See also Joints of the hand

The wrist is variously defined as:

  1. The carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand
  2. The wrist joint or radiocarpal joint, the joint between the radius and the carpus
  3. The anatomical region surrounding the carpus including the distal parts of the bones of the forearm and the proximal parts of the metacarpus or five metacarpal bones and the series of joints between these bones, thus referred to as wrist joints. This region also includes the carpal tunnel, the anatomical snuff box, the flexor retinaculum, and the extensor retinaculum.

As a consequence of these various definitions, fractures to the carpal bones are referred to as carpal fractures, while fractures such as distal radius fracture are considered fractures to the wrist.

Articulations

The radiocarpal, intercarpal, midcarpal, carpometacarpal, and intermetacarpal joints often intercommunicate through a common synovial cavity.

Extrinsic hand

The distal radioulnar joint is a pivot joint located between the bones of the forearm, the radius and ulna. Formed by the head of ulna and the ulnar notch of the radius, this joint is separated from the radiocarpal joint by an articular disk lying between the radius and the styloid process of the ulna. The capsule of the joint is lax and extends from the inferior sacciform recess to the ulnar shaft. Together with the proximal radioulnar joint, the distal radioulnar joint permits pronation and supination.

The radiocarpal joint, or wrist joint, is an ellipsoid joint formed by the radius and the articular disc proximally and the proximal row of carpal bones distally. The carpal bones on the ulnar side only make intermittent contact with the proximal side — the triquetrum makes contact only during ulnar abduction. The capsule, lax and un-branched, is thin on the dorsal side and can contain synovial folds. The capsule is continuous with the midcarpal joint and strengthened by numerous ligaments, including the palmar and dorsal radiocarpal ligaments, and the ulnar and radial collateral ligaments.

The radiocarpal joint is formed by the lower end of the radius and under-surface of the articular disk above and the scaphoid, lunate, and triquetral bones below. The articular surface of the radius and the under-surface of the articular disk form together a transversely elliptical concave surface, the receiving cavity. The superior articular surfaces of the scaphoid, lunate, and triquetrum form a smooth convex surface, the condyle, which is received into the concavity.


Posterior and anterior aspects of the wrist

Intrinsic hand

In the hand proper, a total of 13 bones form part of the wrist: eight carpal bones — scaphoid, lunate, triquetral, pisiform, trapezium, trapezoid, capitate, and hamate — and five metacarpal bones — the first, second, third, fourth, and fifth metacarpal bones.

The midcarpal joint is the S-shaped joint space separating the proximal and distal rows of carpal bones. The intercarpal joints, between the bones of each row, are strengthened by the radiate carpal and pisohamate ligaments and the palmar, interosseous, and dorsal intercarpal ligaments. Some degree of mobility is possible between the bones of the proximal row, while the bones of the distal row are connected to each others and to the metacarpal bones — at the carpometacarpal joints — by strong ligaments — the pisometacarpal and palmar and dorsal carpometacarpal ligament — that makes a functional entity of these bones. Additionally, the joints between the bases of the metacarpal bones — the intermetacarpal articulations — are strengthened by dorsal, interosseous, and palmar intermetacarpal ligaments.

Movements and Muscles

The extrinsic hand muscles are located in the forearm where their bellies form the proximal, fleshy roundness. When contracted, most of the tendons of these muscles are prevented from standing up like taut bowstrings around the wrist by passing under the flexor retinaculum on the palmar side and the extensor retinaculum on the dorsal side. On the palmar side, the carpal bones form the carpal tunnel through which some of the flexor tendons pass in tendon sheaths that enable them to slide back and forth through the narrow passageway.

Starting from the mid-position of the hand, the movements permitted in the wrist proper are (muscles in order of importance):

  • Marginal movements: Radial deviation (abduction, movement towards the thumb) and ulnar deviation (adduction, movement towards the little finger). These movements take place about a dorsopalmar axis (back to front) at the radiocarpal and midcarpal joints passing through the capitate bone.
    • Radial abduction: Extensor carpi radialis longus, abductor pollicis longus, extensor pollicis longus, flexor carpi radialis, flexor pollicis longus
    • Ulnar abduction: Extensor carpi ulnaris, flexor carpi ulnaris, extensor digitorum, extensor digiti minimi
  • Movements in the plane of the hand: Flexion (palmar flexion, tilting towards the palm) and extension (dorsiflexion, tilting towards the back of the hand). These movements take place through a transverse axis passing through the capitate bone. Palmar flexion is the most powerful of these movements because the flexors, especially the finger flexors, are considerably stronger than the extensors.
    • Extension: Extensor digitorum, extensor carpi radialis longus, extensor carpi radialis brevis, extensor indicis, extensor pollicis longus, extensor digiti minimi
    • Palmar flexion: Flexor digitorum superficialis, flexor digitorum profundus, flexor carpi ulnaris, flexor pollicis longus, flexor carpi radialis, abductor pollicis longus
  • Intermediate or combined movements

Movements at the wrist, however, cannot be properly described without including movements in the distal radioulnar joint, in which the rotary actions of supination and pronation occur. This joint, therefore, is therefore normally regarded as part of the wrist.

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Wrist3.jpg (image/jpeg)


Wrist4.jpg (image/jpeg)