Mobility analysis of a posterior sacrospinous fixation using a finite element model of the pelvic system
Authors: Lallemant Marine , Shimojyo Andres Arteaga , Mayeur Olivier , Ramanah Rajeev , Rubod Chrystèle , Kerbage Yohan , Cosson Michel 
Published: March 2024

Introduction and hypothesis
In order to improve the knowledge POP physiopathology and POP repair, a generic biomechanical model of the female pelvic system has been developed. In the literature, no study has currently evaluated apical prolapse repair by posterior sacrospinous ligament fixation using a generic model nor a patient-specific model that personalize the management of POP and predict surgical outcomes based on the patient’s pre-operative Magnetic Resonance Imaging. The aim of our study was to analyze the influence of a right and/or left sacrospinous ligament fixation and the distance between the anchorage area and the ischial spine on the pelvic organ mobility using a generic and a patient-specific Finite Element model (FEM) of the female pelvic system during posterior sacrospinous ligament fixation (SSF).

Methods
Firstly, we used a generic 3D FEM of the female pelvic system previously made by our team that allowed us to simulate the mobility of the pelvic system. To create a patient-specific 3D FEM of the female pelvic system, we used a preoperative dynamic pelvic MRI of a 68 years old woman with a symptomatic stage III apical prolapse and cystocele. With these 2 models, a SSF was simulated. A right and/or left SSF and different distances between the anchorage area and the ischial spine (1 cm, 2 cm and 3 cm.) were compared. Outcomes measures were the pelvic organ displacement using the pubococcygeal line during maximal strain: Ba point for the most posterior and inferior aspect of the bladder base, C point the cervix’s or the vaginal apex and Bp point for the anterior aspect of the anorectal junction.

Results
Overall, pelvic organ mobility decreased regardless of surgical technique and model. According to the generic model, C point was displaced by 14.1 mm and 11.5 mm, Ba point by 12.7 mm, and 12 mm and Bp point by 10.6 mm and 9.9 mm after left and bilateral posterior SSF, respectively. C point was displaced by 15.4 mm and 11.6 mm and Ba point by 12.5 mm and 13.1mm when the suture on the sacrospinous ligament was performed at 1 cm and 3 cm from the ischial spine respectively (bilateral posterior SSF configuration). According to the patient-specific model, the displacement of Ba point could not be analyzed because of a significative and asymmetric organ displacement of the bladder. C point was displaced by 4.74 mm and 2.12 mm, and Bp point by 5.30 mm and 3.24 mm after left and bilateral posterior SSF respectively. C point was displaced by 4.80 mm and 4.85 mm and Bp point by 5.35 mm and 5.38 mm when the suture on the left sacrospinous ligament was performed at 1 cm and 3 cm from the ischial spine, respectively.

Conclusion
According to the generic model from our study, the apex appeared to be less mobile in bilateral SSF. The anchorage area on the sacrospinous ligament seems to have little effect on the pelvic organ mobilities.

Trial registration
ClinicalTrials.gov Identifier: NCT04551859.