Biomechanics of pelvic organ prolapse.

Abstract

Pelvic organ prolapse (POP), caused by damage of the support system in the pelvic floor, is downward descent of female pelvic organs, resulting in protrusion of the vagina, uterus, or both. It has been reported recently that POP has a prevalence of 3%6% when defined by symptoms and up to 50% based on a vaginal examination [1]. POP is basically divided into anterior vaginal wall prolapse and posterior vaginal wall prolapse. The most common type of POP is anterior vaginal wall prolapse, clinically known as the cystocele [2]. Most POP patients have damages in the support muscles or ligaments or both of them. Biomechanical nature of POP is of great significance for clinical prevention and treatments. Risk factors for POP include vaginal delivery, chronic increased intraabdominal pressure caused by obesity, chronic respiratory disease and/or related cough, chronic constipation, repetitive occupational activities, and pregnancy [3,4]. However, the mechanism of POP remains unclear. Delancey [5] divided the support system of the pelvic floor into three levels (Figure 1). The first level is provided by the cardinal and uterosacral ligaments. The second level includes the “hammock-like” levator ani muscle and pelvic fascia that covers the muscles and provides reinforcements. The third level is the distal support by the perineal body, counteracting the downward gravity of the organs. Figure 1 (color online) Three levels of the support system of the normal pelvic floor. R, rectum; CL, cardinal ligament; UL, uterosacral ligament; LA, levator ani muscle; Ut, uterus; Va, vagina; PB, perineal body. The model was reconstructed based on magnetic resonance images from a female volunteer (55 years old, para 2; body mass index (BMI) 20.96 kg m).