Introduction
A biological urinary sphincter prevents urinary flow via mucosal coaptation, compression, and pressure transmission. An artificial urinary sphincter (AUS) mimics the biological urinary sphincter by providing a competent bladder outlet during urinary storage and an open unobstructed outlet to permit voluntary voiding.
An artificial urinary sphincter is the only device that closely simulates the function of a biological urinary sphincter. Decades of advances in mechanical design, applications of new technology, and lessons learned from clinical experience have inspired notable improvements.
Novel and ingenious in technical design, the AMS 800 (American Medical Systems, Minnetonka, Minn) device has restored the quality of life to thousands of patients plagued by severe stress urinary incontinence. The AMS 800 prosthesis is the most effective, reliable, and durable surgical treatment for men with postprostatectomy urinary incontinence, achieving social continence rates of 75-95%.
For additional information on the surgical management of urinary incontinence, see the article Incontinence, Urinary: Surgical Therapies in eMedicine’s Urology volume. For supplementary information on urinary incontinence in general, see Medscape’s Urinary Incontinence and OAB Resource Center.
History of the Procedure
Artificial devices to control incontinence are not new. Foley described an artificial sphincter in 1947 that was an externally worn urethral cuff attached to a pump kept in the patient's pocket. The first artificial urinary sphincter to resemble the current model was developed by Dr. Brantley Scott in 1972. Called the AS 721, it consisted of a fluid reservoir, an inflation pump, a deflation pump, and an inflatable cuff with 4 unidirectional valves. The fluid within the sphincter components conveyed the hydraulic pressure to the cuff. Unfortunately, it was mechanically unreliable and carried high urethral erosion rates.
In 1974, a newer model (AS 761) emerged. This model offered a pressure-regulating balloon that allowed automatic cuff closure. This pressure-regulating balloon provided constant predetermined pressure within the hydraulic system, so that the pressure-volume relationship became very predictable.
The AS 761 device was quickly modified into the AS 742 model. This newer sphincter eliminated the need for an inflation pump. The pressure-regulating balloon functioned as a reservoir for cuff fluid. A delay-fill resistor allowed enough time for the patient to void to completion before the urethral cuff closed. However, this prosthesis still was not ideal for patient use.
Introduced in 1979, the AS 791/792 device featured a control assembly that merged the valves and the resistor into a single unit. Surgical implantation was easier, with fewer components and fewer connections. However, the control pump did not have on-off capability. The risk of urethral atrophy and cuff erosion remained high. A second operation was required for activation of this device.
Through continued evolution and improvement, the AMS 800 device was introduced in 1983. During the modification process, the control assembly (valves and resistor) was moved into the pump chamber. This model featured a new locking mechanism that allowed the cuff to remain in either the open or the closed position; thus, the cuff could be left in a deflated (open) state after implantation and could be activated 6-8 weeks later without the need for a second operation.
In 1987, AMS introduced a narrow-backed cuff. This modification improved transmission of pressure to the underlying urethra or bladder neck, which has been proven to decrease the risk of erosion and tissue atrophy. In 1988, the kink-resistant and color-coded tubing was introduced.
The AMS 800 is the most widely used and successful artificial urinary sphincter available. To date, over 94,000 men worldwide have been treated with an AMS 800.
Problem
An artificial urinary sphincter is reserved for treatment of complex or severe stress urinary incontinence. Type III stress urinary incontinence, or intrinsic sphincteric dysfunction, is the inability of the urethra to maintain effective resting urethral closure pressure sufficient to keep the patient clinically dry at rest and during periods of reasonable physical activity.
Etiology
Patients with intrinsic sphincteric dysfunction include men who have undergone radical retropubic prostatectomy, radical perineal prostatectomy, or transurethral resection of the prostate (TURP); patients with previous pelvic trauma or a history of pelvic radiation; and women in whom anti-incontinence procedures have failed. Patients with spinal cord injuries, myelomeningoceles, or other causes of neurogenic bladder may also have intrinsic sphincter dysfunction.
Pathophysiology
The normal voiding cycle requires that the urinary bladder and the sphincter work as a coordinated unit. The urinary bladder has two functions: it relaxes to store urine (storage or filling phase), and it contracts to eliminate urine (voiding phase). During urinary storage, the bladder is placid and acts as a low-pressure reservoir. During voiding, the bladder actively contracts to act as a pump. The urinary sphincter has two functions: it contracts to store urine and it relaxes to eliminate urine. During urinary storage, the urinary sphincter remains closed to prevent urine loss. At the beginning of the voiding phase, the urinary sphincter opens to allow unobstructed urination.
Urinary incontinence results from dysfunction of the bladder, the sphincter, or a combination of both. Bladder overactivity causes urinary frequency, urgency, and urge incontinence. In neurogenic bladders, this is referred to as detrusor hyperreflexia. Bladder underactivity (atonic bladder) causes urinary retention. Sphincteric overactivity causes urinary retention. Sphincteric underactivity results in stress incontinence. A combination of bladder overactivity and sphincteric underactivity results in mixed urinary incontinence—stress and urge.
Intrinsic sphincteric dysfunction, or type III stress urinary incontinence, is a complex form of stress incontinence whereby the urethra always remains open. Risk factors for intrinsic sphincteric dysfunction include radical prostatectomy, TURP, previous bladder neck surgeries, pelvic radiation, pelvic trauma, and neurologic disorders.
A common denominator of intrinsic sphincteric dysfunction is low urethral resistance at rest and during periods of physical activity. Whenever the intravesical pressure becomes greater than the urethral resistance, stress incontinence ensues. A reliable method of restoring continence is by artificially increasing the urethral resistance. Many approaches to this problem have been devised over the years. The main criterion for implanting an artificial urinary sphincter is a normal detrusor in a setting of intrinsic sphincteric dysfunction.
Presentation
Patients with intrinsic sphincteric dysfunction present with the classic history of stress urinary incontinence. They experience predictable loss of urine whenever the intravesical pressure exceeds that of the urethral pressure (eg, when coughing, laughing, sneezing, sitting down, or performing the Valsalva maneuver).
Often, patients with intrinsic sphincteric dysfunction complain of involuntary urine loss when changing their body position (eg, when rising from a sitting position). Women with intrinsic sphincteric dysfunction experience more urine loss and require thicker pads than women with incontinence due to urethral hypermobility.
Intrinsic sphincteric dysfunction can often be distinguished from other causes of incontinence by patient history and physical examination. In patients with pure intrinsic sphincteric dysfunction, symptoms of urinary frequency, urgency, and nocturia are typically absent. However, when irritative voiding symptoms are also present, coexisting overactive bladder should be suspected. As such, patients should undergo preoperative endoscopic and urodynamic evaluations (see Workup).
Indications
Candidates for artificial urinary sphincter include patients with type III stress urinary incontinence. Indications in men and women of all ages include the following:
- Postprostatectomy incontinence, which is the most common indication for placement of an artificial urinary sphincter. Placement of the artificial urinary sphincter should be deferred for at least 6 months after prostatectomy; many physicians defer placement for up to 1 year because patients often regain some or all continence during this time.
- Intrinsic sphincteric dysfunction following pelvic fracture, spinal cord injury, or urethral reconstruction.
- Neurogenic bladder with associated sphincter or bladder neck incompetence.
Careful patient selection is arguably the most important factor in predicting success of the artificial urinary sphincter, and the following should be considered:
- Female patients and children require bladder neck placement of the sphincter and must be motivated to perform and capable of performing clean intermittent catheterization, as this may be required because of postoperative urinary retention.
- All patients must have sufficient sophistication and hand functionality, as well as manipulative strength, to operate the pump and its associated lock-out mechanism.
- All patients must understand the potential complications of the operation and the possibility of future surgical interventions for tissue atrophy, cuff erosion, cuff migration, mechanical failure, and device infection. The long-term reoperation rate is about 20%.
Essential characteristics of an ideal patient include highly motivated personality, good manual dexterity, normal detrusor, absence of urinary tract infection (UTI), failure of alternative means of incontinence control, and realistic expectations. Although some patients may expect to remain completely dry, a realistic and satisfactory goal is achieving social continence, which is generally defined as requiring no more than one incontinence pad a day. Careful patient selection can greatly reduce the likelihood of a disappointed patient and surgeon.
Relevant Anatomy
The urethra is composed of an inner epithelial lining, a spongy submucosa with rich vascular plexus, a middle smooth muscle layer, and an outer layer of fibroelastic connective tissue. The spongy submucosa is responsible for providing urethral occlusive pressure. The ability of the urethral mucosa to coapt to generate an adequate urethral closing pressure is an important continence mechanism. Urethral smooth muscle and fibroelastic connective tissues serve to circumferentially augment the occlusive pressure generated by the submucosa.
The urinary sphincter is composed of an internal sphincter and an external sphincter. In females, the internal sphincter is composed of the bladder neck and proximal urethra. In males, the internal sphincter is composed of the bladder neck and prostate. Both males and females possess an external sphincter known as the rhabdosphincter. The rhabdosphincter is omega-shaped and is composed of 2 types of striated muscle fibers—fast twitch and slow twitch. Contraction of fast twitch fibers causes sudden stopping of the urinary stream. This is known as the voluntary guarding reflex. These fibers are responsible for allowing Kegel exercises. Slow twitch fibers maintain the constant tonus of the external sphincter, which is important in daily physical activities. This is known as the involuntary guarding reflex.
Contraindications
Contraindications for placement of an artificial urinary sphincter include the following:
- UTI: All candidates for an artificial urinary sphincter should undergo a sterile urine culture result preoperatively.
- Recurrent urethral strictures or diverticula
- Uncontrolled detrusor overactivity: This condition can generate high intravesical pressures that are transmitted to the upper tracts, causing renal damage.
- Small bladder capacity or poor compliance (However, some patients with this contraindication are candidates for artificial urinary sphincter with concomitant or preoperative augmentation cystoplasty.)
There are also many relative contraindications, such as the following:
- Grade 2 or higher vesicoureteral reflux should be corrected before artificial urinary sphincter placement.
- Recurrent disease (eg, stone disease, bladder or ureteral tumors) that requires retrograde endoscopic instrumentation is a relative contraindication. Such instrumentation can predispose to cuff erosion in patients with an artificial urinary sphincter.
- Bladder neck contractures (a not uncommon complication of prostate surgery) should be treated first, and cystoscopy or retrograde urethrography should be performed at least 3 months afterward to ensure continued patency of the bladder neck before proceeding with artificial urinary sphincter placement.
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Further Reading
Keywords
artificial urinary sphincter, AUS, artificial sphincter, AMS 800, artificial genitourinary sphincter, prosthetic sphincter, incontinence, stress incontinence, urge incontinence, post-prostatectomy incontinence, postprostatectomy incontinence, stress urinary incontinence, urinary sphincter, type III stress urinary incontinence, intrinsic sphincter deficiency, ISD, incompetent urethra, intrinsic sphincteric dysfunction, intrinsic sphincter dysfunction
