Anatomical Relation of Ulnar Nerve and Flexor Carpi Ulnaris Muscle at the Wrist

Objective: To verify proper stimulation point of ulnar nerve at the wrist by investigating anatomical relation of ulnar nerve and flexor carpi ulnaris (FCU) muscle. Method: Cadaver dissection of 9 wrists was done to identify gross anatomical relation of ulnar nerve and FCU muscle. Ultrasonography of 17 healthy volunteers was done for the measurement of distance from lateral border of FCU muscle to ulnar nerve at three sites. Ratios of these distances to total width of FCU muscle and FCU tendon were calculated. Results: FCU muscle was composed of lateral tendinous and medial muscular portion, and all ulnar nerves were located under the tendinous portion of FCU muscle on cadaver dissection. Ultrasonographic distances from lateral border of FCU muscle to ulnar nerve were 4.63.3 mm, 4.84.0 mm and 5.93.1 mm from distal to proximal sites. The ratios to total width of FCU muscle were 31.02 23.31%, 24.3026.12% and 24.4813.01%, which showed that the ulnar nerve was closer to the lateral border than the medial border. The ratios to total width of FCU tendon were 49.6341.35%, 51.3050.46% and 64.5936.79%, which showed progressive increment from distal to proximal sites. Conclusion: Proper stimulation point of ulnar nerve at the wrist is the lateral border of FCU muscle than the medial border. However, the proximity of ulnar nerve to the medial or lateral border was not conclusive, because the ratio to FCU tendon was not consistent in three sites of the wrist. Further electrophysiologic study is necessary for the comparison of proper stimulation point based on FCU tendon.