Upright and supine assessment of pelvic floor muscle defects in women with and without prolapse.

The levator ani muscle (LAM), crucial for pelvic organ support, can develop defects that contribute to pelvic floor disorders (PFD) like pelvic organ prolapse (POP). Factors such as childbirth, aging, and menopause increase the risk of LAM damage. While MRI is commonly used to assess LAM, most studies use the supine position, potentially underestimating POP severity. Upright MRI offers a more accurate view of pelvic floor support under natural conditions. The aim of this study was to compare the pelvic floor support across four groups of women-nulliparous, parous premenopausal, parous postmenopausal, and women with POP, by analysing pubococcygeus muscle (PCM) and iliococcygeus muscle (ICM) defects and the iliococcygeus angle (ICA) using a tiltable magnetic resonance imaging (MRI) scanner. Sixty-three women were included and divided into 4 groups: 15 nulliparous (Nulli), 15 parous-premenopausal (Par-pre), 15 parous-postmenopausal (Par-post) and 18 patients with minimum stage 2 prolapse of the anterior vaginal wall or uterus (POP). Women underwent supine and upright MRI scans. PCM and ICM defects were assessed on both the supine and upright scans. Defects were categorized as "none", "minor" or "major" following previously established guidelines. Using upright MRI scans and manual segmentation of the LAM, the ICA was determined in 5planes from anterior to posterior. Statistical testing was performed using one-way ANOVA and Bonferroni post-hoc test. The results show that nulliparous women had no PCM defects. Par-pre, Par-post and POP groups showed varying rates of major PCM defects (7.7%, 16.7%, and 68.8% respectively). Minor ICM defects were present in all groups (21.4% (Nulli), 61.5% (Par-pre), 66.7% (Par-post), and 55.3% (POP)), but only the POP group had major defects (43.8%). The ICA was significantly sharper (p < 0.001) in the POP group compared to other groups. A decrease in pelvic floor support, assessed by PCM damage in supine and ICM damage and a sharper total ICA done in upright, was measured in the POP population, as compared to healthy women. Minor muscle defects were common across all groups, but major defects exclusively in POP patients. This fundamental insight on muscle quality adds to our anatomical knowledge on the occurrence of POP.