Surface Landmarks to Provide a Safe Ulnar Nerve Block in the Wrist

Anatomical Study and Literature Review

Swapnil D. Kachare, MD, MBA; Luke T. Meredith, MD; Milind D. Kachare, MD; Bradley J. Vivace, BS; Christina N. Kapsalis, MD; Claude Muresan, MD; Joshua H. Choo, MD; Morton L. Kasdan, MD; Bradon J. Wilhelmi, MD, FACS

Disclosures

ePlasty. 2020;20(e12) 

In This Article

Abstract and Introduction

Abstract

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.

Introduction

SUMMARY:

Knowledge of distal wrist anatomy is required to execute a safe ulnar nerve block. We performed a cadaveric anatomical study as well as a literature review of cadaveric studies describing various techniques for ulnar nerve blockade at the wrist. The data suggest that an ulnar approach provides the safest method.

Anesthesia modalities in hand surgery range from local blockade to general anesthesia. Recently, wide awake local anesthesia no tourniquet (WALANT) hand surgery has gained popularity, utilizing local anesthetics combined with epinephrine for hemostasis.[1–4] This method provides safe and effective anesthesia while decreasing costs and operating room time.[5–7] However, knowledge of local anatomy to ensure precision of injection is required to avoid iatrogenic injury.[8]

When anesthetizing the ulnar nerve (UN) as part of a wrist block, injury and/or intra-arterial injection of the ulnar artery (UA) can occur due to their proximity in the distal forearm.[9] The UN commonly courses radial to the UA on the surface of the flexor digitorum profundus and deep to the flexor carpi ulnaris (FCU) in the proximal two-thirds of the forearm. As the UN approaches the distal third, it crosses ulnar to the UA, giving off a dorsal cutaneous branch 3 to 5 cm proximal to the ulnar head and continues between the pisiform and the hook of hamate.[10]

Use of surface landmarks to predict nerve locations for injection in the upper limb had been described to avoid iatrogenic injury, with multiple anatomic and cadaveric studies focusing on the median nerve.[8,11] However, limited cadaveric studies exist describing injection for UN blockade at the wrist, with no consensus on technique.[12–14] We sought to review this literature as well as compare the findings with our data. Using the relationship of the UN to the UA, pisiform, and FCU, we aim to describe a safe location for injection of local anesthetic during UN blockade.

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