Clinical significance of upper arm motor nerve conduction velocity in cubital tunnel syndrome.

Background: Retrograde denervation occurs in severe entrapment neuropathy. This study aimed to investigate changes in motor nerve conduction velocity (MNCV) at the upper arm, specifically proximal to the elbow, in cubital tunnel syndrome (CuTS) and to correlate these changes with preoperative severity and postoperative outcomes.

Methods: We retrospectively reviewed 95 elbows with 81 patients with CuTS for preoperative severity, and then 67 elbows with 60 of these patients who underwent anterior subcutaneous transposition surgery for postoperative outcome, classified into favorable and unfavorable groups according to Messina grade.

Results: The reduction of upper arm MNCV was correlated with aging, decreased compound muscle action potentials of abductor digiti minimi muscle, loss of sensory nerve action potentials, and modified McGowan grade. Postoperative assessment revealed lower MNCV values in the "unfavorable" group compared to the "favorable" group at 1 month, 6 months, and the last follow up. At each time point, the optimal cut-off value of upper arm MNCV for predicting postoperative outcomes was 54.1 m/s.

Discussion: Upper arm MNCV might be a useful predictor of poor surgical outcome. Ulnar nerve MNCV at the upper arm should be measured alongside routine assessment of MNCV at the elbow and forearm, especially in clinically severe cases considering surgery.