The radiocarpal articulation or wrist-joint (figs. 540-542) is a condyloid articulation. The parts forming it are the distal end of the radius and lower surface of the articular disc, above and the scaphoid, lunate, and triquetral bones, below. The articular surface of the radius and the lower surface of the articular disc form together a transversely elliptical concave surface, the receiving cavity. The proximal articular surfaces of the scaphoid, lunate, and triquetral bones form a smooth convex surface, which is received into the concavity. The joint is surrounded by an articular capsule.
The anterior radiocarpal ligament (fig. 540) is a broad membranous band, attached above to the anterior margin of the lower end of the radius, to its styloid process, and to the front of the lower end of the ulna; its fibers pass downwards and medially to be attached to the anterior surfaces of the scaphoid, lunate, and triquetral bones. some being continued to the capitate bone. In addition to this broad membrane, there is a rounded fasciculus, superficial to the rest, which reaches from the base of the styloid process of the ulna to the lunate and triquetral bones. The ligament is perforated by apertures for the passage of vessels, and is in relation, in front, with the tendons of the flexor digitorurn profundus and flexor pollicis longus; behind, it is closely adherent to the anterior border of the articular disc of the inferior radio-ulnas articulation.
The posterior radiocarpal ligament (fig. 541), thinner and weaker than the anterior, is attached, above, to the posterior border of the distal end of the radius; its fibers are directed obliquely downwards and medially, and are fixed, below, to the posterior surfaces of the scaphoid, lunate, and triquetral bones, being continuous with those of the dorsal intercarpal ligaments. It is in relation, behind, with the extensor tendons of the wrist and fingers; in front, it is blended with the articular disc of the inferior radio-ulnar articulation.
The lateral (radial collateral) ligament of the wrist-joint (figs. 540, 541) extends from the tip of the styloid process of the radius to the radial side of the scaphoid bone, some of its fibers being prolonged to the trapezium (greater multangular bone). It is in relation with the radial artery, which separates the ligament from the tendons of the abductor pollicis longus and extensor pollicis brevis.
The arteries supplying the joint are the anterior interosseous, the anterior and posterior carpal branches of the radial and ulnar, the palmar and dorsal metacarpals, and some recurrent branches from the deep palmar arch. The nerves are derived from the anterior and posterior interosseous nerves.
Movements.-The movements permitted in this joint are flexion, extension, abduction, adduction, and circumduction. Flexion and extension are the most free, and of these a greater amount of extension than of flexion is permitted since the articulating surfaces extend farther on the posterior than on the anterior surfaces of the carpal bones. In this movement the carpal bones rotate on a transverse axis drawn between the tips of the styloid processes of the radius and ulna. Adduction or ulnar deviation, and abduction or radial deviation are also permitted. The former is considerably greater in extent than the latter on account of the shortness of the styloid process of the ulna; abduction being soon limited by the contact of the styloid process of the radius with the trapezium (greater multangular bone). In this movement the carpals revolves upon an anteroposterior axis drawn through the center of the wrist. Finally, circumduction is permitted by the combined and consecutive movements of adduction, extension, abduction and flexion. No rotation is possible, but the effect of rotation is obtained by the pronation and supination of the radius on the ulna.
Muscles producing the movements:
- Flexion.-Flexor carpi radialis, Flexor carpi ulnaris, Palmaris longus, Flexores digitorum sublimis et profundus, Flexor pollicis longus.
- Extension.-Extensores carpi radiales longus et brevis, Extensor carpi ulnaris, Extensor digitorum, Extensores pollicis longus et brevis. Extensor indicis, Extensor digiti minimi.
- Adduction.-Flexor carpi ulnaris, Extensor carpi ulnaris.
- Abduction.-Abductor pollicis longus, Extensor pollicis brevis, Extensores carpi radiales longus et brevis, Flexor carpi radialis.
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