These articulations (figs. 543, 544) are of the condyloid variety, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges, with the exception of that of the thumb, which presents more of the characteristics of a hinge joint. Each joint has a palmar and two collateral ligaments.
The palmar ligaments (accessory volar ligaments) are thick, dense, fibrocartilaginous structures, placed upon the palmar surfaces of the joints in the intervals between the collateral ligaments, to which they are connected; they are loosely united to the metacarpal bones, but are very firmly attached to the bases of the proximal phalanges. Their palmar surfaces are intimately blended with the deep transverse ligaments of the palm, and grooved for the flexor tendons, the fibrous sheaths of which are connected to the sides of the grooves. Their deep surfaces form parts of the articular areas for the heads of the metacarpal bones.
The deep transverse ligaments of the palm consist of three short, wide, flattened bands which connect the palmar ligaments of the second, third, fourth and fifth metacarpophalangeal joints to one another (fig. 543). They are related, anteriorly, to the lumbrical muscles and the digital vessels and nerves and, posteriorly, to the interosseous muscles. Offsets from the digital slips of the central portion of the palmar aponeurosis join the palmar surface.
The collateral ligaments are strong, rounded cords, placed on the sides of the joints; each is attached by one extremity to the posterior tubercle and adjacent depression on the side of the head of the metacarpal bone, and by the other to the side of the base of the phalanx (fig. 544).
The dorsal surfaces of these joints are covered with the expansions of the extensor tendons, together with some loose areolar tissue, which connects the deep surfaces of the tendons to the bones.
Movements.-The movements which occur in these joints are flexion, extension, adduction, abduction, and circumduction; the movements of abduction and adduction are very limited, and cannot be performed when the fingers are flexed.
- Flexion -Flexores digitorum sublimis et profundus, Lumbricales, Interossei, dorsal and palmar, Flexores pollicis longus et brevis, Flexor digiti minimi.
- Extension.-Extensor digitorum, Extensores pollicis longus et brevis, Extensor indicis, Extensor digiti minimi.
- Adduction. -Palmar interossei, Adductor pollicis, long flexors of fingers and thumb.
- Abduction.-Dorsal interossei, Abductor pollicis brevis, Abductor digiti minimi, long extensors of fingers.
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