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Research Papers

On the Stiffness of the Mesh and Urethral Mobility: A Finite Element Analysis

[+] Author and Article Information
Sofia Brandão

Department of Radiology,
Centro Hospitalar de São João—EPE
(CHSJ-EPE)/Faculty of Medicine,
University of Porto,
Alameda Professor Hernâni Monteiro,
Porto 4200-319, Portugal;
Associated Laboratory for Energy,
Transports and Aeronautics (LAETA),
Institute of Science and Innovation in Mechanical
and Industrial Engineering (INEGI),
Faculty of Engineering,
University of Porto,
Rua Dr. Roberto Frias s/n,
Porto 4200-465, Portugal
e-mail: sofia.brand@gmail.com

Marco Parente

Associated Laboratory for Energy, Transports
and Aeronautics (LAETA),
Institute of Science and Innovation in Mechanical
and Industrial Engineering (INEGI),
Faculty of Engineering,
University of Porto,
Rua Dr. Roberto Frias s/n,
Porto 4200-465, Portugal
e-mail: mparente@fe.up.pt

Thuane Huyer Da Roza

Biomechanics Laboratory,
Center of Health and Sport Sciences, Santa
Catarina State University (CEFID/UDESC),
Rua Paschoal Simone,
358, Bairro dos Coqueiros,
Florianópolis 88080-350, Santa Catarina, Brazil;
Associated Laboratory for Energy, Transports
and Aeronautics (LAETA),
Institute of Science and Innovation in Mechanical
and Industrial Engineering (INEGI),
Faculty of Engineering,
University of Porto,
Rua Dr. Roberto Frias s/n,
Porto 4200-465, Portugal
e-mail: thuaneroza@yahoo.com.br

Elisabete Silva

Associated Laboratory for Energy, Transports
and Aeronautics (LAETA),
Institute of Science and Innovation in Mechanical
and Industrial Engineering (INEGI),
Faculty of Engineering,
University of Porto,
Rua Dr. Roberto Frias s/n,
Porto 4200-465, Portugal
e-mail: silva.elisabete3@gmail.com

Isabel Maria Ramos

Department of Radiology,
CHSJ-EPE/Faculty of Medicine,
University of Porto,
Alameda Professor Hernâni Monteiro,
Porto 4200-319, Portugal
e-mail: radiologia.hsj@gmail.com

Teresa Mascarenhas

Department of Obstetrics and Gynecology,
CHSJ-EPE/Faculty of Medicine,
University of Porto,
Alameda Professor Hernâni Monteiro,
Porto 4200-319, Portugal
e-mail: tqc@sapo.pt

Renato Manuel Natal Jorge

Associated Laboratory for Energy, Transports
and Aeronautics (LAETA),
Institute of Science and Innovation in Mechanical
and Industrial Engineering (INEGI),
Faculty of Engineering,
University of Porto,
Rua Dr. Roberto Frias s/n,
Porto 4200-465, Portugal
e-mail: rnatal@fe.up.pt

1Corresponding author.

Manuscript received October 28, 2016; final manuscript received April 17, 2017; published online June 7, 2017. Assoc. Editor: Steven D. Abramowitch.

J Biomech Eng 139(8), 081002 (Jun 07, 2017) (9 pages) Paper No: BIO-16-1424; doi: 10.1115/1.4036606 History: Received October 28, 2016; Revised April 17, 2017

Midurethral slings are used to correct urethral hypermobility in female stress urinary incontinence (SUI), defined as the complaint of involuntary urine leakage when the intra-abdominal pressure (IAP) is increased. Structural and thermal features influence their mechanical properties, which may explain postoperative complications, e.g., erosion and urethral obstruction. We studied the effect of the mesh stiffness on urethral mobility at Valsalva maneuver, under impairment of the supporting structures (levator ani and/or ligaments), by using a numerical model. For that purpose, we modeled a sling with “lower” versus “higher” stiffness and evaluated the mobility of the bladder and urethra, that of the urethrovesical junction (the α-angle), and the force exerted at the fixation of the sling. The effect of impaired levator ani or pubourethral ligaments (PUL) alone on the organs displacement and α-angle opening was similar, showing their important role together on urethral stabilization. When the levator ani and all the ligaments were simulated as impaired, the descent of the bladder and urethra went up to 25.02 mm, that of the bladder neck was 14.57 mm, and the α-angle was 129.7 deg, in the range of what was found in women with SUI. Both meshes allowed returning to normal positioning, although at the cost of higher force exerted by the mesh with higher stiffness (3.4 N against 2.3 N), which can relate to tissue erosion. This finite element analysis allowed mimicking the biomechanical response of the pelvic structures in response to changing a material property of the midurethral synthetic mesh.

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References

Figures

Grahic Jump Location
Fig. 1

Anatomical perspective of the pelvis, where (a) the pelvic bones, organs, and some of the soft tissue support structures were included in this subject-specific 3D geometrical model, and (b) the positioning of the synthetic midurethral sling is seen illustrating a tension-free vaginal tape (TVT) procedure. (1) pubic bone, (2) bladder, (3) uterus, (4) rectum, (5) arcus tendineous fasciae pelvis, (6) cardinal ligaments, (7) levator ani, (8) uterosacral ligaments, (9) urethra, (10) vagina, (11) anus, and (12) midurethral sling.

Grahic Jump Location
Fig. 2

Evaluation of the α-angle performed (a) at rest and (b) for Valsalva maneuver

Grahic Jump Location
Fig. 3

Finite element model of the pelvis. The pubic bone, the pelvic organs, and the supporting structures (muscles, ligaments, and fascia) were included to achieve a realistic model of the pelvic cavity. In (c) and (d), the position of the sling just above the native pubourethral ligaments is shown. (1) pubic bone, (2) bladder, (3) uterus, (4) rectum, (5) arcus tendineous fasciae pelvis, (6) pelvic fascia, (7) levator ani, (8) lateral ligaments of the rectum, (9) uterosacral ligaments, (10) cardinal ligaments, (11) pubourethral ligaments (vaginal and urethral portions), and (12) midurethral sling.

Grahic Jump Location
Fig. 4

Experimental curves of the five meshes obtained through load–displacement uniaxial tests (data from the work of Afonso et al. [30]), compared with the numerical ones of the two midurethral slings: MeshHS (black straight curve) and MeshLS (black dashed curve)

Grahic Jump Location
Fig. 5

Displacement magnitude after simulation of Valsalva maneuver and in the presence of combined impairment of the levator ani and the pubourethral ligaments, (a) without including the sling, (b) with the MeshHS, and (c) with MeshLS

Grahic Jump Location
Fig. 6

Graphs of force exerted in the extremities of the sling for the (a) MeshHS and (b) MeshLS, for progressive increase in intra-abdominal pressure from rest to Valsalva maneuver

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