Corpus: Metacarpophalangeal joint

There are 5 metacarpophalangeal joints, corresponding to the number of fingers, which are systematically numbered. The metacarpophalangeal joints II-V are morphologically ball and socket joint or ellipsoid joint, where the convex, longitudinally oval head of the metacarpal bone fits into a corresponding concave groove at the proximal end of the base phalanx.

In contrast, the thumb's metacarpophalangeal joint (metacarpophalangeal joint I) is a pure hinge joint, as it possesses very strong collateral ligaments. Two small sesamoid bones are embedded palmarly into the capsule.

Ligaments

Each metacarpophalangeal joint has two collateral ligaments (ligamenta collateralia). These extend dorsally from the metacarpal heads distally and palmarly to the base phalanx and are most pronounced in the thumb's metacarpophalangeal joint. Additionally, the paired ligamentum phalangoglenoidale stabilizes the joint capsule and the sesamoid bones. This ligament has the most superficial position of all the fibrous strands at the metacarpophalangeal joint.

Palmarly, a palmar ligament stabilizes maximum extension. On the dorsal side, the joints are covered by fibrous strands that originate from the tendons of the finger [[Corpus:extensor|extensors.

All structures of the support apparatus are referred to as the Zancolli complex.

Functional anatomy

Active movements include flexion (90°) and extension (30°), as well as radial and ulnar abduction (spreading). Voluntary rotation is not possible; however, passive rotational movements occur in combination with the main movements.

In the flexed position of the metacarpophalangeal joints, the spreading of the fingers is restricted compared to the extended position. This is due to a stronger tension of the collateral ligaments in the flexed position.