Predictive Values of Preoperative Compound Muscle Action Potential Amplitude for Surgical Outcomes in Idiopathic Ulnar Neuropathy at the Elbow

Abstract

Introductions/Aims Despite numerous studies on ulnar neuropathy at the elbow (UNE), the predictive value of preoperative compound muscle action potential (CMAP) amplitude for postoperative intrinsic function remains unclear. This study aimed to evaluate the predictive values of preoperative CMAP amplitude for surgical outcomes in idiopathic UNE.Methods A retrospective study was conducted on patients who underwent ulnar nerve transposition for idiopathic UNE with at least 24 months of follow-up. The primary outcome was the Medical Research Council (MRC) muscle strength of the abductor digiti minimi (ADM), and poor ADM function was defined as an MRC grade <= 2 at the final follow-up or a grade lower than baseline. Secondary outcomes included the key pinch strength ratio, grip strength ratio, and patient-reported outcomes. Correlation and regression analyses were performed to identify factors associated with clinical outcomes, and a ROC curve was used to determine the cut-off value of preoperative CMAP amplitude for predicting poor ADM function.Results A total of 79 patients were included. Preoperative CMAP amplitude showed significant correlations with postoperative ADM MRC grade and key pinch strength ratio. Poor ADM function was observed in 11 patients (14%) and was independently associated with lower CMAP amplitude. The ROC curve analysis revealed a cut-off value of 6.15 mV (AUC 0.83, sensitivity 100%, specificity 71%).Discussion This study indicates that preoperative CMAP amplitude could be a key predictor of postoperative ADM function in idiopathic UNE. A cut-off of 6.15 mV may help identify patients at risk of poor recovery and guide surgical decision-making.