[Compression of the ulnar (cubital) nerve at the wrist by a supernumerary muscle]

The authors report a case of anomaly of the flexor digiti minimi muscle, which extended into the forearm to be inserted 10 centimetres proximal to the carpal flexion crease on flexor carpi radialis. This anomaly was responsible for ulnar nerve compression when grasping objects with the hand. Cases of ulnar nerve compression at the wrist appear to be rare and the great majority of cases are secondary. Anatomical variants of muscles and nerves at the wrist are not exceptional, hence the importance of systematically looking for such anomalies in patients with ulnar nerve compression at the wrist. Excision of the muscle anomaly eliminated nerve compression and the associated symptoms.