6j. Metacarpophalangeal Articulations
(Articulationes Metacarpophalangeæ; Metacarpophalangeal Joints) (Figs. 337, 338)These articulations are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the first phalanges, with the exception of that of the thumb, which presents more of the characters of a ginglymoid joint. Each joint has a volar and two collateral ligaments.
|The Volar Ligaments (glenoid ligaments of Cruveilhier; palmar or vaginal ligaments).The volar ligaments are thick, dense, fibrocartilaginous structures, placed upon the volar 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 first phalanges. Their volar surfaces are intimately blended with the transverse metacarpal ligament, and present grooves for the passage of the Flexor tendons, the sheaths surrounding which are connected to the sides of the grooves. Their deep surfaces form parts of the articular facets for the heads of the metacarpal bones, and are lined by synovial membranes.
|The Collateral Ligaments (ligamenta collateralia; lateral ligaments).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 contiguous extremity of the phalanx.
|The dorsal surfaces of these joints are covered by 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.