Minimally invasive midurethral slings have revolutionized the surgical management of stress urinary incontinence. The tension-free vaginal tape (TVT), introduced in 1996, was the first widely available midurethral sling. Since its introduction over 10 years ago, the TVT has become one of the most popular continence operations worldwide. Numerous studies, including several clinical trials, have demonstrated that it is a quick and safe outpatient operation with efficacy similar to that of the Burch colposuspension.1–3 It is considered by some to be a “gold standard” for the surgical treatment of stress urinary incontinence.4 In spite of its proven efficacy, relative safety and widespread adoption, some authors have expressed concern because of reports of rare but serious and, in some cases, life-threatening complications from this procedure. The blind retropubic passage of trocars from the vagina to the abdomen is unique to the TVT and is associated with a 3–9% bladder perforation rate and, on rare occasion, bowel and major vascular injuries.1,2,5–8
In 2001, Delorme described the transobturator tape midurethral sling.9 Like the TVT, this is a minimally invasive midurethral sling using a synthetic tape, but it is placed using a transobturator approach rather than a retropubic one. The transobturator technique has been advocated because it avoids this retropubic passage and, at least in theory, should reduce the risk of bladder, bowel, and iliac vessel injury. Two recent meta-analyses identified 13 randomized trials comparing retropubic and transobturator midurethral slings.10,11 The majority of these studies were small, had limited follow-up, reported only subjective outcomes, and were not designed to compare the equivalence of these two approaches. After synthesizing these trials and the available cohort studies, the authors of one of these meta-analyses concluded that the transobturator approach is associated with decreased risk of complications, but there is currently no evidence to suggest that one approach results in superior objective or subjective outcomes.11 The aim of this study is to test the hypothesis that the transobturator tape is not inferior to the TVT in the treatment of stress urinary incontinence in patients with and those without concurrent pelvic organ prolapse.
MATERIALS AND METHODS
This investigation was approved by the institutional review board of each participating clinical site, and all patients provided written informed consent for participation. Funding was provided through a research grant from American Medical Systems (Minnetonka, MN). American Medical Systems had no role in the design, implementation, or analysis of this study or in the writing of this manuscript. All methods and definitions conform to the standards proposed by the International Continence Society and the National Institutes of Health (NIH), unless otherwise stated.12–14
Subjects were enrolled from three U.S. tertiary-care academic medical centers. Subjects were eligible if they demonstrated urodynamic stress urinary incontinence on multi-channel urodynamic testing, were at least 21 years of age, and desired surgical correction of their incontinence. Subjects requiring concurrent surgery for pelvic organ prolapse were eligible for the study. Subjects were excluded if they demonstrated: 1) detrusor overactivity on urodynamic testing, 2) had a postvoid residual volume greater than 100 mL, 3) had history of previous sling procedure, 4) desired future childbearing, 5) had a history of hidradenitis suppurativa, inguinal lymphadenopathy, or an inguinal or vulvar mass, 5) had a history of a bleeding diathesis or were currently on anticoagulation therapy, 6) had a current genitourinary fistula or urethral diverticulum, or 7) otherwise had a contraindication for surgery.
At baseline, all participants underwent a standardized evaluation, which included a urogynecologic history, pelvic organ prolapse quantification (POP-Q) examination,13 cotton-tipped swab test evaluation of urethral mobility, and a urodynamic evaluation. The urodynamic evaluation included simple uroflowmetry, a filling cystometrogram, abdominal leak point pressure determination, and a pressure-flow voiding study. Additionally, participants completed the Incontinence Severity Index (ISI),15 Pelvic Floor Distress Inventory, Short Form-20 (PFDI-20),16 Pelvic Floor Impact Questionnaire, Short Form-7 (PFIQ-7),16 the Pelvic Organ Prolapse/Urinary Incontinence Sexual Questionnaire, Short Form (PISQ-12),17 the Medical Outcomes Study 12-Item, Short Form (SF-12),18 and a 3-day bladder diary.
Subjects were randomized with equal probability to TVT or transobturator tape using computer-generated random allocation with randomly permutated blocks of 4 to 8. Randomization was stratified by 1) study site and 2) presence or absence of pelvic organ prolapse beyond the hymen. Group assignments were concealed in consecutively numbered, sealed, opaque envelopes that were opened in the operating room just before the participants’ surgical procedures. Blinding of the surgeon or the participants was not possible postoperatively because of the different incisions required for each procedure. However, all postoperative assessments and examinations were performed by a research nurse at each site who was blinded to treatment assignment.
All study surgeons had substantial experience with TVT and had performed at least 10 transobturator tape procedures before enrolling patients in the study. Method of anesthesia was left to the discretion of the study surgeon. Tension-free vaginal tape procedures were all performed using the vaginal or “bottom up” approach following the technique described by the manufacturer (Gynecare, Ethicon Inc., Somerville, NJ). Transobturator tape procedures were all performed with the Monarc Subfascial Hammock system (American Medical Systems Inc., Minnetonka, MN) using the technique recommended by the manufacturer. For both procedures, surgeons were instructed to place the slings “tension-free.” Beyond this, no other standardization of sling tensioning was dictated. All patients underwent intraoperative cystoscopy to assess for lower urinary tract injury. Concomitant surgery was performed at the discretion of the surgeon but had to be declared before randomization. Perioperative care, including catheter management and pain management, was performed as was routine for the site in which the woman was enrolled.
Postoperatively, participants were evaluated 6 weeks and 6, 12, 18, and 24 months after surgery. Additionally, participants were contacted by the study coordinator on postoperative days 1, 3, and 7 and asked to rate their pain on a 10-point verbal numeric pain scale and to document their use of pain medications in the previous 24 hours. This pain assessment was repeated at the 6-week visit. At 6, 12, 18, and 24 months after surgery, participants completed the ISI, PFDI-20, and PFIQ-7, as well as a Patient Global Index of Improvement (PGI-I).19 At the 12 and 24 month follow-up, participants also underwent a physical examination with POP-Q evaluation, a standing cough stress test (300 mL), and a postvoid residual volume determination. Subjects also completed the SF-12, PISQ-12, and bladder diary at the 12- and 24-month visits.
The primary outcome for this study was the presence or absence of abnormal bladder function, a composite outcome assessed 12 months after surgery and defined as the presence of any of the following: 1) incontinence symptoms of any type (ISI score greater than 0), 2) a positive cough stress test, 3) retreatment for stress urinary incontinence, or 4) postoperative urinary retention. This outcome measure was chosen a priori to provide a measure that captures both efficacy and common lower urinary tract adverse events (eg, prolonged urinary retention, de novo urge incontinence) consistent with the goals of the NIH consensus guidelines.12 Subjects were considered as having urinary retention if they required catheterization beyond 6 weeks after surgery or underwent surgery for obstructed voiding at any time postoperatively. Severity of incontinence was classified pre- and postoperatively into categories of “dry,” “slight,” “moderate,” and “severe” according to the ISI results.15 Subjects were considered as having stress or urge incontinence symptoms based on their responses to corresponding items in the PFDI-20.16 Other secondary outcomes evaluated included the number of incontinence episodes and pad use as recorded on the bladder diary, short-term (less than 6 weeks) and long-term complications, postoperative pain, change in quality of life as assessed by PFDI-20, PFIQ-7, and SF-12, change in sexual function (PISQ-12), and global improvement in bladder function as assessed by the PGI-I.
This study is a noninferiority study design. The null hypothesis was that the difference in the proportion of women with abnormal bladder function in the transobturator tape (TOT) group compared with the TVT group was 15% or more (noninferiority margin) (H0: TVT–TOT≥0.15). In a randomized trial comparing TVT and laparoscopic Burch colposuspension performed by two of the sites participating in this study, the proportion of women in the TVT arm who were considered cured by the present study’s definition was 82% at 12 months.3 Assuming similar results in this study, 82 participants in each group (164 total) provides 80% power to reject the null hypothesis in favor of the alternative hypothesis that transobturator tape is not inferior to TVT (H1: TOT–TVT<0.15) using a two-group large-sample normal approximation test of proportions with a one-sided 5% significance level.20 Anticipating a 10% loss to follow-up and/or dropout rate over the period of the study, the total enrollment goal was 180. The 15% noninferiority margin was chosen because it was felt to be clinically relevant and because it was similar to the margin used by Kitchener et al21 in their noninferiority trial comparing open with laparoscopic colposuspension.
The primary and secondary outcomes were analyzed according to original treatment assignment (intent to treat). The primary outcome is presented as the difference of proportions of women with abnormal bladder function in each group (TVT–TOT). Participants with missing data that did not allow an assessment of the primary outcome were considered failures for purposes of this analysis. The noninferiority hypothesis was tested using the Farrington and Manning test of the difference.22 A significant result of this test statistic (P<.05) indicates that the null hypothesis should be rejected in favor of the alternative hypothesis that transobturator tape is not inferior to TVT by more than the noninferiority margin of 15%. Because a 10% difference might also be clinically relevant, the primary outcome was also tested using a noninferiority margin of 10%. Additionally, to allow comparison of our results with those of other studies, two-sided 95% confidence intervals (CIs) are also shown. The lower limit of this interval is equivalent to the lower limit of a one-sided 97.5% CI (or a significance level of .025) for testing our noninferiority hypothesis. Kaplan-Meier survival curves were generated for the development of any subjective incontinence symptoms and comparisons were made with the log-rank test (two-sided). Secondary outcomes were compared with the Pearson χ2 test for categorical data and the Student t test or Wilcoxon rank-sum test for continuous data, as appropriate. Change in number of incontinence episodes and number of pads used as recorded in the bladder diary, pain scores, and ISI, PFDI-20, PFIQ-7, SF-12, and PISQ-12 scores were analyzed using repeated measures analysis of variance or Friedman test, as appropriate. Statistical analysis was performed with JMP 6.0 (SAS Institute, Cary, NC) and NCSS 2007 (J. Hintze, Kaysville, UT).
One hundred eighty participants were enrolled from three clinical sites between November 2004 and January 2006. Figure 1 shows a flow diagram of patient enrollment and follow-up. Ten women withdrew before randomization and are not included in the analysis. One hundred seventy patients were randomized and underwent surgery. All randomized patients received the allocated treatment. One hundred sixty-two patients (95%) completed at least 12 months of follow-up, with a mean follow-up of 18.2±6 months. Baseline demographic, clinical, and incontinence severity data were similar between the two groups (Table 1). Seven percent of participants had undergone a previous incontinence procedure (retropubic urethropexy or bulking agent injection). Twenty percent of participants (n=34) had vaginal or uterine prolapse that extended beyond the hymen with maximal straining, and 10% had a history of previous surgery for pelvic organ prolapse.
Tension-free vaginal tape or transobturator tape alone was performed in 65 participants (39%), while the remainder received additional surgical procedures (Table 2). Operating time, estimated blood loss, change in hematocrit, length of stay, duration of bladder catheterization, and proportion voiding on the day of surgery were similar between the two groups (Table 3). As expected, participants who received concomitant surgery had longer operating times, greater blood loss, longer lengths of stay, greater duration of bladder catheterization, and a lower proportion of participants voiding normally on the day of surgery than those who received TVT or transobturator tape alone (P<.05 for each). Overall, intraoperative complications occurred more frequently in the TVT group (9% compared with 1%, P=.02). This difference is largely attributable to a difference in bladder perforations, which occurred more frequently in the TVT group (7% compared with 0%, P=.02). Otherwise, the incidence of perioperative complications (6 weeks or less) was similar between the two groups. Median pain scores were not significantly different between the groups on days 1, 3, or 7 after surgery or at the 6-week postoperative visit. Similarly, there was no difference in proportion using narcotic pain medications at each of these intervals (data not shown). During long-term follow-up, mesh erosions developed in five patients who received TVT and in one patient who received a transobturator tape (5.6% compared with 1.2%, respectively, P=.24); five of the six erosions (83%) required a return to the operating room for excision. No leg or obturator complications occurred in either group during the perioperative period. During long-term follow-up, two participants in the TVT group and three participants in the transobturator tape group reported leg pain or difficulty ambulating (2.4% compared with 4%, P=.92); in no case was this felt to be attributable to the sling procedure.
The primary outcome, abnormal bladder function, occurred in 46.6% of TVT participants and 42.7% of transobturator tape participants, with a mean absolute difference of 3.9% favoring transobturator tape (95% CI –11.0% to 18.6%.). The P value for the one-sided noninferiority test using the 15% noninferiority margin was .006, indicating transobturator tape was not inferior to TVT. Using a 10% margin, transobturator tape also demonstrated noninferiority for the primary outcome measure, P=.03. Standard superiority testing revealed no significant differences between groups for the primary outcome or any of its components. Additionally, each of the components of the primary outcome demonstrated noninferiority (Table 4). Using the ISI classification, 58.8% of participants in the TVT group and 62.3% of participants in the transobturator tape group were classified as “dry” (ISI=0) (mean difference 3.5%, 95% CI –11.5 to 18.3, favoring transobturator tape; noninferiority P=.007). Twenty-six percent of participants in the TVT group and 21% in the transobturator tape group had an improvement in their incontinence severity but were not dry, while 15% and 17%, respectively, reported incontinence severity that was the same or worse as measured by the ISI (P=.74). Urinary retention occurred in 5.8% of the TVT group and 2.6% of the transobturator tape group (mean difference 3.2%, 95% CI –3.8 to 10.8) favoring transobturator tape, noninferiority P=.003). The rate of abnormal bladder function 1 year after surgery was not significantly different between those participants undergoing concurrent surgery for pelvic organ prolapse compared with those who underwent a TVT or transobturator tape without prolapse surgery (44% compared with 47%, P=.41). Similarly, the proportion of participants who were classified as “dry” after surgery by the ISI was similar between those with and those without concurrent prolapse surgery (59% compared with 55%, P=.91).
Stress incontinence symptoms were reported postoperatively in 15% of each treatment group, with 13% in the TVT group and 12% in the transobturator tape group classifying these symptoms as bothersome, P = .86 (Table 5). There was no significant difference between groups in the proportion of participants with urge incontinence symptoms (any or bothersome). New or worsened urge incontinence was noted after surgery in 10% of the TVT group and 4% of the transobturator tape group, P=.18. Overall, the median number of incontinence episodes per day and pads used per day recorded on the bladder diary decreased from 2.3 (range 0–16.3) to 0 (range 0–11) and from 1.3 (range 0–7.6) to 0 (range 0–6.3), respectively (P<.02 for each), with no differences between groups. One year after surgery, 79% of participants in the TVT group and 82% of participants in the transobturator tape group reported that their bladder symptoms were either “much better” or “very much better” on the PGI-I, P=.88. Figure 2 illustrates a Kaplan-Meier survival curve of the time to development of any recurrent incontinence symptoms. There was no significant difference in the median time to development of postoperative incontinence symptoms between the two groups (19.1 months for TVT compared with 20.1 months for transobturator tape; P=.88).
Overall, there was a significant improvement in the summary scores of the PFDI-20 (mean change in score –67±44, P<.001) and PFIQ-7 (mean change in score –42±39, P<.001) one year after surgery, with no significant differences between groups. The urinary, prolapse, and colorectal scales of the PFDI-20 and the PFIQ-7 all improved significantly without differences between the two groups (data not shown). Similarly, the physical components summary (PCS) score of the SF-12 improved after surgery (mean change in score 2±9, P=.05), with no differences between treatment groups. No significant change was noted in the mental components summary (MCS) of the SF-12. Sexual function, as measured by the PISQ-12, improved significantly in both groups, with no significant differences between groups (mean change in score 3±5, P<.001).
Two recently published meta-analyses evaluating transobturator and retropubic midurethral slings for the treatment of stress urinary incontinence identified a total of 13 randomized trials comparing these two techniques.10,11 In each of these 13 trials, no significant difference was found in the subjective continence rates between these two procedures.10,11 However, because each of these trials was designed to test the superiority of one approach over the other, a finding of no significant difference does not imply that the two procedures are equivalent or that one is no worse than the other; rather it implies that there is insufficient evidence that one approach is better. When designing this trial, we felt that there was no reason to suggest that the cure rate of transobturator tape would be substantially higher than TVT, given TVT’s proven efficacy, but that it was important to demonstrate that transobturator tape was not worse than TVT by a clinically important degree. This multi-center noninferiority trial confirms that the Monarc transobturator tape is not inferior to TVT for the treatment of stress urinary incontinence.
The NIH has emphasized the importance of evaluating efficacy of urinary incontinence therapies with composite outcomes that include subjective and objective efficacy measures along with an assessment of new unwanted symptoms and adverse events.12 The primary outcome measure used in this study, abnormal bladder function, was chosen a priori to provide a measure that captured both treatment efficacy and common lower urinary tract adverse events (eg, prolonged urinary retention, de novo urge incontinence) consistent with these goals. The transobturator tape demonstrated noninferiority for this primary outcome measure as well as each of the components of the primary outcome: subjective continence, objective continence (ie, negative stress test), need for retreatment, and rate of urinary retention. Our goal was to report and compare the proportion of participants in each group with an optimal surgical outcome (ie, continence with normal voiding function.) In that regard, transobturator tape performed as well as, or at least not worse than, TVT.
Eighty-five percent of participants in both treatment groups had resolution of their stress urinary incontinence symptoms 1 year after surgery, but the rate of participants with complete subjective continence was considerably lower. Overall, 60% reported that they were dry on the ISI, with an additional 23% reporting improvement in their incontinence symptoms without complete continence. Although these subjective cure rates seem relatively low, they are consistent with a number of large randomized trials for the surgical treatment of stress urinary incontinence.1,25,26 Success rates for stress incontinence surgery can be widely variable and are largely dependent upon the definition of cure or the outcome measure used.25,26 Cure rates based on validated patient-reported measures are consistently lower than objective measures of cure such as urodynamics or an office stress test.3,25,26 Additionally, success rates based on a composite outcome measures, as with our study, will naturally be lower than those based upon a single criterion. Notably, however, there is now a consistency in the data from large randomized trials that, while cure rate of stress urinary incontinence symptoms after surgery with procedures with demonstrated efficacy are high, the proportion of participants with complete continence and normal bladder function is considerably lower, and patients should be counseled accordingly.
The anatomic relationship between the sling and the urethra is different for the transobturator tape than for retropubic slings. In retropubic slings, including the TVT, the sling axis is roughly vertical in relation to the urethral axis, whereas the axis of the transobturator tape is more horizontal.27 As such, the transobturator tape provides less circumferential compression of the urethra than does the TVT. This decreased compression may result in fewer postoperative voiding difficulties and irritative bladder symptoms. A recent meta-analysis found fewer voiding difficulties after transobturator midurethral slings compared with retropubic midurethral slings.10 In this trial we found a lower rate of urinary retention and new or worsening urge urinary incontinence with transobturator tape than with TVT, but neither reached statistical significance. Some have expressed concern that the more horizontal axis of the transobturator tape may translate into lower cure rates of stress incontinence, but based on the results of this trial, this does not appear to be the case.
The transobturator technique has been advocated because it avoids the blind retropubic passage of trocars and should, therefore, reduce the risk of bladder, bowel, and iliac vessel injury. In this study, transobturator tape had a significantly lower rate of bladder injury than TVT. In fact, no bladder injuries occurred in the transobturator tape group. Other comparative studies have also found a lower rate of bladder perforations with transobturator tape when compared with the TVT, consistent with our findings.10,28,29 The clinical significance of a bladder perforation after TVT is unclear, however. In each instance of perforation in this study, the perforating trocar was merely removed and replaced outside of the bladder without consequence. LaSala et al30 evaluated the clinical impact of bladder perforation after TVT and found no difference in postoperative urinary tract infections, hematomas, voiding dysfunction, or objective or subjective cure rates in patients who had a cystotomy after TVT compared with those who did not. Other than an increase in bladder perforations in the TVT group, the perioperative complication rate in our study was low overall, with no difference between groups.
The novel anatomic approach of the transobturator tape, while avoiding the space of Retzius and thereby reducing the risk of bladder injury, does allow for other potential complications including obturator neurovascular injury and lower extremity morbidity not seen with other approaches. In this study, we identified no obturator compartment or leg complications. The incidence of leg pain or difficulty with ambulation was low and not significantly different between treatment groups. Similarly, two studies evaluating complications after the Monarc transobturator tape procedure with a combined total of over 400 participants failed to identify any major lower extremity complications.29,31 Thus, although obturator and other leg complications are possible with transobturator tape, their incidence appears to be rare, at least with the technique used in this study. Several different transobturator sling kits are currently available. The Monarc transobturator tape, which was used in this study, uses helical needles passed from the inner thigh through the obturator membrane, around ischiopubic rami, and through a vaginal incision to place a polypropylene mesh under the urethra, or so called “out to in” placement. Transobturator tape techniques that use differently shaped trocars, different methods of passage (ie, “in to out”), or different types of mesh may have different rates of complication or efficacy than those found in this study. It is important to note that the results of this trial may not necessarily be transferable to transobturator or midurethral slings beyond the two specific devices evaluated in this study.
The primary strengths of this multi-center clinical trial are its noninferiority design, the use of standardized validated outcome measures assessed in multiple domains, the use of a blinded clinical examiner to perform follow-up evaluations, and high follow-up rate. The principal limitations include the inability to blind the patient to the treatment assignment and a medium-term length of follow-up. Additionally, a majority of patients had concurrent pelvic reconstructive surgery. Only 39% had a TVT or transobturator tape performed in isolation. Therefore, the complication rates, postoperative pain assessments, and voiding times noted in this study likely overestimate the rates that would be found in a population undergoing the sling operations exclusively. The use of this heterogeneous population does allow us to conclude, however, that concurrent pelvic reconstructive surgery at the time of transobturator tape or TVT does not significantly impact the treatment efficacy of these two midurethral slings.
In conclusion, the Monarc transobturator tape is not inferior to TVT for the treatment of stress urinary incontinence in women with and those without pelvic organ prolapse with 1–2 years of follow-up. Transobturator tape results in fewer bladder perforations than TVT; otherwise perioperative complications are similar between the two procedures. Larger studies are needed to evaluate the relative risk of the less common but potentially severe complications that have been seen with both procedures. Studies with longer follow-up are necessary to determine if the efficacy of transobturator tape is durable.
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© 2008 The American College of Obstetricians and Gynecologists
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