Irreducible skin penetration of the ulnar head in Colles fracture--case report.

Three cases out of four of skin penetration by the ulnar head associated with Colles fractures were found to be irreducible. On exploration they had identical pathologic anatomy, viz, buttonholing of the ulnar head between the flexor carpi ulnaris, flexor digitorum profundus, pronator quadratus, and the flexor retinaculum. Incising the flexor retinaculum facilitated reduction.