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Research Papers

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

[+] Author and Article Information
Yun Peng

Department of Biomedical Engineering,
University of Houston,
E2003 SERC Building,
3605 Cullen Boulevard,
Houston, TX 77204-5060
e-mail: ypeng@uh.edu

Rose Khavari

Department of Urology,
Houston Methodist Hospital and Research Institute,
6565 Fannin Street,
Suite 2100,
Houston, TX 77030-2703
e-mail: rkhavari@houstonmethodist.org

Nissrine A. Nakib

Department of Urology,
University of Minnesota,
420 Delaware Street,
SE MMC 394,
Minneapolis, MN 55455-0341
e-mail: naki0003@umn.edu

Julie N. Stewart

Department of Urology,
Houston Methodist Hospital and Research Institute,
6565 Fannin Street,
Suite 2100,
Houston, TX 77030-2703
e-mail: jnstewart2@houstonmethodist.org

Timothy B. Boone

Department of Urology,
Houston Methodist Hospital and Research Institute,
6565 Fannin Street,
Suite 2100,
Houston, TX 77030-2703
e-mail: TBoone3@houstonmethodist.org

Yingchun Zhang

Department of Biomedical Engineering,
University of Houston,
2027 SERC Building,
3605 Cullen Boulevard,
Houston, TX 77204-5060
e-mail: yzhang94@uh.edu

1Corresponding author.

Manuscript received April 13, 2015; final manuscript received June 27, 2015; published online July 14, 2015. Assoc. Editor: Hai-Chao Han.

J Biomech Eng 137(9), 091007 (Sep 01, 2015) (7 pages) Paper No: BIO-15-1168; doi: 10.1115/1.4030978 History: Received April 13, 2015; Revised June 27, 2015; Online July 14, 2015

Dynamic behaviors of the single-incision sling (SIS) to correct urethral hypermobility are investigated via dynamic biomechanical analysis using a computational model of the female pelvis, developed from a female subject's high-resolution magnetic resonance (MR) images. The urethral hypermobility is simulated by weakening the levator ani muscle in the pelvic model. Four positions along the posterior urethra (proximal, midproximal, middle, and mid-distal) were considered for sling implantation. The α-angle, urethral excursion angle, and sling–urethra interaction force generated during Valsalva maneuver were quantitatively characterized to evaluate the effect of the sling implantation position on treatment outcomes and potential complications. Results show concern for overcorrection with a sling implanted at the bladder neck, based on a relatively larger sling–urethra interaction force of 1.77 N at the proximal implantation position (compared with 0.25 N at mid-distal implantation position). A sling implanted at the mid-distal urethral location provided sufficient correction (urethral excursion angle of 23.8 deg after mid-distal sling implantation versus 24.4 deg in the intact case) with minimal risk of overtightening and represents the optimal choice for sling surgery. This study represents the first effort utilizing a comprehensive pelvic model to investigate the performance of an implanted sling to correct urethral hypermobility. The computational modeling approach presented in the study can also be used to advance presurgery planning, sling product design, and to enhance our understanding of various surgical risk factors which are difficult to obtain in clinical practice.

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References

Figures

Grahic Jump Location
Fig. 1

(a) and (b) show the pelvic muscles and bones in the front and back views (muscles shown include: m. piriformis, m. coccygeus, m. iliococcygeus, m. pubococcygeus, m. obturator internus, and m. puborectalis), organs and fatty tissues are removed for better visualization. (c) The main pelvic organs in the oblique view (from top to bottom: rectum, uterus and bladder). (d) The model and the boundary conditions in the midsagittal view. The solid part in the abdomen represents the bodyfill part.

Grahic Jump Location
Fig. 2

(a) Dimensions of the MiniArcTM SIS (in inches), (b) finite-element meshes of the sling with three control points, and (c) curve fitting results for the MiniArcTM SIS with second polynomial hyperelastic material model

Grahic Jump Location
Fig. 3

Sling implantation positions at rest status. The first column shows the midsagittal view of the pelvic bone (bottom left), bladder (top), urethra (bottom right), urine (inside the bladder), and sling (behind the urethra). The second column shows the sling shape and positions from the posterior view. The alpha-angle is defined as the angle between the urethral axis (right dashed line) and the vertical line (left dashed line), as shown in the first row (test A1). The urethral axis is defined as the line between two reference points (indicated by the cross-marks) along the posterior urethral wall, same for all tests.

Grahic Jump Location
Fig. 4

Illustration of the preparations of the sling for test A4. Three columns show the relative positions of the sling to pelvic organs in the midsagittal, posterolateral, and anterolateral views. Bladder (shown in column 2) and uterus/vagina (shown in column 3) were hidden in some views for visualization purpose. Different rows represent the results at different steps: (a) initial, (b) after step 1, (c) after step 2, and (d) after step 3.

Grahic Jump Location
Fig. 5

(a) Plot of the increase of IAP with time for sling and control tests, (b) plot of urethral excursions angle against IAP for sling tests and control tests, and (c) plot of interaction forces against IAP for sling tests

Grahic Jump Location
Fig. 6

Shapes of sling in the midsagittal view at maximal Valsalva. The two reference points used to define the urethral axis are marked by crosses.

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