A multi-compartment 3-D finite element model of rectocele and its interaction with cystocele

Abstract

We developed a subject-specific 3-D finite element model to understand the mechanics underlying formation of female pelvic organ prolapse, specifically a rectocele and its interaction with a cystocele. The model was created from MRI 3-D geometry of a healthy 45 year-old multiparous woman. It included anterior and posterior vaginal walls, levator ani muscle, cardinal and uterosacral ligaments, anterior and posterior arcus tendineus fascia pelvis, arcus tendineus levator ani, perineal body, perineal membrane and anal sphincter. Material properties were mostly from the literature. Tissue impairment was modeled as decreased tissue stiffness based on previous clinical studies. Model equations were solved using Abaqus v 6.11. The sensitivity of anterior and posterior vaginal wall geometry was calculated for different combinations tissue impairments under increasing intraabdominal pressure. Prolapse size was reported as POP-Q point at point Bp for rectocele and point Ba for cystocele. Results show that a rectocele resulted from impairments of the levator ani and posterior compartment support. For 20% levator and 85% posterior support impairments, simulated rectocele size (at POP-Q point: Bp) increased 0.29 mm/cm H2O without apical impairment and 0.36 mm/cm H2O with 60% apical impairment, as intraabdominal pressures increased from 0 to 150 cm H2O. Apical support impairment could result in the development of either a cystocele or rectocele. Simulated repair of posterior compartment support decreased rectocele but increased a preexisting cystocele. We conclude that development of rectocele and cystocele depend on the presence of anterior, posterior, levator and/or or apical support impairments, as well as the interaction of the prolapse with the opposing compartment.

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

“…Tie constraints in ABAQUS that binds two shared surfaces were used to couple motions of parts which are biologically connected (e.g., the coccygeus muscle and the coccyx) and to model the connecting effects of fasciae (e.g., the tendineous arch of levator ani muscle between the iliococcygeus muscle and the obturator internus muscle). Connector elements, with the ability to model connective tissues such ligaments [12], were employed in this study to model the uterosacral and cardinal ligaments. The Abaqus/Explicit solver was used for finite element method implementation.…”

“…Computer simulation using the finite element method (FEM) has been proven to be a useful tool due to its ability to conveniently simulate various impairment conditions and keep these comparisons based on the same subject, computer simulation using finite element method (FEM) has been proven a useful tool [11]. Several computer models developed from MR images have been reported recently in studies of female pelvic floor dysfunctions such as pelvic organ prolapse [12,13], childbirth related levator ani muscle damages [14,15] and ligament impairment [16]. However, the clinical application of these models and their comparisons to the true dynamic response of the pelvis is limited due to either 1) missing or simplified important anatomical structures (e.g., the bladder, rectum, vaginal canal, uterus are not included [14,15]; buffering fatty tissues are not included [12–16]) or 2) less accurate realization of boundary conditions (e.g., direct inferior displacement is applied on the uterus [13]; intra-abdominal pressure is directly applied on the muscle [16] or vaginal wall [12] that are studied).…”

What's new in the functional anatomy of pelvic organ prolapse?

“…Levator ani muscle impairment caused a larger urogenital hiatus size, longer length of the distal vagina exposed to a pressure differential, larger apical descent, and resulted in a larger cystocele size. Interactions between the anterior and posterior compartments have also been demonstrated 8 that help explain postoperative development of new prolapse in the opposite compartment, despite its support appearing normal prior to the operation. 9 …”

The Single-Incision Sling to Treat Female Stress Urinary Incontinence: A Dynamic Computational Study of Outcomes and Risk Factors

“…Tie constraints that bind two shared surfaces were used to couple motions of parts which are biologically connected and to model the connecting effects of fasciae (e.g., the tendinous arch of levator ani muscle). Connector elements, with the ability to model connective tissues, such as ligaments [17], were employed in this study to model the ligaments surrounding the urethra (e.g., the pubourethral ligament). Although soft tissues show viscoelastic behavior [23,24], a previous study found quasi-linear material property of urological soft tissues when the stress level is under 70% of the maximal stress value [25].…”

“…Computational models, based on realistic female pelvic anatomy, offer a useful tool for quantitative biomechanical analysis to female pelvic floor dysfunctions [14]. Models have been employed to study pelvic organ prolapse [15][16][17], childbirth-related trauma [18,19], and ligament impairment [20]. However, these models often missed some necessary anatomical structures that maintain the integrity of the natural pelvic anatomy, and efforts have been rarely made to study the interventional treatments.…”