The artificial urinary sphincter and male sling for postprostatectomy incontinence: Which patient should get which procedure?

Approximately 4% of radical prostatectomy (RP) patients will have incontinence of sufficient bother to elect surgery to treat their postprostatectomy incontinence (PPI) [1]. In the 20th century, transurethral injection of periurethral bulking agents and placement of an artificial urinary sphincter (AUS) were the two most common surgical treatments for PPI [2]. With periurethral bulking injection, the majority of patients fail to achieve meaningful improvements in continence [3]. In contrast, the AUS has enjoyed a 30-year reign as the most predictably efficacious treatment for PPI. There are, however, well-known surgical complications, including urethral erosion (6%), device infection (5.5%), and mechanical failure (6%) [4] necessitating a revision rate of 21% at 5 years and 50% at 10 years postoperatively [5]. The male sling arose out of necessity for a less invasive and less risky alternative to AUS, and a patient-driven desire to avoid a mechanical device [6].

The modern male sling has evolved over the past 40 years. The Kaufman device, comprised of a hemispherical silicone-gel filled prosthesis and polyurethane straps compressing the urethra, was replaced by the pubourethral sling [7], which was in turn supplanted by the bone-anchored male sling (BAMS, InVance, American Medical Systems, Minnetonka, MN, USA) and the transobturator (TO) sling (AdVance, American Medical Systems). The BAMS is based upon a 4 × 7-cm silicone-coated polyester mesh, secured to the descending pubic rami via 6 titanium bone screws, compressing the perineal urethra [8]. The TO sling, in contrast, improves urinary continence in a noncompressive manner, by relocating the proximal urethra more proximally [9]. Each device has an established track record of success in men with mild to moderate PPI. More recently, the quadratic sling (VIRTUE, Coloplast, Humlebaek, Denmark), a four-armed polypropylene mesh that provides both proximal urethral relocation via a TO component and perineal urethral compression via a prepubic (PP) component, [10] has gained popularity among urologists and patients. Several adjustable slings have been introduced (Argus, Promedon, Cordoba, Argentina and Remeex, Neomedic, Barcelona, Spain) with the potential advantage of postoperative tightening or loosening [11, 12]. As a testament to improvements in design and efficacy, male slings recently superseded the AUS and urethral bulking as the most common surgical procedures for PPI [2].

Despite different mechanisms of action, the primary goals of the various male slings remain: (1) tensioning to adequately compress the bulbous urethra and/or sufficiently relocate the proximal urethra; (2) maintaining tension to prevent recurrent leakage; and (3) balancing sling tension and detrusor contractility in order to avoid urinary retention.

Prior to offering invasive surgery, the urologist must determine the pathophysiology driving the patient's incontinence. PPI may result from bladder dysfunction and/or intrinsic sphincter deficiency (ISD). Additionally, there may be an obstructive anastomotic stricture in 3% to 21% of men [13, 14]. Furthermore, patients with detrusor underactivity may be at increased risk of urinary retention following surgery, as adequate detrusor contractility is necessary to overcome the fixed resistance of a compressive device [5]. Just as the compressive sling is designed to prevent leakage with straining, it is likely to interfere with valsalva voiding in those with inadequate contractility. Measurement of leak point pressure (LPP) is not absolutely necessary, as LPP neither correlates with pad weight, nor does it typically alter the plan of treatment [15]. On the other hand, pad use does correlate with actual urine loss, thereby justifying daily pad use as a measure of incontinence severity [16]. Based on these findings, the degree of incontinence is therefore best quantified by pad use or the pad test.

Urodynamic evidence of bladder dysfunction must be interpreted cautiously in men with PPI. While de novo reduced bladder compliance may affect greater than 25% of patients up to three years post-operatively [17], this finding does not usually impact surgical outcome. In severely incontinent patients, urodynamic diminished compliance and low volume detrusor overactivity are the most likely artifacts identified during supra-physiologic filling of bladders that have been chronically underfilled, and do not typically affect AUS surgical outcome [18, 19].

Detrusor hypocontractility may be seen in 25% to 40% of patients greater than 1 year postoperatively, and can occur de novo in up to 10% [20, 21]. Since the cuff is deflated during voiding, allowing efficient bladder evacuation via bladder contraction or valsalva abdominal straining, AUS success does not differ in patients with normal versus underactive bladders [4, 22]. In contrast, adequate detrusor contractility is necessary to expel urine past a compressive sling [5]. AUS or a TO sling is preferred in those with an underactive bladder, whereas a compressive quadratic sling should be considered only in those with adequate detrusor contractility.

While there is no universally agreed upon measure of normal detrusor contractility following prostate removal, bladder contractility index and measurement of isovolumetric detrusor contraction pressure [17, 23] are commonly used. Voiding pressure is an unreliable determinant of detrusor strength in patients with low urethral resistance, as the contractile pressure required to maintain axial flow can approach zero. Therefore, using nomograms based upon a population of men with prostate enlargement is inaccurate in men status post RP [23]. A direct measure of contractility is the isometric detrusor contraction pressure (Piso), correlating highly with the Watts factor [24], which is generally recognized as the most reliable approximation of bladder contraction strength. Piso can be determined via the mechanical stop test [25, 26], whereby the examiner manually compresses the penile urethra during voiding, preventing urinary flow, but gently enough to prevent causing a pelvic floor contraction, which may otherwise abort a detrusor contraction. A minimum Piso of 60-cm water is necessary to overcome the fixed resistance of a compressive urethral sling, which intraoperatively is typically tensioned to 60-cm retrograde leak point pressure (RLPP).

For more than 30 years, the AUS has been regarded as the most reliable surgical option for treating PPI, with success rates typically above 80%. However, with infection rates of 5% to 6%, erosion rates of 6% to 8%, and mechanical failure in 6% to 23% of cases over 7 to 13 years [4, 32], there has been an incentive to search for an alternative surgical approach.

2. TO sling

The TO sling was introduced in 2005, based upon a minimally invasive approach similar to the female midurethral TO sling (Fig. 1). Whereas this sling only nominally compresses the bulbar urethra, its main mechanism of action relies upon proximal urethral relocation. It is hypothesized that inefficacious coaptation of the urethral sphincter complex results from laxity of posterior urethral support and relative misalignment of the proximal urethra [28]. Therefore a TO sling that restores the pre-prostatectomy configuration by realigning the mobile sphincter complex will ultimately prevent proximal urethral descent and improve intrinsic continence. Following appropriate sling tensioning, the bulbar urethra is relocated proximally by a distance of 2 to 3 cm, into the higher pressure pelvic outlet, thus functioning as a physiologic "backstop" during straining [35].

Fig. 1
Transobturator sling. Upon tensioning, the bulbar urethra will move proximally.

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Success rates from prospective series range from 54% to 80%, with cure rates generally around 50% [36, 37, 38]. Transient urinary retention has been reported in 3% to 23%, typically resolving by 12 weeks [6]. Perineal pain rates vary widely from 0% to greater than 20%, depending on the definition of postoperative pain [39, 40, 41] but most reports show significant pain in less than 10% which resolves by 3 months postoperatively. Serious complications requiring sling explantation are generally less than 1% [8].

3. Quadratic sling

The quadratic sling can increase urethral resistance to a greater degree than either a purely perineal or TO device, by combining the mechanisms of action of the BAMS and TO sling. This additive effect has been mechanistically proven by demonstrating that sequential tightening of the TO and then the PP extensions caused a cumulative increase in RLPP [10, 42].

In a multinational clinical trial, the quadratic sling with fixation achieved an objective success rate (greater than 50% improvement in 24-hour pad weight) of 79%, subjective success rate (Patient Global Impression of Improvement score of much or very much improved) of 71%, and a median 24-hour pad weight reduction of 88% at 1 year. Cure (less than 1.3 g of leakage on 24-hour pad weight) was achieved in 46% at 1 year. In this cohort, the majority of patients had moderate (100 to 400 g/d) or severe (greater than 400 g/d) incontinence and complications were only Clavien grade 1. Overall, only 19% had mild genital paresthesias, and 12% experienced mild perineal pain, which is similar to the rates of pain of the aforementioned slings. By the 6-month follow-up visit, all paresthesias had resolved, and only 2 cases of mild perineal discomfort persisted, with neither requiring further treatment [43]. The results of the various male sling procedures have been summarized (Table 1).

Table 1
Results of postprostatectomy incontinence surgical procedures

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The observation of either proximal relocation of the bulbar urethra or luminal coaptation on cystoscopy suffices for appropriate tensioning of the TO sling. On the other hand, for a compressive perineal sling, a more precise quantification of sling tensioning is necessary-such as RLPP, a standardized measure of urethral sphincteric competence in men with ISD [48, 49, 50]. While abdominal LPP cannot be measured during surgery under general anesthesia, RLPP can be measured via perfusion sphincterometry, and has been validated as a useful quantification of urethral resistance during male anti-incontinence surgery [51, 52].

Sufficient tension must be maintained to achieve long-term continence, whereas loss of tension equates to loss of sling efficacy. Hence it is not surprising that the use of a resorbable allograft or xenograft BAMS has a failure rate of greater than 90% at 6 months [53]. In contrast, 3- to 5-year efficacy does not diminish with a non-absorbable polypropylene BAMS [33, 34, 54]. Objective urodynamic evidence of sustained sling tension has also been demonstrated at 2 years postoperatively [52], thus demonstrating that tension and continence can be maintained with the use of a reliable fixation method and permanent sling material.

Similarly, early reports of the TO sling were associated with a loss of efficacy over time. The Cleveland Clinic group found that patient-determined success decreased from 87% to 63% with the retroluminal sling, with average daily pad use more than doubling over 2 years postoperatively [55]. Specific risk factors predisposing to TO sling failure include the use of absorbable fixation sutures, fewer than 4 sutures, and the absence of subcutaneous sling tunneling [29]. Further experience, however, and improved sling fixation has led to substantially better medium-term results, with 77% success at 3 years attributed to more effective fixation [39]. With the goal of facilitating sling fixation by incorporating a chevron-type tissue anchor, the AdVance XP (American Medical Systems) has recently been introduced, [56] but has not received approval in the United States.

The unfixed quadratic sling, similar to other slings, demonstrated progressive reduction in efficacy over 12 months, prior to the incorporation of an effective method of mesh fixation. Following initial objective and subjective success rates of 61% and 56%, respectively, only 42% of patients realized subjective and objective success at the end of 1 year. The original surgical technique has since been revised with a straight-forward fixation of the TO and PP arms and subsequent improvement in efficacy through the elimination of early sling slippage [43]. Objective success was achieved in 79% and subjective success in over 70% at 1 year, despite patients with moderate to severe incontinence comprising the majority of the cohort-indicative of efficacious sling fixation. In fact, for the fixation cohort, 24-hour pad weight was reduced by 88% at 12 months.

The modern male sling has evolved with respect to both design and surgical technique, from the original Kaufman prosthesis, to the pubourethral sling, to the perineal BAMS, to the noncompressive TO sling, and most recently to the quadratic sling that combines the mechanisms of action of the predecessor devices. No single device should be considered exclusively as the gold-standard option for treating PPI. Rather, different devices are best suited for patients depending on history of radiation, previous incontinence surgery, degree of leakage, and bladder contractility (Table 2).

Table 2
Indications and contraindications for the surgical management of postprostatectomy incontinence

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In a man demonstrating leakage with straining that stops at the cessation of the straining maneuver, the diagnosis of ISD can made without further testing. A voiding diary is sufficient to demonstrate adequate bladder capacity, and a bladder scan can evaluate the patient's ability to empty his bladder. However with regards to bladder contractility, this can only be ascertained by detailed urodynamic evaluation. Given the recent expansion of therapeutic options for treating SUI, a thorough evaluation should also include pad weight and urodynamic studies-to best direct specific surgical therapy.

Adequate urethral tissue compliance is necessary for successful urethral compression and/or proximal repositioning with a sling. Radiation and previous AUS explantation, both of which may result in a relatively noncompressible urethra, are associated with diminished sling efficacy. With the exception of the occasional patient with persistent mild to moderate SUI following prior sling, for persistent PPI and a positive repositioning test, AUS implantation is the treatment of choice because it can provide the circumferential urethral compression necessary for adequate coaptation even in the setting of diminished urethral compliance.

In men who have not been radiated and have not had prior incontinence surgery, factors such as degree of leakage, proximal urethral mobility, and detrusor contractility can help determine the preferred surgical approach. In those with less than 200 g/d leakage and a positive repositioning test as well as adequate urethral mobility on video urodynamics, retroluminal or quadratic sling is the preferred approach, because of the lower complication rates compared to AUS placement and the fact that neither sling complicates future AUS placement. With detrusor underactivity, the TO sling may be preferred, given its noncompressive mechanism of action. For those with 200 to 400 g/d leakage, the quadratic sling may be preferred, given the compressive nature of this surgical device, providing superior resistance compared to a purely TO approach that relies on adequate residual sphincter function. However, adequate detrusor contractility is necessary to overcome the resistance of this compressive device. In the setting of detrusor underactivity and moderate incontinence, AUS is preferred. With leakage greater than 400 g/d, AUS is the recommended option unless the patient refuses a mechanical device, in which case a compressive sling would be recommended over a noncompressive sling.

The evaluation and management of PPI has changed and improved dramatically over the past 2 decades. Further innovations and developments in sling design are likely, as this field continues to evolve.