Intraoperative Nerve Action Potential Amplitude and Functional Recovery After Selective Ulnar-to-Musculocutaneous...

Background: Predicting functional recovery after selective nerve transfer remains challenging. Intraoperative nerve action potential (NAP) recording is widely used to confirm axonal continuity in peripheral nerve surgery; however, its quantitative prognostic value in selective nerve transfer has not been clearly established. This study evaluated whether intraoperative donor fascicle NAP amplitude predicts functional recovery following selective ulnar-to-musculocutaneous nerve transfer (Oberlin procedure) for restoration of elbow flexion. Methods: This retrospective exploratory observational study included 20 patients who underwent selective ulnar-to-musculocutaneous nerve transfer (Oberlin procedure) with standardized intraoperative neurophysiological mapping and quantitative donor fascicle NAP recording. Functional outcome specific to elbow flexion was assessed at last follow-up using the Medical Research Council (MRC) grading system. Time to first electromyographic evidence of biceps reinnervation was recorded. Associations between intraoperative NAP amplitude and functional, temporal, and clinical variables were analyzed using Spearman's rank correlation coefficient and non-parametric tests. Results: Donor NAP amplitude demonstrated substantial interindividual variability (range 60-400 µV; median 137.5 µV, IQR 87.5-200 µV). No significant associations were observed between NAP amplitude and final MRC grade (ρ = -0.103; p = 0.666), time to electromyographic reinnervation (days: ρ = -0.123; p = 0.617), patient age, or time from injury to surgery. A moderate negative correlation between NAP amplitude and lesion severity was observed but did not reach statistical significance in this small cohort (ρ = -0.419; p = 0.0659). In contrast, shorter time to electromyographic reinnervation was significantly associated with improved final functional outcome (ρ = -0.559; p = 0.013). No patient reported postoperative hand weakness. Conclusions: In this exploratory cohort, intraoperative donor NAP amplitude was not associated with time to electromyographic reinnervation or final elbow flexion strength following selective ulnar-to-musculocutaneous nerve transfer. Although intraoperative NAP mapping remains essential to confirm axonal continuity and conduction viability of the donor fascicle, NAP amplitude did not demonstrate prognostic value in this cohort and should be interpreted cautiously as an isolated predictor of functional recovery, particularly given the limited sample size and exploratory design. These findings suggest that recovery after selective nerve transfer may be influenced by broader biological determinants, including regenerative timing, rather than by isolated intraoperative amplitude metrics.