Biomechanical Characterization of the Pelvic Floor in Patients With Organ Prolapse: A Finite Element Analysis Based on MRI and Defecography.

Abstract

Objective: Pelvic organ prolapse (POP) is a prevalent condition with complex biomechanical mechanisms. This retrospective observational study aimed to quantitatively evaluate pelvic floor biomechanics in healthy and POP subjects using subject-specific finite element (FE) models derived from high-resolution MRI and dynamic magnetic resonance defecography (MRD).

Methods: Subject-specific 3D FE models of the pelvic floor were reconstructed for a healthy control and patients with anterior, apical, and posterior POP. To ensure anatomic representativeness, cases closest to the median levator ani muscle (LAM) volume of each cohort were selected. Nonlinear hyperelastic properties were assigned, and physiological intra-abdominal pressures (eg, Valsalva) were simulated to analyze mechanical responses.

Results: Under Valsalva loading, the LAM acted as the primary load-bearing structure. In the healthy model, maximum stress was concentrated at the puborectalis region (1.43 kPa). Conversely, POP models exhibited pathologic remodeling (increased LAM volume and surface area) and significantly altered biomechanics. The posterior POP model demonstrated the most severe mechanical deterioration, with peak stress reaching 5.34 kPa and broader stress concentration zones compared with the control. Furthermore, maximum structural deformation in POP models was substantially greater under identical loads, aligning with clinically observed macroscopic injury patterns.

Conclusions: MRD-driven FE modeling effectively quantifies the biomechanical deterioration in POP. The pathologic stress concentration at the puborectalis and the progressive loss of the LAM's load-dispersing capacity provide crucial imaging-based biomechanical evidence to guide individualized surgical planning and pelvic rehabilitation.