Authors: Katherine Wu, Emily Huang, Kathleen C. Kobashi
Categories: Review Article, Stress urinary incontinence (SUI), female, surgical, outcome, success
Source: Gynecology and Pelvic Medicine
Doi: 10.21037/gpm-24-21
Authors: Katherine Wu, Emily Huang, Kathleen C. Kobashi
Stress urinary incontinence (SUI), the most common type of incontinence in women, is the involuntary loss of urine during physical exertion or moments of increased intra-abdominal pressure such as coughing or sneezing. Numerous clinical studies have compared the long-term safety and efficacy of autologous fascial slings, Burch colposuspension, and synthetic mid-urethral slings (MUS). As the data from these comparative studies has matured over the last 20 years, a universally accepted definition of success remains elusive. This absence of a standardized measure not only compromises inter-center comparison but also impedes the ability of urologists to accurately interpret outcomes of sling procedures and provide patients with informed care. This review aims to examine the characterization of “cure” through the evolution of anti-incontinence surgery as well as to challenge the currently nebulous definition of success.
A comprehensive literature search on PubMed and Web of Science was conducted between September 2023 to February 2024 using the “stress urinary incontinence”, “female”, “success”, “cure”, “outcome”, “surgical”, and “sling”. Select articles focusing on defining success through specific outcome measures and efficacy of surgical interventions were included in this narrative review.
Definitions of success are currently specific only to the exact center and urology group who performed the procedure, thus making comparison amongst centers virtually impossible. Success ranges not only from objective to subjective but more importantly, from lenient to strict. Most common objective factors were negative cough stress test, negative pad test, and absence of SUI retreatment versus reduced degree of bother and improved questionnaire scores for subjective success.
The heterogeneity of definitions of success for SUI surgery outcomes remains a persistent challenge. Even more worrisome is the realization that this diversity is not a recent revelation; studies from the early 2000s highlighted this incongruity, emphasizing a long overdue need for correction.
The first written record of urinary incontinence dates back to ancient Egyptian writings from the 2^nd^ millennium B.C. Manuscripts such as the Papyrus Ebers have described remedies “to remove the urine which runs often” and depicted primordial sketches of pessaries as non-invasive therapy (1). Today, urinary incontinence remains a prevalent issue. Up to 40% of women have SUI, defined by the International Continence Society (ICS) as the involuntary loss of urine during increased intra-abdominal pressure from physical exertion in the absence of detrusor contraction (2-5). The risk of developing SUI increases with pregnancy, childbirth, and age. While one out of every three women in the United States experience SUI in their lifetime, only one in every four women with SUI symptoms will seek medical advice (3,6). Myths, misinformation, and social stigma surrounding urinary incontinence persist and prevent women from seeking treatment despite the prevalence of the condition. While many patients believe it to be a natural part of aging, urinary incontinence is fundamentally a pathologic condition. Prolonged urinary incontinence not only leads to severely reduced quality of life (QOL) and psychological distress but also disrupted social and sexual relationships and hospitalizations from increased urinary tract infections (UTIs) and skin breakdown (3,6). SUI may be improved with lifestyle modifications, such as weight loss, smoking cessation, and dietary changes, as well as non-surgical treatments, such as continence pessaries, vaginal inserts, and pelvic floor physical therapy with or without biofeedback (7,8). If these strategies fail, patients may then consider surgical therapy for increased benefit.
It was not until the 19^th^ century that defined surgical techniques took hold. Von Giordano introduced the first sling operation in 1907, using a gracilis muscle flap to encircle the urethra (9). Today, almost 200 different surgical procedures for anti-incontinence have graced the literature. Since 1907, the progression of anti-incontinence surgery has evolved in parallel with our understanding of the pathophysiology of SUI. The anatomical pathogenesis of SUI is a complex topic that remains heavily debated to this day. The five most widely accepted theories of SUI pathophysiology that have influenced modern-day treatment are the position of the proximal urethra, intrinsic urethral sphincter deficiency, the hammock hypothesis, the integral theory, and damaged urethropelvic and pubourethral ligaments (10,11). Of these five theories, four primary surgical approaches have emerged to target the anatomical periurethral bulking, retropubic suspension, autologous pubovaginal slings, and mid-urethral slings (MUS).
First, proximal urethral hypermobility led to the development of retropubic suspension procedures to support the urethra (7). Closure pressure, which is bladder pressure minus urethral pressure, dictates whether the urethra leaks or not. When the bladder and urethra are in proper anatomical position, an appropriate pressure differential between the bladder and urethra prevents leakage (12). If the urethra were to shift below the urogenital diaphragm from its natural intrapelvic location, pressure is no longer distributed equally. Such urethral hypermobility thus contributes to lower closure pressure and increases the likelihood for leakage. Retropubic surgical approaches aim to improve SUI through stabilization of the urethra in its retropubic position and suspension of the anterior vaginal wall.
Next, intrinsic sphincter deficiency, first described by McGuire, is a weakening of the urethral muscle generally accompanied by the loss of tissue bulk in the periurethral area (2,13). Intrinsic sphincter deficiency is defined as a Valsalva leak point pressure less than 60 cmH2O and maximum urethral closure pressure less than 20 cmH2O often coinciding with minimal urethral mobility (7). This theory may provide a more precise explanation for SUI in women with no urethral hypermobility and thus led to the development of periurethral bulking agents, comprised over the years of various materials that are injected into the bladder neck or proximal urethra. They are a rising non-surgical option for patients who cannot tolerate or decline surgery.
The hammock hypothesis, first proposed by DeLancey in 1994, describes the anterior vaginal wall, levator ani muscle, and periurethral fascia coming together as a “backboard” for the urethra to close against during periods of increased abdominal pressure (14). The urethral support and musculofascial compression together provide urethral integrity. The pubovaginal sling was hence developed in order to re-suspend the hammock and re-establish the urethral backboard (15).
The integral theory, defined by Petros in 1990, describes continence as an equilibrium between several opposing vector forces of the pelvic floor muscles, fascia, and ligaments to keep the bladder neck and urethra closed during abdominal pressure (16). The three pelvic structures—bladder, vagina, and rectum—are suspended to the pelvic brim via arcus tendineus fascia pelvis and three suspensory ligaments—pubourethral, cardinal, or uterosacral, respectively. Laxity of these structures yields greater downward forces, which opens the bladder neck and contributes to subsequent leakage. In addition, fixing the mid-urethra to the pubic bone through pubourethral ligaments creates a natural physiologic backboard, akin to hammock theory, that is essential for the continence mechanism (4). The integral theory led to the development of synthetic MUS, now the most popular and most extensively studied option for surgical treatment of SUI in women (17-19).
The fifth theory outlines how damaged urethropelvic and pubourethral ligaments fail to provide adequate support for the urethra behind the pubic symphysis. This concept provides further support for MUS, whether pubovaginal or synthetic mid-urethral, as slings can restore the disrupted support once provided by intact urethropelvic and pubourethral ligaments (11,19,20). These five theories are by no means mutually exclusive but rather provide a structural and objective explanation for the subjective SUI symptoms women experience that drive contemporary surgical approaches. As stated, the exact pathophysiology of SUI remains a subject of ongoing debate. The prevailing notion suggests the disturbance of supportive bladder and urethral fascia, coupled with the weakening of muscular structures within the pelvic floor, bladder neck, and urethral sphincters.
Contemporary slings were borne out of a century-long evolution of ideas and techniques, starting with Goebel’s introduction in 1910 (21). He first fashioned a sling out of the pyramidalis muscle and sutured it midline under the urethra to treat SUI. This idea continued into the 1940s as Aldridge began using fascia and strips of muscle to pioneer the pubovaginal sling (22). The pubovaginal sling gained considerable traction due to its early success rates and low risk of tissue reaction due to its autologous nature, a unique advantage. Williams then introduced the first synthetic sling using mersiline ribbon in 1962 (23). The procedure had reasonable efficacy for its time but was invasive and came with risks of fistulae, urethral sloughing, and abscesses. The Burch colposuspension, pioneered in 1961 then modified in 1976 by Tanagho, involves retropubic suspension of the bladder neck to Cooper’s ligament and became the gold standard surgical procedure for SUI for decades. The mid-1990s saw the rise of synthetic slings using materials such as polypropylene mesh that were more durable, provided better support than previous autologous tissue, and were associated with fewer risks and a shorter hospital stay than the Burch colposuspension. At this point, anti-incontinence procedures utilizing surgical mesh were considered less invasive than non-mesh repairs such as autologous slings and Burch colposuspension that otherwise required larger abdominal incisions and tissue harvesting.
In 1996, Ulmsten presented a new ambulatory MUS. Supported by the integral theory, the MUS soon gained substantial popularity due to its minimally invasive and tension-free placement, low complication and morbidity rates, and shorter learning curve. As the MUS became more widespread, variations on surgical technique and anatomical anchors soon arose. In the late 1990s, the retropubic placement of MUS using tension-free vaginal tape (TVT) was introduced. Shortly afterwards, the transobturator approach with transobturator tape (TOT) was developed with the hopes of decreasing complications incurred by traversing the retropubic space and reducing the risk of bladder perforation (24,25). The advent of TVT and TOT procedures saw similar global adoption due to their minimally invasive nature, shorter recovery time, and general efficacy. The MUS has now surpassed pubovaginal slings in popularity, becoming the most common SUI surgical treatment performed today in the United States as well as achieving global prominence.
Slings made out of mesh, however, have endured a turbulent legal history marked by an ongoing series of controversies and market withdrawals. Surgical mesh has been used since the 1950s for abdominal hernia repair. It evolved into urogynecologic use first in the 1970s with pelvic organ prolapse (POP) surgery then for the inaugural MUS in the 1990s. When the U.S. Food and Drug Administration (FDA) issued a public health notification on transvaginal mesh for POP and SUI in 2008, concerns of serious complications—including erosion, pain, infection, and mesh migration—permeated mesh usage for both SUI and POP procedures for women (24). Another public health notification issued in 2011 regarding transvaginal mesh specifically for POP resulted in further confusion surrounding the safety of mesh, which had already been used in practice for over 20 years.
Over the next decade, legal actions and regulatory responses have significantly influenced clinical attitudes towards mesh for SUI (25-27). In 2019, the FDA reaffirmed the safety and effectiveness of the MUS via thorough evaluation of adverse events reports and literature review. The adverse events associated with MUS are uncommon but include urinary obstruction, vaginal extrusion, groin pain, voiding dysfunction, and intraoperative injury to the bladder, urethra, vaginal mucosa, major vessels or bowel. Population-based studies found MUS to have less immediate complications, late complications, and need for reoperation for incontinence compared to other anti-incontinence procedures (28). The general attitude today regarding urogynecologic mesh for SUI surgery is positive, largely attributable to the careful differentiation between POP mesh and SUI mesh. Acknowledging and transparently addressing the associated risks has played a crucial role in reshaping the perception of the MUS and allowed for its continued safety and efficacy.
Currently, there are three main iterations of midurethral slings offered to the standard MUS that can be placed via three the retropubic route, transobturator route, and the single-incision or “mini-sling”. MUS operations have been the most extensively researched surgical intervention for SUI, with numerous clinical trials demonstrating impressive short-term success through clinical trials compared to retropubic suspensions, autologous fascial slings, and injections. The transobturator MUS (TMUS) was introduced as a potentially safer option for the retropubic MUS (RMUS) (7). As the newest surgical sling, single-incision slings (SIS) have now also begun to show promising long-term results with maturing data on its safety and efficacy (7,29).
The landscape of surgical interventions for SUI has undergone a fascinating evolution since the introduction of Von Giordano’s gracilis muscle sling at the turn of the 20th century and showcases a diverse array of techniques. Despite the surgical advancements particularly made in the last 20 years, the conditions of post-operative success still have yet to achieve a standard definition across centers. This glaring need to define success is not new by any means. Kobashi and Govier called public attention to the gap in 2005, highlighting the discrepancy between idea and action that other authors have only reaffirmed 10 years later in 2016 (30-32). The Urodynamic Society actually set a standard definition in 1997 on reporting post-treatment success for all surgical SUI procedures that involved a combination of subjective and objective measurements (13). The majority of the clinical trials published since then, however, have neglected to follow these criteria. Instead, definitions of success are currently specific only to the exact center and urology group who performed the procedure, making comparison among other centers virtually impossible.
The Urodynamic Society’s criteria in 1997 were quite stringent. Their guidelines required follow-up at 1, 6, and 12 months after treatment with recorded total sample size, number of patients actually treated, and reasons why patients were lost to follow-up (13). As a result, adherence was predictably low and suboptimal (32). The criteria most urologists rely on now has not changed considerably from the parameters the Urodynamics Society originally put out. The current 2023 SUI Guidelines written by the American Urological Association (AUA) and the Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction (SUFU) describes the surgical management of female SUI and reports surgical outcomes in two levels of cured/dry versus cured/dry/improved (7). Subjective cure is reported through voiding diaries and QOL questionnaires that address symptom bother, QOL, sexual function, satisfaction, and expectation. In addition, the American College of Obstetricians and Gynecologists (ACOG), has put forth several validated urinary incontinence questionnaires, such as the Urogenital Distress Inventory, Incontinence Impact Questionnaire, and Incontinence Severity Index to name a few (33). Grade A or “highly recommended” questionnaires, as noted by the ICS, are those with robust data that demonstrates their viability and reliability and specifically recommended for QOL and outcome assessments (34). Unfortunately, many studies still do not abide by these guidelines and use unvalidated questionnaires that then compounds already difficult inter-center comparability (31). Objective criteria frequently include cough stress test, pad test, urodynamics (UDS), adverse events, need for retreatment, and complications including erosion, extrusion,* de novo *urgency, or recurrent UTI.
We employed a narrative synthesis approach to investigate the current surgical landscape of treating SUI and critically evaluate the goals and limitations of anti-incontinence surgery through its evolution, paying special attention to the poorly defined entity of success. We present this article in accordance with the Narrative Review reporting checklist (available at https://gpm.amegroups.com/article/view/10.21037/gpm-24-21/rc).
A comprehensive literature search was conducted on PubMed and Web of Science from September 2023 to February 2024 using the keywords “stress urinary incontinence”, “female”, “success”, “cure”, “outcome”, “surgical”, and “sling”. The search strategy employed both Medical Subject Headings (MeSH) and free-text keywords to maximize the inclusiveness of relevant articles. The search was limited to articles published in the English language only. One of the objectives of this study was to explore the evolution of surgical approaches to SUI from their inception. For this reason, we deliberately avoided imposing constraints based on publication dates or geographic regions to properly assess the evolution of surgical trends and techniques. The SUI surgeries of interest were the main interventions stated in AUA MUS (retropubic, transobturator, or SIS), pubovaginal sling, and Burch colposuspension with a focus on slings.
Articles included in this narrative review were selected based on their relevance to SUI and efficacy of surgical interventions, particularly focusing on studies that defined specific measurements of success through cure, improvement, or both. Prospective and retrospective studies, observational studies, randomized clinical trials, and systematic reviews were all considered for inclusion. Studies were excluded if they were related to SUI but did not focus on the concept of cure or improvement, were not available in English, or deemed irrelevant based on preliminary title and abstract screening. Data extraction from the included articles involved study design, surgical technique, sling material, length of follow-up, and specific measures of outcome success related to cure or improvement of SUI symptoms as well as reported findings pertaining to surgical outcomes. The search strategy is summarized in Table 1 and a detailed search strategy using the PubMed database is provided as an example in Table S1.
From our review of published clinical trials in PubMed, current parameters of success include a longstanding miscellany of subjective and objective components. The factors range anywhere from completely dry to a reduced degree of bother, reduced pad usage, improved UDS measurements, the absence of re-treatment, or seeking subsequent treatment post-surgery. From Ulmsten’s original definition of success as leakage ≤10 grams of urine a day to Albo’s “no self-reported symptoms”, it was apparent that success not only ranges from objective to subjective but more importantly, from lenient to strict (35-37). Discrepancies ran deep within subjective and objective characterizations too. Not surprisingly, the definition of subjective success typically varies more than objective. While Grade A questionnaires recommended by the ICS are now predominantly used during data acquisition, their integration into definitions of success are still underutilized. The absence of self-reported symptoms and voiding diaries are other routinely used factors of subjective success; however, both are highly variable and unstandardized. For objective criteria, cough stress tests and pad tests were widely adopted options. In their 2010 study, Zimmern* et al. polled SUFU members to determine actual outcome measures used in daily practice among urologists (34). The most consistently used instruments among respondents were short-form questionnaires such as the Urinary Distress Inventory (UDI-6) and Incontinence Impact Questionnaire (IIQ-7), office tests such as urinalysis and post-void residual, Baden-Walker or POP-Q, and cough stress tests. As further elucidated by Carmel et al.*, pad test standardization varies considerably from trial to trial. While the most frequent type of pad test in their review of 95 trials was a 1 hour test, 24-hour pad tests were used in eight studies where the definition of cure ranged from less than five grams to 50% improvement (31). Table 2 further elaborates on the definitions of cure and successful outcomes that have spanned the literature, demonstrating considerable variation that has persisted over the years.
Lack of standardized outcome measures for achieving continence must be remedied before urologists can confidently issue an evidence-based opinion that any surgical technique is a true gold standard. When defining cure, it is also important to consider the idiosyncrasies of continence from patient to patient. The inherently subjective nature of SUI means there is no perfect definition of cure that encapsulates its every nuance. Physiologically, the continence mechanism is a complex process that involves somatic and visceral interaction, dictated by learned behavior. The exact amount of leakage that constitutes continence, therefore, is still nebulous and dependent on patient perception. Further complicating the issue is the significant divergence in patients’ perception of success versus physicians’ grading of continence. What patients may perceive as symptom improvement or satisfaction often does not correlate with objective findings or parameters surgeons use to demonstrate post-procedure success. We know the universal definition of cure must include subjective and objective components to be properly comprehensive. It is simply a matter of coming together and setting the standard that subsequent clinical trials going forward must abide by.
Beyond slings, anti-incontinence surgery is constantly evolving and improving. Modern-day options have seen a significant transformation from those offered five years ago, and it is likely that the selection will continue to undergo substantial changes in the next five years. While slings currently dominate the surgical landscape of SUI treatment, injectables, notably Bulkamid^TM^ (Irvine, CA, USA), are looking increasingly more favorable as a minimally invasive alternative in light of recently published clinical data.
The application of urethral injectables for SUI, however, is not a novel concept. Gersuny reported the use of periurethral paraffin wax in 1900 as one of the earliest applications of bulking agents. Since then, endeavors to refine bulking agents have explored a variety of materials and methods over the last 100 years in order to find the “perfect” injectable. Materials have included carbon beads, hyaluronic acid, silicone-based compounds, and even autologous materials. Current materials fall into two categories. The first type contains particles that induce an inflammatory response, such as glutaraldehyde cross-linked bovine collagen that was one of the earliest agents introduced clinically. The second type are homogeneous polyacrylamide gels that are free from inflammation-inducing particles, of which Bulkamid has emerged as the leading choice in today’s urology clinics (46). The material is injected either periurethrally or more commonly, transurethrally, into the submucosa to elevate the urethral mucosa and increase urethral resistance. Augmenting urethral bulk in this way not only improves urethral coaptation during moments of increased abdominal pressure but also adds additional filler volume to boost sphincter power (45).
Brosche* et al.’s study on Bulkamid as a surgical SUI treatment option has now shed light on the safety and efficacy of Bulkamid at seven years. In accordance with our discussion on the characterization of cure, a successful outcome in Brosche et al.*’s study was measured on a four-point scale of cured, improved, unchanged, or worse (47). Secondary outcomes to evaluate long-term safety and efficacy of Bulkamid were determined via pad count, International Consultation on Incontinence Questionnaire-Short Form score 12, Visual Analog Scale Quality of Life score, patients requiring reinjection, and postoperative complications. Most (67.1% of 388) women who received Bulkamid as a primary procedure for their SUI and completed seven years of follow-up reported cure or improvement of their SUI symptoms. 11% reported no change and 2.3% had worse incontinence. Bulkamid boasts a 77–92% success rate comparable to colposuspension, synthetic MUS, and autologous tissues that all demonstrate an 80–90% success rate (48).
As the largest long-term study of Bulkamid injections to date, the 2021 study by Brosche* et al. *has secured Bulkamid’s place as a frontrunner of surgical SUI treatment and a worthy alternative to traditional slings with long-term studies in the United States still underway (47). Injectables remain a suitable option for patients who cannot tolerate or refuse surgery, cannot undergo anesthesia, and are too elderly or infirmed. The current advantages of Bulkamid to slings are its minimally invasive nature, ability to be done outpatient, and shorter recovery times. As with any surgical intervention, Bulkamid must continue to demonstrate long-term efficacy and a low side effect profile to maintain its clinical justification. For women willing to trade efficacy for lower risk and shorter recovery periods, Bulkamid is a promising alternative to slings for patients prioritizing improvement over a complete cure.
The limitations of this narrative review should be acknowledged to maintain a nuanced understanding of the analysis and potential biases in the selected literature. The included clinical studies vary in terms of design and methodology, surgical technique, patient populations, clinical follow-up, and especially definitions of success as the crux of this review. While these studies were specifically chosen for their heterogeneous definitions of cure, the resulting variability in methodological rigor limits our ability to draw definitive conclusions. The diversity of patient characteristics, including but not limited to age, presence of comorbidities, severity of SUI, and previous surgical intervention all influenced treatment outcomes that were not fully accounted for in this review. Additionally, the nature of this narrative review and the process by which articles were selected to be included in this review reflected the intent of this article as a commentary on the current landscape of post-surgical cure rather than a comprehensive systematic review. We caution that this manner of article selection introduces implicit bias.
The surgical landscape of SUI is dynamic, constantly evolving and improving with the introduction of new techniques and technologies. While this review targeted surgical interventions currently used in urology practices across the nation, it may not fully encompass the most recent iterations or innovations. Surgical techniques also vary accordingly by provider and practice, thus adding to nuanced outcomes that were not fully accounted for in this review. When translating this review to future patient cases and clinical trials, physicians and researchers should be mindful of these constraints. These limitations, however, result from an inherent heterogeneity of outcome measures in all past studies and thus underscore the need for a unified definition of cure to optimize comparability. To move forward, it is imperative that we not only establish a shared consensus but also consistently adhere to these criteria in all future studies, ensuring optimal generalizability.
To date, the MUS carries the most robust clinical assessment with a large body of literature backing its efficacy and safety. As surgical techniques for SUI continue to evolve, urologists must continuously assess and honestly re-evaluate the optimal management option for their patients. Given studies have boasted 60% to 95% cure rates, we challenge this characterization of “cure” from trial to trial. While there is clearly no definitive singular tool to evaluate anti-incontinence success, there are a number of consistent instruments, first identified by Zimmern* et al. *and supported with our review, that offer an easy starting point. Most concerning is that this complacency has persisted despite consistent efforts by the AUA since 1997 to initiate standardization (5,7,49,50) in their SUI guidelines.
Our community of urologists has grown complacent with arbitrary definitions of cure and is long overdue regarding standardizing reports of success. There must be a concerted effort among urologists as well as other surgeons who perform SUI procedures to define exact parameters and ensure their implementation. In particular, physicians managing SUI must be able to look to the literature not only for inter-center comparability but also guidance on their own clinical metrics for improving their personal surgical outcomes. We must prioritize the standardization of outcome measures in the ongoing evolution of anti-incontinence procedures to continue refining patient care and solidify long-term success.