For pelvic pain, the electrode is typically rotated off the midline toward the S2 foramen. For coccygodynia it generally remains midline, but stops at the S3 level (more caudal placements frequently produce painful stimulation). Other disorders may require other targeting. When the electrodes appear appropriately positioned on anteroposterior and lateral fluoroscopy, attention is turned to the physiological assessment of electrode position. When the nerve roots are stimulated, SSEP or motor unit action potentials (MUAPs) via EMG serve as the main monitoring tool used to verify accurate position of the electrodes over the roots of interest. The dermatomal distribution of postoperative paresthesia can be predicted from the pattern of intraoperative stimulation activation and is clearly associated with the specific pattern of responses coming from the muscles of the lower extremities. For example, the placement of an S2–3 paddle may result in EMG activation in adductor hallucis muscle (Fig. 21.2), which will correlate with an S2–3 paresthesia. The typical correlation pattern between muscles in the lower extremity and induced postoperative paresthesia is represented in Table 21.1.