Presented in part at the 2011 ACVS Symposium, Chicago, IL
Original Article - Clinical
Outcome after Placement of an Artificial Urethral Sphincter in 27 Dogs
Article first published online: 19 NOV 2012
© Copyright 2012 by The American College of Veterinary Surgeons
Volume 42, Issue 1, pages 12–18, January 2013
How to Cite
Reeves, L., Adin, C., McLoughlin, M., Ham, K. and Chew, D. (2013), Outcome after Placement of an Artificial Urethral Sphincter in 27 Dogs. Veterinary Surgery, 42: 12–18. doi: 10.1111/j.1532-950X.2012.01043.x
- Issue published online: 3 JAN 2013
- Article first published online: 19 NOV 2012
- Manuscript Accepted: MAR 2012
- Manuscript Received: SEP 2011
To evaluate the safety and efficacy of an adjustable artificial urethral sphincter (AUS) in a population of dogs with acquired or congenital urinary incontinence.
Dogs (n = 27) with naturally occurring urinary incontinence.
Medical records (January 2009–July 2011) of dogs that had AUS implantation for treatment of urinary incontinence were reviewed and owners were interviewed by telephone to assess outcome. Continence was scored using a previously established analogue scale, with 1 representing constant leakage and 10 representing complete continence.
Twenty-four female and 3 male dogs had AUS implantation. Causes of incontinence included urethral sphincter mechanism incompetence (n = 18), continued incontinence after ectopic ureter repair (6), and pelvic bladder (3). Medical therapy was unsuccessful in 25 dogs before AUS implantation. Surgery was performed without major complications in 25 dogs; 2 developed partial urethral obstruction after 5 and 9 months. Median (interquartile range) follow-up for the other 25 dogs was 12.5 (6–19) months. Continence scores were significantly improved (P < .0001) between the preoperative period (2 [1–4]) and last follow-up (9 [8–10]). Overall, 22 owners described themselves as very satisfied, 2 as satisfied, and 3 as unsatisfied.
AUS implantation was successful in restoring continence in male and female dogs with both congenital and acquired urinary incontinence. Dogs that develop partial urethral obstruction may require AUS removal.
Urethral sphincter mechanism incompetence (USMI) occurs in up to 20.1% of female dogs after ovariohysterectomy and as an acquired condition in castrated male dogs.[2, 3] Urethral sphincter dysfunction is also a common cause of persistent incontinence after surgical repair of ureteral ectopia.[4-8] Medical therapy with alpha adrenergic agonists and estrogen are effective in 60–90% of dogs, although these drugs are not without side effects.[9-18] Alpha agonists can produce sympathomimetic effects at higher doses, causing inappetence, gastrointestinal upset, lethargy, aggression, and restlessness. Estrogenic drugs are thought to increase urethral smooth muscle tone via increasing the sensitivity of alpha receptors to catecholamines; therefore, estrogens are more commonly used as a supplement to alpha agonists, rather than as a single drug therapy for medical management of USMI.[9, 10, 13, 17, 19]
Surgical intervention is recommended in dogs that are refractory to pharmacologic therapy, or when medical therapy produces undesired side effects. Urethral submucosal collagen injections have good short-term efficacy, but most treated dogs will experience recurrence of incontinence in less than 2 years. [20, 21] Other reported surgical treatments for USMI include transpelvic sling, cystourethropexy,[23, 24] urethral intussusception, and colposuspension.[26-28] The goal of these surgical treatments is to increase pressure on the proximal to mid urethra either by direct compression, or by cranial advancement of the bladder and proximal urethra into abdomen, exposing the proximal urethra to intra-abdominal pressures similar to those exerted on the bladder.[27, 29-32] Although the short-term efficacy of these surgical procedures can be high, many dogs require additional medical therapies or revision procedures because of recurrence of incontinence over time. In pursuit of improved long-term outcomes, the use of permanent implants that have the potential to produce more consistent and durable urethral compression have been explored. One recent study reported promising results using a transobturator vaginal tape inside out procedure, to provide external compression of the urethral lumen with a strip of polypropylene tape. More recently, our group has developed a permanent, percutaneously adjustable artificial urethral sphincter (AUS) that was effective in providing improved urinary continence for more than 2 years after implantation in a pilot study using 4 client-owned dogs with acquired USMI.[33, 34] We have recently expanded our selection criteria to include both male and female dogs with acquired or congenital forms of urinary incontinence. Our purpose was to provide a retrospective analysis of success rate and complications encountered in a larger and more varied group of dogs receiving AUS implantation. We hypothesized that the AUS would provide a safe and effective means of improving urinary continence in male and female dogs with acquired or congenital urinary incontinence.
MATERIALS AND METHODS
Medical records (January 1, 2009–July 15, 2011) of dogs that had AUS implantation for urinary incontinence were reviewed. Data retrieved included age, body weight, sex, preoperative imaging findings, cystoscopy and urine culture results, cause of incontinence, AUS size, number of postoperative injections into the AUS, and any complications.
A specific anesthetic protocol was determined for each dog by the attending anesthesiologist, but all dogs were premedicated with a pure μ-opioid agonist (hydromorphone or oxymorphone 0.05–0.1 mg/kg subcutaneously) and a tranquilizer (acepromazine 0.05–0.1 mg/kg subcutaneously), anesthesia was induced with propofol (3–6 mg/kg, intravenously [IV]), and maintained with isoflurane in oxygen via a rebreathing system. Cefazolin (22 mg/kg, IV) was administered within 1 hour of induction of anesthesia. After median celiotomy (umbilicus to pubis) with self-retaining retractors to maintain exposure, 1–2 stay sutures were placed in the apex of the bladder, which was then retracted cranially to expose the pelvic urethra. A 2-cm section of the proximal urethra was isolated from the periurethral adipose tissue by blunt dissection with Mixter right angle forceps, taking care to avoid trauma to the urethra or vagina during dissection (Fig 1). In female dogs, the AUS was placed approximately 3 cm caudal to the bladder neck whereas in male dogs the AUS was placed 2 cm caudal to the prostate.
The urethral circumference was estimated by measuring the length of a Penrose drain or strand of suture wrapped loosely around the intended cuff placement site (Fig 2). A silicone AUS (DOCXS, Ukiah, CA) of equal or larger circumference to the pelvic urethra was selected and its size and filling volume were recorded. Before placing the AUS around the previously dissected urethral segment, the unit was primed with sterile saline (0.9% NaCl) solution. Actuating tubing was cut to approximately 15-cm length and air was flushed from the lumen of the AUS and actuating tubing by inserting a long 22 g catheter into the lumen of the actuating tubing and retrograde filling the tubing with sterile saline solution. The AUS ring was then closed temporarily by threading suture through the eyelets and the actuating tubing connected to a titanium vascular access port (CP2u, Access™ Technologies, Skokie, IL). The AUS was completely filled, tested for leakage, and filling volume recorded before emptying the AUS and placing the cuff around the pelvic urethra, 2 cm caudal to the bladder neck. The bladder was replaced, being careful to avoid kinking of the AUS on the urethra as the cuff contacts the pubis and other viscera. The actuator tubing was exited through a stab incision in the abdominal wall and tunneled to just lateral to the rectus abdominis muscle and cranial to the flank fold (Fig 1). It was then reconnected to an infusion port that was anchored to the superficial fascia of the abdominal wall using non-absorbable polypropylene suture. The connection of the actuating tubing to the male adapter on the port was secured using a silicone “boot” supplied by the manufacturer of the port. Before closure, the bladder was inflated with sterile saline solution and manual expression was performed to ensure that urethral patency was maintained. After copious lavage and suction, the celiotomy incision was closed in layers.
Carprofen (2 mg/kg orally twice daily) and tramadol (2–4 mg/kg orally 3 times daily) were administered for 3–5 days after surgery. Buprenorphine (0.01–0.02 mg/kg subcutaneously) or hydromorphone (0.05–0.1 mg/kg subcutaneously) was administered once or twice for additional analgesia during the first 24 hours after surgery, at the discretion of the supervising clinician. Dogs were recovered overnight in the hospital and were discharged the next day after confirmation of spontaneous urination. Urethral catheters were not placed and postoperative antibiotics were not routinely administered unless indicated because of a pre-existing urinary tract or skin infection.
Owners were instructed to return for re-evaluation at 6 weeks for reassessment of continence. Before any AUS inflation, dogs were palpated to rule out incomplete bladder emptying and owners were questioned regarding stranguria secondary to urethral obstruction. In dogs with persistent incontinence, the area over the subcutaneous port was shaved and aseptically prepared and 0.1–0.2 mL of sterile saline solution was injected into the subcutaneous port using a Huber needle (Access Technologies) and 1-mL syringe. Before discharge, voluntary urination was observed to confirm that urethral obstruction had not occurred after AUS inflation. AUS inflation was repeated, typically at weekly intervals, until continence was improved or signs of urethral obstruction (stranguria, decreased urine stream, and incomplete bladder emptying) occurred.
A formal follow-up survey of owners was conducted either at the last veterinary examination or by telephone interview. The survey consisted of a series of questions about urinary continence before and after surgery, current medications, complications secondary to the surgery and overall owner satisfaction with the procedure. Owners were asked to provide any additional information on postoperative injections that may have been performed at other hospitals. Preoperative and postoperative urinary continence were scored by the owners using an analogue scale as previously described by Rose et al  with 1 representing constant leakage and 10 being complete continence.
Descriptive data were reported as median and interquartile range (IQR). Statistical comparison of pre- and postoperative continence scores was performed using a nonparametric Wilcoxon signed rank test. A P value < .05 was considered statistically significant.
Twenty-seven dogs had AUS implantation. Median (IQR) age at surgery was 4.0 (2.0–5.0) years, with ages ranging from 0.5 to 10 years. Median body weight was 23.7 (16.4–31.1) kg, with a minimum of 4.5 kg and maximum of 45 kg. Cause of incontinence was identified as acquired USMI in 18 dogs (1 intact and 14 spayed females, 3 neutered males); 3 spayed females had USMI with pelvic bladder; and 6 (1 intact and 5 spayed females) had failed ectopic ureter repairs. Medical therapy was documented as unsuccessful in 25 dogs before surgery, with 25 dogs having been administered phenylpropanolamine (6.25–75 mg orally every 8–12 hours) and 10 dogs, diethylstilbesterone (0.5 mg orally 1–4 times/week). Information regarding previous medical therapy was not recorded for 2 dogs. Seven dogs had one or more previous surgical or endoscopic procedures for incontinence, including submucosal collagen injections (4 dogs), neoureterocystostomy (4), and laser ablation of intramural ectopic ureters (2).
Urine microbial cultures were performed in 20 dogs at surgery and were positive in 3 dogs (Escherichia coli, Staphylococcus pseudointermedius, Pseudomonas sp). Abdominal ultrasonography was performed in 11 dogs at time of surgery; urinary tract abnormalities included suspect pelvic bladder (3 dogs), thickened bladder wall (2), pyelectasia and hydroureter (2), and cystic calculi (1). There were no abnormal ultrasound findings in 3 dogs. Of the 4 dogs that had cystoscopy at surgery, 1 was interpreted as normal and 3 had hypervascularity and inflammation of the bladder mucosa.
AUS sizing for female dogs was compared to body weight (Table 1); 1 dog received a 6 × 11 mm AUS, 11 dogs an 8 × 14 mm AUS, 7 dogs a 10 × 14 mm AUS, and 8 dogs (including all 3 males) a 12 × 14 mm AUS. Body weight was not a precise predictor of AUS size suggesting that intraoperative measurement of urethral circumference is crucial in selecting the appropriate sized cuff. Additional procedures were performed at the time of AUS implantation in 12 dogs, including cystourethroscopy (n = 4), episioplasty (3), neoureterostomy (1), cystotomy (1), elective gastropexy (1), and ovariohysterectomy (2).
|AUS diameter × width (mm)||8 × 14||10 × 14||12 × 14|
|body weight (kg)||(4.9–28.0)||(17.2–44.9)||(23.5–36.2)|
|Number of dogs||11||7||5|
Cuff inflation was performed after surgery in 15 dogs to adjust urethral resistance. Cuff inflation was achieved in all dogs without sedation. Dogs showed no discomfort aside from that involved with needle insertion through the skin. In those dogs that required cuff inflation, the median (IQR) total volume of saline solution required to achieve maximal continence was 0.4 (0.1–0.7) mL.
Minor complications included temporary worsening of incontinence during the first 14 days after surgery (5 dogs), mild stranguria (2), and seroma formation over the injection port (3). Stranguria in this early postoperative period was treated by the administration of an additional 1-week course of nonsteroidal anti-inflammatory drugs to address any residual discomfort or urethral inflammation that was contributing to signs. Seromas were treated with application of a warm compress for 10 minutes, 3 times daily until resolution. All minor complications resolved during the first month after surgery. Major complications occurred in 2 female dogs, with each developing progressive urethral obstruction at 5 and 9 months after surgery. Before that time both dogs were assessed as having an excellent outcome, with a continence score of 10 and no previous evidence of stranguria. Neither dog had received any injections into the AUS after surgery. On re-examination, both dogs were easily catheterized, but were unable to voluntarily empty the bladder. Treatment with prazosin (1 mg/15 kg once or twice daily) and aspiration of all fluid from the AUS failed to resolve signs in both dogs. In both dogs, contrast was injected into the AUS and orthogonal radiographs were obtained to investigate the displacement of the AUS and kinking of the urethra. The AUS was normally positioned and aligned with the urethral axis in both dogs.
Removal of the AUS was recommended in both dogs. Device removal was performed in 1 dog and signs of urethral obstruction resolved. At the time of AUS removal, it was noted that a series of adhesions were present between the small intestine and the actuating tubing of the AUS, with the tubing perforating the small intestine before passing out the abdominal wall. It was presumed that a loop of small intestine had been perforated when the actuating tubing was exited from the abdominal wall during the original surgery, but had healed without incident. The AUS was removed and an intestinal resection-anastomosis was performed to remove the affected small intestine. This dog is now continent (scored 10/10 by owner) when receiving oral phenylpropanolamine. In the second dog, device removal was declined and the dog was euthanatized at the owner's request. Necropsy findings showed no gross evidence of urethral luminal obstruction at the site of AUS placement, although a ring of thickened fibrous tissue surrounded the urethra at the site of the AUS.
Final continence scores were obtained in 25 of 27 dogs (Fig 3), with a median follow-up of 12.5 (6–19) months. Median (IQR) continence scores were significantly improved (P < .0001) between the preoperative period (2 [1–4]) and last follow-up period (9 [8–10]). Overall owner satisfaction was high, with 22 owners describing themselves as very satisfied, 2 as satisfied, and 3 as unsatisfied. Two dogs received low postoperative continence scores when we were unable to achieve a balance between continence and urethral obstruction, despite making incremental injections into the AUS. Both these dogs had congenital incontinence and multiple pre-existing anatomic abnormalities, but it was unclear whether these contributed to difficulties in maintaining continence with the AUS. One dog that had pre-existing hydronephrosis, hydroureter, recurrent urinary tract infections, and ureteral ectopia had been previously treated with neoureterostomy. The second dog had severe vulvar fold pyoderma and recurrent urinary tract infections. In both cases, the dogs were left with minimal inflation of the AUS and incontinence was managed medically.
The AUS was effective in treatment of most congenital and acquired forms of urinary incontinence, including dogs that had failed the conventional surgical therapy for ureteral ectopia and in dogs with pelvic bladder. Implantation of the AUS significantly improved postoperative continence scores, with a median score of 9 on our continence scale (a score of 10 represented complete continence) at last follow-up. Although median follow-up time was 12.5 months after surgery, 11 dogs were followed for more than 1.5 years. The distinct advantage of the AUS compared to other surgical treatment options for USMI is that the inflation volume can be titrated after surgery, adjusting the pressure exerted on the pelvic urethra to meet the needs of the individual patient. Interestingly, only 15 (55%) dogs required AUS inflation after surgery while the remaining dogs were continent after placement of the uninflated AUS. We have previously noted that the AUS does not form a circle when closed, but hinges at a single point as the cuff is closed around the urethra (Fig 4). As a result, the uninflated AUS can cause focal compression of the urethra even when the cuff has a measured “circumference” that is equal to or larger than the circumference of the urethra.
In general, we have avoided performing additional diagnostic procedures at the time of AUS implantation out of concern that urethral trauma and inflammation that can occur during urethroscopy may contribute to postoperative urethral obstruction or stricture. However, in an effort to reduce owner costs associated with repeated anesthetic episodes, some dogs had additional procedures that may have affected outcome. Neoureterostomy performed in 1 dog with ectopic ureter is likely to have contributed to improved continence after surgery. On the contrary, ovariohysterectomy performed in 2 young dogs with congenital incontinence would tend to exacerbate clinical signs after surgery. Clinicians are advised to weigh the goals of the owner and the potential effects of additional procedures when performing AUS implantation.
Progressive urethral obstruction developed in 2 dogs at 5 and 9 months after the application. Selection of inappropriately small AUS sizes could have contributed to the development of postoperative urethral obstruction, but the late timing of the 2 complications is more consistent with the development of a progressive foreign body reaction around the AUS causing urethral compression or chronic bladder atony because of increased urethral resistance. In both instances, urethral obstruction was assumed to be the result of compression at the site of AUS implantation and removal of the device was recommended without performing contrast urethrography. Surgical findings revealed that a ring of fibrous tissue encased the AUS and urethra, but no histopathology was available to allow comment on the microscopic appearance of the tissues at this location. Although this tissue did not appear to grossly affect the luminal diameter of the urethra, the firm nature of the tissue may have affected the ability of the urethra to dilate under pressure. Despite the clinical signs of urethral obstruction, a Foley urethral catheter was placed in both dogs without resistance, and manual expression of the bladder was subjectively easy to achieve. These findings suggest that poor bladder function (pre-existing or acquired) was a contributing factor in both dogs. Evaluation of bladder function is commonly performed in people before recommending procedures that will increase urethral resistance, to avoid the occurrence of incomplete bladder emptying in patients with poor detrusor activity. Similar examination may be indicated in dogs when AUS implantation is being considered, although the conscious voiding studies performed in people are not possible in dogs, with nearly all urodynamic variables being assessed under heavy sedation or anesthesia.[9, 17, 25-27] One minor complication noted by owners after surgery was a temporary worsening of incontinence and/or stranguria in some dogs during the first 7–10 days after surgery. In our experience, dogs with USMI commonly show a worsening of incontinence after undergoing fluid diuresis during an anesthetic period. In dogs with stranguria, physical examination confirmed complete bladder emptying and signs were attributed to lower urinary tract inflammation secondary to surgical manipulation. In all cases, clinical signs improved within 10 days after discharge.
Approximately 4% of people undergoing AUS implantation develop infection at the site of surgical implantation. Two dogs developed a seroma over the injection port, but no surgical site infections were diagnosed. It is possible that the abdominal approach used in dogs will decrease the overall rate of infection compared to the perineal location that is used in people, although future studies with larger numbers of dogs will be required to accurately determine the infection rate associated with this procedure.
Previous attempts at pharmacologic or surgical treatment of male dogs with urinary incontinence have yielded poor results.[3, 36] Although only 3 male dogs were included in this series, the outcome in these dogs does suggest that the technique can be effective in male dogs with USMI. In men with urinary incontinence, AUS is placed around the perineal urethra between the anus and scrotum. Based on cadaver studies in dogs and on our experience with female dogs with USMI, we elected to place the AUS caudal to the prostate through a caudal median celiotomy. The external circumference of the postprostatic urethra in the male dog was larger than that of a similar sized female dog and large (12 mm diameter by 14 mm wide) AUS was applied in all 3 males. Substantial cranial traction on the bladder was required to achieve exposure of the postprostatic urethra, but this was achieved in all dogs without a need to consider pubic osteotomy.
The retrospective nature of our study and the involvement of multiple surgeons do not allow for strict control of experimental variables. In addition, we are unable to directly compare outcomes with the AUS to alternative therapies without a prospective randomized clinical trial. It would seem that assessment of incontinence therapies would be relatively simple (eg is the dog continent?), but there are a number of difficulties associated with comparing degrees of continence between patients and over time. In our studies, we elected to use a visual analog continence scoring system that ranged from 2 end points: 1 (constant leakage) to 10 (complete continence). Visual analog scales have the advantage of being simple to explain and do not require owners to read a long series of instructions or detailed descriptions of each category. Accuracy and consistency of the results depends largely on the choice of well-defined end points, such as the ones used in our study. Despite their challenges, subjective or objective assessment of owner satisfaction is the most important method to assess outcome of treatments for urinary incontinence. Based on the successful results obtained in a larger population of dogs with variable causes of urinary incontinence, application of a silicone AUS appears to offer an effective method of improving urinary continence in a variety of naturally occurring disease conditions. Owners should be warned that partial urethral obstruction may occur in some dogs over time and that AUS removal may be required.