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The flexor retinaculum and carpal tunnel (Fig. 38.1)
Flexion/extension movements occurring at the wrist are accompanied
The carpal tunnel is formed by the carpal bones and the overlying flexor
by movements at the midcarpal joint. Of a total of 80° of wrist flexion
retinaculum. It is through this tunnel that most, but not all, of the fore-
the majority occurs at the midcarpal joint whereas in extension a corres-
arm tendons and the median nerve pass. The flexor retinaculum is Wrist movements
attached to four bony pointsathe pisiform, the hook of the hamate, the ponding increased amount occurs at the wrist joint.
scaphoid and the trapezium. The muscles acting on the wrist joint include:
The carpal tunnel is narrow and no arteries or veins are transmitted • Flexion: all long muscles crossing the joint anteriorly.
through it for risk of potential compression. The median nerve is how- • Extension: all long muscles crossing the joint posteriorly.
ever at risk of compression when the tunnel is narrowed for any reason. • Abduction: flexor carpi radialis and extensors carpi radialis longus
This is the carpal tunnel syndrome and results in signs of median nerve and brevis.
motor and sensory impairment. Note that the ulnar nerve and artery • Adduction: flexor carpi ulnaris and extensor carpi ulnaris.
pass over the retinaculum and are thus outside the carpal tunnel.
The joints of the hand (Fig. 38.3)
The synovial sheaths of the flexor tendons (Fig. 38.2) • Intercarpal joints: the midcarpal joint, located between the prox-
The diagram illustrates the arrangement of the synovial sheaths that imal and distal rows of carpal bones, is the most important of these as it
surround the flexor tendons. It can be seen that flexor pollicis longus participates in wrist movement (see above).
has its own sheath and flexor digitorum superficialis and profundus • Carpometacarpal joints: the most important of these is the 1st car-
share one which ends in the palm (except that for the little finger). pometacarpal (thumb) joint. This is a saddle-shaped joint between the
trapezium and the 1st metacarpal. It is a condyloid synovial joint which
The wrist (radiocarpal) joint (Fig. 38.3) is separate from others in the hand, permitting a range of movement
• Type: the wrist is a condyloid synovial joint. The distal radius and a similar to that of a ball and socket joint. The most important movement
triangular disc of fibrocartilage covering the distal ulna form the prox- of the thumb is opposition in which the thumb is opposed to the fingers
imal articulating surface. This disc is attached to the edge of the ulnar as in holding a pen.
notch of the radius and to the base of the styloid process of the ulna and • Metacarpophalangeal joints: are synovial condyloid joints.
separates the wrist joint from the inferior radio-ulnar joint. The distal • Interphalangeal joints: are synovial hinge joints.
articulating surface is formed by the scaphoid and lunate bones with the
triquetral participating in adduction. The anatomical snuffbox
• Capsule: a defined capsule surrounds the joint. It is thickened on Figure 38.4 illustrates the boundaries and contents of the anatomical
either side by the radial and ulnar collateral ligaments. snuffbox.
• Nerve supply: from the anterior interosseous (median) and posterior
interosseous (radial) nerves.

The carpal tunnel and joints of the wrist and hand 87