Wrist

The wrist is the part of the upper limb between the forearm and the palm.

Bony framework:

A.      The bony framework consists of a wrist joint (radiocarpal joint).

• The proximal surface is concave and includes the distal end of the radius and a fibrocartilaginous disc at the distal end of the ulna. The ulna does NOT contribute to the wrist joint due to the disc.

• The distal surface is convex and comprises the proximal row of carpal bones: scaphoid, lunate, and triquetrum.

• The wrist joint is an ellipsoid or condyloid synovial joint covered by a fibrous capsule and contains a synovial membrane.

• The condyloid nature allows movements in two directions: (1)-anteroposterior/palmodorsal for flexion and extension, and (2)-side-to-side for adduction (ulnar deviation) and abduction (radial deviation) at the wrist.

B.      There are eight carpal bones, organized in two rows:

• Proximal row (medial to lateral): scaphoid, lunate, triquetrum, and pisiform.

• Distal row (medial to lateral): trapezium, trapezoid, capitate, and hamate.

• Intercarpal synovial joints exist between the carpal bones.

• The carpal bones in the distal row articulate with the metacarpals, forming carpometacarpal synovial joints.

Ligaments:

The ligaments supporting the wrist joint include:

• Dorsal and palmar radiocarpal ligaments passing from the radius to both rows of carpal bones, dorsally and ventrally.

• Radial collateral ligament passing from the styloid process of the radius to the scaphoid and trapezium, preventing excessive ulnar deviation.

• Ulnar collateral ligament passing from ulnar styloid processes to the triquetrum and pisiform, preventing excessive radial deviation.

Muscles and long tendons:

• Long tendons from the forearm cross over the wrist joint to reach the palm and dorsum of the hand. These tendons are held in place by retinacular thickenings of the deep fascia: the flexor retinaculum on the palmar side and the extensor retinaculum on the extensor side of the wrist.

• The flexor retinaculum forms the roof of the carpal tunnel, where several tendons pass, including four long tendons of the flexor digitorum superficialis and flexor digitorum profundus each, as well as a single tendon of the flexor pollicis longus. The median nerve also passes through this tunnel, becoming compressed in carpal tunnel syndrome, often seen in individuals with repetitive hand movements involving flexion and extension.

• The anatomical snuff box is an important region on the dorsum of the wrist, bounded laterally by the long tendons of the abductor pollicis longus and extensor pollicis brevis muscles, and medially by the extensor pollicis longus. The floor of the snuff box is formed by the scaphoid bone, which commonly fractures in falls that involve outstretched hands, leading to severe wrist pain.