Impact of vaginal parity and aging on the architectural design of pelvic floor muscles

Abstract

Background Vaginal delivery and aging are key risk factors for pelvic floor muscle dysfunction, which is a critical component of pelvic floor disorders. However, alterations in the pelvic floor muscle intrinsic structure that lead to muscle dysfunction because of childbirth and aging remain elusive. Objectives The purpose of this study was to determine the impact of vaginal deliveries and aging on human cadaveric pelvic floor muscle architecture, which is the strongest predictor of active muscle function. Study Design Coccygeus, iliococcygeus, and pubovisceralis were obtained from younger donors who were ≤51 years old, vaginally nulliparous (n = 5) and vaginally parous (n = 6) and older donors who were >51 years old, vaginally nulliparous (n = 6) and vaginally parous (n = 6), all of whom had no history of pelvic floor disorders. Architectural parameters, which are predictive of muscle's excursion and force-generating capacity, were determined with the use of validated methods. Intramuscular collagen content was quantified by hydroxyproline assay. Main effects of parity and aging and the interactions were determined with the use of 2-way analysis of variance, with Tukey's post-hoc testing and a significance level of.05. Results The mean age of younger and older donors differed by approximately 40 years (P =.001) but was similar between nulliparous and parous donors within each age group (P >.9). The median parity was 2 (range, 1-3) in younger and older vaginally parous groups (P =.7). The main impact of parity was increased fiber length in the more proximal coccygeus (P =.03) and iliococcygeus (P =.04). Aging changes manifested as decreased physiologic cross-sectional area across all pelvic floor muscles (P