Biologic bladder neck slings for stress urinary incontinence

Introduction

The concept of using a patient’s own tissue as a “sling” to provide support under the urethra to treat urinary incontinence dates to the beginning of the twentieth century; however, it was not until the last quarter of the century that the procedure gained widespread appreciation and evolved into its current identity. Initially, the procedure was described as using a strip of mobilized abdominal muscle (either rectus or pyramidalis). One end of the strip was freed from its attachment, passed under the bladder neck, and then reaffixed to the abdominal muscle wall, thus forming a “U”-shaped sling of muscle tissue around the bladder outlet. Subsequently, overlying abdominal fascia was included in the sling, and eventually replaced the muscle altogether. In 1942, Aldridge reported his fascial suburethral sling procedure, which is the forerunner of the modern pubovaginal sling. Aldridge described the procedure as a salvage-type operation for those women who had failed previous operations for stress incontinence. For the sling, he used rectus fascial strips that remained attached to the anterior abdominal wall and were passed bilaterally along the urethra and sutured together under the bladder neck. The final innovation involved using an isolated strip of fascia suspended by free sutures that were then tied to the abdominal wall directly or on top of the abdominal rectus sheath.

Despite its roots as an autologous procedure, many different types of materials have been used as sling substitutions, including various sources of autologous tissue, allografts, xenografts, and synthetic materials. Almost all these attempts at substitution have been made to help limit patient morbidity, as the procedure requires the additional morbidity of a sling tissue harvest site. Nevertheless, the most popular variety of the pubovaginal sling remains associated with the use of autologous rectus abdominis fascia.

Regardless of the material used, the pubovaginal sling is meant to be placed at the proximal urethra and bladder neck. The concept of the autologous pubovaginal sling involves supporting the proximal urethra and bladder neck with a piece of graft material, achieving continence either by providing a direct compressive force on the urethra/bladder outlet or by reestablishing a reinforcing platform or hammock against which the urethra is compressed during increased abdominal pressure. The sling is suspended with free sutures on each end that are either attached directly to the abdominal wall musculature or tied to each other on the anterior surface of the abdominal wall. The long-term success of the procedure relies not on the integrity of the suspensory sutures, but rather on the healing and fibrotic process involving the sling, which occurs primarily where the sling passes through the endopelvic fascia.

Indications

The pubovaginal sling is a surgical option for both primary and recurrent stress urinary incontinence (SUI). Although pioneered as a surgical treatment for intrinsic sphincter deficiency (ISD), its indications have been broadened to encompass all types of SUI. Because of its reliable results and durable outcomes, it is one of the main standards of treatment of SUI and has been used extensively as a primary therapy for SUI (both for ISD and urethral hypermobility), as a salvage procedure for recurrent SUI, as an adjunct for urethral and bladder reconstruction, and even as a way to functionally “close” the urethra to abandon urethral access to the bladder altogether. Another indication is in patients with SUI who decline to have a synthetic material implanted because of long-term concerns related to synthetic mesh. Also, women who have recurrent incontinence or experience a complication after implantation of a synthetic sling (such as vaginal erosion) may be good candidates for the autologous fascial sling. Finally, we prefer to use an autologous sling in patients who have been irradiated, who have had urethral injuries, and who are undergoing either simultaneous or prior urethrovaginal fistula or diverticulum repair.

Sling materials

With the increasing popularity of primary sling procedures, the escalating demand for minimally invasive techniques, and the need for nonmesh options, numerous materials have become available for use in suburethral slings. Current biologic materials can be categorized as autologous fascia, allograft fascia, or xenograft fascia. Within these categories, different variants can be subgrouped into individual materials: autologous (rectus fascia, fascia lata, vaginal wall), allograft (freeze-dried irradiated cadaveric fascia lata, solvent dehydrated cadaveric fascia lata, fresh frozen cadaveric fascia lata, cadaveric dermis), and xenograft (porcine dermis, porcine intestinal submucosa) which has been used historically but is no longer commercially available. Autologous rectus fascia and fascia lata are the most common materials in use, and the standard to which the outcome of other new materials should be compared. Both have been studied extensively and have proven to be efficacious and reliable. Of the two, most surgeons prefer rectus fascia as an autologous material because it is easier and quicker to harvest.

The application of newer tissue harvesting technologies has made multiple human- and animal-based materials available. The theoretical rationale for using allografts and xenografts for suburethral slings is reinforcement of inherently weak endopelvic fascia. Allogenic grafts harvested from cadaveric donors are widely used and do not seem to carry a significant risk of erosion or infection. Cadaveric fascia lata and cadaveric dermis provide reasonable efficacy, although durability remains an issue because higher failure rates compared with allogenic grafts have been reported in some studies. The long-term durability of allograft fascia continues to be studied, and there seems to be wide variability in the quality of tissue, depending on its source and processing. The type of sling material probably does not significantly affect cure rates, provided that the characteristics of the chosen material are considered carefully, however it may affect durability.

Synthetic graft materials of various designs and substances have been used as sling material. As with other types of synthetic graft materials, monofilament, large-pore weave grafts (type I mesh) are recommended for implantation in the vagina. Good efficacy can be achieved with synthetic mesh; although synthetic mesh also poses risks of unique complications, including infection, vaginal extrusion, and genitourinary erosion. Thus, synthetic slings are currently not usually recommended for use underneath the proximal urethra or bladder neck.

Surgical techniques