In 2014, Vetspecs instigated a new approach to the surgical treatment of canine urethral sphincter mechanism incompetence (USMI). 

Welcome to the world of the Hydraulic Artificial Urethral Sphincter (HAUS)! 


USMI is a condition which can seriously impact on the pet’s ability to remain happily in the family unit.  USMI is the most common cause of acquired urinary incontinence in the bitch and is second only to ectopic ureters as a congenital cause of incontinence in juvenile bitches. The aetiology of USMI is multifactorial and predominates in older, spayed, overweight, large breed bitches but can be seen in both sexes and in a variety of ages, breeds and in entire animals.  Medical management of dogs diagnosed with USMI are life-long, can thus be associated with high costs and morbidities and are not consistently successful.  Hence, surgical remedies for USMI should be considered for suitable candidates.  The general aims of surgical treatments are to increase urethral resistance, increase urethral length and or to move the bladder neck into an intra-abdominal position.  A variety of surgical treatments have been used to treat USMI in the dog, including colposuspension, urethropexy, various urethroplasties, transpelvic slings, endoscopic peri-urethral bioimplant injections such as collagen, and prosthetic sphincter implantation. 

So, how do they work?  Hydraulic urethral occlusion employs a silicon cuff placed around the proximal urethral.  The cuff is initially applied at its largest (loosest) circumference but, if necessary, it can be incrementally inflated post-operatively via a subcutaneous injection port with variable amounts of saline to provide mechanical obstruction to urine outflow. 

Previous techniques, such as colposuspension and collagen injections, depend on stretching or expanding soft tissues, respectively, to increase resistant to urine outflow.  Soft tissues ultimately relax (the “face-lift” quandary) which means that many of these soft tissue procedures will lose their efficacy over time.  Similarly, surgical correction for ureteral ectopia leaves approximately 50% of dogs incontinent due to ongoing USMI.  Thus, surgical procedures may need to be repeated, augmented with another surgery (a “belt and braces” approach), and or assisted with a return to medications.  In contrast, the obstruction to urinary outflow provided by the HAUS is mechanical and thus static.  That is, its effect should last as long as the device is in place.

Candidates for HAUS placement should have a comprehensive “work up”, like any other dysuria case, in order to correctly diagnose and eliminate other possible co-morbidities which may significantly affect the treatment plan and prognosis, such as urinary tract infection (UTI), urolithiasis, ureteral ectopia, hydronephrosis or hydroureters.  “Work up” means assessing the signalment and history, performing urinalysis, complete blood counts, serum chemistry, microbiological culture of a cystocentesis sample and diagnostic imaging.  Diagnostic imaging may include plain radiography followed by positive contrast intravenous urography and retrograde (vagino)urethrography.  Contrast CT imaging is currently our imaging modality of choice, frequently followed by retrograde urethrography.  Doppler ultrasonography can be utilised in these cases too.  With ultrasound or contrast CT, we can measure the urethral diameter which helps us predict the likely HAUS size that will be needed intraoperatively. 

Following surgery, patients are not discharged home until it is confirmed that the dog can urinate.  Any previously administered medications are stopped on the day of surgery, if not prior.  Dogs tend to be “profoundly continent” postoperatively; often a dramatic change to the preoperative situation.  

The port is not injected for at least 6 weeks post operatively.  After this time, if required to improve the level of continence, small volumes (eg 0.1-0.2mls) of saline can be injected into the port via a specialised Huber needle, after aseptic preparation of the overlying skin.

We have implanted occluders in three dogs since January 2014 and all dogs have responded well to the surgery.   None have experienced any difficulty urinating and all have vastly improved continence scores.  All are off oral medications and have normal activity levels.  One dog, a female spayed 3year old Labrador that had ectopic ureter surgery at the age of 6months, was profoundly incontinent preoperatively.  A HAUS was applied in January this year with instant and sustained improvement in her continence. However, she has experienced antimicrobial-responsive recurrent bacterial cystitis which we theorise is due to pre-existing alterations in her ureteral and urethral peristalsis and her increased bladder residual volume, which may be facilitating infection.  Our second patient, a 7.5year old male neutered Rottweiler, had surgery in mid-May and has had a significant improvement in his incontinence.  He had been experiencing regular nocturia and bed wetting which has resolved post-HAUS placement.  However, as he was experiencing infrequent and intermittent dripping every few days, we elected to inject 0.1ml into his subcutaneous port 8 weeks post operatively. Response to this injection is not yet known.  Our third patient, a 3year old Hungarian Vizsla, had a HAUS placed at the end of May, after having failed to respond to long term medication with phenylpropanalomine and or estrogens.  She had also had colposuspension surgery performed in the year prior to the HAUS surgery with an initial but not sustained improvement in her urinary incontinence.  She became immediately continent following HAUS surgery and has been off all medications since. 

Hydraulic urethral occluders appear to offer a new and highly successful option for the control of urinary incontinence in the dog.  The single-procedure technique offers a medication-free and sustained control of incontinence in the dog.  I would very much encourage pet owners to consider surgery for USMI-related urinary incontinence before getting exasperated with high medical bills and continual husbandry problems.  The success rates are very good.  Such improvement can make a significant difference to the ability of an animal to remain a happy part of the family.