An artificial urinary sphincter (AUS) is an implanted device to treat moderate to severe stress urinary incontinence, most commonly in men. The AUS is designed to supplement the function of the natural urinary sphincter that restricts urine flow out of the bladder.
Description
There are two types of artificial urinary sphincters: The artificial urinary sphincter with a balloon reservoir (3-component): cuff, pump and balloon. The cuff is placed around the urethra; the pump is inserted in the scrotum and the balloon reservoir is implanted in the retropubic space – between bladder and iliac vein. The pressure in the hydraulic circuit is generated by the elastic balloon reservoir and from retropubic pressure. The artificial urinary sphincter with a spring (2-component): cuff and pump unit. The cuff is placed around the urethra and the pump unit is inserted in the scrotum. The pressure in the hydraulic circuit is generated by the spring of the pump unit. The pressure in the retropubic space does not have any influence for this type of sphincter.
The common theme among currently available designs is a mechanical constriction mechanism – an inflatable cuff filled with sterile saline solution and placed around the urethra which keeps the urethral lumen closed; this is due to the pressure produced inside the device and an externally accessible control pump mechanism placed between two skin layers of the scrotum (subdartos pouch) which allows the user to manually relieve the constriction to allow urination.
History
Frederic Foley was the first to describe an externally worn artificial urinary sphincter to treat urinary incontinence, published in 1947. In 1972, F. Brantley Scott and colleagues from Baylor College of Medicine designed the first precursor of contemporary artificial urinary sphincter. The first AUS model on the market was the AMS 800 (Boston Scientific, Marlborough, MA), developed 50 years ago. It is a 3-component device with a cuff placed around the urethra, a pump inserted in the scrotum and a pressure generating reservoir placed in the pelvis, which comes as a kit to prepare and to fill up before implantation.
Another AUS model is the ZSI 375 (Zephyr Surgical Implants, Geneva, Switzerland), introduced in 2008. It is a one-piece two-part device with a cuff and a pump unit with an integrated spring; it comes in one piece, pre-connected and pre-filled. There is no abdominal component in the ZSI 375, which along with its ready-to-implant configuration reduces the operating time. Furthermore, because there is no abdominal component, surgical interventions in the retroperitoneal space are not required. Previous surgeries, such as radical prostatectomy, may lead to post-operative scarring and fibrosis in the retroperitoneal space. Thus, avoiding dissection of retroperitoneal tissues avoids risks of surgical complications. Another advantage of the ZSI 375 model is the possibility to increase or decrease the pressure inside the device after implantation to meet the desired continence rate and satisfaction of the patient. These adjustments particularly help to control continence in cases of post-implantation urethral atrophy or urinary retention (poor urine flow). Adjustment of the pressure can be done in an outpatient setting by adding or removing sterile saline solution via a syringe through the scrotum. By 2019, more than 4,500 ZSI 375 artificial urinary sphincters have been implanted worldwide. In addition to the devices mentioned above, new devices are being brought to market, such as the Rigicon ContiClassic and ContiReflex Artificial Urinary Sphincter systems.
In both models sterile saline solution inside the system is used to generate pressure and compress the urethra (to prevent urine from leaking). The urethral cuff is deflated manually by pressing the control pump that is placed in the scrotum, allowing the patient to empty the bladder. The urethral cuff then re-inflates automatically to refill the urethral cuff and once again prevent urine from leaking.
The list includes AUS models available in 2023:
Medical use
The intrinsic sphincter deficiency leading to stress incontinence is the most common indication for AUS implantation. The European Association of Urology recommends AUS implantation for moderate-to-severe stress incontinence in men. Additionally, despite the novel treatment options (slings, urethral bulking injections, stem-cell therapy), AUS is considered to be the gold standard surgical management both for stress incontinence in men and for urinary incontinence developed as a complication of surgery, such as prostatectomy, cystectomy and TURP.