Symphyseal distraction-osteotomy using a novel spacer of spirally fashioned orthopaedic wire for the management of obstipation

Abstract

Three domestic shorthair cats, one male and two females, 17.6±6.5 months old and 3.5±0.4 kg body weight, were admitted with a 6.6±1.1 (range 6–8) month history of recurrent bouts of obstipation. Defecatory difficulties had started within a month of conservatively managed pelvic fractures. Clinical and radiographic examination revealed severe colonic distension with faeces and a narrow pelvic canal caused by malunion of the pelvic fractures. A pelvic symphyseal distraction-osteotomy (SDO) technique was performed, using a novel metal spacer of spirally fashioned orthopaedic wire. Pelvic canal enlargement allowed the insertion of an index finger into the rectum. Following this, no further episodes of obstipation occurred during a follow-up period of 1–3 years. The SDO technique may be successful for the treatment of obstipation secondary to post-traumatic pelvic canal stenosis in the cat, if the colon motility is not already permanently affected.

Pelvic fractures and sacroiliac luxation are common injuries in cats. In particular, the former accounts for approximately 20% of all fractures in cats (Schrader 1992). The majority of these orthopaedic problems are managed conservatively and the functional end results tend to be good (Denny and Butterworth 2000). However, medial collapse of bone fragments, callus formation and/or malunion can result in narrowing of the pelvic canal, causing rectal impingement, chronic obstipation and, finally, megacolon (Ward 1967, Matthiesen et al 1991, McKee and Wong 1994). Furthermore, in queens, dystocia can be another complication of pelvic canal stenosis (Ward 1967, Schrader 1992).

Cats with obstipation caused by post-traumatic stenosis of the pelvic canal may be treated medically with dietary management, stool softeners, laxatives, enemas and/or manual colonic evacuation (Matthiesen et al 1991, McKee and Wong 1994). Surgical treatment is generally directed at widening the pelvic canal by removing the impinging bone (partial pelvectomy) (Leighton 1969, Schrader 1992, Denny and Butterworth 2000), redirecting the impinging bone (corrective osteotomy) (Schrader 1992, Ferguson 1996), or separating and distracting the symphysis (symphyseal distraction-osteotomy – SDO) (Ward 1967, Leighton 1969, Evans 1980, Webb 1985, Schrader 1992, McKee and Wong 1994). Alternatively, a subtotal colectomy may help to produce semi-formed stools that can more readily pass through a stenotic canal (Matthiesen et al 1991).

A variety of SDO techniques have been described in the literature, using different materials to maintain the distraction; including metal or plastic spacers (Ward 1967, Leighton 1969, Webb 1985) and allogenic or autogenous bone grafts (Ward 1967, Evans 1980, Schrader 1992, McKee and Wong 1994).

In this paper, the successful treatment of obstipation in three cats, secondary to post-traumatic pelvic canal stenosis, by the application of a new SDO implant is described.

Materials and Methods

The criteria for the inclusion of the cats in this study were the presence of post-traumatic obstipation caused by a markedly narrow pelvic canal that did not permit the insertion of an index finger into the rectum, and the suitability of the SDO technique for pelvic canal enlargement. The latter was judged from lateral and ventrodorsal pelvic radiographs, and palpation per rectum. The SDO technique was considered appropriate if the pelvic symphysis was intact and pelvic canal stenosis was mainly due to a diminished horizontal as opposed to vertical pelvic canal diameter.

Case reports

The data, clinical details and outcome of three cats that fulfilled the above criteria are summarised in Table 1. Follow-up information was obtained by physical examination, including rectal palpation, by the referring veterinary surgeons, for a minimum time interval of 12 months following surgery.

Table 1.

Signalment, historical data and follow-up information of three cats with pelvic canal stenosis treated by SDO using spirally fashioned orthopaedic wire

Cat	Age (months)	Breed	Sex	Weight (kg)	Duration of obstipation (months)	Follow-up (months)	Result of surgery
1	11	DSH	Male	3.2	8	36	Normal defecation
2	24	DSH	Female	4.0	6	23	Normal defecation
3	18	DSH	Female neutered	3.5	6	12	Normal defecation

DSH=domestic shorthair.

Cat 1

An 11-month-old intact male domestic shorthair cat was admitted for evaluation of severe faecal impaction of 8 months' duration. Defecatory difficulties together with pelvic limb lameness were present after a road traffic accident. Pelvic trauma had been diagnosed, but radiographs had not been obtained. Restricted activity for a month had been recommended and normal gait was regained. However, progressive obstipation required the use of stool softeners (magnesium hydroxide, Milk of Magnesium; Famar, 7 ml, bid, PO), warm water enemas and dietary management (w/d Hill's prescription diet).

Clinical and radiographic examination of the cat revealed severe colonic distension with faeces and an asymmetric pelvis (Fig. 1). The narrowing of the pelvic canal was caused by malunion of fractures of the left ilium, ischium and pubis and of the right iliac body. The cat was otherwise normal.

Fig 1.

Ventrodorsal radiograph of the pelvis (left) and lateral radiograph of the abdomen and pelvis (right) of a cat with obstipation secondary to pelvic canal stenosis due to fracture malunion (case 1). There is severe colonic distension with faeces and pelvic asymmetry.

Pelvic SDO was performed. The osteotomy was distracted about 10 mm to permit insertion of an index finger into the rectum (Fig. 2). The cat recovered uneventfully, except for a 5-day postoperative period of mild pelvic limb lameness. Faeces were passed 48 h postoperatively and no further episodes of obstipation occurred. Three years following surgery the cat was defecating normally, the size of the colon was normal on abdominal palpation and the insertion of an index finger into the rectum was still possible.

Fig 2.

Ventrodorsal postoperative radiograph of the pelvis of a cat with pelvic canal stenosis (case 1) showing two spacers of spirally fashioned orthopaedic wire placed in the symphyseal osteotomy to maintain distraction.

Cat 2

A 2-year-old intact female domestic shorthair cat was admitted with a 6-month history of recurrent bouts of obstipation. The cat had been hit by a car 1 month before the onset of faecal tenesmus. Pelvic trauma had been diagnosed and conservative management, consisting of cage rest for a month, had been instituted. Progressive obstipation was observed and temporary relief had been obtained by repeated use of oral laxatives (lactulose, Duphalac; Solvay Pharma, 2–3 ml, tid, PO), warm water enemas, manual evacuation of stools from the colon and dietary management (w/d Hill's prescription diet).

Clinical examination of the cat revealed a distended bowel and an asymmetric pelvis. Radiography showed severe colonic distension with retained faeces. Narrowing of the pelvic canal was caused by malunion of multiple bilateral pelvic fractures. The cat was in a good physical condition.

Pelvic SDO was performed. The osteotomy was distracted approximately 7 mm in order to permit insertion of an index finger into the rectum. The cat had no gait abnormalities postoperatively. It ate and drank the day after surgery and defecated voluntarily 24 h after surgery. No further episodes of obstipation were reported by the owner. Twenty-three months following surgery the cat was defecating normally, the size of the colon was normal on abdominal palpation and the insertion of an index finger into the rectum was still possible.

Cat 3

An 18-month-old spayed female domestic shorthair cat was admitted for the evaluation of obstipation of 6 months' duration. The cat had sustained a left sacroiliac separation and fractures of the right ischium and pubis after a fall, 1 month before the onset of faecal tenesmus. Conservative treatment had been instituted but the increasing frequency of bouts of obstipation necessitated the repeated use of oral laxatives (lactulose, Duphalac; Solvay Pharma, 2–3 ml, tid, PO), warm water enemas and dietary management (w/d Hill's prescription diet).

Clinical examination of the cat revealed a distended bowel and an asymmetric pelvis. Radiography showed severe colonic distension and faecal retention. The narrowing of the pelvic canal was caused by malunion of the pelvic fractures. The cat showed signs of lethargy, inappetence and weight loss.

Pelvic SDO was performed. The osteotomy was distracted approximately 9 mm to permit insertion of an index finger into the rectum. The cat had no gait abnormalities postoperatively. Faeces were passed 48 h postoperatively, and no further episodes of obstipation occurred. One year following surgery the cat was defecating normally, the size of the colon was normal on abdominal palpation and the insertion of an index finger into the rectum was still possible.

Surgical technique

After administration of antibiotics (cefoxitin, Mefoxil; Vianex, 25 mg/kg, IV) and analgesics (morphine 0.1 mg/kg, IM), the three cats were anaesthetised and positioned in dorsal recumbency with pelvic limbs abducted. The ventro-caudal abdominal and pelvic areas were prepared for surgery. The pubic symphysis was exposed through a ventral midline approach with elevation and retraction of the gracilis and adductor muscles (Piermattei and Johnson 2004). A 1 mm Kirschner wire was used to drill two holes in the pubis and ischium, 3–4 mm either side of the symphysis and approximately 1 cm from the cranial and caudal edge of the symphysis, respectively. The symphysis was split carefully, to avoid damaging the pelvic organs, along its entire length using an osteotome and mallet, and the two halves of the pelvis gently levered apart. Then the urethra was catheterised so that it could be easily identified and protected from trauma during surgery.

The degree of distraction desired was determined by the ability to easily insert an index finger (diameter approximately 1.5–2 cm) into the rectum within the pelvic canal. The width of the osteotomy was measured and two spirally fashioned wires of appropriate length were prepared. For this task, a piece of orthopaedic wire (18 gauge) was wrapped snugly around a Steinmann pin (3 mm) (Fig. 3). One spirally fashioned wire was inserted transversely, both cranially and caudally into the distracted osteotomy, at the exact site of the previously drilled holes (Fig. 4). The wire inserts were secured in place with strands of orthopaedic wire (20 gauge), which were passed through both the spiral wires and the pre-drilled holes, and then tightened with twisted knots.

Fig 3.

A strand of 18 gauge orthopaedic wire is wrapped snugly around a 3 mm Steinmann pin for the construction of a metal spacer. Insert: Two metal spacers of spirally fashioned orthopaedic wire.

Fig 4.

Diagram showing pelvic SDO using spirally fashioned orthopaedic wire as a spacer. Two such spacers are transversely placed in the distracted osteotomy and secured through holes in the pelvis with 20 gauge orthopaedic wire.

The fascia of the gracilis and adductor muscles was apposed and sutured to close the pelvic cavity. Approximation of the muscles was facilitated by adducting the pelvic limbs. The subcutaneous tissues and skin were sutured in a routine manner. The urethral catheter was removed.

Immediately after surgery, the colon and the rectum were evacuated, as much as possible, by use of external massage and a fine sponge forceps. Postoperatively, carprofen (Rimadyl; Pfizer, 4 mg/kg, IV), amoxycillin plus clavulanic acid (Synulox; Pfizer, 15 mg/kg, bid, for 6 days, PO), lactulose (Duphalac; Solvay Pharma, 2–3 ml, tid for 10 days, PO) and cisapride (Alimix; Janssen, 1 mg/kg, bid, for 10 days, PO) were administered. All cats were put onto a canned diet (w/d Hill's prescription diet) for at least 2 weeks. Restricted activity was recommended for 6 weeks. The cats were monitored postoperatively for pain, stool output and lameness.

Discussion

Conservative treatment of pelvic fractures and sacroiliac separation is appropriate for most cats with pelvic trauma (Denny and Butterworth 2000). However, surgical widening of the pelvis is sometimes needed to treat obstipation caused by compressive pelvic fracture malunion (Schrader 1992). The choice of widening technique should be tailored to the individual cat and be determined by palpation per rectum and pelvic radiography (Schrader 1992, McKee and Wong 1994, Ferguson 1996, Lanz 2002). Partial pelvectomy and corrective osteotomy are difficult if the injury is long standing (Schrader 1992, Lanz 2002). Also, with either technique, a substantial amount of soft tissue dissection is necessary and injury to the sciatic and obturator nerves, urethra or rectum may occur (Matthiesen et al 1991, Schrader 1992, Denny and Butterworth 2000, Lanz 2002). In this study, SDO was judged applicable for pelvic enlargement, as the pelvic symphyses were intact and the pelvic canal stenosis was mainly because of a reduced horizontal rather than vertical pelvic canal diameter.

SDO is readily performed and is effective in widening the pelvic canal (Ward 1967, Evans 1980, Webb 1985, McKee and Wong 1994). The use of a spacer in the symphyseal osteotomy achieves a more stable configuration and prevents the medial displacement of the hemipelvis postoperatively (Ferguson 1996). Both bone grafts and non-osseous implants have been used to maintain pelvic symphyseal distraction (Ward 1967, Leighton 1969, Evans 1980, Webb 1985, Schrader 1992, McKee and Wong 1994). Surgical principles suggest that using an autogenous bone graft may be preferable to using an allograft or non-osseous implant as a spacer (McKee and Wong 1994). However, its use requires a second operation to be performed on the same animal in order to obtain the graft (Matthiesen et al 1991); this means increased operative time, anaesthetic risk, cost, pain and potential complications. Alternatively, allogenic bone grafts are not readily available and there is the danger of rejection.

The use of spacers made from stainless steel plate, prepared preoperatively in several sizes to meet the individual needs, has been described (Ward 1967, Leighton 1969). However, a significant disadvantage of this type of spacer was its frequent dislodgement, as it was not firmly secured to the pelvis (Ward 1967, Leighton 1969). Leighton (1969), in an attempt to overcome this problem in a single cat, secured the sharp prong ends of the spacer in holes drilled in the ischial fragments, but follow-up information was not available.

In the present study, spirally fashioned orthopaedic wire, securely fixed in the pelvis, was used as a spacer, and it proved effective in maintaining the pelvic symphyseal distraction for at least 1–3 years in three clinical cases. This technique is simple and inexpensive one and requires no special instrumentation. Furthermore, it is a versatile technique as it permits construction of spacers of the appropriate length and width during the operation, when the degree of desirable distraction has been determined. The diameter of the wire used for spacer construction (18 gauge) was chosen arbitrarily and was effective for all the cats; however, it could be adjusted individually, based on pelvic conformation and body weight. The authors would recommend that the diameter of the wire used to fix the spacers to the pelvis be no heavier than 20 gauge, otherwise the bone may fracture at the drill hole when the wire is tightened.

Surgery was effective in enlarging the pelvic canal to a size deemed adequate to allow unobstructed passage of faeces in all cats. This size was determined by rectal examination during surgery as that permitting the insertion of an index finger into the pelvic canal. The symphyseal osteotomies in these three cats were distracted between 7 and 10 mm in order to achieve the desirable pelvic canal enlargement. The use of two spacers to maintain distraction proved adequate. However, if greater tension is anticipated in the osteotomy site, due to pelvic conformation and body weight, the use of at least one more spacer is recommended (Ward 1967).

Ward (1967) carried out SDO using metal spacers in two cats, with a resulting spread of 11–12 mm, and noticed that the osteotomy site progressively filled with new bone and that the pelvic floor was partially or completely restored in 1.5 months. This finding suggests that the spacers have to be functional for at least 1.5–2 months postoperatively and it is advisable that restricted activity for this period may help achieve this. Unfortunately, postoperative radiographs were not available in this series; however, the follow-up of at least 1 year with no defecatory difficulties is good evidence that the technique was effective.

The main clinical feature of the three cats presented here was the gradually worsening constipation, which eventually led to chronic obstipation. This persistent obstruction can result in irreversible colonic dilation (megacolon) (Sherding 2003). Surgical widening of the pelvic canal has a good prognosis if performed less than 6 months after the onset of defecatory disturbances, ie, before the colon becomes severely distended (Matthiesen et al 1991, Schrader 1992, McKee and Wong 1994, Ferguson 1996). Surgical relief of pelvic stenosis in these chronic cases is unlikely to be of any benefit, with affected cats requiring continued medical treatment (Matthiesen et al 1991, Schrader 1992); however, all three cats in this series had obstipation and constipation for 6 months or more prior to surgery with excellent outcomes. It, therefore, seems that cats may benefit from this surgical procedure even if the clinical signs have been present for longer than 6 months. However, if the response to pelvic widening is poor because of irreversible colonic dilation, colectomy may be performed (Washabau and Holt 1999). Subtotal colectomy has been successfully used either alone or in conjunction with pelvic widening techniques in the treatment of cats with obstipation/megacolon secondary to pelvic narrowing (Webb 1985, Matthiesen et al 1991, Schrader 1992).

We believe that the SDO implant presented here has advantages over the other previously described implants, and it could be successfully used for the treatment of obstipation secondary to post-traumatic pelvic canal stenosis in the cat, if the colon motility is not permanently affected.