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

Abstract

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.