Many surgical procedures to repair pelvic organ prolapse (POP) have been proposed, but their long-term benefits have been poorly evaluated, particularly regarding native tissue repair techniques (with recurrence rates around 29%) [1]. Alternatively, surgeons began to augment native tissue repairs with synthetic meshes. Initially, mesh-augmented repair using polypropylene was introduced taking into consideration the high success rates in correcting abdominal hernias, based on the concept that POP also results from fascial defects.
Several post-operative complications such as infections, chronic pain and voiding dysfunction symptoms were previously described, as well as mesh erosion, a phenomenon whereby soft tissues become damaged as a result of contact with the prosthetic mesh. These mesh-related complications prompted the Food and Drug Administration (FDA) to issue safety communications regarding its use [2]. Therefore, the development of innovative tools to increase the biomechanical knowledge associated with POP may be crucial to carry out effective and viable therapeutic procedures.
The study of pelvic biomechanics is still a relatively new field of research. It relies on translational knowledge, from advances in medical imaging, improved tissue modelling and also noninvasive biomechanical measurement methods and increased computational power, which make in silico analysis very relevant in this field. 
Recently, a biomechanical study simulated a laparoscopic surgery to correct an apical prolapse using synthetic meshes computational models, concluding that different meshes provide different support to the vaginal wall.
The main objectives of this study are (1) to simulate the effect of the process of the transvaginal reconstructive surgery to reinforce/replace the apical ligaments and (2) to simulate the effect of mesh anchoring technique, and compare the displacement magnitude of the pelvic tissues, during Valsalva maneuver. Previous studies showed that POP recurrence is common after vaginal mesh implantation that may be related to a strong attachment point for mesh anchorage [3]. These authors showed that mesh anchoring failure was observed in 38% of patients on average 1.8 years after mesh implantation.
The suturing technique with two different anchoring points (simple stich - a set of four nodes and continuous stitch - a line of nodes) was simulated. The effect of this technique was verified on the pelvic structures, namely the displacement magnitude and supero-inferior displacement of the uterus and vaginal wall.

In this work, one commercial synthetic mesh (to transvaginal repair of POP) was subjected to experimental uniaxial tensile tests: three specimens were tested, estimating the experimental mechanical behavior of the uniaxial nominal stress-stretch response and their mechanical properties.
To mimic the apical ligaments (cardinal ligaments (CLs) and uterosacral ligaments (USLs), after impairment (90%) and total rupture, computational models of the synthetic implants were developed (see Figure 1a) and b)). The geometric dimensions of these synthetic implants were based on existing literature specifications. These implants have been used in the surgical repair of POP, mimicking the functional component of the CLs and USLs.
Biocomputational model of the female pelvic cavity (Figure 1c)), used in the present study, corresponding a nulliparous 24 years old healthy female - (1) symphysis pubis, (2) bladder, (3) uterus, (4) rectum, (5) levator ani muscle, (6) pelvic fascia, (7) arcus tendineous fasciae pelvis, (8) lateral ligaments of the rectum, (9) uterosacral ligaments (USLs), (10) cardinal ligaments (CLs), (11) pubourethral ligaments, (12) urethra, (13) vagina, (14) anus. This model was adapted, including the impairment (90%) (changing the stiffness of the apical ligaments) and the total rupture of the apical ligaments (CLs and USLs).
Regarding to anchoring technique, two anchoring points (simple stich (Figure 1d)) and continuous stitch (Figure (1e))), corresponding to the fixation between the USLs implant and the sacrum and CLs implant and the arcus tendineous fasciae pelvis, were considered fixed.
The Valsalva maneuver was simulated without muscle activation, considering an IAP of 4kPa.

Impairment and total rupture of the USLs and CLs cause variation in the supero-inferior displacement (SI-disp) of the vaginal wall. The Table c) of the Figure 2 shows the SI-disp of the vaginal wall, measured on the red point of the Figure 2b), when impairment of 90% and total rupture of the USLs and CLs occurs. The simulations showed that there was an increase of the displacement when impairment or rupture of the CLs and USLs occurs and the incorporation of the implants (with a continuous stitch) caused a reverse impact, decreasing the vaginal wall displacement. The non-existence/existence of the synthetic implant, when total rupture of the CLs and USLs occurs, caused a variation of the vaginal displacement (9% for the CLs and 27% for the USLs).

The Table of the Figure 2d) shows the variation of the supero-inferior displacement of the vaginal wall between different anchoring points, showing a difference of approximately 10% for the simulation USLs and CLs implant.

The supero-inferior displacement (SI-disp) of the vagina, when a total rupture of USLs and CLs occurs, increased approximately 4.98mm and 0.84mm, respectively, when compared to healthy numerical cases, being more pronounced when USLs rupture occurs. This result is consistent with literature showing a strong relationship between impairment of apical support and anterior vaginal wall prolapse descent.
The proposed methodology also showed that the simple suture (simple stich) causes a higher supero-inferior displacement of the vagina than the continuous suture, because this allows more freedom of the implant since it is only fixed in a set a loose point rather than a continuous suture (continuous stitch). These results showed that different types of sutures influence the numerical results and probably the outcomes of the surgery.

The development of in silico computational simulations can be used to predict the outcome of a pelvic surgery, with native tissues and/or synthetic meshes, and has the potential to change the way the clinicians manage surgical treatment for women with POP and prevent post-operative complications. The simulation of the pelvic cavity can also be an important tool in the design and development of new meshes, shortening the lead time of launching novel, safer and more effective meshes. The computational outcomes will also contribute to developing new methodologies to get more rigorous clinical data for premarket approval of the new materials.

Z. Guler and J. P. Roovers, “Role of Fibroblasts and Myofibroblasts on the Pathogenesis and Treatment of Pelvic Organ Prolapse,” Biomolecules, vol. 12, no. 1, 2022.
FDA, “FDA takes action to protect women’s health, orders manufacturers of surgical mesh intended for transvaginal repair of pelvic organ prolapse to stop selling all devices,” https://www.fda.gov/news-events/press-announcements/fda-takes-action-protect-womens-health-orders-manufacturers-surgical-mesh-intended-transvaginal, 2019
K. L. Shek et al., “Anterior compartment mesh: A descriptive study of mesh anchoring failure,” Ultrasound Obstet. Gynecol., vol. 42, pp. 699–704, 2013.

Continence 2S2 (2022) 100281
DOI: 10.1016/j.cont.2022.100281