Assessment of urethral support using MRI-derived computational modeling of the female pelvis

Abstract

Introduction and Hypothesis This study aims to assess the role of individual anatomical structures and their combinations to urethral support function. Methods A realistic pelvic model was developed from an asymptomatic female subject’s MR images for dynamic biomechanical analysis using the finite element method. Validation was performed by comparing simulation results with dynamic MR imaging observations. Weaknesses of anatomical support structures were simulated by reducing their material stiffness. Urethral mobility was quantified by examining the urethral axis excursion from rest to the final state (Intra-abdominal pressure = 100cmH2O). Seven individual support structures and five of their combinations were studied. Result Among seven urethral support structures, weakening the vaginal walls, puborectalis muscle and pubococcygeus muscle generated the top three largest urethral excursion angles. A linear relationship was found between urethral axis excursions and intra-abdominal pressure. Weakening all three levator ani components together caused a larger weakening effect than the sum of each individually weakened component, indicating a nonlinearly-additive pattern. The pelvic floor responded to different weakening conditions distinctly: weakening the vaginal wall developed urethral mobility through collapsed vaginal canal while weakening the levator ani showed a more uniform pelvic floor deformation. Conclusions The computational modeling and dynamic biomechanical analysis provides a powerful tool to better understand the dynamics of the female pelvis under pressure events. The vaginal walls, puborectalis and pubococcygeus are the most important individual structures in providing urethral support. The levator ani muscle group provides urethral support in a well-coordinated way with a nonlinearly-additive pattern.

Functional mapping of the pelvic floor and sphincter muscles from high-density surface EMG recordings

“…The EMG probes can also help advance pelvic biomechanical modeling and muscle imaging research [20,21]. Many computational pelvic floor models have been developed recently to investigate the biomechanics of incontinence and prolapse [22].…”

Pelvic floor dynamics during high-impact athletic activities: A computational modeling study

“…The 3D computational model of the female pelvis used in this study was adopted from previous modeling works [13, 14]. Briefly, T2 weighted MR images of the pelvis of a healthy female (21-year-old, white, Caucasian, nulliparous, nonsmoker, non-athletic, body mass index=22) were obtained axially with a 3T MR imaging scanner (Trio Tim, Siemens, Germany), with a slice thickness of 3mm, matrix of 320 × 160, field of view of 430mm and pixel size of 1.344mm.…”

“…A specially-designed bodyfill part was used to represent the intra-abdominal contents and to allow the transmission of IAP during athletic activities. This modeling approach has been validated using dynamic MR imaging in our previous study [13]. …”

“…Consequently, elastic material properties were used to represent mechanical behaviors of soft tissues. Most soft tissues were modeled as linear elastic materials [13, 14], as it has been found that linear elasticity produces a displacement field similar to that produced using nonlinear elasticity, while benefiting the computation efficiency [19]. However, to better characterize the behaviors of the bladder and LAM, hyperelastic models were adopted [16, 31].…”

“…Recent advances in medical imaging allowed the reconstruction of computer models based on high-resolution MR images [13, 14], maximally preserving anatomical integrity and correctness. Computer simulation provides a reliable tool for characterizing dynamic biological processes that are otherwise difficult to observe through traditional techniques [15–24].…”