Introduction

Urinary incontinence in dogs is commonly seen in veterinary practice.¹ Urethral sphincter mechanism incompetence (USMI) is the most common cause of acquired urinary incontinence in female dogs, and it is also seen, less commonly, in males.^1,2 USMI is a multifactorial condition. Contributory factors include urethral tone, urethral length, bladder neck position, hormonal status, neutering status, obesity, body size, and breed.³ Medical management with α-adrenergic agonists, such as phenylpropanolamine (PPA) or ephedrine, increases sympathetic bladder neck tone and has been shown to increase maximal urethral closure pressure in cases of urethral sphincter mechanism incompetence.⁴ It has been shown to improve urinary incontinence in acquired USMI in up to 85% of dogs. However, between 15 and 27% of female dogs with USMI cases remain refractory to medical management with PPA.^4,5 The same percentage of refractory cases is also found following treatment with estriol.⁶

Surgical management of USMI is recommended when medical management fails or if long-term medical management is not an option. Several different procedures are described for controlling USMI in bitches, including colposuspension, urethropexy, or a combination of both; urethral submucosal injections with either collagen, polytetrafluoroethylene, or extracellular matrix bioscaffold; transobturator vaginal tape inside out; Dacron coated Silastic sheet urethral sphincter; and, most recently, static hydraulic urethral sphincter (SHUS).^7–24 Complications reported with these techniques include persistent incontinence (immediate or delayed), dysuria, urinary obstruction, hematuria, and recurrent urinary tract infection (UTI).^{8,11,13–15,21,23}

The static hydraulic urethral sphincter (also known as artificial urethral sphincter) is a silicone device surgically placed around the urethra. It can be incrementally inflated postoperatively, via a subcutaneous port, to progressively compress the proximal urethra and achieve continence. Should dysuria result, the SHUS can also be partially or fully deflated.²² SHUS has been investigated in bitches who have ongoing or recurrent incontinence after surgery. A preliminary in vivo experimental study, followed by a clinical pilot study in four spayed bitches, showed good results up to 2 yr postoperatively, with all dogs achieving full continence at last follow-up at 26–30 mo.^22,25 A larger study (27 dogs, including 3 male dogs) was published by the same institution, and improved incontinence scores were seen in all dogs, with a median follow-up of 12.5 (6–19) mo.²³ This series also reported minimal complications. The authors of the present study have also previously reported high success rates and low complication rates for this technique at their institution but only with a short-term follow-up; several reports have defined long-term follow-up as follow-up of 12 mo and over.^7,21,26 To our knowledge, no studies to date have described long-term follow-up (>12 mo) of female dogs treated for USMI with SHUS implantation.

The primary aim of this study was therefore to report the long-term (>12 mo) outcome of SHUS for the control of USMI in female dogs. A second aim was to document any long-term complications and therefore assess the ongoing safety of the SHUS in dogs with naturally occurring disease.

Materials and Methods

Results

Twenty female dogs met the inclusion criteria. Eighteen were spayed, and two were entire. Table 1 shows the signalment, preoperative treatment, diagnostic imaging findings, and cuff size used along with their respective volumes of total inflation. Mean age was 61.0 mo (±24.0), and median weight was 27.7 kg (9.6–62.7). All included spayed female dogs were first noticed to be incontinent soon after routine ovariohysterectomy (days to weeks). Seventeen of the twenty dogs had either failed to respond completely to medical management with one or more of a combination of PPA, estriol, or ephedrine, or had initially responded but then become incontinent despite medication. None of the dogs had experienced adverse effects attributable to medication. Dog 13 did not receive any medical treatment for USMI prior to surgical treatment as the owner wished to pursue surgery only. Dogs 2 and 10 were selected for surgery despite adequate medical control of incontinence due to difficulties with administering medication. Physical examination and diagnostic imaging revealed urogenital abnormalities in 11/20 dogs (Table 1). No dog had a UTI at the time of surgery, based on the results of urinalysis and bacteriology assessment. The median preoperative continence score was 3.0 (2–6).

TABLE 1 Signalment, Preoperative Findings, and Inflation/Deflation Volumes for SHUS for 20 Female Dogs

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No intraoperative complications were encountered during surgery, and all dogs were urinating without difficulty the following day, although 12/20 remained incontinent at discharge (Table 2). Median immediate postoperative continence score (8.0 [2–10]) was significantly higher than median preoperative score (P < .001). Median postoperative hospitalization time was 2 days (1–3).

TABLE 2 Owner-Rated Continence Scores, Total Number and Volume of Inflations/Deflations Performed, and Time at Last Follow-Up

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Median continence scores at 6 and 12 mo postoperatively were 8.5 (4–10) and 9.0 (5–10), respectively. These were both significantly higher than preoperative scores (P < .001). Mean time at latest follow-up was 1,205.4 days (627.4; Table 2). At this time, 80% of dogs (16) were continent without any other treatment, 10% of dogs (2) were continent and on continued medical therapy (dog 3 on 1 mg estriol q 24 hr and PPA and dog 14 on PPA and estriol), and 2 dogs were judged incontinent based on lower continence scores (both had continence scores of 7). The continence score was 9.0 (7–10) and was significantly higher than preoperatively (P < .001). Communication was not possible with the owners of four dogs (dogs 9, 13, 19, and 20) at the time of latest follow-up; therefore, information was gathered through communication with the referring veterinarian. Over the study period, 4/20 dogs (dogs 1, 2, 6, and 12) were euthanized for reasons unrelated to USMI. All of these dogs had a follow-up time >12 mo before euthanasia.

Regarding management of ongoing incontinence, one dog (dog 8) received a course of PPA to control persistent postoperative incontinence, as the authors were reluctant to inflate the cuff in this dog because of concurrent dysuria. Dysuria resolved without treatment after several weeks, and incontinence subsequently resolved with inflation of the SHUS and cessation of the PPA. Seven of the twenty dogs (35%) did not require any inflation of the SHUS. Thirteen required inflation, and four of these dogs required subsequent deflation of the cuff, due to urinary retention (dog 1), severe dysuria (dogs 2 and 6), or urethral obstruction (dog 11). Two dogs (dogs 1 and 2) had their cuff completely deflated, and two dogs (dogs 6 and 11) had partial deflation (Table 2).

Minor complications were reported in 13/20 dogs (65%) and are further detailed in Table 3. Complications were experienced at a variety of times postoperatively. All complications, with one exception, were minor. One dog (dog 1) experienced a major complication event and required surgical intervention for SHUS removal 28 mo postoperatively due to persistent postoperative stranguria. Seven dogs had postoperative UTIs. One additional dog (dog 10) had a UTI before (but not at the time of surgery) and after surgery. Escherichia coli infection was initially identified in this dog, which was sensitive to and treated with amoxicillin/clavulanic acid. Persistent recurrent dysuria was reported postoperatively, and this was treated presumptively by the referring veterinarian with amoxicillin/clavulanic acid. Culture and sensitivity was then performed 6 days postoperatively; multidrug-resistant E coli, Enterobacteriaceae, and Pseudomonas spp. were identified, which were sensitive to amoxicillin/clavulanic acid. For all other dogs in whom a UTI was suspected based on clinical signs, urinalysis, and a positive response to antibiotics, no culture and sensitivity information was available. Pain surrounding the subcutaneous port, which was responsive to analgesia, was noted in two dogs during the first 2–3 wk postoperatively.

TABLE 3 Severity Scores (0–3 in Increasing Severity) of Complications Following SHUS Placement

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Median owner satisfaction score was 9.5 (5–10). All but one owner, who said he was unsure (dog 15, satisfaction score of 8), said that they would have the procedure performed again if they had another dog with the same problem. We also noted lack of compliance with our recommendations (i.e., owner unwilling to come back for cuff inflation) from two owners. Those were the dogs with the lower continence scores at follow-up (continence score of 7).

Discussion

This retrospective study reports the long-term outcome of SHUS for the management of USMI in female dogs, with a longer time to follow-up (mean 40 mo) than has previously been described (13.5 mo; 26–30 mo; 12.5 mo; 32 mo).^21–24 It is important to document long-term efficacy of surgical techniques for USMI, as, for example, dogs treated with urethral injections of collagen showed good initial success, but over half of dogs become incontinent approximately 12–16 mo postoperatively, and polytetrafluoroethylene injections had an initial 100% success rate, but many dogs developed recurrent incontinence over time.^14,15 It is vital that veterinarians have a good understanding of the likely outcomes of the technique and are aware of the possible short- and long-term complications. The long-term continence rate is higher (90% with two cases having medical management) than for colposuspension (53% and 37% being improved or more responsive to medical treatment), urethropexy (56%), or a combination of both (70%), or urethral bulking agents (68%); mean follow-up in the latter two studies was comparable to this study at around 3 yr.^7,11,12,14 Furthermore, the two dogs classified as incontinent (continence scores <8) did not have a proper cuff management due to lack of owner compliance. Avoiding the financial costs associated with ongoing medical management and expensive repeat surgery is a benefit of SHUS placement compared with other techniques (only one dog required repeat surgery in this study). Another major benefit of the SHUS that is not possible with any other reported technique is the flexibility provided by the ability to inflate or deflate the SHUS at any stage following surgery, in a conscious dog with minimal equipment. Importantly, owner satisfaction scores were very high in this study, and all but one owner agreed that they would have the same treatment performed again. This is similar to owner satisfaction reported in another study in which 24/27 owners were satisfied or very satisfied with the procedure.²³

In the authors’ experience, the surgical procedure is simple to perform and requires minimal additional specialized equipment, apart from the implants and a non-coring Huber needle. Certain aspects of the technique, however, require special attention. Care must be taken to avoid bubble formation in the system and to ensure adequate slack is left in the tubing to avoid kinking of the SHUS at the urethra. Secure attachment of the tubing to the injection port is also particularly important. Finally, close monitoring of the dog for at least 24 hr postoperatively for ease and character of urination is essential.

SHUS can be used to treat dogs with incontinence due to multiple different causes other than USMI and in male dogs with USMI.^23,24 We have purposely decided to restrict this study to the female population of dogs treated for USMI (which is the most common cause of incontinence seen in our hospital). We believed that adding male dogs or dogs presented for urinary incontinence due to conditions other than USMI would add variability and would have weakened the conclusions of the present report.

Ninety percent of our dogs (where two are being managed medically) achieved continence at long-term follow-up, similar to the Currao et al. study in which all 18 dogs had significantly improved continence scores immediately after SHUS placement, and 67% with continence scores >9 at long-term follow-up.²⁴ A median continence score of 9 out of 10 at last follow-up was reported by Reeves et al.²³ In the Rose et al. study, all dogs were continent after the placement of the SHUS (including one dog on medical management for a few months to maintain a continence score of 9 out of 10) and were continent at mean latest follow-up of 30 mo without complications.²² The two dogs on medical management postoperatively in this study achieved good continence scores, despite not being responsive to medical management before surgery. They were not completely continent as their owners decided to not pursue further inflations and decided to continue with medication; the authors believe it is likely that medications could have been stopped if further cuff inflation had been performed.

Despite the SHUS being left uninflated at the time of surgery (only a small residual primer volume was used to fill the tubing and injection port), 85% of dogs showed improved continence immediately after surgery. A period of 6–8 wk was allowed between surgical placement and inflation of the SHUS based on previous recommendations in human and veterinary studies.^22,27 This is proposed to allow adequate revascularization of the dissected urethra and minimize the risk of urethral atrophy and erosion. The immediate postoperative improvement in continence seen in this study was also appreciated in previous reports.^22,23 It is hypothesized that this occurs due to the passive increase in urethral tone created by the presence of the semirigid backing on the urethral part of the implant.^22,23 Similar to our results (seven dogs, 35%), 33% of dogs reported by Currao et al. did not require inflation to achieve continence.²⁴

Only one major complication was reported in the current case series (one dog who had to have the SHUS removed), in agreement with previous reports of the SHUS technique.^22,23 One or more minor complications occurred in 65% of dogs, a lower incidence than in our previous study (81.8%).²¹ This report included the first 11 dogs of the current study, suggesting that the complication rate has improved with more experience using the technique. Although complications were encountered more commonly than reported with other techniques, they were minor and self-limiting.^7,11 Only one dog required further surgery to remove the cuff, 28 mo after it was placed. This dog was moderately persistently stranguric despite complete deflation of the cuff. Postoperative or post–cuff inflation stranguria was seen in seven additional cases. Deflation of the SHUS was performed, resulting in resolution of stranguria in all dogs without further intervention. This is a similar experience to stranguric dogs previously reported.²² The severity of the stranguria and the presence of urinary retention were considered when determining whether cuff deflation was indicated. It was thought in retrospect that stranguria was caused by overinflation of the cuff in dog 1, where 33% of the total cuff volume was instilled initially. In subsequent dogs, a more gradual SHUS inflation (10–20% increments) was therefore performed to reduce the risk of stranguria, in line with the recommendations by Rose et al.²² Reeves et al. reported mild stranguria 7–10 days after surgery in five dogs, which responded to nonsteroidal anti-inflammatories in all animals.²³ Stranguria and anuria are reported complications of colposuspension and urethropexy, requiring postoperative catheterization in the case of colposuspension and repeat surgery and suture removal in urethropexy.^7,11 Martinoli et al. reported dysuria in some dogs where both techniques were combined.¹² When these complications occur following SHUS placement, this study shows that they are more easily and less invasively managed than with the two aforementioned techniques.

The most common complication in this population appeared to be postoperative UTIs. According to a study by Wong et al., dogs who had one or two single events of UTI documented were considered to have uncomplicated UTIs, which may even have been related to USMI.²⁸ Olin and Bartges proposed that all dogs with UTIs related to USMI would be called complicated.²⁹ UTIs occurred in 8 of 20 dogs (40%), based on a combination of urinalysis, positive urine bacterial culture, and response to antibiotics. This is a significant proportion of dogs, although two out of eight cases for which information was available had single UTIs. Three dogs had multiple (three and over) UTI events; the authors consider these animals to have had complicated UTIs. Due to a lack of records, the nature of these infections (e.g., if they involved the same organism or multidrug-resistant organisms and whether significant clinical signs were associated) was unknown. All UTIs were successfully treated with antibiotics based on resolution of clinical signs. It is clear that more information is needed regarding the association between SHUS and UTIs, as it is possible that some of the cases of UTIs post SHUS placement may simply be related to the higher prevalence of UTIs in incontinent female dogs and not necessarily linked with the presence of the SHUS. Only a more stringent protocol involving routine urine culture and sensitivity irrespective of the presence of clinical signs could provide information on the prevalence of subclinical infections. Therefore, we cannot exclude the presence of subclinical infection in some of the dogs included in this study, as only dogs with clinical signs consistent with UTIs were further investigated with urine culture and sensitivity.

Because pain surrounding the subcutaneous port was noted in two dogs during the first 2–3 wk postoperatively, the authors modified the port placement technique by moving the location of the port from the medial musculature of the pelvic limb/inguinal region to the paramedian abdominal wall. Pain was not suspected in any subsequent dog, and that location of the port allowed it to be more easily identified on palpation and also likely reduced port movement.

Prolonged duration of micturition compared with that preoperatively was reported in 50% dogs. This is far less frequent than that noted in a previous study in which three out of four animals (75%) presented with this complication.²² To the authors’ knowledge, this is not a reported complication following colposuspension or urethropexy and is considered a more severe form of prolonged emptying. The significance of prolonged micturition in these dogs is unknown but may indicate discomfort when urinating, or smaller urethral diameter due to the SHUS placement and rather inelastic fibrous tissue formation around the urethra at this particular level.

One dog had a known obstructive episode (managed by slight cuff deflation), and three additional dogs had suspected low-grade ongoing urinary retention. Although urinary retention did not result in obvious additional complications, it is a known risk factor for UTI development. This may contribute to UTI development in dogs treated with SHUS cases, although this case series is too small to allow this association to be evaluated fully. It is now considered prudent to counsel owners regarding the potential postoperative risks of urinary retention. We recommend that the bladder is routinely checked postmicturition (by palpation and/or ultrasound examination) by the referring veterinarian every 3 mo during the first year postoperatively and then as required, based on the initial presence or degree of urinary retention.

This study has a number of limitations, primarily due to its retrospective nature. Some data was reliant on owner recall ability and in any case was subjective, despite efforts to classify continence scores and complication severity on numeric scales. Interobserver variability and bias were unavoidable disadvantages of data collection by owner questionnaire. Owner satisfaction would also have depended on pre-existing expectations, influenced by preoperative counseling, owner education, understanding of the procedure, and expected outcome. A contemporaneous record of the continence levels, recorded at the specified time intervals, would be more reliable. This said, owners’ perceptions are increasingly being recognized as important outcome indicators, rather than using objective scientific criteria alone.³⁰ Additionally, bacteriuria may have been missed due to clinical signs only prompting further investigations for a possible infection.

Conclusion

Overall, SHUS is an effective treatment for USMI in bitches, resulting in a significant improvement in continence scores, in both the short- and long-term (>12 mo). This study shows that 90% of dogs achieve continence and that owners were very satisfied with their dogs’ outcome. It confirms that a major advantage of the SHUS is that it provides scope for potentially further improving continence postoperatively (without surgery and without further medication) by cuff inflation, although this is not required in all dogs. According to this study, long-term management of SHUS does not seem to result in a high incidence of implant-related complications. Results are of importance as they add to the currently limited body of evidence available for veterinarians regarding the use of SHUS.