This large, multicenter, comparative-effectiveness trial showed that there was statistical and clinical equivalence in the rates of treatment success according to objective criteria between the two most commonly performed midurethral sling procedures for the treatment of stress incontinence in women. The rates of treatment success according to subjective criteria appeared to be similar between the two procedures, but did not reach the predetermined criteria for equivalence. Patient-reported satisfaction with the results of the procedure, postoperative bother scores, and improvement in quality of life were also similar between the two procedures. The types of complications differed between the procedures; there was a higher frequency of bladder perforations, postoperative voiding dysfunction requiring surgical intervention, and urinary tract infections in the retropubic-sling group, whereas the frequency of neurologic symptoms was higher in the transobturator-sling group.
The rates of treatment success according to objective criteria that were reported in a recent Cochrane review8
(84% with the transobturator sling and 88% with the retropubic sling; relative risk, 0.96; 95% CI, 0.93 to 0.99) and in two meta-analyses7,13
(86 to 99% with the retropubic sling and 84 to 98% with the transobturator sling) are slightly higher than the rates of treatment success reported here. The use of a composite outcome to define treatment success in this trial, in contrast to the single outcome measure used in many of the previous studies of midurethral slings, may account for the apparently lower rates of treatment success in this study. Rates of treatment success as defined by validated subjective measures that evaluate many factors of continence and bladder function have been shown to be lower than rates of treatment success as defined by objective measures.21,22
However, subjective measures may be a more important outcome measure for patients, since they quantitate the effect of treatment on the patient’s quality of life. The inclusion of both objective and subjective outcomes is a strength of the present trial, particularly given the increasing recognition of the importance of measuring patient-oriented outcomes.
The overall number of serious adverse events as categorized according to the Dindo classification was higher in the retropubic-sling group than in the transobturator-sling group. Most of this difference was due to an increase in mesh exposure, voiding dysfunction requiring surgical intervention, and bladder perforation at the time of sling placement (although bladder perforation did not require surgical intervention other than replacement of the trocar). The frequency of non-serious adverse events (which were managed by expectant care or pharmacologic or other non-surgical interventions) varied according to the sling procedure. Patients in the transobturator-sling group were more likely to report neurologic symptoms, such as leg weakness and groin numbness (which were managed with expectant care), whereas postoperative urinary tract infections were more common after placement of retropubic slings. Our findings are consistent with previous reports of higher rates of voiding dysfunction after a retropubic-sling procedure than after a transobturator-sling procedure.23
The higher rate of this complication in the retropubic-sling group may be due to the relatively greater urethral obstruction that results from the fact that the retropubic sling is placed at a more vertical angle than is the transobturator sling.21,24
Two different approaches to the transobturator route were used in our trial, with the choice between the two left to the discretion of the surgeon. Although our study was not designed to compare these approaches, a subanalysis suggested that they resulted in similar rates of efficacy and adverse events, except that there was a higher rate of vaginal epithelial perforations with the in-to-out approach.
The number of retropubic and transobturator sling procedures that are performed to treat stress incontinence has increased dramatically in the United States and Europe.25
A recent Cochrane review8
and three meta-analyses7,13,23
evaluating outcomes after retropubic and transobturator sling procedures showed no significant differences in objective and subjective outcomes between the two sling approaches. However, most of the studies had insufficient sample sizes to assess differences in adverse events associated with each approach. Furthermore, the majority of the studies were designed as superiority trials. Therefore, when no significant difference was found between groups, investigators could not conclude that the treatments were equivalent or that one was not inferior to the other. One previous noninferiority trial that was performed at three clinical sites involved 180 women with urodynamic stress incontinence who were randomly assigned to undergo either a transobturator or a retropubic sling procedure.21
Treatment failure, defined as the presence of abnormal bladder function (incontinence, voiding dysfunction, or both), occurred in 46.6% of the women in the transobturator-sling group and 42.7% of the women in the retropubic-sling group. The authors concluded that the transobturator midurethral sling was not inferior to the retropubic sling; however, they could not determine whether the treatments were equivalent. In contrast to the present results, concomitant surgery for pro-lapse did not affect the treatment outcomes.
Our data suggest that patients with more severe urethral dysfunction, as reflected by lower Valsalva leak-point pressure or maximal urethral-closure pressure values, were no more likely to have treatment failure with the transobturator midurethral sling than with the retropubic midurethral sling, although the number of women in our study with a Valsalva leak-point pressure of 60 cm of water or less or a maximal urethral closure pressure of 20 cm of water or less was small. Although women who underwent the retropubic-sling procedure had lower baseline Valsalva leak-point pressures, this measure did not influence the relationship between the treatment and the outcome. Similar to the results of previous studies,26,27
we found that the transobturator and retropubic sling methods had similar efficacy regardless of sphincteric function. A large observational study of women undergoing a midurethral sling procedure showed that a Valsalva leak-point pressure of 60 cm of water or less or a maximal urethral closure pressure of 20 cm of water or less was an independent predictor of treatment failure with both retropubic and transobturator slings,28
whereas, in a randomized trial, a low Valsalva leak-point pressure was a predictor of a poor outcome with a transobturator sling but not with a retropubic sling.29
Further study is warranted.
Some strengths of the present trial include the relatively large sample size, the randomized, multicenter, nationally representative design (9 centers and 43 certified surgeons), the large, well-defined surgical cohort that included patients undergoing concomitant prolapse surgery, and the use of a well-defined composite outcome that included both objective and subjective criteria for treatment success. Furthermore, the postoperative course was monitored closely, to carefully identify and characterize early differences in side effects such as pain, voiding dysfunction, neurologic impairment, and mesh complications.
In summary, the rates of objectively assessed success of treatment for stress incontinence with a transobturator-sling approach and a retropubic-sling approach were equivalent at 1 year. The rates of subjectively assessed treatment success were slightly higher in the retropubic-sling group than in the transobturator-sling group and did not meet the predefined criteria for equivalence. However, the complications associated with the two procedures differ, and clinicians should counsel patients regarding these complications when discussing surgical options for stress urinary incontinence.