Dorsal Dislocation of the Fourth and Fifth Metacarpals

Several hours after striking his closed fist against the side pillar of a passenger car, a 28-year-old man presented with acute pain and swelling of the left hand. The dorsum of the left hand appeared deformed and edematous; there were scattered abrasions but no lacerations, exposed bony fragments, ecchymosis, or active bleeding. The ulnar aspect of the dorsum of the hand was moderately tender. The patient was able to move all 5 digits slightly but was unable to fully open the left hand. The remainder of the sensory and vascular examination showed no deficits. The patient was given an oral analgesic and a tetanus booster.

Radiographs of the hand revealed a dorsal dislocation of the proximal fourth and fifth metacarpals. No fracture was evident.

Because of the number and strength of the supporting ligaments, carpometacarpal (CMC) joint dislocations are exceedingly rare. A dorsal dislocation occurs primarily from axial impact combined with forceful dorsal or palmar flexion (as a result of punching or falling onto the hand). This type of dislocation is commonly a fracture-dislocation injury (usually a chip fracture of the metacarpal base or a dorsal carpal fracture). Fracture-dislocation of the fifth metacarpal base is also known as the reverse Bennett fracture.

"Balloon hand" is the term used to describe the degree of inflammation, because swelling can be disproportionate to the elapsed time from the inciting event. This finding strongly suggests a CMC joint dislocation. A complete hand x-ray series is the imaging study of choice; the oblique and true lateral views usually render the diagnosis.

In this patient, closed reduction of the fourth and fifth metacarpals was achieved. Lidocaine anesthetic was instilled dorsally into CMC spaces, followed by simultaneous longitudinal traction at the metacarpal heads, mild palmar flexion of the digits, and direct longitudinal pressure at the metacarpal bases. A short forearm splint was placed, and post-reduction films were obtained. The patient was referred for prompt orthopedic follow-up. The orthopedist repaired the injury through open reduction and an internal fixation method using K-wires.