The urethral resistance responsible for maintaining continence in female dogs combines contributions from the internal and external urethral sphincters, comprised respectively of smooth and striated muscles, the elasticity of the urethral wall, and engorgement of suburothelial venous plexuses. Collectively, these are termed the urethral sphincter mechanism (USM). In adult female dogs, the most common cause of urinary incontinence is failure of this mechanism, so called urethral sphincter mechanism incompetence (USMI),[1-3] a term proposed by Holt to describe weakness of the urethral sphincter. Although USMI can occur as a congenital or acquired disorder, in both sexually entire and spayed bitches, the condition occurs mostly in adults particularly after neutering.[1, 3, 5, 6] It is unclear which of the neuromuscular, vascular, and passive elastic components of the sphincter mechanism fail in USMI incontinence and it is possible that more than one form of the condition exists.
The incidence of USMI is further influenced by a complex of interacting factors including urethral tone and length, position of the bladder neck,[8-10] body size and breed, neuter status,[11-15] sex hormone concentrations,[15-17] obesity, age, and tail docking.[3, 19-21] Female dogs affected by USMI tend to have shorter urethras than continent dogs and this is associated with “pelvic bladder” syndrome thought to cause changes in the pressure gradient between the urinary bladder and the urethra itself[2, 8, 10, 22] resulting in a non-simultaneous effect of the intra-abdominal pressure on the bladder and on the bladder neck/proximal urethra[1, 23] leading to urinary leakage. Urinalysis often reveals the presence of urinary tract infection (UTI) but treatment of this does not appear to impact the incontinence.
Urethral pressure profilometry has been reported as a useful technique for confirming poor urethral tone but requires specialized equipment and is associated with artifacts that make interpretation of the result difficult.[25, 26] In our hospital, diagnosis of USMI is typically based on clinical history and demonstration of a caudally-displaced bladder on retrograde vaginourethrography.
Medical therapy usually addresses only one of numerous potential causes of USM failure and is unlikely to achieve a long-term cure. Sympathomimetic or parasympathomimetic drugs are commonly administered to increase urethral tone and decrease intravesicular pressure, respectively. The α-adrenergic, phenylpropanolamine (PPA) is commonly used to increased urethral tone[28, 29] and response rates range from 85% to 97%.[30, 31] Estrogens increase the sensitivity of the α-adrenergic receptors to stimulation and also improve smooth muscle contractility with 40–83% responding favorably.[3, 32, 33]
Surgical management is recommended for USMI patients that are non-responsive or refractory to medical treatment. Techniques that increase urethral resistance include periurethral slings, trans-pelvic sling urethroplasty, transobturator vaginal tapes, artificial sphincters,[37-39] and intra-urethral injection of bulking agents.[40-44] Techniques for repositioning of the bladder more cranially in the abdomen include colposuspension,[27, 35, 45] urethropexy, cystourethropexy, and bladder neck reconstruction. Success rates of 53% are reported for colposuspension and 56% for urethropexy with complication rates of 11% and 21% respectively; however, White reported that incontinence recurred in 8 dogs after urethropexy.
Our purpose was to report medium term (>6 months) outcome after combined colposuspension and urethropexy (CUC) for management of urinary incontinence associated with USMI in adult female dogs. We hypothesized that the combination of these 2 techniques would 1) lead to improved outcomes (>6 months) compared with those reported after either technique alone and 2) reduce recurrence of incontinence after urethropexy.
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- MATERIALS AND METHODS
Complete data sets were available for 30 bitches with a history of urinary incontinence refractory to medical management that subsequently had CUC. The most frequently represented breeds included Border collie (n = 5), English springer spaniel (4), Irish setter (3). Median age was 36.5 months (range, 10–144 months) and median weight was 22 kg (range, 4–45 kg). Urine leakage during recumbency or excitement was a consistent presenting clinical sign in all bitches with a median duration before admission of 24 months (range, 2–120 months) and median duration of medical management of 6 months (range, 2–48 months). All but 1 bitch were spayed and the time of onset of incontinence ranged from before to 10 years after spaying. All bitches failed to demonstrate sustained response to medical management, either phenylpropanolamine (20) or estrogen (3) or a combination (7). Five dogs had previously had urethropexy but signs of incontinence recurred because of failure of the urethropexy site and recurrence of the pelvic bladder displacement. Hematologic and serum biochemical findings were normal, except for dog 3 that had mild elevation in urea and creatinine concentrations; this resolved within 24 hours after fluid therapy. All bitches had been previously administered antibiotics and all urine specimens were negative on microbial culture.
Median operative time was 40 minutes (range, 25–45 minutes); any minor bleeding from the urethral suture sites was easily controlled by brief digital pressure and no other major intraoperative complications were recorded. Median duration of postoperative urinary catheterization was 36.5 hours (range, 25–48 hours). Median duration of postoperative hospitalization was 2 days (range, 1–3 days). Three bitches (2, 14, 21) developed mild dysuria after catheter removal, but all responded to management with diazepam (0.2 mg/kg orally every 8 hours) within 7 days. One dog had urinary tract infection when examined at 2 weeks; this resolved after administration of amoxicillin-clavulanate (12.5 mg/kg twice daily for 10 days).
Follow up ranged from 6 months to 6 years (median, 39.5 months). Dogs with an excellent outcome had a follow up ranging from 6–84 months (median, 41 months), whereas dogs with a good outcome were followed for 6–69 months (median, 28.5 months). Twenty-one bitches were considered by their owners to meet the criteria to be categorized as excellent outcome (70%), 8 (26.6%) good and 1 as poor. The owner declined further investigation of this bitch.
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- MATERIALS AND METHODS
Surgical intervention for management of urinary incontinence associated with USMI aims to achieve 1 of 3 goals: increasing urethral resistance, relocation of the bladder neck into an intra-abdominal position, or increasing urethral length.[1, 5, 21]
Techniques designed to increase urethral resistance all necessitate implantation of a prosthetic material or device. These include artificial sphincters[38, 39]; intra-urethral injections of bulking agents[40, 41, 43]; and peri-urethral slings.[35, 36, 48] Rose et al reported consistent success after implantation of a static hydraulic urethral sphincter (SHUS) in 4 bitches. Delisser et al however, reported a success rate of only 36.4% for SHUS in 11 bitches; additionally, there was a significant complication rate, 82%. Claeys et al reported a successful outcome in 6/7 dogs with a trans-obturator vaginal tape used to increase the maximal urethral closure pressure; no postoperative complications were reported.
Colposuspension is thought to reposition the bladder within the abdominal pressure zone cranial to the pubic brim allowing any rise in intra-abdominal pressure to act simultaneously on the bladder and urethra such that any increase in intravesical pressure will be counteracted by an equal increase in urethral pressure maintaining continence.[1, 8] In 150 bitches treated with this procedure, a success rate of 53% and complication rate of 11.3% was reported. Complications were mainly related to urinary retention and dysuria. It was speculated that the lack of response in some dogs may have been because of progressive deterioration of the urethral mechanism sphincter or detrusor instability.
Urethropexy also aims to relocate the bladder neck into a more cranial position to allow any rise of intra-abdominal pressure to act simultaneously on the bladder and the urethra, and to increase urethral resistance to urine flow; however, urethral length is not always significantly increased postoperatively.[4, 24] An overall success rate (56%) similar to colposuspension was reported after urethropexy in 100 bitches. However, there was a lack of objective variables when gauging how much the urethra should be tractioned before pexy was performed and this may have explained the significantly higher postoperative complication rate of 21%. Although most of these complications resolved spontaneously, some dogs had marked dysuria and required surgical revision.
Our aim was to relocate the bladder as close to its anatomically normal abdominal position without creating undue urethral tension. Occasionally, the urethra was sufficiently short that this was not feasible, so we lengthened the urethra as much as possible without creating tension, a subjective assessment.
Massat et al reported cystourethropexy, fixing the urethra more ventrally and repositioning the bladder toward an abdominal location, in 10 bitches. Continence was restored in 5 bitches when combined with medical therapy; however, the improvement was temporary in most dogs. Bladder neck reconstruction techniques aim to increase urethral length, but are technically more demanding, may require bilateral ureteral transplantation and are only possible in some dogs.
White reported relapse in 8 dogs (8%) undergoing urethropexy (mean relapse time, 18.2 months [range, 9–25 months]) and we were prompted to explore the combination of urethropexy and colposuspension after our similar experience with a number of dogs that had urethropexy and showed marked initial improvement only to relapse subsequently. Further investigation indicated that the urethropexy site had avulsed in these dogs. Although CUC involves surgery at 2 sites, both procedures are technically simple and do not require implantation of major prosthetic devices; overall operative times (<40 minutes) were consequently brief. Relapse was not encountered in any dog (>6 months follow-up) supporting our hypothesis that the combination of the 2 techniques reduced the risk of avulsion of the urethral pexy site. Indeed, 5 dogs that had CUC after failed urethropexy had excellent outcomes. Medium term (>6 months) success of 70% is better than previously reported for either colposuspension or urethropexy alone. Although these results appear promising, a direct comparison with the 2 previous major studies was not possible because of the difference in sample size (P = .24) and length of follow up (Table 1). A further limitation of our study was the restricted grading scale we used to evaluate outcomes. More detailed outcome assessment systems in which owner satisfaction is evaluated on a 5-point scale ranging from 0 to 100% (Byron) provide greater insight into the degree of incontinence. However, since the only 2 major previous studies (Holt, White) used a restricted grading scale we felt it necessary to adopt the same assessment system to make direct comparison.
Table 1. Comparison of Data for Combined Colposuspension and Urethropexy With Previously Published Data for Colposuspension (Holt) and Urethropexy (White) alone
|Technique||Number||Complication Rate (%)||Success Rate (%)||95% CI (Success Rate)||Mean Follow-up (Months)|
|Colposuspension||150||11||53||45–61||32 (range, 6–108)|
|Urethropexy||100||21||56||46–65||33 (range, 12–84)|
|Colposuspension and urethropexy||30||10||70||52–83||38.5 (range, 6–72) Median 39.5|
Holt stated that no single surgical procedure resolves all types of USMI abnormalities; it is possible therefore that colposuspension and urethropexy exert their improvement on incontinence through differing mechanisms for instance, not only repositioning the bladder intra-abdominally but also increasing urethral resistance. We postulated that the results of urethropexy alone may be compromised by caudal tension caused by the intrapelvic bladder position leading to suture avulsion, whilst colposuspension alone may not adequately reposition the bladder. CUC provides both adequate bladder repositioning through urethropexy whilst the support provided by colposuspension prevents avulsion of these sutures. Although CUC requires more sutures to be placed than either individual technique, it does not entail substantially more dissection; the more complete urogenital support may result in less opportunity for the development of tension and paradoxically lead to lower complication rates.
Postoperative hospitalization periods were brief and the complication rate of 10% compares favorably with previous reports. Furthermore, all complications were mild and transient with none requiring any further surgical intervention.
Although the number of dogs reported here are modest by comparison with 2 previous studies on colposuspension and urethropexy,[23, 24] we believe that these results are sufficiently encouraging to warrant further exploration and also review of the selection criteria for dogs undergoing CUC. Given the overall improvement rate (combined excellent and good outcomes) of 96% and the absence of any major complications, consideration might be given to use of CUC as an alternative to medical management for dogs with USMI.