Ultrasound diagnosis of ulnar nerve entrapment by confirming baseline cross-sectional area measurement for normal and abnormal nerves

Abstract

Background: Magnetic resonance imaging is most commonly employed, alongside electrodiagnostic studies, in the diagnosis of ulnar nerve entrapment. It is expensive, time consuming, not readily available to the general public, and limits imaging to a segment of the nerve at any given time. In contrast, high-frequency ultrasound is an inexpensive imaging modality with a flexible field of view through which the nerve can be traced. An ultrasound cross-sectional area (CSA) >0.075 cm2 has previously been suggested as indicative of nerve entrapment. Objectives: To confirm the suggested CSA measurement of 0.075 cm2 and discuss the difference in CSA measurement between abnormal nerves, nerves in the contra-lateral elbow of the same participant, and those of asymptomatic participants. Methods: Ultrasonography was performed on both elbows of 25 patients with confirmed unilateral ulnar nerve entrapment and on 25 healthy controls for comparison. Three CSA measurements were taken of the ulnar nerve along its course, and the mean measurement was recorded. Results: CSA measurements were significantly different between patients with ulnar nerve entrapment and healthy controls (p < 0.05). In our study, a CSA >0.070 cm2 defined ulnar nerve entrapment at the elbow. Conclusion: Ultrasound CSA measurement of the ulnar nerve is accurate in the diagnosis of ulnar nerve entrapment. The range of values and varied criteria previously reported call for standardisation of the procedure and CSA measurement. We suggest that a measurement of 0.070 cm2 be considered as a new baseline for the optimal diagnosis of ulnar nerve entrapment.