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

BACKGROUND

The aim of this study was to investigate the course of the transobturator posterior anal sling and its relationship to anatomical structures.

METHODS

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.

RESULTS

The transobturator posterior anal sling was inserted 2 ± 0.5 cm posteriorly to the anus, and 2.5 ± 0.5 cm caudal to the coccyx under the levator plate at the level of the puborectalis muscle. The tape was 3.5 ± 0.5 cm from the pubic symphysis and 2.3 ± 0.3 cm from the obturator canal at entry into the pelvic cavity. The tape passed 2.3 ± 0.3 cm 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 ± 0.5 cm over the iliococcygeus muscle and perforated the iliococcygeus fibers 0-2 cm medial to arcus tendinous levator ani. The posterior division of the obturator nerve was 2.8 ± 0.7 cm from the tape. The anterior division of the obturator nerve was 3.4 ± 0.8 cm from the tape. The device passed 1.1 ± 0.4 cm from the most medial branch of the obturator vessels.

CONCLUSIONS

The transobturator posterior anal sling travels mostly in the avascular area of the ischiorectal fossa and posterior to the puborectalis muscle as intended.