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

Background: Evaluation of the ulnar nerve at the elbow is one of the most challenging areas in electrodiagnosis. The goal of this study is to determine the changes in motor and sensory nerve conduction velocity (NCV) of the ulnar nerve at the elbow area in different angles of the elbow flexion and also to define the optimum angle at which there is an ideal correlation between the elbow across and below NCVs of the ulnar nerve. Methods: Motor and sensory NCVs of the ulnar nerve were studied in 50 able-bodied subjects (100 limbs below and across the elbow segments to determine the effect of 5 different angles of the elbow (0º, 45º, 90º, 110º and 135º of the elbow flexion) on NCV changes of the ulnar nerve. At each angle, the elbow NCVs were compared with below and across segments. Results: At 0º of the elbow flexion, the across elbow NCVs were slower than the below elbow segments and at 45º there was no statistical difference between below and across elbow NCVs. At each subsequent angles of the elbow flexion, there was an increment in motor and sensory NCVs for the across compared to below elbow segment (P<0.05). This increment rose as the degree of flexion increased. So the most erroneous increment was found at 135º of the elbow flexion. Conclusion: Since elbow flexion at 45º was found to be the position of the least variation in motor and sensory NCVs between the across and below elbow segments, this position of the elbow flexion seems to be the ideal angle during the nerve conduction study of the ulnar nerve at the elbow area. In this position, the upper limit of normal difference between the across and below elbow motor NCVs (mean+2SD) was calculated 8 m/sec.