Biomechanics in Stress Urinary Incontinence A Computational Modeling Approach

Project Summary Stress urinary incontinence is defined as the involuntary leakage of urine associated with an increase in intra-abdominal pressure. The main cause of incontinence is a weakened urethral support structure. Without strong supporting structures, there is minimal posterior support to the urethra, which contributes to urethral hypermobility.  Imaging studies have successfully investigated the pathophysiology through ultrasound and MRI. It is impossible to isolate and impair one anatomical component in vivo to study its effects on pelvic floor integrity. Computer modeling using MRI and finite element modeling provides a convenient avenue to simulate specific impairment conditions. Project 1 - Urethral Support Function This study aimed to assess the role of individual anatomical structures in maintaining urinary incontinence. A computational model was developed from an asymptomatic female subject’s MR images. Material definitions were modified to weaken target anatomy. Changes in urethral mobility were examined. We found that the vaginal walls, puborectalis muscle, and pubococcygeus muscle provided the most contribution to urethral support. This study demonstrated that computational modeling and dynamic biomechanical analysis can provide a powerful tool to better understand the dynamics of the female pelvis during high-pressure events. Project 2 – Assessment of Urethral Sling Placement Urethral sling has been routinely used to compensate weakened pelvic floor muscles. The optimal positioning of sling is crucial to maximal treatment outcome and minimum complication such as retention. This study aimed to assess the efficacy of locations along the urethra where a mid-urethral sling is placed. A sling was included in the model at different implantation positions, while simulation of weakened pelvic floor muscle in response to an increased intra-abdominal pressure was performed. Results showed that mid-distal sling placement corrects urethral hypermobility to a level similar to a normal, intact pelvic floor. This study represented the first effort to use computational modeling to investigate the performance of an implanted sling to correct urethral hypermobility. This model can be used to advance presurgery planning, to minimize post-surgery risk factors like retention. Project 3- Assessment of Urethral Support During Athletic Activities This study aimed to assess the pathophysiology of stress urinary incontinence in young female athletes. The jump landing process was simulated using realistic boundary conditions captured from an accelerometer. Hypothesized alterations in muscular function were simulated by weakening and strengthening the levator ani muscle stiffness. We showed that alterations in levator ani stiffness only mildly affected urethral mobility, which suggests that urethral hypermobility may be a less dominant factor in athletic stress urinary incontinence.  Our biomechanical modeling projects have greatly added to the knowledge of pelvic floor muscle pathophysiology and can aid physicians in designing effective, personalized, treatment strategies for their patients. ABAQUS provides accurate and reliable results when compared to dynamic MRI images. ABAQUS’s user routines allow future studies to accurately model active muscle contractions, which would greatly broaden the application of our model.