Rupture of the radial collateral ligament of the fifth metacarpophalangeal joint.

Isolated rupture of the radial collateral ligament of the metacarpophalangeal joint of the fifth digit is a rare but disabling injury. Treatment is complicated by the influence of the hypothenar musculature, which deviates toward the ulna and flexes the digit. We have managed two cases, one chronic and one acute, by open reduction and repair. Both cases demonstrated distraction of the collateral ligament ends by the extensor sagittal band. This operative finding is not too dissimilar from the interposition of the adductor pollicis tendon between the ends of a ruptured ulnar collateral ligament in a gamekeeper's thumb injury. Because of this finding, we believe that open reduction and repair of a ruptured radial collateral ligament of the metacarpophalangeal joint of the fifth digit is indicated.