Established and novel quantitative electromyographic techniques with potential for planning nerve transfer surgery: a pilot study

Donor nerve health likely underlies much variability in nerve transfer outcomes. Standard electromyography (EMG) and clinical examination suffer from subjectivity and a lack of standardization when assessing nerve health. Quantitative electromyography promises to assess nerve health more accurately. The objective of this retrospective pilot study was to evaluate rapid and feasible quantitative electromyography methods in determining donor nerve health for planning nerve transfer surgery and its correlation with functional outcomes. For this study, the branch of the radial nerve supplying the supinator muscle was chosen as the donor nerve and the recipient nerve was the posterior interosseous nerve supplying finger extensors. Fifteen supinator muscle electromyographic recordings from 12 patients were analyzed using quantitative electromyography techniques and compared with the most readily available gold standard neurophysiology metric (full electromyographic signal decomposition) and the average finger extensor Medical Research Council (MRC) grading scores at least 12 mo after surgery. Two multiple regression models were developed to predict MRC grade and decomposition results. Moderate to good correlation was observed between the quantitative electromyography techniques and both the gold standard decomposition-based neurophysiology metric and average MRC finger extension strength outcomes. Both regression models were highly significant. This pilot study highlights the importance of understanding the degree of innervation within the donor nerve and introduces a promising novel quantitative electromyography technique, stimulation-free concentric needle-based motor unit number estimation. Automation and rapid application, using standard EMG signals and widely available software, lowers the threshold for clinical uptake to potentially benefit surgical outcomes.<b>NEW & NOTEWORTHY</b> We introduce a novel quantitative electromyography technique, stimulation-free concentric needle-based motor unit number estimation, which could potentially aid surgical planning in the management of peripheral nerve injury. The ability to apply this technique to any muscle as part of a standard electromyography protocol without imposing additional time burden suggests this technique may represent a practical and feasible approach to optimize surgical outcomes.