Modelling of Soft Connective Tissues to Investigate Female Pelvic Floor Dysfunctions.

Aroj Bhattarai,Manfred Staat

doi:10.1155/2018/9518076

Abstract

After menopause, decreased levels of estrogen and progesterone remodel the collagen of the soft tissues thereby reducing their stiffness. Stress urinary incontinence is associated with involuntary urine leakage due to pathological movement of the pelvic organs resulting from lax suspension system, fasciae, and ligaments. This study compares the changes in the orientation and position of the female pelvic organs due to weakened fasciae, ligaments, and their combined laxity. A mixture theory weighted by respective volume fraction of elastin-collagen fibre compound (5%), adipose tissue (85%), and smooth muscle (5%) is adopted to characterize the mechanical behaviour of the fascia. The load carrying response (other than the functional response to the pelvic organs) of each fascia component, pelvic organs, muscles, and ligaments are assumed to be isotropic, hyperelastic, and incompressible. Finite element simulations are conducted during Valsalva manoeuvre with weakened tissues modelled by reduced tissue stiffness. A significant dislocation of the urethrovesical junction is observed due to weakness of the fascia (13.89 mm) compared to the ligaments (5.47 mm). The dynamics of the pelvic floor observed in this study during Valsalva manoeuvre is associated with urethral-bladder hypermobility, greater levator plate angulation, and positive Q-tip test which are observed in incontinent females.

Highlights

The structure of the female pelvic floor is an interrelated system of bony pelvis, muscles, fasciae, and ligaments with multiple functions
The results presented in this study offer the capability of a robust computational model of the female pelvic floor which poses a good start to improve our understanding of the stress urinary incontinence (SUI)
A three-dimensional computer model presented in this numerical study shows its capability to better understand the dynamics of the female pelvic floor and the phenomena of stress urinary incontinence

Summary

Introduction

The structure of the female pelvic floor is an interrelated system of bony pelvis, muscles, fasciae, and ligaments with multiple functions. Several computational models have appeared to study the phenomenon of the pelvic floor dysfunctions focusing mainly on the anatomy of the pelvic viscera, dense fibromuscular ligaments, and the muscles [18,19,20,21,22,23]. Wherever studied as an integrated structure, alteration of the fascia constituents, mainly elastin-collagen fibres, adipose tissue and smooth muscles could greatly influence the overall tissue mechanics. As a step, we have considered the soft tissue mechanics at microscopic level using the mixture model On this basis, this study describes improvements in a 3D finite element model of the female pelvic floor which considers the realistic support of the organs at the pelvic side walls, employs the improvement of our previous FE model [24, 25], and incorporates the realistic anatomy and boundary conditions of the endopelvic (pubocervical and rectovaginal) fascia. Several computations are carried out with the presented computational model with healthy and damaged supporting tissues, and comparisons are made to understand the pathophysiology of the SUI

Sheet Plastination to Finite Element Models

Assumptions on the Mathematical Modelling of Fascia

Model Formation

Results and Discussion

Conclusions