wrist joint.pdf

The Wrist Joint The wrist joint (also known as the radiocarpal joint) is a synovial joint in the upper limb, marking the area of transition between the forearm and the hand. In this article, we shall look at the structures of the wrist joint, the movements of  the joint, and the relevant clinical syndromes.

Structures of the Wrist Joint  Articulating Surfaces Surfaces The wrist joint is formed by:  – The proximal row of the t he carpal bones (except the pisiform). The distal end of the radius, and the articular disk (see below).  – it articulates with the radius, just proximal to the wrist joint, at the distal radioulnar joint. It is prevented from articulating  with the carpal bones by a fibrocartilaginous ligament, called the articular disk,  which lies over the superior surface of the ulna. Together, the carpal bones form a

 surface, which articulates with the

 surface of the radius and articular disk.

Fig 1.0 – Articular surfaces of the wrist joint.

Joint Capsule Like any synovial joint, the capsule is dual layered. The fibrous outer layer attaches to the radius, ulna and the proximal row of the carpal bones. The internal layer is comprised of a synovial membrane, secreting synovial fluid which lubricates the  joint.

Ligaments There are four ligaments of note in the wrist joint, one for each side of the joint – It is found on the palmar (anterior) side of the hand. It passes from the radius to both rows of carpal bones. Its function, apart from increasing stability, is to ensure that the hand follows the forearm during supination.  – It is found on the dorsum (posterior) side of the hand. It passes from the radius to both rows of carpal bones. It contributes to the stability of the wrist, but also ensures that the hand follows the forearm during pronation. – Runs from the ulnar styloid process to the triquetrum and pisiform. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

 – Runs from the radial styloid process to the scaphoid and trapezium. Works in union with the other collateral ligament to prevent excessive lateral joint displacement.

Fig 1.1 – Palmar view of the ligaments of the wrist joint.

Neurovascular Supply  The wrist joint receives blood from branches of the dorsal and palmar carpal arches, which are derived from the

 and

 arteries (for more information,

see Blood Supply to the Upper Limb) Innervation to the wrist is delivered by branches of three nerves:  – Anterior interosseous branch.  – Posterior interosseous branch.  – deep and dorsal branches.

Movements of the Wrist Joint The wrist is an

 type synovial joint, allowing for movement along two axes.

This means that flexion, extension, adduction and abduction can all occur at the  wrist joint.  All the movements of the wrist are performed by the muscles of the forearm.

–  Produced mainly by the flexor carpi ulnaris, flexor carpi radialis, with assistance from the flexor digitorum superficialis.

– Produced mainly by the extensor carpi radialis longus and brevis, and extensor carpi ulnaris, with assistance from the extensor digitorum.

– Produced by the extensor carpi ulnaris and flexor carpi ulnaris – Produced by the abductor pollicis longus, flexor carpi radialis, extensor carpi radialis longus and brevis. By Gilo1969 (Own work) [CC-BY-SA-3.0], via Wikimedia Commons

Fig 1.2 – Radiograph of a scaphoid fracture. In the event of a blow to the wrist (e.g falling on an outstretched hand), the scaphoid takes most of the force. A fractured scaphoid is more common in the  younger population.

The scaphoid has a unique blood supply, which runs of the scaphoid can disrupt the blood supply to the

. A fracture  portion – this is an

emergency. Failure to revascularise the scaphoid can lead to avascular necrosis, and future arthritis for the patient. The main clinical sign of a scaphoid fracture is tenderness in the anatomical snuffbox.

 Anterior Dislocation of the Lunate This can occur by falling on a

 wrist. The lunate is forced anteriorly, and

compresses the carpal tunnel, causing the symptoms of carpal tunnel syndrome. This manifests clinically as paraesthesia in the sensory distribution of the median nerve and weakness of thenar muscles. The lunate can also undergo avascular necrosis, so immediate clinical attention to the fracture is needed.

Colles’ Fracture The Colles’ fracture is the

 fracture involving the wrist, caused by 

falling onto an outstretched hand. The radius fractures, with the distal fragment being displaced

. The

ulnar styloid process can also be damaged, and is avulsed in the majority of cases. This clinical condition produces what is known as the ‘dinner fork deformity’.

The Carpal Tunnel

The carpal tunnel is a narrow passageway found on the anterior portion of the  wrist. It serves as the entrance to the palm for several tendons and the median nerve. In this article, we will look at the borders and contents of the carpal tunnel and its clinical significance.

Borders The carpal tunnel is formed by two layers: a

 and a

. The deep carpal arch forms a concave surface, which is converted into a tunnel by the overlying flexor retinaculum.

Carpal Arch Concave on the palmar side, forming the base and sides of the carpal tunnel. Formed laterally by the scaphoid and trapezium tubercles Formed medially by the hook of the hamate and the pisiform

Flexor Retinaculum Thick connective tissue which forms the roof of the carpal tunnel. Turns the carpal arch into the carpal tunnel by bridging the space between the medial and lateral parts of the arch. Originates on the lateral side and inserts on the medial side of the carpal arch. To find where the carpal tunnel begins on yourself, locate your distal wrist crease,  which aligns with the entrance of the carpal tunnel.

Fig 1 – Transverse section of the carpal tunnel.

Contents The carpal tunnel contains a total of and the

, surrounded by synovial sheaths,

. The palmar cutaneous branch of the median nerve is given

off prior to the carpal tunnel, travelling superficially to the flexor retinaculum.

Tendons The tendon of  Four tendons of Four tendons of The 8 tendons of the flexor digitorum profundus and flexor digitorum superficialis are surrounded by a single synovial sheath. The tendon of flexor pollicis longus is surrounded by its own synovial sheath. These sheaths allow free movement of the tendons. Sometimes you may hear that the carpal tunnel contains another tendon, the flexor carpi radialis tendon, but this is located within the flexor retinaculum and not  within the carpal tunnel itself!

Fig 2 – The muscular and tendinous components of the carpal tunnel

Median Nerve Once it passes through the carpal tunnel, the median nerve divides into 2 branches: the

 and

nerves.

The palmar digital nerves give sensory innervation to the  of the to the

 and

 They also provide motor innervation . The recurrent branch supplies the

 muscle

group. For a more detailed look at the median nerve, take a look here. Compression of the median nerve within the carpal tunnel can cause . It is the most common mononeuropathy and can be caused by  thickened ligaments and tendon sheaths. Its aetiology is, however, most often idiopathic. If left untreated, CTS can cause weakness and atrophy of the muscles.

Clinical features include numbness, tingling and pain in the . The pain will usually radiate to the forearm. Symptoms are often associated with waking the patient from their sleep and being worse in the mornings. Tests for CTS can be performed during physical examination: Tapping the nerve in the carpal tunnel to elicit pain in median nerve distribution (

)

Holding the wrist in flexion for 60 seconds to elicit numbness/pain in median nerve distribution ( Treatment involves the use of a

) , holding the wrist in dorsiflexion overnight

to relieve symptoms. If this is unsuccessful,

 injections into the

carpal tunnel can be used. In severe case, surgical decompression of the carpal tunnel may be required.

Fig 3 – Thenar muscle wasting, secondary to carpal tunnel syndrome.