MP52-16: Elucidation of urinary incontinence mechanism after robot-assisted radical prostatectomy focusing on the sling mechanism by the levator ani muscle.

Masao Kataoka*, Tomoyuki Koguchi, Junya Sato, Yuichi Sato, Hidenori Akaihata, Yoshiyuki Kojima, Fukushima, Japan

Introduction: The aim of this study was to clarify the mechanism of urinary incontinence after robot-assisted radical prostatectomy (RARP) focusing on changes in the pelvic floor muscles and function of sling mechanism.

Methods: A total of 323 patients underwent RARP in our hospital from 2014 to 2019 were included and retrospectively analyzed. All patients were analyzed levator ani muscles, especially puborectalis muscle (PRM) and rectourethral muscle (RUM) by preoperative and postoperative MRI. The movement of the levator ani muscle was analyzed by postoperative cine MRI. One-hour pad test was underwent 1, 3, 6, 9 and 12 months after surgery to evaluate urinary continence. The maximum urethral closure pressure (MUCP) was also measured before and after surgery by measuring urethral pressure (UPP). The correlation between postprostatectomy incontinence (PPI) and various factors was analyzed by regression analysis.

Results: The urinary incontinence rates which was evaluated by one-hour pad test, at 1, 3, 6, 9 and 12 months after surgery were 40.2%, 63.5%, 73.1%, 74.6% and 76.8%, respectively. A significant correlation between PPI (1,3,6,9 and 12M) and postoperative PRM cross-sectional area change after RARP (p-value: <0.01, <0.001, <0.001, <0.01, <0.001) was observed. A significant correlation was also observed between changes PRM cross sectional area and pubic bone-perineal body (PP) distance changes and vesicourethral junction (VUJ) distance change (p-value: <0.01, <0.01). A significant correlation between PPI (1,3,6,9 and 12M) and PP (OR:-0.20,-0.32,-0.26,-0.22,-0.20, p-value: <0.001, <0.001, <0.001, <0.001, <0.001, respectively), VUJ before and after abdominal pressure loading (OR: -0.31, -0.42, -0.34, -0.28, -0.31, p-value: <0.01, <0.001, <0.001, <0.01, <0.001, respectively) was observed by cineMRI.

Conclusions: The PRM is thought to be directly or indirectly connected to the RUM. It is speculated that the PRM muscle and the RUM work as a sling and affect urinary continence. Postoperative reduction of PRM cross-sectional area caused a decrease in the function of the support mechanism as a urethral sling, which affected distance between PP or VUJ and as a result, induced PPI. The levator ani muscles functioned as a sling and was thought to be associated with urinary continence by adding force toward the pubis to the VUJ.

Source of Funding: none