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Research Papers

Vaginal Changes Due to Varying Degrees of Rectocele Prolapse: A Computational Study

[+] Author and Article Information
Arnab Chanda

Department of Aerospace Engineering
and Mechanics,
University of Alabama,
Tuscaloosa, AL 35487
e-mail: achanda@crimson.ua.edu

Isuzu Meyer

Department of Obstetrics and Gynecology,
University of Alabama at Birmingham,
Birmingham, AL 35233
e-mail: imeyer@uabmc.edu

Holly E. Richter

J Marion Sims Professor of Obstetrics
and Gynecology, Urology and Geriatrics
Division of Urogynecology and Pelvic
Reconstructive Surgery,
Department of Obstetrics and Gynecology,
University of Alabama at Birmingham,
Birmingham, AL 35233
e-mail: hrichter@uabmc.edu

Mark E. Lockhart

Professor
Diagnostic Radiology,
Department of Radiology,
University of Alabama at Birmingham,
Birmingham, AL 35233
e-mail: mlockhart@uabmc.edu

Fabia R. D. Moraes

Department of Mechanical Engineering,
Sao Paulo State University,
Sao Paulo 01049, Brazil
e-mail: fabia_moraes@hotmail.com

Vinu Unnikrishnan

Department of Aerospace Engineering
and Mechanics,
University of Alabama,
Tuscaloosa, AL 35487
e-mail: vunnikrishnan@ua.edu

1Corresponding author.

Manuscript received December 8, 2016; final manuscript received June 15, 2017; published online July 28, 2017. Assoc. Editor: Steven D. Abramowitch.

J Biomech Eng 139(10), 101001 (Jul 28, 2017) (11 pages) Paper No: BIO-16-1504; doi: 10.1115/1.4037222 History: Received December 08, 2016; Revised June 15, 2017

Pelvic organ prolapse (POP), downward descent of the pelvic organs resulting in a protrusion of the vagina, is a highly prevalent condition, responsible for 300,000 surgeries in the U.S. annually. Rectocele, a posterior vaginal wall (PVW) prolapse of the rectum, is the second most common type of POP after cystocele. A rectocele usually manifests itself along with other types of prolapse with multicompartment pelvic floor defects. To date, the specific mechanics of rectocele formation are poorly understood, which does not allow its early stage detection and progression prediction over time. Recently, with the advancement of imaging and computational modeling techniques, a plethora of finite element (FE) models have been developed to study vaginal prolapse from different perspectives and allow a better understanding of dynamic interactions of pelvic organs and their supporting structures. So far, most studies have focused on anterior vaginal prolapse (AVP) (or cystocele) and limited data exist on the role of pelvic muscles and ligaments on the development and progression of rectocele. In this work, a full-scale magnetic resonance imaging (MRI) based three-dimensional (3D) computational model of the female pelvic anatomy, comprising the vaginal canal, uterus, and rectum, was developed to study the effect of varying degrees (or sizes) of rectocele prolapse on the vaginal canal for the first time. Vaginal wall displacements and stresses generated due to the varying rectocele size and average abdominal pressures were estimated. Considering the direction pointing from anterior to posterior side of the pelvic system as the positive Y-direction, it was found that rectocele leads to negative Y-direction displacements, causing the vaginal cross section to shrink significantly at the lower half of the vaginal canal. Besides the negative Y displacements, the rectocele bulging was observed to push the PVW downward toward the vaginal hiatus, exhibiting the well-known “kneeling effect.” Also, the stress field on the PVW was found to localize at the upper half of the vaginal canal and shift eventually to the lower half with increase in rectocele size. Additionally, clinical relevance and implications of the results were discussed.

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Figures

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Fig. 1

Schematic of the anatomy of normal female pelvic system and rectocele

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Fig. 2

Image segmentation in turtleseg

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Fig. 4

Three-dimensional (3D) finite element meshes of the pelvic organs, and fascial contact pair at the location of perineal body

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Fig. 5

Constraints (in blue color) and boundary conditions: (a) constraint at uterus fundus, (b) vaginal hiatus constraint, (c) AVW abdominal pressure (white-colored mesh region), (d) rectal hiatus constraint, (e) part of rectum belonging to the intestine is constrained, and (f) posterior rectal wall constraint

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Fig. 6

Schematic of measurement of rectocele size with respect to anorectal axis

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Fig. 7

Various simulated cases of rectocele prolapse used in our analyses

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Fig. 8

Sectioning of vaginal length to evaluate the changes in rectocele cases (Y–Z plane)

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Fig. 9

Sectional AVW and PVW displacements due to prolapse (X axis with 0 referring to normal pelvic condition followed by 1–10 rectocele cases) and Y axis referring to the estimated displacements: (a) section 1, (b) section 2, (c) section 3, and (d) section 4

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Fig. 10

PVW displacements (mm) in Y-direction due to varying degrees of rectocele

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Fig. 11

AVW displacements (mm) in Y-direction due to varying degrees of rectocele

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Fig. 12

PVW stresses (von Mises, MPa) developed due to varying degrees of rectocele

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