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Midurethral Sling Procedures: Review and Update

Vivian W. Sung, MD, MPH; Renée M. Ward, MD

Although the midurethral sling procedure is considered a tried-and-true treatment for urinary incontinence, the emergence of many variations mandates that surgeons keep pace with the latest developments—even when the data are difficult to compare.

Urinary incontinence (UI) can have a significant impact on women’s social, practical, and behavioral functioning. It is more common in women than in men, with an overall prevalence of 49%, peaking in the fifth decade.1 The annual direct cost of UI in the United States for women alone is estimated at $12.4 billion (1995 dollars), mostly for routine care (70%).2 Because of its prevalence and cost, UI is a significant public health issue.

Stress UI (SUI) is the most common type of incontinence. Nonsurgical options for SUI should be offered to all women seeking help, including pelvic floor exercises, pessaries, and behavioral management. Surgical options include urethral bulking agents, Burch colposuspension, and urethral slings. The sling was introduced by Von Giordano in 1907, using gracilis muscle flaps. Since then, many modifications have been introduced, such as variations in sling materials, methods of performing the procedure, and location of sling placement.

Tension-free midurethral sling procedures were introduced in 1995 by Ulmsten,3 and have made a significant difference in the surgical management of SUI in women. The midurethral sling has also undergone various modifications, resulting in practice variations often driven by local norms, surgical training and preference, and manufacturer influence.

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MECHANISM OF ACTION

There are two complementary theories regarding the mechanism of continence. The “integral theory” introduced by Petros and Ulmsten4 describes 3 opposing vaginal muscle forces: the forward activating pubococcygeus and 2 backward forces from the levator ani and longitudinal muscle of the anus. These 3 forces stretch the vaginal membrane and endopelvic fascia to secure urethral closure during increased intra-abdominal pressure. The “hammock theory” introduced by DeLancey5 theorizes that the anterior vaginal wall provides a hammock-like support for the urethra that is critically important for continence. It is proposed that the midurethral sling stabilizes the vagina and urethra during times of increased intra-abdominal pressure. The midurethral sling is said to be “tension free,” as it is not anchored to any bone, ligament, or fascia. Unlike traditional slings, which are placed at the urethrovesical junction, these tension-free slings are placed at the midurethra.

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RETROPUBIC APPROACH

The advent of minimally invasive midurethral sling procedures using tension-free vaginal tape (TVT) in 1996 marked a major shift in the surgical treatment of SUI.3 Initially heralded for its ease of placement in an outpatient procedure, the technique gained further acceptance due to low complication rates and success rates in comparison with traditional procedures.6 In a randomized trial comparing TVT to Burch colposuspension, similar objective cure rates (defined as a negative pad test) were reported at 2 years between the two procedures (63% and 51%, respectively, assuming women lost to follow-up were failures; 78% and 68%, respectively, carrying the last observed result forward).6

For the TVT procedure, 2 needles are placed vaginally through 2 paraurethral tunnels made at the level of the midurethra, then into the retropubic (RP) space via a “bottom up” approach, and exiting the RP space through 2 small suprapubic skin incisions. The sling itself forms a U shape, cradling the urethra. No suspension sutures are required, and the sling is held in place initially via friction between the mesh and tissue, and ultimately through fibrosis. As little dissection is required, this procedure can be done under local anesthesia with minimal patient morbidity and recovery time. Surgeons more comfortable with the “top down” approach have the option of placing the midurethral sling using the TVT abdominal guide or the SPARC Female Sling System (American Medical Systems, Minnetonka, Minnesota). Studies comparing the TVT and SPARC methods have yielded conflicting results regarding success rates, and there is some concern that success may be lower with SPARC procedures.7-9

Case series have reported longer-term success rates (defined as cure or significant improvement) following TVT procedures, ranging from 84% to 94% at approximately 5 years.10 One randomized trial reported success rates of 81% following TVT at 5 years for women who returned, but many subjects were lost to follow-up.11 Overall complication rates following the TVT procedure are low, ranging from less than 1% to 7%, and include bladder perforation, bleeding, voiding dysfunction, irritative voiding symptoms, urinary tract infection, and other organ perforation. Most trocar perforations occur at the bladder dome, and if diagnosed at the time of surgery, are easily treated by replacing the trocar in the correct position, and leaving an indwelling catheter for 24 to 48 hours. Most bleeding complications can be managed conservatively, as vessel injury usually occurs in the retropubic space and is self-limiting. Major complications usually result from intraperitoneal passage of the needles, resulting in injury to major vessels or bowel perforation.

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TRANSOBTURATOR APPROACH

In an effort to decrease complications, the transobturator approach (TO) to midurethral slings was developed in 2001 by Delorme.12 This approach can use either an “outside-in” or an “inside-out” method. In the former, the mesh is attached to 2 helical needles on fixed handles specifically designed for right-side or left-side use. The needle tip is passed through the upper inside corner of the obturator foramen, following the posterior surface of the pubic ramus and exiting vaginally through a small incision at the midurethra. This approach avoids passage through the retropubic space to prevent injury to the bladder, bowel, and other major vessels. Initial case series reported similar cure rates between the RP and the TO approaches, but few randomized trials were powered to detect differences between the two approaches.

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CLINICAL RESULTS

There are 3 meta-analyses comparing the efficacy of the RP versus the TO approaches (Table).9,13,14 It is important to remember that methods, variables, and outcomes—eg, inclusion criteria, indications for surgery, outcome definitions, and quality of life—are often inconsistent or lacking in the literature, making clear comparisons between different sling surgeries difficult.

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Table. Comparison of Midurethral Sling Procedures*

Cure Rates

Currently, randomized trials comparing objective cure rates following RP versus TO approaches have mean follow-up times ranging from 2 to 18 months. Objective cure definitions differ among studies, and include negative cough stress test, 1-hour pad test, and urodynamic evaluation. In general, most randomized trials and meta-analyses showed no difference in objective cure rates between the RP and TO approaches. However, most were not powered to detect equivalence. To address this issue, Barber et al15 conducted a trial in which 180 women were randomized to undergo either an RP (TVT) or a TO procedure, with power to detect a 15% noninferiority difference. The primary outcome was “abnormal bladder function,” defined as incontinence symptoms of any type, a positive cough stress test, retreatment for SUI, or postoperative urinary retention. At a mean of 18.2 months, abnormal bladder function occurred in 46.6% of RP patients and 42.7% of TO patients, indicating that the TO approach was not inferior to the RP approach.

Subjective cure definitions among studies also vary, including patient reports of being “dry,” “improved,” or “failed,” as well as both nonvalidated and validated quality-of-life questionnaires. Similar to objective cure rates, randomized trials and meta-analyses showed no difference in subjective outcomes between the 2 approaches, with 74% to 90% of women reporting subjective cure.

It remains unclear whether there are clinical factors that place a patient at higher risk for objective or subjective failure following a mid-urethral sling procedure via either approach. A retrospective cohort study with 3-month outcomes comparing the RP and TO approaches reported that women with a maximum urethral closure pressure of 42 cm H2O or less were 5 times more likely to fail following a TO versus an RP procedure (failure was defined as postoperative SUI on urodynamic testing at 3 months).16 It is unclear whether recurrent SUI, prior anti-incontinence surgery, concurrent urge incontinence and/or prolapse, concomitant prolapse procedures, age, or incontinence severity affect success rates with either approach.

Complications

Minor and major complications may occur with either the RP or TO approach. Meta-analyses comparing complication rates between the procedures showed that bladder perforations are more common following the RP approach (3.5% versus 0.2%), as well as pelvic hematoma (1.6% versus 0.08%).13,14,17 Because bladder injuries have been reported following the TO approach, cystoscopy should be considered after both approaches.

Groin pain is more common following the TO approach (16% versus 1.5%), but this usually resolves by 2 months postoperatively.14,18 Although individual randomized trials showed no difference in prolonged urinary retention, a recent meta-analysis found that voiding difficulty was less common after the TO approach compared with the RP approach (odds ratio=0.55; 95% confidence interval, 0.31-0.98).14

Between 5% and 18% of patients develop de novo urgency following midurethral sling surgery. A randomized trial found that women with a TO sling reported a decrease in urinary frequency, but no difference in overactive bladder complaints when compared to the RP group.19 Other randomized trials and meta-analyses showed no significant difference in de novo urge incontinence. 13-15,20

Other than the risk of bladder injury and groin pain, most meta-analyses and trials showed similar complication rates for both approaches. Vaginal erosions (1% to 5%), urinary tract infections (4% to 13%) and reoperation rates for SUI (1.2% to 7%) were similar between the two procedures.14,15

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RECENT DEVELOPMENTS

Two newer midurethral sling options include the adjustable and the needleless slings. The Remeex adjustable sling system (Tri-anim, Sylmer, California) includes a sling with two traction-thread sutures connected to a regulation device positioned above the rectus fascia that stays in place postoperatively. On postoperative day 1, the bladder is filled with 300 mL of fluid and the patient is asked to stand and perform Valsalva maneuvers. The sling is then tightened with the manipulator until any incontinence disappears. A voiding trial is then performed, and the sling is readjusted as needed to achieve a balance between continence and normal voiding. In theory, the sling can be readjusted as needed throughout the patient’s lifetime.

The needleless midurethral sling is an 8-cm mesh device placed through a single vaginal incision, eliminating the need to pass needles through the RP space or obturator foramen (Figure). In theory, this further decreases potential complications. The efficacy of the adjustable and needleless slings has not yet been established.

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Figure. Example of needleless sling. Image courtesy of Vivian W. Sung, MD, MPH.

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CONCLUSION

The RP and TO approaches to the midurethral sling procedure are safe and effective, with low complication rates overall. The TO approach has a lower risk of bladder injury and possibly voiding dysfunction, but is associated with short-term groin pain. The most common complication following the RP approach is bladder perforation, which often has no long-term consequences. Meta-analyses and a noninferiority trial showed no difference between objective and subjective cure rates. Although studies found that the RP approach has outcomes comparable to those of more traditional surgeries (eg, Burch procedure), similar studies comparing the TO approach to traditional procedures are lacking. Finally, it is still unclear whether certain subgroups of patients may benefit more from one approach versus the other.

The authors report no actual or potential conflicts of interest in relation to this article.

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Vivian W. Sung, MD, MPH, is Assistant Professor; and Renée M. Ward, MD, is Fellow, both in the Division of Urogynecology and Reconstructive Pelvic Surgery; Department of Obstetrics and Gynecology, Women and Infants Hospital, Warren Alpert Medical School at Brown University, Providence, RI.

References

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