Effect of retropubic sling on urethral dynamic shape after one year

Objectives: The mechanism behind the success of a mid-urethral sling (MUS) in reducing the symptoms of incontinence is assumed to be explained by increased intra-abdominal pressure applied to the bladder base and urethra, which during a cough, would compress the urethra against the sling (back stop) and result in urethral closure and continence. However, this hypothesis has not been examined with biomechanical studies. The aim of this study was to investigate the effect of retropubic sling on urethral shape and motion using dynamic anterior compartment ultrasound at 12 months following a sling procedure.

Methods: This is an ongoing prospective cohort study. Women who presented to our tertiary urogynecology clinic with a complaint of stress dominant urinary incontinence and decided to proceed with a MUS to treat the condition were recruited to the study. All patients underwent a comprehensive interview including PFDI-20 questionnaire, pelvic exam with POP-Q evaluation, and static and dynamic pelvic floor ultrasounds pre-operatively, and at 2- and 12-months post-operatively.

The dynamic imaging during Valsalva takes a 5 second video of a midsagittal view of the bladder and urethra including urethral meatus, pubic symphysis, and bladder neck. Parameters measured included urethral length, retropubic urethral length, bladder-neck-retropubic angle, bladder-neck-pubic bone angle, urethral-knee swing angle and urethral anterior-posterior diameter. Surgical success was defined as complete or significant (over 50%) improvement of SUI at 12-month post-operatively. Patients’ demographics, symptoms, PFDI-20 scores, POP-Q, and changes in dynamic ultrasound measurements were compared before and after surgery using Fisher’s exact or chi-squared test for categorical variables and ANOVA (parametric) or Kruskal-Wallis test (nonparametric) for continuous variables.

Results: A total of 131 participants have been recruited thus far, of which 41 women reached the 12-month follow-up point and were included in this analysis. Mean age was 56.0 ± 12.6 and the majority of participants were Caucasian (82.9%). ~37% of subjects underwent concomitant prolapse repair surgeries (Table 1).

Surgical success was reported in 95.1% of participants. In this cohort, the average self-reported SUI episodes per day decreased from 1.7 ± 2.0 pre-operatively to 0.1 ± 0.6 at 12 months post-operatively (p < 0.001). Comparing pre and post operative shape and motion of urethra during valsalva using described measurements, MUS limited the extent of urethral swing toward outside at the level of the bladder neck and also at the level of the mid-distal urethra (Figure 1). Additionally, the MUS enabled a larger portion of the urethra to remain retropubic.

Conclusions: The preliminary results of this ongoing cohort study show that a properly placed and functional retropubic mid-urethral sling stabilizes bladder neck behind pubic bone and increases retropubic urethral length by limiting the extent of urethral swinging. Urethral compression or thinning at level of sling was not visualized.