To stimulate the foot, a quadrapolar electrode enters the midline at L2–3 crossing over the L3–4 disc space before it is then rotated to, but not through, the L4 foramen (Figs. 18.11 and 18.14). This positioning allows the electrode to remain “in line” with the ipsilateral L4, L5, and S1 roots. It is then programmed at the foramen with an anode and up to three proximal contacts as cathodes. This allows depolarization of all three roots as they course cephalad lateral to medial. A second electrode can be applied if needed depending on the stimulation pattern obtained (Fig. 18.11). Given the reduced cerebrospinal fluid and proximity to the root, most patients feel initial paresthesia at low thresholds (1.0–1.5 V), with maximal tolerable intensity approximately 1.5 times that level (1.5–2.5 V).

To stimulate the pelvic roots, a quadrapolar electrode enters the midline at L2–3 and remains there until it crosses S1 before it is rotated to, but not through, the ipsilateral S2 foramen. A second electrode is positioned in the same fashion contralaterally for bilateral pathology (Figs. 18.1, 18.2, 18.3, 18.4, 18.5, 18.6, 18.7, 18.8, 18.9, and 18.10). These electrodes are also programmed with a distal anode at the foramen, and up to three cathodes over the proximal S2–4 roots, respectively. This allows an anatomical placement for stimulating all of the following conditions: urge incontinence, neurogenic bowel dysfunction, urgency-frequency syndromes (including detrusor dysfunction), pudendal neuralgia, vulvadynia, and interstitial cystitis [15, 16]. This may be done as well with small paddle style electrodes through a small S1 laminotomy (Fig. 18.12). To ease placement of the paddle toward the S2 foramen, a Penfield 3 can be used at the laminotomy to elevate the electrode into position (Fig. 18.13). Given the relative lack of cerebrospinal fluid at the S2 level, most patients feel initial paresthesia at low thresholds (0.7–1.2 V) with maximal tolerable intensity approximately 1.5 times that level (1.2–1.7 V).