Ulnar nerve compression at the wrist by a synovial cyst successfully treated with percutaneous puncture and corticosteroid injection.

A case of ulnar nerve palsy due to a conduction block in the deep motor branch at the wrist is reported. The cause was a rapidly growing synovial cyst. Ultrasonography and computed tomography were performed to determine the exact location of the cyst, which was punctured and injected with corticosteroid. Function promptly returned to normal after this procedure.