Multimodal evaluation of pelvic floor muscle function using ultrasound strain imaging and surface electromyography

The levator ani muscle (LAM), comprising the puborectalis, pubococcygeus, and iliococcygeus muscles, is essential for pelvic organ support. Damage to the LAM due to vaginal childbirth, aging, heavy lifting, or high BMI can lead to pelvic floor disorders, including pelvic organ prolapse (POP). Conservative treatment by means of a pessary is successful in approximately 60% of the patients. However, the interaction between LAM function and pessary success is poorly understood, limiting the successful treatment rates. This study investigates LAM function in three different groups of women: POP patients with a successful ring pessary fit (n=17), POP patients with an unsuccessful ring pessary fit (n=20), and asymptomatic parous women (n=20). The objective of this study is to test whether PFM function differs between these groups. Measurement included 4D transperineal ultrasound (TPUS) mean principal strain imaging and vaginal surface electromyography (sEMG, 24-electrode MAPLe probe) during maximal voluntary contraction (MVC). Anatomical integrity of the LAM was scored using standardized ultrasound-based avulsion criteria. Non-parametric statistical tests evaluated group differences and strain-EMG correlations. Analysis of 57 women revealed no significant differences in mean LAM principal strain or peak sEMG amplitude between successful pessary users, unsuccessful pessary users, and asymptomatic controls. Unsuccessful pessary users showed higher rates of levator avulsions compared to asymptomatic women. A moderate negative correlation between mean principal strain and sEMG validated the anticipated inverse relationship between muscle deformation and electrical activation during contraction. These results suggest voluntary pelvic floor muscle function remains comparable across groups despite anatomical defects, implying that anatomical integrity may predict pessary success more than muscle function. Findings highlight complementary roles of strain-based muscle assessment and sEMG in functional muscle assessment and call for larger studies to confirm implications for POP management.