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

3D Observation of Pelvic Organs with Dynamic MRI Segmentation: A Bridge Toward Patient-Specific Models

INTRODUCTION AND HYPOTHESIS

Female pelvic organ prolapses are common, but their treatment is challenging. Notably, diagnosis and understanding of these troubles remain incomplete. Tridimensional observations of displacement and deformation of the pelvic organs during a strain could support a better understanding and help to develop comprehensive tools for preoperative planning.

METHODS

The present feasibility study evaluates tridimensional dynamic MRI in 12 healthy volunteers. Tridimensional acquisitions were approximated using five intersecting slices, each recorded twice per second. MRI was performed during rest and strain, with intrarectal and intravaginal contrast gel. Subject-specific dynamic 3D models were built for each volunteer through segmentation.

RESULTS

For each volunteer, pelvic organs could be segmented in three dimensions with a rate of acquisition of two cycles per second on five slices, allowing for a fluid observation of displacements and deformations during strain. Manual segmentation of a full strain required 2 h and 33 min on average. The upper limit of the rectum and the pelvic floor were the most difficult structures to identify. This technique is limited by its time-consuming manual segmentation, which impedes its implantation for routine clinical use. This method must be tried in patients with pelvic organ prolapse.

CONCLUSIONS

This multi-planar acquisition technique applied during a dynamic MRI allows for observation of displacement and deformations of pelvic organs during a strain.

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.

Effects of swelling and anatomical location on the viscoelastic behavior of the porcine urinary bladder wall

The ability of the urinary bladder to perform its physiological function depends largely on its mechanical characteristics. Understanding the mechanics of this tissue is crucial to the development of accurate models of not just this specific organ, but of the pelvic floor overall. In this study, we tested porcine bladder to identify variations in the tissue's viscoelastic characteristics associated with anatomical locations and swelling. We investigated this relationship using a series of stress-relaxation experiments as well as a modified Maxwell-Wiechert model to aid in the interpretation of the experimental data. Our results highlight that tissue located near the neck of the bladder presents significantly different viscoelastic characteristics than the body of the organ. This supports what was previously observed and is a valuable contribution to the understanding of the location-specific properties of the bladder. We also tested the effect of swelling, revealing that the bladder's viscoelastic behavior is mostly independent of solution osmolarity in hypoosmotic solutions, but the use of a hyperosmotic solution can significantly affect its behavior. This is significant, since several urinary tract pathologies can lead to chronic inflammation and disrupt the urothelial barrier causing increased urothelial permeability, thus subjecting the bladder wall to non-physiologic osmotic challenge.

Laparoscopic minimally invasive sacrocolpopexy or hysteropexy and transobturator tape combined with native tissue repair of the vaginal compartments in patients with advanced pelvic organ prolapse and incontinence

INTRODUCTION AND HYPOTHESIS

The aim of the study was to evaluate hysterectomized and non-hysterectomized patients with prolapse and incontinence. Laparoscopic sacrohysteropexy (LSHP) and minimally invasive sacrocolpopexy (LMSCP) were done in combination with transobturator tape (TOT) and native tissue repair of the anterior and posterior vaginal compartments in patients with pelvic organ prolapse (POP) and occult, stress, or urinary incontinence (SUI). The hypothesis is that both methods are successful.

METHODS

A total of 81 patients with POP were evaluated: 44 had vaginal vault prolapse (POPQ points Ba, C, and Bp were 1.2, 2.6, and 0.4, respectively) and 37 had uterine prolapse (POPQ points Ba, C, and Bp were 1.8, 1.7, and 1.3, respectively). LMSCP (which means less dissection of the vagina in its upper third and avoiding possible collision with the ureters anteriorly or the rectum posteriorly) was performed in patients with vault prolapse, whereas patients with uterine prolapse underwent LSHP. Transobturator tape (TOT) was placed in all patients to treat symptomatic and occult urinary incontinence. Systematic anterior and posterior colporrhaphy was performed in both groups.

RESULTS

Both groups showed anatomic (p < 0.0001) and symptomatic improvement (p < 0.001-p < 0.05). Voiding was significantly improved after surgery without postoperative incontinence (p < 0.001). There was no significant difference between groups regarding duration of surgery (p = 0.06), hospital stay (p = 0.13), blood loss (0.83), Clavien-Dindo grade 3 (p = 0.87), and Clavien-Dindo grade 1-2 (p = 0.92) complications.

CONCLUSION

Minimally invasive LSCP or LSHP combined with TOT and native tissue repair of the anterior and posterior vaginal compartment is a successful treatment for POP.

Dynamic magnetic resonance imaging to quantify pelvic organ mobility after treatment for uterine descent: differences between surgical procedures

INTRODUCTION AND HYPOTHESIS

Pelvic organ mobility is defined as the displacement of pelvic organs between rest and maximal straining. We hypothesized that pelvic organ mobility after vaginal sacrospinous hysteropexy (SSHP) might be increased compared with other surgeries for uterine descent, which may contribute to the high occurrence of postoperative cystocele after this surgery. Pelvic organ mobility and the vaginal axes after SSHP are compared with other surgical procedures for uterine descent: vaginal hysterectomy with uterosacral suspension (VH) and laparoscopic sacrohysteropexy (LSH).

METHODS

In this prospective pilot study, 15 women were included (5 for each procedure). Six months postoperatively, POP-Q examination and dynamic MRI were performed and questionnaires were filled out regarding prolapse complaints. Pelvic organ mobility on MRI was defined as vertical displacement of pelvic organs at rest and maximal straining. The displacements and angles were measured using an image registration method. Furthermore, the angle of displacement of cervix/vaginal vault and vaginal axes were assessed.

RESULTS

No anatomical recurrences of pelvic organ prolapse were found. No difference in pelvic organ mobility was demonstrated. After VH, a more posterior position of the upper vagina was found compared with SSHP and LSH.

CONCLUSIONS

Based on these data, the higher recurrence risk in the anterior compartment after SSHP cannot be explained. Larger sample sizes, studying women with recurrence or de novo cystocele after SSHP or using an upright MRI scanner would be of interest to further assess the relationship between pelvic organ mobility and the occurrence of anterior vaginal wall prolapse.

Managing female pelvic floor disorders: a medical device review and appraisal

Pelvic floor disorders (PFDs) will affect most women during their lifetime. Sequelae such as pelvic organ prolapse, stress urinary incontinence, chronic pain and dyspareunia significantly impact overall quality of life. Interventions to manage or eliminate symptoms from PFDs aim to restore support of the pelvic floor. Pessaries have been used to mechanically counteract PFDs for thousands of years, but do not offer a cure. By contrast, surgically implanted grafts or mesh offer patients a more permanent resolution but have been in wide use within the pelvis for less than 30 years. In this perspective review, we provide an overview of the main theories underpinning PFD pathogenesis and the animal models used to investigate it. We highlight the clinical outcomes of mesh and grafts before exploring studies performed to elucidate tissue level effects and bioengineering considerations. Considering recent turmoil surrounding transvaginal mesh, the role of pessaries, an impermanent method, is examined as a means to address patients with PFDs.

Laparoscopic prolapse surgery: types and evidence

PURPOSE OF REVIEW

Recommendations for the surgical treatment of pelvic organ prolapse have undergone significant changes over the last few decades.First described to be too difficult, the laparoscopic technique has gained popularity but is still controversial. The recent warning on vaginal mesh was the sign of revival and we start now to have many articles published on results and on techniques for laparoscopic prolapse repair.

RECENT FINDINGS

If nothing is new in the comparison of the routes including vaginal mesh placement, the new articles are very interesting in terms of technical information and recommendations. Those articles are very important and help us understand some failures in the laparoscopic approach mainly in the anterior compartment.

SUMMARY

New models have been created and eventually in the future, we will be able to simulate the repair on our own patients and to assess virtually the mobility of each compartment preoperatively. This will allow us to adjust and tailor the treatment to each patient.

Female pelvic floor biomechanics: bridging the gap

PURPOSE OF REVIEW

The pelvic floor is a complex assembly of connective tissues and striated muscles that simultaneously counteracts gravitational forces, inertial forces, and intra-abdominal pressures while maintaining the position of the pelvic organs. In 30% of women, injury or failure of the pelvic floor results in pelvic organ prolapse. Surgical treatments have high recurrence rates, due, in part, to a limited understanding of physiologic loading conditions. It is critical to apply biomechanics to help elucidate how altered loading conditions of the pelvis contribute to the development of pelvic organ prolapse and to define surgeries to restore normal support.

RECENT FINDINGS

Evidence suggests the ewe is a potential animal model for studying vaginal properties and that uterosacral and cardinal ligaments experience significant creep, which may be affecting surgical outcomes. A new method of measuring ligament displacements in vivo was developed, and finite element models that simulate urethral support, pelvic floor dynamics, and the impact of episiotomies on the pelvic floor were studied.

SUMMARY

The current review highlights some contributions over the past year, including mechanical testing and the creation of models, which are used to understand pelvic floor changes with loading and the impact of surgical procedures, to illustrate how biomechanics is being utilized.