Neurophysiological grading tool of ulnar nerve entrapment across the elbow
Authors: Salim Hirani 
Published: May 2023

Ulnar nerve entrapment across the elbow (UNEAE) is the second most common entrapment of the hand after carpal tunnel syndrome. There are few grades available for UNEAE with their limitations. The aim of this research is to establish, using the best available evidence, a clinically appropriate revision of the current ulnar nerve conduction grading tool and to evaluate its effectiveness in terms of acceptability, without any invasive tests. To compare the recording from the first dorsal interosseous (FDI) muscles with the abductor digiti minimi (ADM) muscle to see which muscle is more sensitive and shows early changes in ulnar nerve entrapment. The revised scale is designed from a clinical physiologist’s perspective and is based on the numerical values of nerve conduction findings. It could also assist surgeons to use this as a tool for interventional prediction. The proposed revised grading system is based on more nuanced, descriptive categories, ranging from “normal, “early, “mild, “moderate, “severe,” and “complete” absence. An additional category of clinical grading is therefore proposed. Method: Data was collected based on the extensive and detailed grading system previously described by Padua. The tests were performed by a qualified clinical physiologist (neurophysiology) using a Keypoint 9033A07 machine, used in line with the departmental protocol (peripheral protocol 1, 2015). The Association of Neurophysiological Scientists (ANS) and British Society of Clinical Neurophysiology (BSCN) (2014) guidelines and minimum standards for the practice of clinical neurophysiology in the United Kingdom were followed. All data was recorded numerically to ensure methodological reliability. Result: The data was collected over the course of one year (2017). A total of 190 patients were involved in this study. A collection of 278 consecutive symptomatic hands was tested for conduction block across the elbow while recording from the first dorsal interosseous FDI muscles. Out of the 278 samples, 201 hands were graded as having normal conduction velocity: 9 hands showed early changes, 51 hands showed mild changes, 14 hands showed moderate changes, 2 hands showed severe changes, and 1 hand showed complete absence or no response from the wrist and across the elbow. Additional studies were carried out from the abductor digiti minimi (ADM) muscles for those patients who showed conduction block across the elbow while recording from the FDI muscles. Only 57 patients underwent a nerve conduction study for ADM. 77 symptomatic hands were tested for conduction block in the ADM muscle. 18 hands were graded as normal; 48 hands showed mild changes; 10 hands showed moderate changes; and 1 hand showed complete absence or no response from the wrist and across the elbow. Out of 278 hands, 266 hands were graded as having normal amplitude across the elbow while recording from FDI muscles; 7 hands showed early changes in amplitude; 1 hand showed moderate amplitude change; 4 hands showed severe amplitude changes; and 1 hand showed complete absence or no response from the wrist and across the elbow. Out of 77 hands, 73 hands showed normal amplitude across the elbow while recording from ADM muscles; 2 hands showed mild changes; 1 hand showed a moderate change; and 1 hand showed complete absence or no response from the wrist and across the elbow. Conclusion: Finding show that FDI is more sensitive in comparison to ADM to record early changes in ulnar nerve entrapment across the elbow. In addition, it shows that a drop in amplitude is not as significant when compared to a conduction block across the elbow.