Topographic anatomy of the ulnar tunnel

Purpose: The aim of this study was to clarify the definition of the anterior wall of the ulnar tunnel and to reveal the topographical characteristics of the various components of the ulnar tunnel. Materials and methods: Twenty-two forearms from 11 embalmed cadavers (7 males, 4 females; mean age, 67.8 years) were carefully dissected. Results: In all cases, the anterior wall of the ulnar tunnel comprised the hypothenar fascia, which originated from the tendon of the flexor carpi ulnaris muscle. The palmar carpal ligament, the distal extent of the antebrachial fascia, was located deep to the anterior wall and formed only the anterior boundary of the proximal hiatus of the ulnar tunnel. The hypothenar fascia was attached to the flexor retinaculum at 15.2 mm lateral to the pisiform bone. However, the palmar carpal ligament was attached to the flexor retinaculum just lateral to the ulnar artery; the distance between the attachment of the palmar carpal ligament and the pisiform bone was 8.7 mm. Anatomical variations potentially associated with ulnar nerve compression were observed. The accessory abductor digiti minimi muscle and the fibrous band crossing the ulnar nerve in the ulnar tunnel were found in 27 and 23 % of forearms, respectively. Conclusion: A more detailed description of the anterior wall of the ulnar tunnel than was previously available is presented herein, and topographic and metric data regarding each structure of the tunnel are reported.