Ulnar Nerve Enlargement at the Medial Epicondyle Negatively Correlates With Nerve Conduction Velocity in Cubital Tunnel Syndrome

Background: In cubital tunnel syndrome (CuTS), chronic compression often occurs at the origin of the flexor carpi ulnaris at the medial epicondyle. Motor nerve conduction velocity (NCV) across the elbow is assessed preoperatively to corroborate the clinical impression of CuTS. The purpose of this study was to correlate preoperative NCV to the direct measurements of ulnar nerve size about the elbow at the time of surgery in patients with clinical and/or electrodiagnostic evidence of CuTS. Methods: Data from 51 consecutive patients who underwent cubital tunnel release over a 2-year period were reviewed. Intraoperative measurements of the decompressed nerve were taken at 3 locations: at 4 cm proximal to the medial epicondyle, at the medial epicondyle, and at the distal aspect of Osborne fascia at the flexor aponeurotic origin. Correlation analysis was performed comparing nerve size measurements to slowing of ulnar motor nerve conduction velocities (NCV) below the normal threshold of 49 m/s across the elbow. Results: Enlargement of the ulnar nerve at the medial epicondyle and nerve compression at the flexor aponeurotic origin was a consistent finding. The mean calculated cross-sectional area of the ulnar nerve was 0.21 cm² above the medial epicondyle, 0.30 cm² at the medial epicondyle, and 0.20 cm² at the flexor aponeurotic origin (P < .001). There was an inverse correlation between change in nerve diameter and NCV slowing (r = -0.529, P < .001). Conclusions: For patients with significantly reduced preoperative NCV and clinical findings of advanced ulnar neuropathy, surgeons can expect nerve enlargement, all of which may affect their surgical decision-making.