Introduction and hypothesis: We investigated whether factors influencing pelvic floor hiatal closure are inter-related or independent, hypothesizing that (1) hiatus size is moderately correlated with levator defect, pelvic floor muscle strength, and change in hiatus size with contraction and (2) urogenital hiatus (UGH) and levator hiatus (LH) measures are similar in patients with anterior wall (AW) and posterior wall (PW) prolapse.
Methods: This cross-sectional case-control study included subjects with AW prolapse (n = 50), PW prolapse (n = 50), and normal support (n = 50). Hiatus measurements and levator defects were assessed on MRI, and vaginal closure force was measured with an instrumented speculum. Pearson correlation coefficients and simple and multivariable linear regression models were performed.
Results: During contraction, LH narrowed 47% more in the PW compared to AW group (p = 0.001). With straining, LH lengthened 34% more in the PW than AW group (p < 0.001). With straining, UGH and LH lengthening was greater by 72% and 44% in those with major compared to no/minor defect (p < 0.001 and p = 0.004). Contraction strength explained, at most, 4% of UGH (r = 0.17) or LH (r = 0.20) shortening during contraction (r = 0.17 and r = 0.20, respectively), indicating that these factors are largely independent. After controlling for prolapse size, resting UGH and levator defect status were associated with straining UGH (p < 0.001, p = 0.004), but muscle strength and resting tone were not.
Conclusions: Hiatus measures are complex and differ according to prolapse occurrence and type. They are, at best, only weakly correlated with pelvic floor muscle strength and movement during contraction.
Keywords: Levator defect; Levator hiatus; MRI; Muscle strength; Urogenital hiatus.