MRI biomarker of muscle composition is associated with severity of pelvic organ prolapse

Background: The pathophysiology of pelvic organ prolapse is largely unknown. We hypothesized that reduced muscle mass on magnetic resonance defecography (MRD) is associated with increased pelvic floor laxity. The aim of this study was to compare the psoas and puborectalis muscle mass composition and cross-sectional area among patients with or without pelvic laxity. Methods: An observational retrospective study was conducted on women > age 18 years old who had undergone MRD for pelvic floor complaints from January 2020 to December 2020 at Stanford Pelvic Health Center. Pelvic floor laxity, pelvic organ descent, and rectal prolapse were characterized by standard measurements on MRD and compared to the psoas (L4 level) and puborectalis muscle index (cross-sectional area adjusted by height) and relative fat fraction, quantified by utilizing a 2-point Dixon technique. Regression analysis was used to quantify the association between muscle characteristics and pelvic organ measurements. Results: The psoas fat fraction was significantly elevated in patients with abnormally increased resting and strain H and M lines (p < 0.05) and increased with rising grades of Oxford rectal prolapse (p = 0.0001), uterovaginal descent (p = 0.001) and bladder descent (p = 0.0005). In multivariate regression analysis, adjusted for age and body mass index, the psoas fat fraction (not muscle index) was an independent risk factor for abnormal strain H and M line; odds ratio (95% confidence interval) of 17.8 (2–155.4) and 18.5 (1.3–258.3) respectively, and rising Oxford grade of rectal prolapse 153.9 (4.4–5383) and bladder descent 12.4 (1.5–106). Puborectalis fat fraction was increased by rising grades of Oxford rectal prolapse (p = 0.0002). Conclusions: Severity of pelvic organ prolapse appears to be associated with increasing psoas muscle fat fraction, a biomarker for reduced skeletal muscle mass. Future prospective research is needed to determine if sarcopenia may predict postsurgical outcomes after pelvic organ prolapse repair.