Optimal location for eliciting the tibial H-reflex and motor response

Abstract

Introduction: Although there are numerous protocols to adjust the amplitude of the Hoffmann reflex (H-reflex) relative to the size of the direct motor response (M-response), the optimal stimulating location has not been described. We sought to determine the optimal positioning of the stimulating cathode when evoking the tibial nerve H-reflex and M-response. Methods: A small cathode was placed on defined points in the popliteal fossa while an anode was fixed on the patella. The tibial nerve was stimulated electrically, and the response of the soleus muscle was recorded using intramuscular and surface electromyography. Results: We found that more-lateral points along a line drawn across the popliteal fossa were the best locations to obtain only the M-response, whereas stimulating the midpoint was optimal for obtaining only the H-reflex. Discussion: By using specified locations for electrical stimulation to evoke H-reflex and M-response, the functionality of the tibial nerve can be assessed.