The mechanism of dorsal fracture dislocation of the fifth carpometacarpal joint.

Fracture dislocation at the base of the fifth metacarpal is a rare injury. Fewer than 25 cases have been published in the English-language literature. A force acting along the longitudinal axis of the fifth metacarpal causes a fracture dislocation at the base of the bone in a dorsal-ulnar direction, because of the anatomy of the joint and the mechanical properties of the bone and the intermetacarpal ligament. The mechanism of other types of injury to this joint, namely dorsal-radial or palmar-radial dislocation of the base of the fifth metacarpal is different. A case is presented which demonstrates the mechanism of the fracture dislocation.