Summary and Introduction

Summary

Use of urethral slings in the treatment of incontinence started in the early 20^th century. An evolution in understanding the pathogenesis of urinary incontinence led to development of the midurethral sling, which was designed to replace the natural suburethral vectors of support, as described in the integral theory. Since the introduction of tension-free vaginal tape in 1995, multiple other commercially available types of midurethral sling have been introduced. In general, these sling types share the common characteristics of using a thin, type I synthetic mesh inserted at a midurethral level and applied without tension. The midurethral sling procedure has subsequently undergone multiple technical modifications, predominantly alterations to the technique and route used for sling insertion. Despite the variety in techniques, available evidence suggests that all sling types provide efficacious and durable outcomes. Several adverse effects have been reported that are specific to certain techniques, and include the risk of vascular, enteric or nerve injury, lower urinary tract injury, urinary retention or voiding dysfunction, and vaginal erosion. Nonetheless, the midurethral sling provides a safe surgical option overall, and represents a notable advance in the treatment of stress urinary incontinence.

Introduction

At the beginning of the 20^th century, VonGiordano described the first urethral sling, which used gracilis muscle.^[1] Modifications to the technique were subsequently described that predominantly used other muscle bodies, such as a pyramidalis muscle flap and plication of the perivesical muscular structures.^[2-4] Common to these techniques was the belief that muscle placed around the bladder neck would provide a sphincteric function.

As sling techniques evolved, a variety of materials came into use. Price^[5] described the first fascia lata sling in 1933. The origin of the contemporary pubovaginal sling may be found in the classic technique described by Aldridge in 1942,^[6] in which a strip of rectus fascia was secured beneath the urethra to provide increased resistance at times of heightened abdominal pressures. This technique was later modified to leave the external oblique aponeurosis attached to the pubic tubercle and suture the fascial ends beneath the proximal urethra.^[7]

This era of sling development was also notable for the popularity of abdominal retropubic and transvaginal suspension procedures, characterized by techniques to suspend the bladder neck by fixation of surrounding tissues. Accordingly, in 1949, Marshall et al.^[8] pioneered a technique for bladderneck suspension through the fixation of perivesical bladder-neck tissue to the pubic symphysis. Rare but severe bony complications were attributed to pubic symphyseal fixation, however, and consequently Burch^[9] described a modified retropubic suspension in which the fixation point was positioned laterally along Cooper’s ligament.

Although satisfactory continence rates were achieved by retropubic procedures, the invasive nature of the abdominal approach and consequently long durations of hospital stay and postoperative convalescence rendered them less ideal than the vaginal approach. Additionally, perioperative morbidity was notable. Despite the reduced morbidity associated with the transvaginal needle suspensions, however, the effects of these procedures on stress urinary incontinence (SUI) were not durable.

In an effort to improve the efficacy of surgical treatment of SUI, McGuire and Lytton^[10] revived, in 1978, the use of the pubovaginal sling. They described a combined abdominovaginal approach with complete detachment of the rectus fascia, which was repositioned suburethrally as a sling. The morbidity associated with autologous graft harvesting led, eventually, to exploration of the use of allografts and xenografts, for example, the use of cadaveric fascia lata anchored over the rectus fascia or via transvaginal bone anchors. Irrespective of allograft type or fixation method, however, early reports of isolated failure were attributed to weak tensile strength and suture pull-out.^[11] Continued refinements in materials were sought to identify an ideal compound for use in transvaginal slings that would be inert, sterile, noncarcinogenic, and mechanically durable. In this Review we provide an overview of the pathogenesis of SUI and of the evolution of the midurethral sling, with a focus on the types of slings currently available and the outcomes of this therapy.