Palmar dislocation of the thumb metacarpophalangeal joint: report of four cases and a review of the literature.

We report four cases of palmar dislocation of the thumb metacarpophalangeal joint and review of an additional 22 cases in the literature. Our four cases were associated with ligamentous injuries that prevented stable closed reduction. The patients were treated with open reduction and ligament repair and ultimately had a decreased range of motion. Our four cases and the 22 cases from literature fall into three types: Type A - stable joint (the metacarpophalangeal joint is stable, without severe ligament injury); Type B - tendon block (palmar displaced extensor tendons within the metacarpophalangeal joint prevents reduction); and Type C - joint instability (the metacarpophalangeal joint is unstable because of severe collateral ligament disruption). Type B is the most commonly reported type of palmar dislocation of the thumb metacarpophalangeal joint, with distinct features of the involvement of the collateral ligaments and failure of attempted manual reduction. The patients without severe collateral ligament disruption were managed with conservative treatment. The patients with interposition of extensor tendons and the patients with instability resulting from severe ligamentous injuries require surgical treatment.