Dislocations of the Metacarpophalangeal Joint of the Thumb

Abstract

We report 13 cases of thumb metacarpophalangeal dislocations, ten dorsal and three palmar. Eleven had complex dislocations requiring open reductions. With dorsal dislocations the palmar plate, the tendon of flexor pollicis longus and the “thenar trap” (adductor pollicis, flexor pollicis brevis and abductor pollicis brevis) were the main impediments to reduction. The dorsal capsule, extensor expansion and extensor pollicis longus and brevis prevented reduction with the uncommon palmar dislocations.

Cadaver studies showed that dorsal dislocations are hyperextension and pronation injuries and palmar dislocations are hyperflexion and supination injuries. The unique “handlebar grip” injury which can cause either dorsal or palmar dislocations is also discussed. The palmar plate is the single most important stabilizer of the metacarpophalangeal joint and it is impossible to sustain a dislocation without tearing it. It is most likely to get entrapped within the joint in dorsal dislocations. Ulnar collateral ligament tears are more common with palmar dislocations.