A 2D equivalent mechanical model of the whole pelvic floor and impairment simulation

We developed a complete 2D equivalent mechanical model of the pelvic floor based on magnetic resonance imaging (MRI) images of a 35-year-old healthy woman. This model can simulate anterior vaginal prolapse (AVP) due to soft tissue impairment. Thus, we can study the mechanism of prolapse formation from a mechanical perspective and improve the assessment and treatment of the condition in clinical practice. Based on 2D MRI image parameter measurements and computer-aided design methods, the 2D equivalent mechanical model of the whole pelvic floor in the sagittal plane was accurately reconstructed, which includes all necessary tissues of the pelvic floor system. Material parameters were mainly from the literature. We simulated the impairment by reducing the tissue's mechanical properties, and numerical simulations predicted the mechanical response and morphological changes of the healthy and impaired pelvic floor in different states. In six intra-abdominal pressure (IAP) states (8.4-208.9 cmH₂ O), the maximum cervical descent in the impaired pelvic floor was 0.3-18.521 mm, which was much greater than that in the healthy pelvic floor (0.14-6.55 mm). Once the impairment occurred (0%-25%), there was a significant increase in maximum displacement, stress, and cervical descent (30.9-36.5 mm, 0.56-1.12 MPa, 4.6-12.1 mm), and a clinically similar prolapse shape occurred. Simple supine and standing will not cause prolapse. The formation of prolapse is closely related to vaginal tissue impairment. In the standing position, the main forces on the healthy pelvic floor system are distributed horizontally posteriorly and inferiorly, reducing the burden in the vertically downward direction.