Ultrasound Measurements of the Ulnar Nerve at the Medial Epicondyle Correlate With Electrodiagnostic Studies.

Background: Cubital tunnel syndrome is the second most common compressive neuropathy in the upper extremity and is commonly evaluated with electrodiagnostic studies (EDS). Ultrasound (US) has emerged as a potentially more efficient alternative to EDS. The purpose of this study is to evaluate whether measurements of the cross-sectional area (CSA) of the ulnar nerve at the elbow correlate with EDS results.

Methods: This study was a prospective analysis of patients who presented with signs and symptoms consistent of cubital tunnel syndrome, who received USs of the ulnar nerve at the elbow and nerve conduction tests. Pearson correlation coefficients were used to evaluate the correlation between ulnar nerve CSA and electrodiagnostic data. t Tests were used to evaluate statistical differences between the mean ulnar nerve CSA of patients with positive or negative nerve conduction study results. Youden Index was used to calculate the optimal cut-off point for US CSA based on maximal sensitivity and specificity. Statistical significance was based on a two-sided P less than .05.

Results: The association between increasing US CSA at the medial epicondyle with slowing of the conduction velocity of the ulnar motor nerve across the elbow was statistically significant (r = -0.35, P = .02). Patients with positive EDS tests had significantly larger nerve size than those with negative tests (all Ps < .03). A cut-off point of greater than or equal to 11 mm² had a sensitivity of 70.83% and specificity of 66.67%.

Conclusions: Larger ulnar nerve CSAs correlate with slowing of the conduction velocity on EDSs, and those with positive EDSs have larger nerve sizes than those with negative tests.