Changes in ulnar nerve conduction velocity across the elbow in different angles of elbow flexion

The goal of this study is to determine the changes in motor and sensory nerve conduction velocity (NCV) of ulnar nerve at elbow area in different angles of elbow flexion and also to define the optimum angle at which there is an ideal correlation between the across elbow and below elbow NCVs of ulnar nerve.

Motor and sensory NCVs of ulnar nerve were studied in 50 able-bodied subjects (100 limbs) for the below elbow and across elbow segments to evaluate the effect of 5 different angles of elbow (0 degrees, 45 degrees, 90 degrees, 110 degrees 135 degrees of elbow flexion) on NCV changes of ulnar nerve. At each angle the across elbow NCVs were measured and compared with below elbow segments.

At 0 degrees of elbow flexion the across elbow NCVs were found to be slower than below elbow segments and at 45 degrees there was no statistical difference between below elbow and across elbow NCV. At each subsequent angles of elbow flexion there was an increment in motor and sensory NCVs for the across elbow compared to below elbow segment (P < 0.05). This increment progressed as the degree of flexion increased, so the most erroneous increment was found at 135 degrees of elbow flexion.

Since the 45 degrees of elbow flexion was found to be the position of least variation in motor and sensory NCVs between the across elbow and below elbow segments, this position of elbow flexion seems to be the ideal angle during nerve conduction study of ulnar nerve at elbow area. In this position the upper limit of normal difference between across elbow and below elbow motor NCVs (mean + 2SD) was calculated 8 m/sec.