Quantitative Electromyography as a Predictor of Nerve Transfer Outcome
Ross Mandeville, MD; University of California, San Diego, La Jolla, CA; Justin M. Brown, MD; Department of Neurosurgery, University of California, San Diego, San Diego, CA
Introduction: The pre-operative assessment for nerve transfer surgery is key to a successful outcome, however reliance on clinical exam with only basic neurophysiological studies is the norm. Significantly more neurophysiological information can be obtained pre-operatively to aid in planning of nerve transfer surgery - in particular, quantitatively electromyography (qEMG). Usual neurophysiological evaluation lacks granularity, often only grading a muscle as mild, moderate, or severe. Within the severe grade, greater precision can be obtained through quantifying the number of motor units (MU) within the interference pattern. This study evaluates the ability of pre-operative donor nerve qEMG using MU counts to predict the post-operative force outcome in nerve transfer surgery.
Methods: We performed a retrospective review of pre-operative donor nerve quantitative neurophysiology and post-operative recipient muscle force after at least one year follow-up. The quantitative technique applied was Motor Unit (MU) count, which was correlated with hand-held manometry, standardized as a percent of the contralateral arm, using multivariable linear regression with backward selection.
Results: Twenty-eight nerve transfer cases were included. The correlation between the donor nerve MU count and the recipient muscle strength was strong and highly significant (Fig. 1: r = 0.67, p<0.001). Importantly, in these 28 cases, pre-operative Medical Research Council (MRC) grading did not predict strength outcome (p>0.54).
Conclusions: The technique of qEMG Motor Unit count is a good predictor of strength outcome after nerve transfer surgery and could be considered useful in the evaluation and planning of patients undergoing nerve transfer surgery to aid in donor nerve selection. Caution is advised when relying solely on MRC grading to select donor nerves.
Figure 1. Graph depicting the relationship between Motor Unit count (MUC) and the Force outcome as a percent of the contralateral unaffected limb. MUC of 7 indicates at least 7 motor units (r = 0.67, p<0.001).
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