Abnormal disposition of a branch of the ulnar nerve in the flexor retinaculum.

The most frequent disposition of the structures within the ulnar tunnel is for the ulnar nerve to be located medial or posteromedial to the ulnar artery. The structures within the ulnar tunnel are closely related to the medial part of the flexor retinaculum. Lesions of the ulnar nerve and artery during endoscopic decompression of the carpal tunnel have been reported (Agee et al. 1992; Lee et al. 1992; Nath et al. 1993; De Smets & Fabry, 1995). An adequate anatomical knowledge of such structures and their variations is therefore important. During a study of the palmar region, we found that a special branch originated from the ulnar nerve in relation to the flexor retinaculum. Documentation of this variation will contribute to the knowledge of the anatomy of the ulnar nerve and its distal branches. The variation was detected in the right hand of a 63-y-old