Mobility analysis of a posterior sacrospinous fixation using a finite element model of the pelvic system.

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.

3D-printed model for gingival flap surgery simulation: Development and pilot test.

INTRODUCTION: To assess the feasibility of a realistic model for learning oral flaps using 3D printing technology. MATERIALS AND METHODS: A mould was designed to reproduce the mandibular gingival mucosa, and a mandibular model was created using a three-dimensional printer for training undergraduate students to perform gingival flaps. After a short interview about its use, the participants were asked to use the simulator and provide feedback using a 5-point Likert questionnaire. RESULTS: The 3D-printed oral surgery flap training model was practical and inexpensive. The model was very realistic, educational and useful for hands-on training. CONCLUSIONS: 3D printing technology offers new possibilities for training in dental treatments that are currently difficult to replicate. The use of this simulator for oral flap surgery was well-received and considered promising by the participants.

Simulation of the mobility of the pelvic system: influence of fascia between organs.

The mobility of pelvic organs is the result of an equilibrium called Pelvic Static characterizing the balance between the properties and geometries of organs, suspensions and support system. Any imbalance in this complex system can cause of pelvic static disorder. Genital prolapse is a common hypermobility pathology which is complex, multi factorial and its surgical management has high rate of complications. The use of 3 D numerical models and simulation enables the role of the various suspension structures to be objectively studied and quantified. Fascias are connective tissues located between organs. Although their role are described as important in various descriptions of pelvic statics, their influence and role has never been quantitatively objectified. This article presents a refine Finite Element (FE) model for a better understanding of biomechanical contribution of inter-organ fascia. The model is built from MRI images of a young volunteer, the mechanical properties derived from literature data to take into account the age of the patient and new experimental results have enabled an order of magnitude of the mechanical properties of the fascias to be defined. The FE results allows to quantify the biomechanical role of the fascia on pelvic mobility quantified by an analysis of dynamic MRI images and a local mapping of the gap between calculated and measured displacements. This improved numerical model integrating the fascias makes it possible to describe pelvic mobilities with a gap of 1 mm between numerical simulations and measurements, whereas without taking them into account this gap locally reaches 20 mm.

Complete 3 dimensional reconstruction of parturient pelvic floor.

INTRODUCTION: The women pelvic floor is a complex system, which seems to endure several modifications during pregnancy and childbirth. Our primary purpose was to build an extensive 3 dimensional (3D) numerical anatomical model of the women pelvic floor. METHODS: First, the role and the location of each organ, muscle, or ligament, were identified through an extensive literature review. Then, different entities were selected because of their visibility and importance in the pelvic floor. Each entity was identified using anatomical knowledge, and outlined on 2 dimensional (2D) MRI images, that were carried out on 4 pregnant women, using sequences T1, T2 and proton density weighted, through AVIZO program. The overlay of these 2D outlines produced a 3D geometrical reconstruction, which was then reworked with the program CATIA to obtain a usable geometric model. RESULTS: We identified and integrated 15 anatomical structures to the geometrical model, including organs, ligament and muscles from the pelvis and perineum. This geometrical model allowed us to obtain a visual interactive representation with 3D images. These different steps resulted in the creation of a complete numerical model of the female pelvic floor, which might be used in Finite Element simulation. CONCLUSION: A new complete and accurate 3D numerical anatomical model of the women pelvic floor was elaborated. It presents simultaneously analytical prospects, through the observation of the strains and deformations that are imposed on the different structures, and educational prospects, through the detailed visual representation of several situations.

Pregnancy impact on uterosacral ligament and pelvic muscles using a 3D numerical and finite element model: preliminary results.

INTRODUCTION AND HYPOTHESIS: We studied the geometry of and changes in structures that play an important role in stabilizing the pelvic system during pregnancy using a numerical system at different gestational ages and postpartum. METHODS: We developed a parturient numerical model to assess pelvic structures at different gestational stages (16, 32, and 38 weeks) and postpartum (2 months and 1 year) using magnetic resonance imaging (MRI). Organs, muscles, and ligaments were segmented to generate a 3D model of the pelvis. We studied changes in the length of uterosacral ligaments (USL) and thickness of the puborectal portion of the levator ani muscle (LAM) during and after pregnancy. We used this model to perform finite element (FE) simulation and analyze deformations of these structures under stress from the increase in uterine weight. RESULTS: Analysis reveals an increase in the length of US ligaments at 16, 32, and 38 weeks. Two months after delivery, it decreases without returning to the length at 16 weeks of pregnancy. Similar changes were observed for the puborectal portion of the LAM. Variations observed in these structures are not equivalent to other anatomical structures of pelvic suspension. FE simulation with increased uterus weight does not lead to those findings. CONCLUSION: This analysis brings new elements and a new focus for discussion relating to changes in pelvic balance of parturient women that are not simply linked to the increase in uterine volume.

Pathophysiological aspects of cystocele with a 3D finite elements model.

PURPOSES: The objective of this study is to design a 3D biomechanical model of the female pelvic system to assess pelvic organ suspension theories and understand cystocele mechanisms. METHODS: A finite elements (FE) model was constructed to calculate the impact of suspension structure geometry on cystocele. The sample was a geometric model of a control patient's pelvic organs. The method used geometric reconstruction, implemented by the biomechanical properties of each anatomic structure. Various geometric configurations were simulated on the FE method to analyse the role of each structure and compare the two main anatomic theories. RESULTS: The main outcome measure was a 3D biomechanical model of the female pelvic system. The various configurations of bladder displacement simulated mechanisms underlying medial, lateral and apical cystocele. FE simulation revealed that pubocervical fascia is the most influential structure in the onset of median cystocele (essentially after 40 % impairment). Lateral cystocele showed a stronger influence of arcus tendineus fasciae pelvis (ATFP) on vaginal wall displacement under short ATFP lengthening. In apical cystocele, the uterosacral ligament showed greater influence than the cardinal ligament. Suspension system elongation increased displacement by 25 % in each type of cystocele. CONCLUSIONS: A 3D digital model enabled simulations of anatomic structures underlying cystocele to better understand cystocele pathophysiology. The model could be used to predict cystocele surgery results and personalising technique by preoperative simulation.

Mobility and stress analysis of different surgical simulations during a sacral colpopexy, using a finite element model of the pelvic system.

INTRODUCTION AND HYPOTHESIS: We aim to analyze the combined influence of the size of the mesh, the number of sutures, the combined use of an anterior and posterior mesh, and the tension applied to the promontory, on the mobility of the pelvic organs and on the sutures, using a Finite Element (FE) model of the female pelvic system during abdominal sacral colpopexy. METHODS: We used a FE model of the female pelvic system, which allowed us to simulate the mobility of the pelvic system and to evaluate problems related to female prolapse. The meshes were added to the geometrical model and then transferred to computing software. This analysis allowed us to compare the stress and mobility during a thrust effort in different situations. RESULTS: The bigger the mesh, the less mobility of both anterior and posterior organs there would be. This is accompanied by an increase in stress at the suture level. The combination of a posterior mesh with an anterior one decreases mobility and stress at the suture level. There is a particularly relevant stressing zone on the suture at the cervix. The increase in the number of sutures induces a decrease in the tension applied at each suture zone and has no impact on organ mobility. CONCLUSION: Our model enables us to simulate and analyze an infinite number of surgical hypotheses. Even if these results are not validated at a clinical level, we can observe the importance of the association of both an anterior and a posterior mesh or the number of sutures.

Influence of Geometry and Mechanical Properties on the Accuracy of Patient-Specific Simulation of Women Pelvic Floor.

The woman pelvic system involves multiple organs, muscles, ligaments, and fasciae where different pathologies may occur. Here we are most interested in abnormal mobility, often caused by complex and not fully understood mechanisms. Computer simulation and modeling using the finite element (FE) method are the tools helping to better understand the pathological mobility, but of course patient-specific models are required to make contribution to patient care. These models require a good representation of the pelvic system geometry, information on the material properties, boundary conditions and loading. In this contribution we focus on the relative influence of the inaccuracies in geometry description and of uncertainty of patient-specific material properties of soft connective tissues. We conducted a comparative study using several constitutive behavior laws and variations in geometry description resulting from the imprecision of clinical imaging and image analysis. We find that geometry seems to have the dominant effect on the pelvic organ mobility simulation results. Provided that proper finite deformation non-linear FE solution procedures are used, the influence of the functional form of the constitutive law might be for practical purposes negligible. These last findings confirm similar results from the fields of modeling neurosurgery and abdominal aortic aneurysms.