400 Section - Comparison of Segmental Nerve Conduction Changes According to Ulnar Nerve Dislocation in Patients with Ulnar Neuropathy at the Elbow

Ulnar nerve dislocation around the elbow can alter its course, leading to technical errors in nerve conduction studies (NCS). Previous studies in healthy subjects showed that false-positive conduction block findings may normalize after ultrasonographic (US) correction, but this has not been systematically assessed in patients with ulnar neuropathy at the elbow (UNE).
This study aimed to evaluate the effects of US-guided pathway correction on segmental conduction velocity and compound muscle action potential (CMAP) amplitude in UNE patients with ulnar nerve dislocation.

Design: A prospective single-center observational study was conducted in seven patients (mean age 48.7 years; six males, one female) with electrophysiologically confirmed UNE and US-verified ulnar nerve dislocation. Segmental motor NCS was performed across the elbow at 2-cm intervals (total 10 cm) with the elbow flexed at 135°, first along the anatomical path and then along the true nerve course identified by US mapping.
Conduction velocity and CMAP amplitude were compared before and after correction using the Wilcoxon signed-rank test (p < 0.05).

Results:

After US correction, significant conduction slowing was newly detected in the segment between the medial epicondyle (ME) and 2 cm below ME (p = 0.047) and in the segment between 2 cm and 4 cm below ME (p = 0.016). CMAP amplitude at the ME level increased (median 6.6 → 7.6 mV, p = 0.022), indicating improved current alignment and reduced temporal dispersion. Conventional NCS produced both false-negative (velocity) and false-positive (amplitude) results.

Conclusion:

Ulnar nerve dislocation can distort electrodiagnostic findings and reduce diagnostic reliability. Ultrasound-guided pathway mapping enables stimulation along the true nerve trajectory, improving accuracy, sensitivity, and localization of focal lesions. This combined US–NCS approach enhances diagnostic utility in evaluating cubital tunnel syndrome.