Midurethral slings are the most frequently performed surgeries in women with stress urinary incontinence (SUI) in the United States. Despite the popularity of these procedures, information characterizing those women most likely to benefit from these surgeries is meager and conflicting. Possible reasons for this include use of a wide variety of noncomparable outcome measures, nonuniform assessment of study participants, and inadequate sample size. Among clinical and demographic factors, increasing age,1,2 preoperative use of anticholinergic medications for overactive bladder symptoms,1 mixed incontinence,3,4 urge incontinence and comorbid disease,5 concurrent surgery for pelvic organ prolapse,1,3 bladder neck immobility,4 obesity,3 and previous continence surgery2,6 have all been suggested as predictors of failure with midurethral sling surgery. These associations have not been confirmed or explored by others.7
Larger, prospective studies with well-characterized patients are needed to confirm factors that may predict outcomes with mesh slings. One such study, the Trial of Midurethral Slings, compared efficacy between the retropubic and transobturator midurethral slings at 12 months in women with stress predominant urinary incontinence (UI). The rates of objectively assessed success (outcomes included a 24-hour pad test, bladder fill stress test, and retreatment) were considered equivalent between the two approaches at 12 months. Although the rates of subjectively assessed success (outcomes included bladder diary, SUI symptoms, and retreatment) were similar, they did not meet the predetermined criteria for equivalence.8 This analysis examines baseline demographic and clinical factors as possible predictors of “overall” surgical failure (objective failure, subjective failure, or both) compared with treatment success. We also wished to explore the factors associated with objective compared with subjective failure, where objective failure may define a higher threshold for failure, potentially reflecting failure more directly aligned with successful placement of the sling and the mechanism of action of the procedure itself.
MATERIALS AND METHODS
The design and primary results of this two-arm randomized equivalence trial comparing retropubic to transobturator midurethral slings have been described previously.8,9 Women aged 21 years or older planning stress incontinence surgery were invited to participate. Eligibility requirements included pure or predominant stress incontinence symptoms for at least 3 months and a positive urinary stress test at a bladder volume of 300 mL or less. Women were randomized to a retropubic or transobturator midurethral sling. Randomization was performed after anesthesia was administered with the use of a permuted-block randomization schedule stratified according to clinical site. Institutional Review Board approval was obtained at nine clinical sites and the coordinating center. Written informed consent was obtained. An independent data and safety monitoring board reviewed the progress, interim results, and safety of the study.
Definitions of clinical terms, methods of evaluation, and key surgical elements, including cystoscopic evaluation, were standardized across nine participating sites.10,11 Tension-free vaginal tape (TVT) was used as the retropubic sling, and transobturator tension-free vaginal tape (in-to-out) or transobturator midurethral sling (out-to-in) was used as the transobturator sling. Surgeons declared which transobturator approach they would use before trial initiation should the participant be randomized to the transobturator midurethral sling arm. Concomitant vaginal surgery was permitted.
Surgical success was determined at 12 months after randomization by the following outcome measures of objective failure: a positive provocative stress test at 300 mL or a positive 24-hour pad test (at least 15 mL leakage over 24 hours) or retreatment for stress incontinence and subjective measures including a self-reported stress-type UI symptoms on the Medical Epidemiological and Social Aspects of Aging 12 questionnaire or leakage on a 3-day voiding diary or retreatment (behavioral, pharmacologic, or surgical) for stress incontinence. Women were considered overall failures if they experienced either objective or subjective failure or both. Data were collected preoperatively, at 2 and 6 weeks, and at 6 and 12 months postoperatively by interview and clinical examination. For this analysis, potential variables thought to be associated with treatment failure were sociodemographic characteristics (age, race or ethnicity, education, marital status); medical or surgical history (body mass index, smoking status, menopausal status or hormone therapy, previous prolapse surgery, estimated blood loss during sling surgery, previous UI surgery, fecal incontinence symptoms, number of vaginal deliveries); characteristics of UI (self-reported frequency of stress and urge incontinence symptoms from the Medical, Epidemiologic and Social Aspect of Aging (MESA) questionnaire12; symptom bother and incontinence-related quality of life as measured by the Urogenital Distress Inventory (UDI) and Incontinence Impact Questionnaire (IIQ)13; number of incontinence episodes per day by 3-day voiding diary; quantity of urine leakage from 24-hour pad test14; physical examination findings (urethral hypermobility measured by the Q-tip test15 with Q-tip delta and maximum straining considered; pelvic floor muscle strength16; pelvic organ prolapse17; postvoid residual at discharge [100 mL or less, more than 100 mL], and outcome of baseline empty bladder stress test [positive or negative]). Performance of concomitant surgery (yes or no) and number of comorbid illnesses reported (0, 1, 2 or more) was included.18,19
To identify predictors of treatment failure, univariable logistic regression models were fit modeling the probability of overall failure and objective failure as a function of each covariate separately, adjusting for treatment group (retropubic and transobturator midurethral sling approaches) and site. The models predicting overall failure compare the women with overall failure to those with overall success. A subanalysis of the women with objective failure was performed where models were fit to compare women with objective failure to those with subjective failure but objective success. Both continuous and categorical predictors were considered. Odds ratios and 95% confidence intervals described the associations between clinical parameters and the outcomes. Based on significance at the .05 level from the univariable logistic regression models and clinical relevance, multivariable logistic regression models were fit for each defined outcome. To assess whether the relationships between the predictors and failure were similar for each of the treatment groups, interaction terms between each predictor and treatment were considered. Interaction terms between significant main effects were also tested for inclusion in the multivariable models. Hosmer-Lemeshow goodness-of-fit tests were calculated to assess the fit of the models. A 5% two-sided significance level was used for all statistical testing. Data from women with missing covariate values were included when possible (eg, available case analysis was used). Analyses were performed using SAS 9.2.
Baseline data were obtained from 597 women. Of those, 565 (95%) were assessed for surgical success at 12 months postsurgery, 280 (94%) individuals in the retropubic arm and 285 (95%) participants in the transobturator arm. Overall treatment failure was seen in 260 (46.0%) participants compared with treatment success in 305 (54.0%) participants (Fig. 1). Of the overall failures, 130 failed by subjective measures only; 109 failed by both objective and subjective measures, and 15 failed by objective measures only.
Baseline characteristics of women with overall failure compared with those with overall success are noted in Table 1. Univariable and multivariable analyses controlling for treatment group and clinical site for each of these baseline characteristics are reported in Table 2. Increasing age and body mass index, previous incontinence surgery, Q-tip excursion and maximum straining angle of less than 30°, as well as higher baseline leakage, Brink score, pad weight, and symptom scores (UDI, IIQ, and MESA questionnaires) were each associated with increased odds of overall failure on initial bivariate analysis. Multivariable logistic regression analysis showed that women who had previous UI surgery had an increased odds of overall failure of approximately two times that of women who had no previous UI surgery controlling for other factors. Women with a maximum Q-tip excursion less than 30° (less bladder neck mobility) had nearly twofold increased odds of failure compared with those with hypermobility. Baseline severity measures including increasing MESA questionnaire urge scores and increasing pad weights were also associated with overall failure. For each 10-point increase in urge score the odds of overall failure nearly doubled, and for each 10-g increase in pad weight the odds of overall failure increased by approximately 6%.
We also explored differences in baseline characteristics of the women with objective failure consisting of a positive stress test, pad test, and retreatment (regardless of subjective report) compared with those with subjective failure only (negative stress and pad tests) (Table 3). In univariable analysis, individuals with previous incontinence surgery, concomitant surgery, presence of comorbid conditions, age, and baseline UDI, IIQ, and MESA questionnaire urge and stress, and increasing pad weight were significantly associated with objective failure compared with patients with only subjective failure. Multivariable analyses revealed that for each 10-year increase in age there was a nearly 50% increase in the odds of objective failure compared with subjective-only failure controlling for other factors. Increased baseline UDI score and pad weight also predicted a nearly 5–10% increase in the odds of objective failure for each 10-unit increase in value. Further, women who had concomitant surgery were half as likely to fail objectively compared with women who failed subjectively (Table 4). Associations of risk factors with overall and objective or subjective failure were similar for both sling types.
The clinical evaluation of women with UI includes patient history, physical examination, and measures of incontinence severity. An understanding of the patient factors associated with treatment failure and success can help us more robustly counsel patients regarding realistic expectations from midurethral sling surgery for stress incontinence. In this analysis we hypothesized that objective and subjective outcome measures capture different postoperative processes and those that failed objectively may be a more “severe” failure or have a greater degree of failure. Objective measures may be a more sensitive reflection of the sling procedures mechanism of action, with the dynamic urethral kinking that occurs with the TVT serving as a fulcrum reflecting surgical technique and quality of host tissue in-growth.20 An understanding of the types of patients at risk for these types of failures may help us more effectively target patients for these or other treatment options. Subjective failures may capture urge symptoms, less severe leakage, or other perceived leakage that may or may not be related to sling function in preventing SUI.
In our study, women who had previous UI surgery had nearly twice the odds of overall failure compared with women having their first surgery for SUI. Previous incontinence surgery as a risk factor for failure after midurethral sling surgery has been described by several authors2,3,6 and may be due to scarring, nerve damage during periurethral dissection, or more severe neuromuscular compromise. We observed that women with less urethral mobility (Q-tip maximum straining angle less than 30°) had about twice the odds of overall failure than patients with more urethral mobility (Q-tip angle of 30° or more) despite preoperative urethral hypermobility not being associated with objective failure. Others have reported similar findings.21,22 For example, Liapis et al observed that women with a less mobile urethra (maximum Q-tip straining angle less than 30) undergoing TVT for recurrent SUI had a 50% failure rate compared with a 10% failure rate in patients with greater mobility (Q-tip excursion 30° or more).21 Therefore, patients with less mobility may have a more neurologically impaired baseline urethral function, and other treatments such as bulking agents may be a more appropriate consideration.
For every 10-point increase in the baseline MESA questionnaire urge incontinence score the odds of overall failure nearly doubled. In addition, for every 10-point increase in urge incontinence bother as measured by the UDI, the odds of objective failure increased by nearly 10%. We and others have also previously described this association.23,5,24 To this point, Holmgren et al reported that the long-term cure rate after TVT in women with mixed UI was 30% at 8 years compared with an 85% cure rate in women with pure SUI.24 However, others have found the presence of urge symptoms in stress-predominant mixed UI does not affect success negatively.25,26 Whether patients with more urgency incontinence symptoms reflect a more complex neuromuscular dysfunction is not clear. Nonetheless, patients with mixed UI should be strongly counseled about the possibility of lower cure rates, and perhaps more robust perioperative treatment with behavioral therapy, medical therapy, or both should be considered.
We found that greater pad weight at baseline increased the odds of both overall failure and objective failure after midurethral sling, and this has been corroborated by others.2 In the current study, pad weight was the only clinical measure associated with both overall and objective surgical failure. Perhaps pad testing should be used more frequently in the evaluation of our patients considering midurethral sling surgery for stress incontinence.
Concomitant prolapse surgery was not associated with overall failure but did decrease the odds of objective compared with subjective failure by nearly 50%. Similarly, a large retrospective study showed that concomitant pelvic organ prolapse (POP) surgery decreased the likelihood of failure of retropubic or transobturator midurethral sling surgery.3 These data conflict with another study that reported concurrent POP surgery increased the odds of developing any recurrent incontinence.1
Strengths of the study included its multicenter design including sites throughout the United States, with a variety of urologic and urogynecologic surgeons making our study more generalizable. We included extensive preoperative clinical and demographic variables, used clearly defined validated outcome measures, and had a high rate of ascertainment at 12 months after surgery. In the patient evaluation process for urinary incontinence, after obtaining the baseline clinical evaluation and examination, urodynamic testing is often used to confirm the diagnosis or provide additional functional information, severity information, or both. This current report focuses only on those demographic and clinical factors that may predict failure.
In conclusion, women with previous incontinence surgery, urethral hypomobility, and more severe urge urinary incontinence symptoms demonstrated greater overall odds of failure 12 months after undergoing retropubic or transobturator midurethral sling surgery. Pad weight testing seems to be a powerful predictor of failure. Although surgical history and urethral mobility are not modifiable risk factors, this information will assist in counseling patients regarding the efficacy of these procedures, help identify patients who may benefit from additional or alternate therapies, and assist in setting appropriate expectations for women with increased odds for treatment failure.
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