Laparoscopic implantation of neural electrodes on pelvic nerves: an experimental study on the obturator nerve in a chronic minipig model

Abstract

Laparoscopic exposure of pelvic nerves has opened a new area in the field of neuromodulation. However, electrode design and material deterioration remain issues that limit clinical application. The objective of this study was to evaluate experimentally the laparoscopic implantation of different types of neural electrodes in order to achieve functional and selective electrical stimulation of pelvic nerves. This was a prospective comparative study of the laparoscopic implantation and tolerance and efficacy of three monopolar cuff electrodes implanted on the obturator nerve in ten Göttingen minipigs (18-20 months old; 14.5-24 kg body weight). Animals were allocated to two groups. A 3-mm-diameter laparoscopic instrument was used during dissection of paravesical fossa and obturator nerve on both sides in order to minimize nerve damage. In all animals, a "split-cylinder" cuff electrode was implanted around the left obturator nerve. On the right side, a "lasso" cuff electrode was implanted in the first group and a "closed-cylinder" cuff was implanted in the second group. Electrical stimulation (0-5 V, 20 Hz) was performed for implanted electrodes on days 0, 7, 15, 30, 45, 60, and 90. Current intensity thresholds were identified by palpation of muscle contraction. Strength developed according to stimulation level and was measured using weight transducers. All procedures were performed by laparoscopy. Mean operative times differed significantly among groups, the shortest being for split-cylinder electrodes (P = 0.0002). No electrical spread phenomena were observed. Initial thresholds were below 1.5 V (range = 0.5-1.3); however, a significant rise was observed, with time to a maximum of 2.7 V (P < 0.0001). Only split-cylinder electrodes remained functional after 3 months. The mean value of maximum strength remained stable during the study period (P = 0.21, NS). The laparoscopic approach to implanting neuroprostheses seems to be very attractive. Furthermore, this approach could allow highly selective nerve stimulation to be achieved using simpler devices such as split-cylinder monopolar electrodes.