The anatomy of Trans-Obturator Posterior Anal Sling (TOPAS) and dynamics of potential mechanism of action.

Abstract

The aim of this study was to investigate the course of the transobturator posterior anal sling and its relationship to anatomical structures. The transobturator anal sling procedure was performed in four fresh-frozen pelvises. The pelvises were dissected and the structures adjacent to the sling and the course of the sling were identified and measurements obtained. The transobturator posterior anal sling was inserted 2 ± 0.5cm posteriorly to the anus, and 2.5 ± 0.5cm caudal to the coccyx under the levator plate at the level of the puborectalis muscle. The tape was 3.5 ± 0.5cm from the pubic symphysis and 2.3 ± 0.3cm from the obturator canal at entry into the pelvic cavity. The tape passed 2.3 ± 0.3cm inferior-medial to the obturator canal. At entry, the sling passed lateral to the ischiopubic ramus through the following structures: gracilis, adductor brevis, obturator externus, obturator membrane, and beneath the obturator internus muscle. The sling traveled 2-3 ± 0.5cm over the iliococcygeus muscle and perforated the iliococcygeus fibers 0-2cm medial to arcus tendinous levator ani. The posterior division of the obturator nerve was 2.8 ± 0.7cm from the tape. The anterior division of the obturator nerve was 3.4 ± 0.8cm from the tape. The device passed 1.1 ± 0.4cm from the most medial branch of the obturator vessels. The transobturator posterior anal sling travels mostly in the avascular area of the ischiorectal fossa and posterior to the puborectalis muscle as intended.