The wrist-joint (Class. - Diarthrosis. Subdivision. - Condylarthrosis.) is formed by the union of the radius and articular disc above, articulating -with the navicular, lunate, and triquetral bones below; the ulna being excluded by the intervention of the articular disc. The radius and disc together present a smooth surface, slightly concave both from before backward, and from side to side, whilst the three bones of the carpus present a smooth, convex surface, made uniformly even by the interosseous ligaments which bind them together.
The capsule of the wrist-joint has been usually described as four separate ligaments, and it will be convenient for the sake of a complete description to follow this method; but it must be understood that these four portions are continuous around the joint, extending from styloid process to styloid process on both its aspects. The four portions are:
- Volar radio-carpal.
- Dorsal radio-carpal.
- Ulnar collateral.
- Radial collateral.
The volar (or anterior) radio-carpal is a thick strong ligament, attached superiorly to the radius immediately above the anterior margin of the terminal articular facet, to the curved ridge at the root of the styloid process of the radius, and to the anterior margin of the articular disc, blending with some fibers of the capsule of the inferior radio-ulnar joint. It passes downward and in a medial direction to be attached to both rows of carpal bones, especially the second, and to the volar intercarpal ligament.
The strongest and most oblique fibers arise from the root of the styloid process of the radius, and pass obliquely over the navicular, with which only a few fibers are connected, to be inserted into the lunate, capitate, and triquetral bones. Another set, less oblique, passes from the margin of the facet for the lunate to be attached to the adjacent parts of the capitate, hamate, and triquetral bones. Between the two sets of fibers, small vessels pass into the joint.
The dorsal (or posterior) radio-carpal ligament is attached above to the dorsal edge of the lower end of the radius, the back of the styloid process, and the posterior margin of the fibro-cartilage. It passes downward and in a medial direction to be connected with the first row of the carpal bones, chiefly with the lunate and triquetral, and the dorsal intercarpal ligament. This ligament is thin and membranous.
It is strengthened by (i) strong fibers passing from the back of the articular disc where they are blended with the posterior inferior radio-ulnar ligament, and, from the edge of the radius just behind the ulnar notch, to the triquetral bone; (ii) from the ridge and groove for the extensor pollicis longus to the back of the lunate and triquetral bones; and (iii) from the groove for the radial extensors to the back of the navicular and lunate. It is in relation with, and strengthened by, the extensor tendons which pass over it.
The ulnar collateral ligament is fan-shaped, with its apex above, at the styloid process of the ulna, to which it is attached on all sides, blending with the apex of the articular disc. Some of the fibers pass forward and laterally to the base of the pisiform bone and to the medial part of the upper border of the transverse carpal ligament, where it is attached to the pisiform bone; they form a thick, rounded fasciculus on the front of the wrist. Other fibers descend vertically to the medial side of the triquetral bone, and others again laterally to the dorsal surface of the triquetral. The tendon of the extensor carpi ulnaris is posterior to, and passes over, part of the fibers of the ligament.
The radial collateral ligament consists of fibers which radiate from the fore part and tip of the styloid process of the radius. Some pass downward and medially, in front, to the navicular and adjacent edge of the capitate; some downward, a little forward and medially, to the tubercle of the navicular and ridge of the greater multangular; and others downward and laterally to the rough dorsal surface of the navicular.
The fibers of this ligament are not so long and strong, nor do they radiate so much as those of the ulnar collateral ligament. It is in relation with the radial artery, and the abductor pollicis longus {extensor ossis metacarpi pollicis) and extensor pollicis brevis, the artery separating the tendons from the ligament.
The synovial membrane is extensive, but does not usually communicate with the synovial membrane of the inferior radio-ulnar joint, being shut out by the articular disc. It is also excluded, in almost every instance, from that of the carpal joints by the interosseous ligaments between the first row of carpal bones. The styloid process of the radius is cartilage-covered medially, and forms part of the articular cavity, while that of the ulna does not.
Vessels and nerves the radio-carpal or wrist-joint
The arterial supply is derived from the anterior and posterior carpal rami, the dorsal division of the volar interosseous, and from twigs direct from the radial and ulnar arteries.
The nerve -supply is derived from the ulnar and median in front, and the deep branch of the radial (posterior interosseous) behind.
Relations the radio-carpal or wrist-joint
In front of the radio-carpal joint are the tendons of the flexor muscles of the wrist and fingers, the synovial sheaths associated with thern, the radial and ulnar arteries, and the median and ulnar nerves.
Behind the joint are the majority of the tendons of the extensor muscles of the wrist and fingers, with their synovial sheaths, the terminal part of the anterior and posterior interosseous arteries, and the deep branch of the radial nerve (posterior interosseous). On the radial side lie the tendons of the abductor pollicis longus {extensor ossis metacarpi pollicis) and the extensor pollicis brevis. On the ulnar side the joint is subcutaneous and it is crossed by the dorsal cutaneous branch of the ulnar nerve.
Movements of the radio-carpal or wrist-joint
The wrist is a condyloid joint, the carpus forming the condyle. It allows of movements upon a transverse axis, i. e., flexion and extension; and around an antero-posterior axis, i. e., abduction and adduction; together with a combination of these in quick succession - circumduction. Lacking only rotation on a vertical axis, it thus possesses most of the movements of a ball-and-socket joint, without the weakness and liability to dislocation which are peculiar to these joints. This deficiency of rotation is compensated for by the movements of the radius at the radio-ulnar joints, viz., supination and pronation. Its strength depends chiefly upon the number of tendons which pass over it, and the close connection which exists between the fibrous tissue of their sheaths and the capsule of the wrist; also upon the proximity of the medio-carpal and carpo-metacarpal joints, which permits shocks and jars to be shared and distributed between them; another source of strength is the absence of any long bone on the distal side of the joint. In flexion and extension, the carpus rolls backward and forward, respectively, beneath the arch formed by the radius and articular disc; flexion being limited by the dorsal ligament and dorsal portions of the collateral; extension by the volar, and volar portions of the collateral ligaments. In adduction and abduction, the carpal bones glide from the ulnar to the radial side and from the radial to the ulnar side, respectively. Abduction is more limited than adduction, and is checked by the ulnar collateral ligament and by contact of the styloid process of the radius with the greater multangular; adduction is checked by the radial collateral ligament alone. One reason for adduction being more free than abduction is that the ulna does not reach so low down as the radius, and the yielding articular disc allows of greater movement upward of the ulnar end of the carpus. In circumduction, the hand moves so as to describe a cone, the apex of which is at the wrist. These movements are made more easy and extensive by the slight gliding of the carpal bones upon one another, and the comparatively free motion at the medio-carpal joint. The oblique direction of the fibers of the collateral ligaments prevents any rotation at the radio-carpal joint, while it permits considerable freedom of abduction and adduction.
Muscles which act upon the radio-carpal joint
Flexors
- The flexors of the carpus and the long flexors of the fingers and the thumb, and the palmaris longus.
Extensors
- The extensors of the carpus and fingers.
Abductors
- Extensor carpi radialis longus, the abductor pollicis longus (extensor ossis metacarpi pollicis.
Adductors
- Flexor carpi ulnaris, extensor carpi ulnaris.
Anterior view of wrist
Ulnar - radio-ulnar ligament - Ulnar collateral ligament of wrist - Flexor carpi ulnaris - Volar radio-carpal ligament - Tendon of flexor carpi radialis - Capsular ligament of first - carpo-metacarpal joint
Posterior view of wrist
Dorsal radio-carpal ligament - Posterior radio-ulnar ligament - Ulnar collateral ligament of wrist
