff’s law and Moss’ functional matrix
theory. Moss’ theory states that as the craniofacial skeleton grows, its soft-tissue environment may have a significant role in shaping its morphology. He believed that the body has predetermined physical boundaries that have a major role in bone graft survival. He hypothesized that onlay grafts, by virtue of their position, generally disturbed these boundaries and would elicit a response from the body’s natural tendency to maintain the boundary by resorbing the graft. Whitaker noted that inlay bone grafts did not disturb biological boundaries, while basal bone advancements established new ones. But the mechanism for this theory was not proved. Role of growth factors in bone healing:5 Growth factors that can help in bone healing are Platelet derived growth factor Transforming growth factor Insulin deriver growth factor Fibroblast derived growth factor Platelet derived growth factorIt is released from platelet alpha granule, macrophages or monocytes,endothelial cells & as well as from osteoblast cells. The specific activities of PDGF includes mitogenesis(increase in the cell population of healing cells), angiogenesis(endothelial mitosis into functional capillaries), & macrophage activation(debridement of the wound site &second phase source of growth factors for continued repair & bone regeneration). Transforming growth factor: It is present in abundance in the bone matrix, with bone representing the major site for the storage of the TGF –beta in the body.the primary effect of TGF –beta is on the bone formation, particularly in the early phase of the osteoblast development.it stimulates matrix protein synthesis by human osteoblasts.the most important function of TGF beta 1 & TGF beta 2seems to be chemotaxis &mitogenesis of osteoblast precursors, & they also have the ability to stimulate osteoblast deposition of the collagen matrix of wound healing & of the bone. In addition they also inhibit osteoclast formation & also bone resorption, thus favoring bone formation than resorption. It directly inhibits both proliferation & differentiation of the osteoclast precursor cells & inhibits the function of the mature osteoclasts with reduction in reactive e oxygen radicals. Insulin like growth factor: It consists of two proteins-IGF 1(somatomedin c) & IGF2 (skeletal growth factor) which are secreted by osteoblasts,both the factors induce preosteoblast proliferation & differentiation, osteoblast collagen synthesis,& inhibit collagen breakdown.IGF bound to the protein in the matrix may be released in the active form following osteoclastic resoeption.locaaly produced IGF1secreted by fibroblast& cells in the bone & cartilage is controlled by variety of factors. Corticosteroids reduces IGF1 synthesis.
Fibroblast growth factor: The matrix proteins, acidic FGF & basic FGFare produced by osteoblast,bind heparin & are angiogenic factors. But there effects on bone invivo are not known.in vitro they cause proliferation of osteoblast progenitor cells but inhibit differentiation, & do not appear to effect the osteoclast.FGFs stimute new bone formation.
SKIN GRAFTS A skin graft is the removal and transplantation of healthy skin from one area of the body (source area or donor site) to another area (recipient area) where the skin has been damaged. The source sites most commonly used for skin grafts are the inner thigh, leg, buttocks, upper arm, and forearm. There are three main types of skin graft techniques: 1. Split-thickness graft—this is the removal of the top layer of skin (epidermis) and part of the middle layer (dermis). This type of graft allows the source site to heal more quickly. However, the graft is also more fragile, and may be abnormally pigmented. This is the most common skin graft used. 2. Full-thickness graft—this is the removal and transfer of an entire area of skin. Although this type of graft requires stitches to heal the source site, the final outcome is usually better. Full-thickness grafts are usually recommended for areas where cosmetic appearance is important, such as the face. However, full-thickness grafts can only be placed on areas of the body that have significant vascularization (blood vessels), so its use is somewhat limited. 3. Composite grafts—this is the combination of skin and fat; skin and cartilage; or dermis and fat, which are used in areas that require three-dimensionality, such as the nose. The use of one's own skin as the source area is called an autograft. However, if there is not enough skin on the body to provide graft coverage for another area on the same body, then skin may be harvested from outside sources. These alternate sources are only meant for temporary use until your own skin grows back. Three common options: 1. Allograft—Skin taken from another human source, such as a cadaver. 2. Xenograft—Skin taken from an animal source. 3. Synthetic tissue Indications of the skin graft: 1. Treatment of burn 2. Chronic ulcers (such as venous pressure, traumatic &radiation induced ulcers) 3. Skin defects caused by removal of skin cancer.
4. Damaged areas are too large to be closed by stitching.
Full-thickness skin grafts Full-thickness skin grafts are ideal for visible areas of the face that are inaccessible to local flaps or when local flaps are not indicated. Full-thickness grafts retain more of the characteristics of normal skin, including color, texture, and thickness, when compared with split-thickness grafts. It contains the entire dermis, so primary contraction is greater than the contraction seen with the split thickness graft. Secondary contraction however, which occurs as graft heals is minimal. This is important on the face as well as on the hands and over mobile joint surfaces. Full-thickness grafts in children are more likely to grow with the individual. However, full-thickness skin grafts are limited to relatively small, uncontaminated, well-vascularized wounds and thus do not have as wide a range of application as split-thickness grafts. Donor sites must be closed primarily or, more rarely, resurfaced with a split-thickness graft from another site. Split-thickness skin grafts Split-thickness skin grafts can tolerate less ideal conditions for survival and have a much broader range of application. They are used to resurface large wounds, line cavities, resurface mucosal deficits, close donor sites of flaps, and resurface muscle flaps. They also are used to achieve temporary closure of wounds created by the removal of lesions that require pathologic examination prior to definitive reconstruction. Split-thickness skin graft donor sites heal spontaneously with cells supplied by the remaining epidermal appendages, and these donor sites may be reharvested once healing is complete. Split-thickness grafts also have significant disadvantages that must be considered. Splitthickness grafts are more fragile, especially when placed over areas with little underlying soft tissue bulk for support, and usually cannot withstand subsequent radiation therapy. They contract more during healing, do not grow with the individual, and tend to be smoother and shinier than normal skin because of the absence of skin appendages in the graft. They tend to be abnormally pigmented, either pale or white, or alternatively, hyperpigmented, particularly in darker-skinned individuals. Their lack of thickness, abnormally smooth texture, lack of hair growth, and abnormal pigmentation make these grafts more functional than cosmetic. When used to resurface large burns of the face, split-thickness grafts may produce an undesirable masklike appearance. Finally, the wound created at the donor site from which the graft is harvested is often more painful than the recipient site to which the graft is applied Donor sitesSplit thickness graft: anterior & lateral aspect of thigh, buttocks Full thickness graft: Retroauricular & pre auricular region Mucosal graft: cheek & palate.
OPERATIVE TECHNIQUE: Wound preparationOptimal skin graft success is influenced by several factors that should be addressed with thorough recipient site preparation prior to grafting, A well vascularized recipient bed is of utmost importance in survival of the skin graft. With some exceptions, skin grafts rarely take when placed on bone, cartilage, or tendon without the presence of periosteum, perichondrium, or paratenon. The procedure for harvesting and grafting skin varies somewhat according to the size, the extent of grafting needed to cover the wounded site, and the type of cosmetic reconstruction required,extensive facial wounds that involve the nose, lips, or eyes may require skin grafting and a series of plastic surgery interventions to reconstruct normal function and appearance. The size of the wound (recipient site) is measured, and a template or pattern of the area to be covered is made. Then a donor site is selected Donor site selection: Donor site selection is based on multiple factors, including skin color, texture, dermal thickness, vascularity, and anticipated donor site morbidity. Full-thickness grafts provide a suitable color match for defects of the face. The pattern for the graft should be enlarged by 3-5% to compensate for the immediate primary contraction that occurs because of the elastin fibers contained in the graft dermis, and the donor site then may be infiltrated with local anesthetic with or without epinephrine. The full-thickness skin graft is excised with a scalpel at the subdermal level of the superficial fat. The residual adipose tissue is subsequently removed with sharp curved scissors prior to placement in the recipient bed, as the fat is poorly vascularized and prevents direct contact between the graft dermis and the wound bed. Donor site defects resulting from full-thickness grafts must be closed primarily or, rarely, with a with a split-thickness graft, since no epithelial structures for regeneration remain. Split-thickness skin grafts are commonly harvested from the thigh, buttocks, abdominal wall, or scalp. The method of harvesting the split-thickness skin graft depends primarily on the size and thickness needed for coverage of the defect. Smaller grafts can be taken using a "pinch graft" technique using a scalpel blade; slightly larger freehand grafts can be obtained with a Weck blade. Powered dermatomes are most commonly used to harvest split-thickness skin grafts, as they have a rapidly oscillating blade that can be set at an adjustable depth and width for the graft. Lidocaine with epinephrine may be injected subcutaneously at the donor site prior to harvesting, which aids in reducing blood loss and providing greater tissue turgor to facilitate graft harvest. The skin and dermatome can be lubricated with mineral oil or sterile saline to enable easy gliding of the dermatome over the skin. Epinephrine-soaked gauze may be applied to the donor site immediately following harvest to achieve hemostasis.
Meticulous hemostasis of the recipient bed is also key in preventing hematoma formation between the graft and wound bed. Hemostasis is typically achieved through use of epinephrine and saline-soaked gauze, particularly in freshly excised burns, in combination with precise electrocoagulation. Infection also compromises graft survival; therefore, careful preparation of the recipient bed is necessary. A recipient bed that contains a bacteria concentration greater than 105 organisms per gram of tissue will not support a skin graft. Graft survival &healing: The ultimate success of a skin graft, or its “take,” depends on nutrient uptake and vascular ingrowth from the recipient bed, which occurs in 3 phases. The first phase takes place during the first 24-48 hours. The graft is initially bound to the recipient site through formation of a fibrin layer and undergoes diffusion of nutrients by capillary action from the recipient bed by a process called plasmatic imbibition. The second phase involves the process of inosculation, in which the donor and recipient end capillaries are aligned and establish a vascular network. Revascularization of the graft is accomplished through those capillaries as well as by ingrowth of new vessels through neovascularization in the third and final phase, which is generally complete within 4-7 days. Reinnervation of skin grafts begins approximately 2-4 weeks after grafting and occurs by ingrowth of nerve fibers from the recipient bed and surrounding tissue. Sensory return is greater in full-thickness grafts because they contain a higher content of neurilemmal sheaths. Similarly, hair follicles may be transferred with a full-thickness graft, which allows the graft to demonstrate the hair growth of the donor site. Split-thickness grafts are ultimately hairless. The amount of dermis present in the graft determines the degree of contraction immediately after harvest from the donor site and following placement and revascularization in the recipient bed. Freshly harvested grafts undergo immediate recoil as a result of elastin in the dermis in a phenomenon termed primary contraction. Therefore, a full-thickness skin graft contracts more initially following harvest as it contains the dermis in its entirety. Secondary contraction is likely due to myofibroblast activity and is defined as the contraction of a healed graft. The degree of secondary contraction is inversely related to the thickness of the skin graft. Accordingly, split-thickness skin grafts contract more than full-thickness grafts following placement in the recipient bed. For that reason, full-thickness grafts are preferably used in areas that would be significantly impacted functionally or aesthetically by scarring or scar contracture, such as the head and neck, hands, genitals, or breast. Factors influencing graft survival1. Secure fixation, which permits inosculation of the delicate neovasculature 2. Dressing on the graft, to prevent dessication &protect the graft from the shearing forces that might disrupt neovascularisation. 3. Healthy recipient bed. 4. Certain conditions like chronic venous ulcers, irradiated wound beds; contaminated wound site will impair proper neovascularisation.
Graft application: One of the more common and expeditious methods of affixing a graft to the recipient site is with surgical staples, particularly to large recipient areas. In children or in sensitive areas of adults, sewing the graft into place using absorbable sutures may be more prudent. In selection of the final dressing, the prevention of shearing forces, seroma, or hematoma formation between the graft and recipient site is essential. Meshing or "piecrusting" the graft minimizes the risk of graft loss secondary to hematoma or seroma formation. The prevention of shearing forces that may disrupt graft take is accomplished by properly securing the graft to the site, which typically involves use of a bolster dressing or a negative pressure dressing. A bolster dressing typically is composed of moistened cotton balls wrapped in a petroleum gauze such as Xeroform , which is secured by placing sutures radially around the wound and tying them to each other over the bolster dressing to provide constant, light pressure to the graft. For skin grafts to the upper or lower extremity, an Unna boot dressing may be applied, as it performs the necessary action of maintaining graft integrity but also allows for earlymobilization. Alternatively, negative pressure dressings prevent shearing forces and reduce fluid collection between the graft and recipient bed, thereby facilitating plasmatic imbibition and revascularization, leading to a significant improvement in overall split-thickness skin graft survival.A nonadherent material such as Adaptic must be placed as an interface between the skin graft and the sponge to prevent disruption of the graft when removing the dressing. The initial dressing should be left in place for approximately 5 days (3-7 days) unless pain, odor, discharge, or other sign of a complication develops. A hematoma or seroma encountered at the dressing change should be addressed by making a small incision directly over the collection and expressing the underlying contents in order to minimize disruption of graft adherence.
References: 1. Alireza Ghassemi, MD, DMD, PhD,Mehrangiz Ghassemi, DMD, Dieter Riediger, MD, DMD, PhD, Ralf-Dieter Hilgers, DSc, PhD,andMarcus Gerressen, MD, DMD, PhD,Comparison of Donor-Site Engraftment After Harvesting Vascularized and Nonvascularized Iliac Bone Grafts, J Oral Maxillofac Surg 67:1589-1594, 2009 2. Benjamin C Wood, MD, Skin, Grafts. eMedicine Specialties > Plastic Surgery
3. Bishara S. Atiyeh, MD, FACS , Christian A. Al-Amm, MD , Ali A. Nasser, MD , Improved Healing of Split Thickness Skin Graft Donor Sites, The Journal of Applied Research vol 1 -2001
4. Bone Grafting: Bone Graft Incorporation, Medscape CME, Neurosurg Focus. 2003;14(2) © 2003 American Association of Neurological Surgeons 5. Bone Healing and Spinal Fusion: Role of Growth Factors in Bone Metabolism Medscape CME, Neurosurg Focus. 2002;13(6) © 2002 American Association of Neurological Surgeons 6. Constantinos E. Nikolopoulos, Andreas F. Mavrogenis, Glykeria Petrochei, A three-dimensional medical imaging model for quantitative assessment of proximal tibia vs. anterior iliac crest cancellous bone. The Knee 15 (2008) 233–237 7. Christopher G. Finkemeier, MD Current Concepts Review, Bone-Grafting and Bone -graft Substitute, THE JOURNAL OF BONE & JOINT SURGERY VOLUME 84-A · NUMBER 3 · MARCH 2002 8. David H. Kim, MD,*, Richard Rhim, MD, Ling Li, MPH, Julia Martha, BA,Bryan Swaim, BA, Robert J. Banco, MD, Louis G. Jenis, MD, Scott G. Tromanhauser, MD,Prospective study of iliac crest bone graft harvest site pain and morbidity.The Spine Journal - (2009) 9. Donald J Grande, MD, Skin Grafting, eMedicine Specialties > Dermatology
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12. MATS HALLMAN & ANDREAS THOR.Bone substitutes and growth factors as an alternative ⁄ Complement to autogenous bone for grafting in implant dentistry, Periodontology 2000, Vol. 47, 2008, 172–192 13. Robert E. Marx, DDS, Bone and Bone Graft Healing, Oral Maxillofacial Surg Clin N Am 19 (2007) 455–466 14. Seoung-Ho Lee, DDS, PhD, Byung-Ho Choi, DDS, PhD, Jingxu Li, DDS,Seung-Mi Jeong, DDS, PhD,Han-Sung Kim, PhD, and Chang-Yong K, Comparison of corticocancellous block and particulate bone grafts in maxillary sinus floor augmentation for bone healing around dental implants(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2007;104:324-8) 15. Skin grafting, Encyclopedia of Surgery: A Guide for Patients and Caregivers
16. Thomas J. Cypher, DPM, Jordan P. Grossman, DPM.Biological Principles of Bone Graft Healing (The Journal of Foot and Ankle Surgery 35(5):413-417,1996) 17. W. L. Adeyemo, T. Reuther, W. Bloch, Y. Korkmaz, J. H. Fischer, J. E. Zo¨ ller, A. C.Kuebler: Healing of onlay mandibular bone grafts covered with collagen membrane or bovine bone substitutes: A microscopical and immunohistochemical study in the sheep. Int. J. Oral Maxillofac. Surg. 2008; 37: 651–659.
18. WILLIS C. CAMPBELL, THE AUTOGENOUS BONE GRAFT, J Bone Joint Surg Am. 1939;21:694-700