Surface Landmarks to Provide a Safe Ulnar Nerve Block in the Wrist: Anatomical Study and Literature Review

Introduction: Use of local anesthesia in awake patients undergoing hand surgery has become increasingly popular. A thorough understanding of local anatomy, such as the distal wrist for ulnar nerve block, is required to provide safe blockade. We sought to conduct an anatomic study of the distal wrist and review cadaveric studies describing various techniques for ulnar nerve block. Methods: Dissection of fresh-frozen cadaver forearms at the University of Louisville Robert Acland Fresh Tissue Lab assessing relationships between the flexor carpi ulnaris tendon and the ulnar nerve and the ulnar artery was performed. Three cadaveric studies on ulnar nerve blockade using the ulnar, volar, and/or transtendinous technique were identified and reviewed. Results: A total of 16 cadaver forearms of equal male to female ratio were obtained. The ulnar nerve was noted to be directly posterior to the flexor carpi ulnaris tendon in 15 (93.8%) forearms, with 1 (6.3%) specimen having the nerve extend along the ulnar border of the flexor carpi ulnaris. The ulnar artery was radial to the ulnar nerve 1 cm proximal to the pisiform in all specimens. In all 3 cadaveric studies, only the ulnar technique was associated with no ulnar artery and/or ulnar nerve injury. Conclusion: Knowledge of distal wrist anatomy can help minimize risk of iatrogenic injury during local blockade. On review, the ulnar approach provides the safest method for ulnar nerve block.