Abstract 67: Electrical Muscle Stimulation Does Not Influence Synkinetic Reinnervation in a Novel Rat Model of Peripheral Nerve Injury and Repair

Joseph Catapano, MD, Michael P. Willand, MASc, PhD, Tessa Gordon, PhD, Gregory H. Borschel, MD From the University of Toronto, Toronto, ON, Canada. PURPOSE: Recovery after nerve repair is limited by axon misdirection. Studies have shown that electrical muscle stimulation (EMS) after nerve repair reduces synkinetic reinnervation. Conclusions were based on functional measurements with no direct evidence. Here, we used a novel rat model to directly investigate whether EMS increases the proportion of motoneurons reinnervating original targets after injury. METHODS: The original soleus motoneuron pool was labeled with True-Blue. After 1 week, the right lateral gastrocnemius soleus nerve was transected and repaired, and the soleus muscle was implanted with electrodes. One group received EMS with a natural activation paradigm. Two months later, the right soleus nerve was retrograde labeled with Fluoro-Ruby to label regenerated motoneurons. The contralateral uninjured lateral gastrocnemius and soleus nerves were labeled with True-Blue and Fluoro-Ruby, respectively, to compare the spatial distribution of the contralateral motoneuron pool with the injured side. The number of regenerated axons was counted with histomorphometry. RESULTS: Three-dimensional reconstructions of labeled motoneuron pools demonstrated the majority of motoneurons regenerating to the soleus muscle derived from the lateral gastrocnemius motoneuron pool. EMS did not increase the proportion of original soleus motoneurons regenerating toward the soleus muscle (EMS: 10.9% ± 2.3% vs Sham: 15.5% ± 9.9%). There were no differences in axons counts (EMS: 200 ± 68 vs Sham: 163 ± 47). CONCLUSIONS: Although studies suggest that EMS reduces muscle atrophy, our model does not support the use of EMS to reduce axonal misdirection after nerve repair.