Urethral Obstruction as a Complication of Staged Bilateral Triple Pelvic Osteotomy

Introduction

Canine hip dysplasia is a very common hereditary disease that develops secondary to coxofemoral joint laxity in the immature dog. This laxity ultimately leads to the formation of degenerative joint disease, also known as osteoarthrosis.^1–4 Various therapeutic options are available for treating canine hip dysplasia, including both medical and surgical alternatives. Medical therapy typically consists of nonsteroidal anti-inflammatory drugs (NSAIDS), chondroprotective agents, weight management, and controlled exercise. Common surgical options include femoral head and neck ostectomy, triple pelvic osteotomy (TPO), and total hip arthroplasty. Triple pelvic osteotomy is frequently used with success in immature dogs.¹³⁵ During this procedure, the dorsal rim of the acetabulum is rotated laterally to improve dorsal coverage of the femoral head, resulting in reduced laxity and a more stable coxofemoral joint. This surgery also helps minimize the formation of further degenerative joint disease. The TPO procedure has been well described in the veterinary literature;¹³⁵⁶ however, there is a paucity of information describing the complications associated with TPO. While many articles list potential complications, few actually discuss them in any detail.^3–8

Case Report

A 5-month-old, neutered male Labrador retriever was presented for a 3-week history of exercise intolerance. The dog had no current or previous medical problems. Diet consisted of a large-breed formulation of a commercial dog food. On physical examination, there was no appreciable lameness and no pain on manipulation of the coxofemoral joints. The muscle mass of both hind limbs was deemed normal. Radiographs revealed bilateral coxofemoral joint subluxation with minimal degenerative changes. After discussing both medical and surgical options, the owner elected to pursue staged bilateral TPO surgery.

The dog was premedicated with hydromorphone (0.1 mg/kg intramuscularly [IM]) and acepromazine (0.04 mg/kg IM). Anesthesia was induced with propofol (5 mg/kg intravenously [IV]), and the dog was maintained on isoflurane and oxygen. Preoperatively, both hips were palpated under anesthesia; the angle of reduction of the right and left hips was estimated at 25° to 30° and 30° to 40°, respectively. Surgery was performed on the right hip first. Prior to surgery, an epidural block was performed using morphine (0.1 mg/kg) and bupivacaine (0.5 mg/kg). A single dose of perioperative cefazolin (22 mg/kg IV) was also administered. A standard TPO was performed on the right hip.¹³⁵⁶ For the pubic osteotomy, a 1-cm segment of bone centered on the iliopubic eminence was removed using a large rongeur. The acetabulum was rotated 30° and stabilized using a canine pelvic osteotomy plate^a and cancellous screws. Postoperative medications included hydromorphone (0.1 mg/kg IM) as needed and carprofen (2.2 mg/kg per os [PO]). Recovery was routine, and the dog was discharged from the hospital the day after surgery.

The dog was presented again 5 weeks later for reevaluation and possible TPO surgery on the left hip. Based on radiographs, healing was adequate on the right side, and surgery was performed on the second hip. Premedications and anesthesia were identical to the first procedure. Perioperative antibiotics consisted of both a single dose of cefazolin (22 mg/kg IV) and enrofloxacin (5 mg/kg IV). A standard TPO procedure was again performed, and the method of pubic osteotomy was identical to the first surgery. As with the right hip, the left was rotated 30° and secured with a canine pelvic osteotomy plate. Postoperative medications were also the same as with the previous surgery. Initial recovery was routine.

The night of surgery and the following morning, the dog’s urination consisted of a moderate to weak stream. By later that evening, the urine stream was only pulsatile and very weak. No pain or discomfort during urination was appreciated. A moderately large urinary bladder was palpable and was very difficult to manually express. On the second postoperative day, the straining and pulsatile stream continued and urinary catheterization was required twice. In the morning, 600 mL of urine was removed, and 300 mL was removed 12 hours later. The catheter passed easily with no resistance each time. By 3 days postoperatively, the dog’s urination had progressed to nonproductive straining. An indwelling Foley urinary catheter attached to a closed collection system was placed, and the dog was started on oral bethanecol (10 mg PO q 8 hours). The urinary catheter was maintained for 48 hours. On the fifth postoperative day, the urinary catheter was removed, and urination was closely monitored. The dog urinated twice overnight with no appreciable straining or dribbling. The following morning, the dog’s urination consisted of a thin stream with some dribbling. A urinary bladder could not be palpated, so it was assumed the dog was emptying the bladder despite straining. The dog was discharged from the hospital with bethanecol as prescribed earlier and with instructions for the owners to closely monitor urination.

The following day, the dog was presented because the owner reported the dog was having difficulty urinating. A moderately large urinary bladder was again present. An indwelling urinary catheter was easily reinserted, and the dog was started on oral phenoxybenzamine (10 mg PO q 24 hours) in addition to bethanecol. The urinary catheter was removed approximately 18 hours later, and urination was closely monitored. No urination was observed overnight. The following morning (9 days postoperatively), the dog initially dribbled urine when attempting to urinate and then continued to void a steady stream. For the next 24 hours, urination consisted mostly of dribbling; but the bladder remained empty on abdominal palpation. The dog was discharged (10 days postoperatively) on bethanecol and phenoxybenzamine as prescribed above.

The dog was presented 5 days later (15 days postoperatively) for complete lack of urination. Approximately 520 mL of urine was evacuated from the bladder via catheterization. No urination was observed overnight, and the following morning 420 mL of urine was removed via catheterization, again with no resistance. At that time, the frequency of the phenoxybenzamine was increased (10 mg PO q 12 hours). Overnight and the following morning, stranguria continued, the urinary bladder could not be manually expressed, and bladder emptying was accomplished via intermittent catheterization.

A positive-contrast urethrogram was performed to determine if a physical obstruction was present in the urethra. Attenuation of the contrast media was observed along the region of the pubis, with distention of the urethra distally [Figure 1]. Based on the urethrogram, a tentative diagnosis of urethral obstruction secondary to bilateral TPO surgery was made. An indwelling catheter was maintained in the dog over the weekend, and he was operated on the twentieth postoperative day to remove the remaining pubic remnant on each hemipelvis.

Premedications and anesthesia were identical to those described above. Perioperative antibiotics consisted of only a single dose of cefazolin (22 mg/kg IV). The standard approach to the pubis for TPO surgery was used on both the right and left hemipelvis. A moderate to large amount of fibrous tissue and adhesions were dissected to gain access to the pubic remnants. On each side, an additional 1 cm of bone was excised from the remaining lateral pubis. Additional digital dissection was also performed to free any visible adhesions around the pubis and surrounding soft tissues. The exact location or cause of urethral impingement could not be identified during surgery. A urinary catheter was left in place for approximately 48 hours after surgery. After the catheter was removed, the dog urinated without difficulty for 24 hours. He was sent home on tapering dosages of bethanecol and phenoxybenzamine and restricted exercise for 6 weeks.

The dog was presented for follow-up radiographs 8 weeks after the second TPO was performed. At that time, the dog was urinating normally. Four months later, the owner reported that the dog continued to urinate normally and the exercise intolerance had resolved.

Discussion

Reported potential complications of TPO surgery include implant failure, infection, decreased range of motion of the coxofemoral joint, continued degenerative changes in the hip despite surgery, sciatic nerve palsy, narrowing of the pelvic canal, constipation, and stranguria secondary to urethral injury.^3–8 There is a paucity of information actually describing these complications in detail, however. A few studies have evaluated implant complications directly related to the type of plate and screws used.⁴⁷

In the case reported here, urethral dysfunction was the only complication encountered. To the authors’ knowledge, there are no reports in the literature describing a similar postoperative complication in detail. In one of the first published reports describing the TPO procedure, urethral impingement was noted in one dog that underwent bilateral procedures, but the impingement appeared to occur before excision of a segment of the pubis.⁵ The canine pelvic osteotomy plate was subsequently developed to lateralize the acetabular segment to help minimize impingement of pelvic structures. The exact mechanism for urethral dysfunction after bilateral TPO surgery is unknown. Sukhiani, et al., evaluated the amount of pelvic canal narrowing secondary to the TPO procedure and found that the length of the pubic remnant has a significant effect on pelvic canal narrowing.⁸ They therefore concluded that the pubic osteotomy should be made as laterally as possible to prevent possible impingement on intrapelvic organs.⁸

Several anecdotal reports exist regarding urinary dysfunction after bilateral TPO procedures in male dogs.^b Some of these cases were managed with an indwelling urinary catheter and/or treated medically with bethanecol, phenoxybenzamine, or both. When compared to the case described here, however, the urinary dysfunction typically lasted no more than 3 to 4 days, and none of the anecdotal cases required surgical intervention. The dog in this case report never fully responded to medical management, and only temporary improvement in urination was obtained after adjusting medications and removing the urinary catheter.

Contrast urethrography proved to be a valuable diagnostic procedure for evaluating urethral patency in this case and identified an obvious narrowing of the urethra. Based on its radiographic appearance, a focal, extraluminal compressive lesion was suspected. The urethrogram also localized the compression to the region of the pubis. Based on these findings, the authors suspected one or both pubic remnants were compressing the urethral region, necessitating surgical intervention. For surgical correction, initial consideration was given to revising the left hemipelvis by either returning the ilium to its normal anatomical position or using a 20° canine pelvic osteotomy plate with the hope of decompressing the urethra. Ultimately it was decided to remove the remaining pubic remnants attached to the acetabulum of each hemipelvis. The procedure was straightforward and achieved an excellent outcome for this dog. In retrospect, a contrast urethrogram with subsequent surgery should have been performed earlier in the management of this case.

Conclusion

Currently, the exact mechanism and pathophysiology of urethral impingement after bilateral TPO remain unknown. In this case report, it is suspected that either the amount of lateral pubis remaining on each hemipelvis, the adhesions present, or a combination of the two, was the underlying cause of urethral dysfunction. Unlike other anecdotal cases, medical management was not successful in this dog. This report describes a potential surgical correction for cases of urethral dysfunction following bilateral TPO that are refractory to appropriate medical therapy.