Patterns and parameters describing nerve thickening in compression and entrapment ulnar neuropathies at the elbow

Objective: To compare pattern and parameters describing nerve thickening in ulnar neuropathy at the elbow (UNE) due to external compression in the retrocondylar groove (RTC), and entrapment under the humeroulnar aponeurosis (HUA). Methods: In a group of our previously reported UNE patients we ultrasonographically (US) measured ulnar nerve cross-sectional areas (CSA) on 6-8 standard locations in the elbow segment. We compared CSA patterns in both groups, and determined diagnostic utility of selected CSA based parameters. Results: We studied 79 patients (81 arms) with UNE due to external compression, and 53 patients (55 arms) due to entrapment. Maximal ulnar nerve CSA (>16 mm(2)), maximal CSA change (>7 mm(2)/1- 2 cm) and maximal/minimal CSA ratio (>2.6) were significantly larger in UNE due to entrapment. They also differentiated these arms from arms with compression with sensitivities of 78%, 87% and 80%, and specificities of 90%, 94%, and 85%, respectively. Conclusion: Maximal difference in CSA between points separated by 1-2 cm (>7 mm(2)/1-2 cm) very efficiently differentiated between UNE due to external compression and entrapment. Significance: The proposed parameter will hopefully complement precise localization in determining underlying mechanism of UNE. This may help physicians to determine the most appropriate treatment for UNE and possibly other focal neuropathies of unknown cause; i.e., conservative treatment for external compression and surgery for entrapment. (c) 2020 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.