Biomechanical Analyses of Posterior Vaginal Prolapse: MR Imaging and Computer Modeling Studies.

Pelvic organ prolapse is an abnormal downward displacement and deformation of the female pelvic organs. Because it adversely affects quality of life, over 200,000 operations are performed annually for prolapse in the U.S at a cost exceeding $1 billion. Approximately 87% of those procedures involve repair of a posterior vaginal prolapse, the etiology of which is a focus of this dissertation. But, because operative failure rates can approach 30%, new insights are needed as to how and why a posterior vaginal prolapse develops in the first place so that treatment can be improved. We hypothesize that the occurrence, size and type of posterior vaginal prolapse is not explained by failure of any single structure; rather it involves failure of connective tissue supports at two and possibly up to as many as 20 anatomical sites, along with impairment of the levator ani muscle. Using in vivo magnetic resonance imaging we first visualized the detailed 3-D pelvic floor anatomy of 84 healthy women. From these we then selected images from a pelvis of average dimensions and used them to create a detailed three-dimensional interactive model of the female pelvic floor complete with 23 structures. We then developed a method to measure and quantify the geometry of prolapse in forty 3-D magnetic resonance image-based models. Two main structures relating to the development of prolapse, fascia and apical vaginal supports, were then analyzed via two case-control studies. Finally, 2- and 3-D computer-based models were developed to identify the biomechanical interactions which lead to prolapse: levator muscle and connective tissue failure, and organ competition. These methodological approaches and computer models provide new insights into the biomechanical mechanisms underlying the development of posterior vaginal prolapse. Our hope is that they will lead to more effective surgical treatment strategies for this vexing condition.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/95942/1/jjluo_1.pd

Mechanical Characterization of Synthetic Mesh for Pelvic Organ Prolapse Repair

Pelvic organ prolapse (POP) is characterized by the abnormal descent of the pelvic organs into the vaginal canal. POP is associated with urinary, defacatory, and sexual dysfunction, in addition to psychological disorders including depression. Prolapse is quite common, with ~50% of women over the age of 50 exhibiting some degree of prolapse, and over 200,000 surgical repairs in the United States annually. During surgical repair, a graft is used to restore support to the vagina, re-approximating the normal anatomy. Given the high failure rate of native tissue repair, use of polypropylene mesh has become widespread. Despite the prevalence of synthetic mesh, complication rates are ~20%, with little known about its behavior following implantation. Therefore, this dissertation aims to rigorously characterize the mechanical behavior of synthetic mesh, with the goal of optimizing device design for use in the pelvic floor. First, micro- and macro-level deformation of mesh was assessed in response to mechanical loads using uniaxial testing and 3D reconstruction. Upon loading, mesh pores significantly deformed, yielding textile dimensions that are known to heighten the foreign body response. In addition, point loads significantly wrinkled the mesh surface, further reducing mesh dimensions and producing configurations consistent with those found clinically. Next, a finite element model for synthetic mesh was developed, using a novel method to allow for textile properties to be measured in-silico. This model was validated using a custom testing apparatus to simultaneously load and image transvaginal mesh products. Evaluation of mesh deformation found experimental and computational results to be similar, demonstrating the predictive capabilities of this model. The validated model was then used to examine the sensitivity of mesh behavior to variable loading conditions. Here the magnitude and orientation of tensile forces were found to significantly predict undesired deformations. Finally, computational mesh models were combined with MRI reconstructions of patient specific anatomy to simulate the development of prolapse and mesh repair. Again, mesh pores experienced significant deformation upon anatomical fixation, corresponding with clinical sites of exposure and pain. In total, this dissertation provides a tool for the evaluation and optimization of synthetic mesh devices prior to implantation and pre-surgical evaluation of mesh procedures

Pelvic Floor Dysfunction

Pelvic floor disorders (PFDs) refer to a group of conditions, such as urinary incontinence, fecal incontinence, and pelvic organ prolapse, due to weakened or injured pelvic muscles and connective tissues. People with PFDs face several social, mental, and physical health effects due to the bothersome symptoms. In this book, experts and researchers from different countries present the latest evidence in diagnosis and treatment of PFDs. Chapters cover such topics as pelvic floor muscle activity, PFDs and pregnancy and childbirth, non-invasive therapy, dysfunctional voiding in children, and much more

Influence de la géométrie et des propriétés mécaniques sur la simulation Eléments Finis du système pelvien.

The woman pelvic system is an anatomical area involving 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. Mathematical modelling and computer simulation 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, derived from medical images, and of uncertainty of patient-specific material properties of tissues. We conducted a comparative study using several constitutive behavior laws, different material coefficients and variations in geometry description resulting from the imprecision of clinical imaging and image analysis. We find that it is the geometry that has the dominant effect on the pelvic organ mobility simulation results. Provided that proper finite deformation non-linear Finite Element solution procedures are used, the influence of the functional form of the constitutive law is for practical purposes negligible and the influence of the stress parameter in the constitutive law is relatively small. These last findings confirm similar results from the fields of modelling neurosurgery and abdominal aortic aneurysms

Biomechanics of the pelvic floor during vaginal delivery

Tese de doutoramento. Engenharia Mecânica. Faculdade de Engenharia. Universidade do Porto, Instituto Superior Técnico. Universidade de Lisboa, Faculdade de Medicina. Universidade do Porto. 200

IMPACT OF VAGINAL SYNTHETIC PROLAPSE MESHES ON THE MECHANICS OF THE HOST TISSUE RESPONSE

The vagina helps support the bladder, urethra, uterus, and rectum. A lack of support leads to pelvic organ prolapse, and vaginal delivery is a prevalent risk factor; however, there is little research on vaginal biomechanical properties. Despite numerous complications, clinical practice involves surgical repair with synthetic meshes. Complications can be partially attributed to our lack of knowledge regarding the mesh-tissue complex (MTC) after implantation. However, it is difficult to perform rigorous studies without utilizing animal models. Therefore, we evaluated how parity affected the mechanical properties of vaginal tissue in three animal models: rodent, sheep, and non-human primate (NHP) to compare their mechanically properties to parous women who typically undergo prolapse surgery. Parity negatively impacted the mechanical properties of the vagina in NHP, which were biomechanically similar to parous women, making it a suitable model for studying the effects of mesh implantation. Second, we examined the textile and structural properties of commonly used meshes (Gynemesh, UltraPro, SmartMesh, Novasilk, and Polyform) utilizing uniaxial and ball-burst tests. These meshes had significantly different porosity and structural properties. To investigate the host response, three meshes were implanted into the abdominal wall of the rodent and NHP, and on the vagina in the NHP. The MTC was removed, and the tissue contribution was calculated. We did not observe notable changes in the tissue properties following mesh implantation in the rodent; however, implantation of the stiffest mesh (Gynemesh) in the NHP resulted in an exhibition of a stress-shielding response manifested by inferior biomechanical properties of the abdominal and vaginal tissues. Less stiff meshes (UltraPro and SmartMesh) resulted in preservation of tissue properties. To gain insight into how mesh properties affect the tissue contribution, we began developing a finite element model. Utilizing the co-rotational theory with a fiber-recruitment stress-strain relationship, we could describe the behavior of SmartMesh and UltraPro. While an in-depth characterization of these meshes revealed multiple fiber populations, further development of modeling may be instrumental in closing the current knowledge gap. Ultimately, understanding the mesh-tissue interaction will improve clinical outcomes by identifying mesh properties that are essential for providing structural support while maintaining tissue integrity

Biomechanics and Electromyography Inassessing Female Stress Urinary Incontinence

Introduction: Stress urinary incontinence (SUI), the involuntary urinary leakage associated with increases in intra-abdominal pressure, has a prevalence of 25–50% in U.S. women and the number of those who will undergo surgery will increase by half in the next forty years. SUI negatively affects the patient’s quality of life and places a great burden to the society. The functional anatomy of the continence mechanism remains vaguely understood. Hence my dissertation aims at offering a complete description of the pelvic floor muscles (PFM), the key contributor to the continence, thorough biomechanical and neurophysiological approaches. Methods: The biomechanical approach involves the development of a subject-specific finite element (FE) model of the female pelvic floor region. Subsequent computer simulations are targeted at finding the most contributive muscle to the urethral support function and evaluating current treatment strategies using a mini-sling. The neurophysiological approach involves the implementation of a novel surface electromyography (EMG) probe to acquire bioelectrical information of PFMs and the assessment of their innervations in healthy subjects and patients. Results: An FE pelvic floor model was developed which incorporates 40+ anatomical structural in the pelvis, representing the most complete model in the field. Simulation results showed that the vaginal walls, puborectalis, and pubococcygeus are the most important structures and that mid-distal post-urethral implantation represents the optimal location. Innervation zones of PFMs have been successfully identified and described for multiple PFMs. An high-density surface EMG-based motor unit number estimation approach was developed, providing a novel tool to evaluate the condition of neurologically impaired PFM. Conclusions: The combined information greatly advances our understanding of the physiology of PFM and would lay a firm foundation to novel, non-invasive, patient-specific interventional strategies in the future.Biomedical Engineering, Department o