EMG monitoring of stimulating electrode position in implantation of subcutaneous peroneal stimulators.
Implantation of subcutaneous peroneal stimulators requires careful positioning to obtain a good response. With the patient lying down during the surgical procedure, ankle dorsal flexion was not always satisfactory during gait. Instead of dorsal flexion the stimulus could give an excessive eversion or a coactivation of ankle antagonists. To select the correct electrode position, the responses to single stimulation pulses were monitored in the tibialis anterior, peroneus longus and triceps surae muscles by surface EMG electrodes. With the patient standing, a strong contraction of the anterior tibial muscle without excessive contraction of the peroneus longus muscle was first determined by surface stimulation. The EMG responses were then recorded with the patient lying in the position required for implantation. The records were used as a guideline during surgery, during which positioning of the electrodes was monitored by the EMG responses. The method, tested on 2 healthy adults and 13 patients, resulted in reliable positioning of the stimulating electrodes.