Comparison of the Volar and Medial Approach in Peripheral Block of Ulnar Nerve at the Wrist – A Cadaveric Study

CONTEXT: Two standard approaches are described to block the ulnar nerve at wrist. These include a) the traditional Volar approach where the needle is inserted lateral to tendon of flexor carpi ulnaris (FCU) b) Medial approach where the needle is inserted posterior to the tendon of FCU. Caution must be exercised to avoid puncture of the ulnar artery and/or intraneural injection of the ulnar nerve in both the approaches. AIM: This study compares the volar and medial approach to the peripheral block of ulnar nerve at the wrist. The objective was two fold: a) to analyze the position of the ulnar nerve and the ulnar artery in relation to the Flexor Carpi Ulnaris tendon b) to assess the risk of injury to ulnar artery in both the volar and medial approach. SETTINGS AND DESIGNS: Twelve cadaveric upper limbs were used and both approaches compared by an observational study. MATERIALS AND METHODS: Two 18 G needles were inserted up to a depth of 7 mm using the standard volar and medial approach. The pattern of arrangement and positions of the ulnar artery and nerve in relation to FCU tendon were observed. The distance between the tip of needle and its proximity to the ulnar artery, and risk of injury were determined. Statistical analysis was done using SPSS for Windows, Version 16.0. Chicago, SPSS Inc. RESULTS: Three patterns of arrangement and position of the ulnar nerve and artery were observed. Puncture of ulnar artery was seen in 50% of cases in the volar approach as compared to no injury at all in the medial approach. The ulnar artery is highly liable to injury during the volar approach in type I and II and safe only in type III arrangement of ulnar artery. The medial approach showed no injury to the ulnar artery or nerve at a penetration depth of 7mm. CONCLUSION: The medial approach is safer compared to volar approach for peripheral block of ulnar nerve at wrist.