Complete dorsal dislocation of the metacarpophalangeal joint of the thumb.

In the pathology of simple complete dislocation involving the metacarpophalangeal joint of the thumb, whether or not the palmar plate is interposed within the joint is controversial. Nine cases of complete dorsal dislocation of the joint were reviewed, and cadaver dissection was performed to study the pathology of this injury. Eight of the nine patients were seen within 4 days of injury and treated successfully by closed manipulation. One patient treated 7 days after the injury required open reduction. We were able to reproduce the pathological anatomy of the dislocation, wedging of the palmar plate in the joint of the cadaver. In this cadaver and in all clinical cases, radiographs showed a complete dislocation with an increased distance between the palmar edge of the base of the proximal phalanx and the metacarpal head, indicating an interposition of the palmar plate. Our study suggests that in simple complete dislocations of this joint, the palmar plate is interposed between the displaced bones.