Internal Device for Control of Urinary Incontinence
By Orvar Swenson
NUMBER of congenital maIformations, such as exstrophy of the bladder, sacral agenesis, and myelomeningocele, are associated with urinary incontinence. A mechanical device that would successfully produce urinary control would be highly desirable in these patients, but it would have to satisfy the following conditions: (1) It should be outside the urinary system. Any foreign body within the system fails because of incrustation on its surface and chronic infection. (2) The control mechanism should be activated by pressure applied through the skin to tighten and release the device. (3) Pressure on the skin over the control should fully release urethral compression. This is particularly important in patients with poor bladder detrusor function in whom voiding depends upon a completely unobstructed urethra. (4) The device should be implanted completely under the skin. Successful clinical experience with implantation of foreign material into the human body has been achieved with cardiac pacemakers, shunts to drain the ventricular system, and, more recently, total hip replacement. (5) Pressure on the urethra produced by such a device must not cause stricture or necrosis. Our first problem was whether pressure on the urethra sufficient to produce continence would result in stricture or tissue necrosis. A series of experiments was devised, using an apparatus that accurateIy produced a known amount of pressure on the urethra for 24 hr or longer. We found that in dogs urethral pressures up to 20 cm of water could be tolerated without tissue necrosis. Necrosis occurred when the pressure was increased above 30 cm of water (Table 1). Since the resting pressure within the bladder is less than 15 cm of water, these studies suggested that sufficient occlusion could be applied to the urethra to block the flow of urine without producing tissue necrosis. We then studied the transient increases of intravesical pressure that occur during coughing and laughing. We found that in children with indwelling bladder catheters intravesical pressures did not exceed 50 cm of water. We felt that an augmenting mechanism that would momentarily increase pressure on the urethra during such periods of stress might be necessary. With this information, we were encouraged to begin designing and testing an implantable device to occlude the urethra. Initially, a hydraulic system was favored. However, hydraulic engineers at IIT Research Institute decided that since the system would be constructed of permeable plastics, leakage From the Northwestern University School of Medicine and the Children’s Memorial Hospital, Chicago, 111. Presented at the Third Annual Meeting of fhe American Pediatric Surgical Association, Hot Springs, Va., April 13-15, 1972. Orvar Swenson, M.D.: Professor of Surgery, Northwestern University School of Medicine, and Surgeon-in-Chief, The Children’s Memorial Hospital, Chicago, 111. 542
Vol. 7, No. 5 (October-November),
CONTROL OF URINARY INCONTINENCE Table 1. Summary of Necrosis Experiments Dog. No.
2 3 5 6 6 9 10 11
Estimated Pressure (cm H,D)
11 20 20 26 48 58 38 42 30
No No No
Yes Yes Yes Yes
would prevent the maintenance of a constant pressure over a long period of time. Since reliability of the mechanism is of prime importance to reduce the need for repeated implantations, we abandoned the hydraulic design in favor of a mechanical device. We then selected a stretched-out spring, covered with silastic, with a small stainless-steel cable inside. Tension on the cable shortens the spring and produces compression. Release of the cable allows the spring to regain its extended position, moving it away from the urethra and completely relieving obstruction (Fig. 1). The control mechanism under the skin that shortens and releases the sphincter contains a cable wrapped around a spool. Each time one pinches the lower end of the device, the spool turns a partial revolution, shortening the cable and eventually occluding the urethra. Five to eight applications of pressure result in complete occlusion of the urethra. One advantage of this design is that the degree of tightness of the sphincter can be readily controlled by the number of pressure applications. With a single application of pressure on the upper end of the control box, the sphincter is completely released (Fig. 2). The device was implanted in normal female dogs. After healing took place, the device was operated daily, occluding the urethra for 4-6 hr. Intermittently, it was tightened and left in this position for 24 hr to see if it would block even normal voiding efforts by the animal. We found that animals could not void in spite of repeated efforts to do so. During such periods, the animals were confined in metabolism cages to be sure that no voiding occurred. The second problem that concerned us was the possibility of stricture formation at the site of the device. In our follow-up studies of up to 4 mo, no strictures have developed. Devices of various designs were implanted in ten animals. The longest period of observation was 4 mo. In most instances, the period of observation was shorter, because the device was removed for inspection or because of infection. We cannot explain why the small amount of pressure applied to the urethra prevented the animal from producing more than a few drops of urine, despite
Fig. 1. (A) Urethrogram with the device closed. Pressure on the injected fluid was 40 cm of water. No contrast material entered the bladder. (B) Device is open. The contrast material flows through the urethra without any constriction in the area of the artificial sphincter.
Fig. 2. One application of pressure on the upper end of the control box completely releases the sphincter.
CONTROL OF URINARY INCONTINENCE
repeated efforts to urinate. This suggests that the device is effective for a higher intravesical pressure than we had anticipated and that an auxiliary device to increase urethral compression during stress is unnecessary. This device has a number of potential uses. We have inserted such a device around ileostomies and colostomies in dogs to eliminate the need for outside appliances. It might also be implanted in patients with imperforate anus who have failed to develop control following surgical repair of their anorectal malformation. CONCLUSIONS The urethra will tolerate sufficient extrinsic pressure to produce continence without stricture or necrotic changes. A device that will occlude the urethra and that can be activated by outside pressure on the skin has been designed and tested. Occlusion of ileostomies and colostomies can also be achieved by this device. However, further testing of the device is required before its clinical application. ACKNOWLEDGMENT The author is indebted to Marvin Burns, Manager-Life Systems and Biomechanics, and Charles Ogden, Design Engineer-Life Systems and Biomechanics, IIT Research Institute, Chicago, 111.