Stress urinary incontinence (SUI) is a prevalent condition affecting up to 45% of women in the United States.1 Although not life threatening, it greatly affects quality of life2,3 and produces a heavy economic burden.4 Approximately 200,000 SUI procedures are performed annually; with a woman's lifetime risk of needing SUI surgery in the United States of approximately 14%.5
Midurethral slings, first introduced by Ulmsten in 1996,6 have quickly replaced the Burch retropubic urethropexy as the gold standard surgical treatment for SUI as they are minimally invasive and have high continence rates with low complication rates.7–9 The transobturator modification was made to reduce theoretical risks associated with the original retropubic procedure. Although numerous clinical trials and systematic reviews have shown similar efficacy and safety for these two approaches in the short term7,10–13 there is a paucity of long-term studies.14–16 The only two long-term studies assessing reoperation for recurrent SUI, spanned time frames (1987–2005 and 2000–2009) that employed distinct surgeries for SUI than presently and did not adjust for potential confounders.17,18 Given the changes in SUI procedure utilization and decreasing efficacy if a woman requires a reoperation for SUI, it is imperative to understand the long-term reoperation rates for these contemporary surgeries.
To address this knowledge gap, we undertook a cohort study of reoperation for recurrent SUI after primary retropubic or transobturator midurethral sling procedure at our institution. To limit the effect of uncontrolled bias inherent with historical cohorts design, the groups were matched for known confounders.
The Mayo Clinic Institutional Review Board (Rochester, Minnesota) approved the study. A surgical database was used to identify all patients who underwent an anti-incontinence procedure at Mayo Clinic, Rochester, Minnesota, from January 1, 2002 to December 31, 2012. Among those with research authorization, the medical records were reviewed by one of the authors (D.C.) to identify those women with SUI, stress-predominant mixed urinary incontinence, or occult urinary incontinence whose primary procedure was a transobturator or retropubic midurethral sling. Patients were excluded if they were younger than 21 years of age, had a history of previous incontinence surgery (midurethral sling, retropubic urethropexy, bulking agent, bladder neck pubovaginal sling, needle suspensions, or paravaginal defect repair), had neurologic disease known to affect bladder function (eg, multiple sclerosis, spinal cord injury, or Parkinson’s disease), had concomitant or history of urethral diverticulectomy, had urethral reconstruction, or severe pelvic trauma or fracture.
Baseline demographic information, incontinence diagnosis, urodynamic evaluation (if available) and standardized surgical and clinical historical information were retrospectively collected from the patient’s medical record in 2014. Diagnostic definitions used for this study complied with International Continence Society Standardization of Terminology.19 We defined stress incontinence as the “complaint of involuntary leakage on effort or exertion, or on sneezing or coughing” and mixed incontinence as the “complaint of involuntary leakage associated with urgency and also with exertion, effort, sneezing or coughing.”21 Occult incontinence was defined as the loss of urine on urodynamic studies in the absence of patient report of SUI symptoms. To standardize the preoperative designation, the diagnoses were based on review of the patients’ reports detailed on the preoperative note. Each operative report was also reviewed to ensure that the surgery was the first procedure for SUI, to document additional procedures performed, and to capture intraoperative complications. Additional morbidity information was captured by reviewing hospital discharge summaries and all information documented between discharge from the hospital and the last medical visit or correspondence in the medical record.
The following retropubic midurethral slings were used during the study period: GYNECARE TVT EXACT, Supris, Align, Pelvilace, Sabre, Uretex, and SPARC. ObTape, GYNECARE TVT-Obturator System, Monarc, and Aris were used in the transobturator sling group. All slings where placed in a tension-free fashion according to the manufacturers’ recommendations. Suprapubic catheters were used in most patients during the first two years of the study period, and then only in those patients who had a combined anterior compartment repair. Patients who had a suprapubic catheter underwent a similar clamping routine before catheter removal. All patients had a postoperative voiding trial before being discharged. Patients without a concomitant procedure or those undergoing a nonprolapse concomitant procedure (eg, hysterectomy for nonprolapse indication, nongynecologic surgery, laparoscopy, or hysteroscopy) were considered to have an “isolated” procedure. Women undergoing any concomitant prolapse repair (eg, hysterectomy for prolapse repair, apical suspension, sacrocolpopexy, or anterior or posterior repair) were classified as having a “combined” procedure. Because these additional procedures may affect surgical complications, subgroup analysis was also conducted in which only patients having isolated sling procedures were compared.
The primary outcome was based on review of the medical record and defined as reoperation for recurrent SUI. Patients who underwent a repeat midurethral sling procedure (any kind), urethral bulking agent, bladder neck pubovaginal sling (autologous or allografts), or paravaginal defect repair were considered to have recurrent SUI. Secondary outcomes included intraoperative complications and mesh-related complications requiring reoperation after the index sling procedure (eg, sling revision for urinary retention or mesh exposure).
Because the type of sling was not randomly assigned in this retrospective cohort, women in the retropubic and transobturator groups were matched using a greedy algorithm on age (±3 years), body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) category (less than 25, 25–29, 30–39, 40 or greater), isolated compared with combined procedure, and preoperative diagnosis to reduce the covariate imbalance in these baseline covariates and to obtain a less-biased comparison of outcomes. The goal was two retropubic case matches for each transobturator case (76.7% had two matches, 19.4% had one match, 3.9% had no matches). Results are presented for both the full cohort and the covariate-matched cohort. Baseline patient characteristics were compared between the retropubic and transobturator groups using the two-sample t-test for age and BMI and the χ2 test or Fisher's exact test for all other variables. Need for transfusion and occurrence of intraoperative complications were each compared between the two groups using either the χ2 test or Fisher's exact test. Subsequent surgeries for recurrent SUI or for sling-related complications were evaluated using time-to-event methodology. Duration of follow-up was calculated from the date of the primary sling procedure to the date of the event or last follow-up. Survival-free of the event was estimated using the Kaplan-Meier method, reported as 100 minus the Kaplan-Meier estimate, and herein referred to as the cumulative incidence of the event. This calculation did not take into account the competing risk of death, because only 0.6% of the full cohort was deceased at the time of the medical record review. The association between type of sling and each of these time-to-event outcomes was assessed based on fitting a separate Cox proportional hazards model. The strength of each association was summarized by calculating the hazard ratios (HR) and 95% CI. All calculated P values were two-sided and considered statistically significant if P<.05. Statistical analysis was performed using the SAS 9.4.
Three thousand four hundred and seventy two women underwent an anti-incontinence procedure during the study period. One thousand five hundred ninety-one patients did not fulfill our inclusion criteria, did not have a retropubic or transobturator midurethral sling procedure, did not have known primary diagnosis, or did not undergo their retropubic or transobturator sling procedures at Mayo Clinic during our timeframe of interest (Fig. 1). Among the 1,881 remaining women, 1,551 received a retropubic sling and 330 received a transobturator sling. Women in the two groups were subsequently matched on age (±3 years), BMI category (less than 25, 25–29, 30–39, 40 or greater), isolated or combined procedure, and preoperative diagnosis. Of the 330 women who underwent a transobturator sling procedure, we identified matches with a retropubic sling procedure for 317 women; 253 women had two matches identified, and 64 had one match identified, for a total of 570 women with a retropubic sling.
Overall, 1,774 of the 1,881 women (94.3%) had a preoperative diagnosis of either stress or mixed incontinence (urgency and stress) and 5.7% had a preoperative diagnosis of occult incontinence. Women who underwent a retropubic sling procedure were younger (SD 57.9 years [13.5] vs 60.4 years [13.6]; P=.002), more likely to have a midurethral sling procedure combined with other concomitant prolapse repairs (50.2% vs 15.2%; P<.001), and less likely to have a preoperative diagnosis of SUI (53.3% vs 69.4%, P<.001) compared with those who underwent a transobturator sling procedure in the full cohort. However, in the covariate-matched cohort, women who underwent a retropubic sling procedure were similar to those who underwent a transobturator sling procedure with respect to mean age (SD 58.9 [12.9] vs 59.9 [13.2], P=.32), proportion with combined procedures (17.0% vs 15.8%; P=.63), and preoperative diagnosis of SUI at baseline (66.7% vs 68.5%, P=.59). In fact, there was no difference between the groups in any of the evaluated baseline variables in the covariate-matched cohort suggesting the matching reduced some of the selection bias between groups in this nonrandomized cohort (Table 1).
Within the full cohort, 75 women underwent reoperation for recurrent SUI (50/1,551 with a retropubic sling and 25/330 with a transobturator sling). In the retropubic group, 24 underwent a repeat midurethral sling procedure, four underwent autologous fascial sling procedures, and 22 had a urethral bulking agent. Among the 25 women who underwent reoperation in the transobturator group, 20 underwent a repeat midurethral sling procedure, one underwent autologous fascial sling, and four had a urethral bulking agent. Median time to reoperation was 1.3 years (interquartile range 0.4–3.5) and 1.4 years (interquartile range 0.6–3.4) for the retropubic and transobturator groups, respectively. Among the remaining patients without a documented reoperation, the median duration of follow-up was 4.9 years (interquartile range 2.4–7.5 years) and 3.7 years (interquartile range 1.1–6.4 years), respectively, in the retropubic and transobturator sling groups.
Women undergoing a transobturator sling procedure had an increased risk of reoperation for recurrent SUI compared with women undergoing a retropubic sling procedure in both the full and covariate-matched analyses (full cohort: HR 2.88, 95% CI 1.78–4.66, P<.001; covariate-matched cohort: HR 2.42, 95% CI 1.37–4.29, P=.002) (Fig. 2). In the covariate-matched cohort, the cumulative incidence rates of reoperation for SUI at 5 and 8 years were 4.1% (95% CI 2.2–5.9%) and 5.2% (95% CI 3.0–7.4%) in the retropubic group and 9.2% (95% CI 5.3–12.9%) and 11.2% (95% CI 6.4–15.8%) in the transobturator group. This increased risk of undergoing reoperation for SUI for women with a transobturator sling (vs retropubic sling) was higher among the women with a combined procedure (full cohort: HR 7.87, 95% CI 3.70–16.72, P<.001; covariate-matched cohort: HR 5.96, 95% CI 1.64–21.67, P=.007) than among the women with an isolated procedure (full cohort: HR 1.92, 95% CI 1.03–3.61, P=.04; covariate-matched cohort: HR 1.77, 95% CI 0.90–3.50, P=.10) (Fig. 3).
The results for the secondary outcomes are reported in Table 2. In the covariate-matched cohort, women in the retropubic group had a higher rate of intraoperative complication compared with women in the transobturator group (13.7% vs 4.7%; difference=9.0%, 95% CI for difference 5.3–12.6%; P<.001); the majority of this difference was due to bladder perforation (7.0% vs 0.6%; difference=6.4%, 95% CI for difference 4.1–8.7%; P<.001) and hemorrhage (estimated blood loss greater than 300 mL; 6.5% vs 3.8%; difference=2.7%, 95% CI for difference –0.2–5.6%; P=.09). There was no difference between the groups with respect to need for blood transfusion or other complications. Enterotomies were rare and unrelated to the index sling procedure. Women in the retropubic group had an increased risk of subsequent surgery for urinary retention (HR 8.11, 95% CI 1.08–61.17, P=.04) but not subsequent surgery for mesh exposure (HR 0.50, 95% CI 0.18–1.41, P=.19) compared with women in the transobturator group. The cumulative incidence of sling revision for urinary retention plateaued at 3.2% by 5 years and remained higher for the retropubic group compared with the transobturator group for the duration of follow-up (3.2% vs 0.4%, respectively, by 8 years). There were no sling-related vascular or bowel injuries or sling-related deaths.
Because additional prolapse procedures may affect surgical complications, a subgroup analysis of the secondary outcomes was conducted using the women in the covariate-matched cohort who had isolated midurethral sling procedures (473 with a retropubic sling and 267 with a transobturator sling). There was no difference between groups in the risk of sling revision for urinary retention (HR 4.96, 95% CI 0.64–38.80, P=.13) or subsequent surgery for mesh exposure (HR 0.43, 95% CI 0.15–1.25, P=.12). Women undergoing a retropubic sling procedure were more likely to have intraoperative complications compared with women undergoing a transobturator sling procedure (9.3% vs 1.5%; difference=7.8%, 95% CI for difference 4.8–10.8%; P<.001). As noted previously, this difference was attributed primarily to increased risk of bladder perforations during trocar passage (6.8% for retropubic vs 0.7% for transobturator; difference=6.1%, 95% CI for difference 3.5–8.5%; P<.001). There was no difference in the rate of intraoperative hemorrhage between groups (1.9% for retropubic vs 0.4% for transobturator; difference=1.5%, 95% CI for difference 0.1–3.0%; P=.10).
This article describes long-term reoperation rates in a large, covariate-matched cohort of women undergoing retropubic or transobturator midurethral sling procedures for primary SUI. After adjusting for known confounders, our finding suggests that women who undergo a retropubic sling procedure are less likely to need reoperation for recurrent SUI during the subsequent decade. Although the cumulative incidence of a reoperation by 8 years appears small (11.2% for transobturator vs 5.2% for retropubic), this finding may have significant public health implications. In the United States alone, 200,000 incontinence procedures are performed annually. Assuming that 50% of these surgeries are for transobturator slings, 6,000 reoperations for recurrent SUI could be avoided if all procedures were converted to the retropubic route.
A systematic review similarly reported higher failures but fewer sling revisions for urinary retention associated with the transobturator sling.11 Two population-based studies evaluating long-term reoperation rates after SUI surgery found that “sling” procedures were not as effective compared with the Burch retropubic urethropexy.17,18 There are several key distinctions between these studies and our publication. First, both of these studies used International Classification of Diseases, 9th Revision codes that could not distinguish synthetic midurethral sling procedures from bladder neck autologous sling or other procedures. The time frames evaluated, 1987–2005 and 2000–2009 predate widespread utilization of modern midurethral sling procedures. Lastly, use of health encounter18 and Washington State17 databases precluded determination of significant cofounders of continence and whether or not the index procedure was the first or subsequent SUI procedure. As a result, these studies cannot provide an accurate estimate of long-term reoperation for contemporaneous surgery for SUI.
Similar to others, we found that retropubic sling procedures were associated with higher intraoperative complication rates and voiding dysfunction necessitating sling revision.20 In addition, we found similar mesh exposure rates between the two procedures. However, the majority of difference in the intraoperative complications was due to bladder perforation and hemorrhage (estimated blood loss greater 300 mL). Bladder perforations were all recognized intraoperatively and had no short-term or long-term sequelae for the patient. Even though there were more “hemorrhages,” the transfusion rate was similar between groups and most of the bleeding complications were due to the concomitant procedures performed during the index sling procedure (data not shown). Although the retropubic approach was associated with higher rates of sling revision for retention, the cumulative incidence was overall low (stabilizing at 3.2% at 5 years) and only 2.8% higher than that associated with the transobturator sling procedure. Moreover, all women had resumption of normal voiding after sling revision and none necessitated prolonged catheterization. It is relevant to highlight that no sling-related vascular or bowel injury or sling-related death was observed during the 9-year follow-up of the 1,551 retropubic sling procedures. This finding further highlights the safety of retropubic macroporous polypropylene sling procedures.
Our study has several strengths. We describe a large, homogenous cohort of women undergoing the two most commonly performed procedures for primary SUI. Because cohort studies are prone to bias, we achieved group balance for known confounders of reoperation by matching on a number of variables. This allowed for minimization of baseline group differences inherent with a retrospective cohort study. Lastly, data from multiple types of retropubic and transobturator sling procedures were included, improving the external validity of our findings.
Our study had some shortcomings. First, it is possible that selection bias may have contributed to the differences detected. This is likely minimized because groups were matched to minimize the effect of known confounders. Second, although most women underwent urodynamics, most did not have a complex evaluation and hence we could not compare outcomes between women with and without intrinsic sphincter deficiency. Previous studies from our institution revealed that few women undergoing primary SUI procedure had intrinsic sphincter deficiency, and hence the proportion of women with intrinsic sphincter deficiency is likely small and unlikely to have contributed significantly to our findings.9 Third, outcome assessment depended on continued follow-up at our institution and hence it is possible that some women may have reoperation at another hospital. However, 85% of the full cohort had follow-up beyond 1 year. Although the median duration of follow-up was 4.9 years and 3.7 years for women without a documented reoperation for SUI in the retropubic and transobturator sling groups, respectively, the rates for the cumulative incidence of a reoperation for recurrent SUI beyond 5 years may be underestimated. Lastly, all surgeons were fellowship trained and hence our finding may not apply to surgeons with less experience.
In summary, women treated with a retropubic sling procedure have a significantly lower cumulative incidence of reoperation for recurrent SUI compared with women who were treated with a transobturator sling procedure. This finding should help providers counsel women presenting for surgical treatment of SUI.
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