Irreducible palmar metacarpophalangeal joint dislocation due to junctura tendinum interposition: a case report and review of the literature.

Three different anatomic structures have been reported to prevent reduction of a palmar dislocation of metacarpophalangeal joint: dorsal capsule, palmar plate, and a ruptured collateral ligament. In our case, extensor digitorum communis of the fifth finger and extensor digiti minimi subluxated on the ulnar side of the fifth metacarpal neck. Extensor digitorum communis of the fourth finger remained in its anatomic location. The junctura tendinum connecting the fourth and fifth extensor digitorum communis tendons slipped distal and then palmar to the metacarpal head, where it was trapped between the metacarpal neck and the base of the proximal phalanx. It was easily pulled out and the joint promptly reduced. Residual subluxation persisted due to rupture of the radial collateral ligament and the dorsal capsule. Repair restored joint reduction and stability. (J Hand Surg 2000; 25A:166-172.