Sacral neuromodulation is an established technique for the treatment of chronic intractable pelvic and anorectal pain. Stimulation of sacral roots S2–4 is typically associated with therapeutic paresthesia, while stimulation of the S1 nerve root causes unwanted leg paresthesia. Here we describe and evaluate the use of intraoperative electromyography (EMG) of the gastrocnemius, foot intrinsic muscles, and anal sphincter as an adjunct to epidural stimulator placement.Materials and Methods:
Two female patients with intractable pelvic pain underwent implantation of sacral epidural paddles with intraoperative EMG. These cases were retrospectively reviewed to evaluate intraoperative EMG activation and therapeutic paresthesia.Results:
We found cephalad-to-caudal transitions in EMG activation with stimulation: medial gastrocnemius to foot intrinsics to anal sphincter. Coactivation of foot intrinsic muscles with anal sphincter and absence of medial gastrocnemius stimulation correlated with therapeutic perineal paresthesia.Conclusions:
Intraoperative EMG of the gastrocnemius, foot intrinsics, and anal sphincter may be a useful adjunct to sacral stimulation for pelvic pain.