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Early Reinnervation is Improved by Daily Electrical Muscle Stimulation Following Nerve Injury and Immediate Repair
Michael P. Willand, PhD, MASc , Jennifer J. Zhang, MD, PhD, Cameron D. Chiang, BSc, Stephen W. P. Kemp, PhD, MSc, Tessa Gordon, PhD and Gregory H. Borschel, MD
Division of Plastic and Reconstructive Surgery, The Hospital for Sick Children, Toronto, ON, Canada
Background: The use of chronic electrical muscle stimulation for treating partially or completely denervated muscle has been met with much controversy. Our previous work has shown that a moderate stimulation paradigm can significantly improve muscle weight, force, and numbers of motor units following long term muscle denervation and subsequent nerve repair. More recently, this same paradigm was used to investigate long term recovery following nerve transection and immediate repair with no negative impact on reinnervation. However, early effects of this treatment were not evaluated. Research question: Does a moderate electrical muscle stimulation paradigm improve early outcome measures following nerve transection and immediate repair? Methods: Two groups of Thy1-GFP transgenic male rats were subjected to tibial nerve transection and immediate repair using two epineurial sutures. One group of rats underwent daily electrical muscle stimulation of the gastrocnemius with a paradigm comprising of 600 equally separated contractions throughout one hour, delivered 5 days per week. Rat gastrocnemius muscles were electrically stimulated for 2 weeks and then underwent terminal assessments which included evaluating muscle force, contractile properties, motor unit numbers, and wet weight. Muscles were then harvested for immunohistological examination of motor end plate reinnervation. Results: Muscles that received daily electrical stimulation had a significantly greater (2-fold) number of motor units as characterized using electromyographic methods (8.7 ± 0.9 vs. 3.0 ± 0.4, p<0.01). This result was confirmed when muscle end plates were visualized showing a much greater number of intramuscular axons and innervated end plates. Muscle weights, forces, contractile, and fatiguing properties were no different between groups. These results provide evidence that the improved reinnervation may be due to antidromic depolarization of axons proximal to the repair site. Significance: Early treatment of denervated muscle using electrical stimulation can significantly enhance early muscle reinnervation. As the muscle continues to become reinnervated, tailoring the stimulation paradigm to improve muscle force and fatigability may lead to shorter recovery times and reduce extensive physiotherapy and rehabilitation requirements.
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