Introduction

Pelvic fractures are common and, due to the box-like structure of the pelvis, tend to be multiple; however, the high cancellous-cortical bone ratio of the bones involved and the stability provided by the surrounding musculature favour fracture healing. As pelvic fractures are normally the result of major trauma, concomitant injuries are common. These must be evaluated before formulating a therapeutic plan, as they may have major influences on patient management and potentially prognosis.

Anatomy

The pelvis is a box-like structure consisting of the two os coxae and the sacrum. The os coxa is composed of four distinct bones developmentally: the ilium, the ischium, the pubis, and the acetabular bone. All four bones form part of the acetabulum, and these bones fuse at approximately 12 weeks of age in dogs. In cats, data on fusion of the acetabular physis is limited, with only one report on the closure times of the ilioischial physis where closure time was reported as between 20–25 weeks.¹ The acetabulum, ilium, and sacroiliac joint are the main weightbearing structures of the pelvis and form the weightbearing axis. Palpable bony prominences useful both during physical examination and as surgical landmarks include the tuber coxae and tuber sacrale of the ilial wing and the tuber ischii.

The ilium is slimmer and straighter in the cat than in the dog. While the body of the ilium has a relatively thick cortical shell, the ilial wing is mainly composed of cancellous bone. This affects placement of implants in this region. The medial surface of the ilium articulates with the wing of the sacrum by a synchondrosis that forms the auricular surface. This synchondrosis has two parts - a fibrocartilaginous part and a synovial part. The synovial part is covered with hyaline cartilage, which is visible as a crescent-shaped structure on the sacral wing, often called the auricular cartilage. This is an important intraoperative landmark that is used when stabilising sacroiliac luxations.

The lumbosacral plexus and sciatic nerve are in close proximity to the pelvis and are therefore vulnerable to injury both during pelvic trauma and during surgery. The lumbosacral plexus consists of the intercommunicating branches of the last five lumbar nerves and the three sacral nerves. The resulting nerves travel ventrolateral to the sacrum and along the medial surface of the ilium from where the sciatic nerve separates to leave the pelvic canal caudodorsal to the hip joint. In general, lumbar nerves 3, 4 and 5 contribute to the femoral nerve; L3 and 4 to the genitofemoral; L4, 5 and 6 to the obturator; L6, 7 and S1 to the cranial gluteal; L6, 7, S1 and 2 to the sciatic; and S1, 2 and 3 to the pudendal. Damage to any of these nerves may result in significant neurological deficits.

Aetiology

The usual causes of pelvic fractures are road traffic accidents or falls from a height. Patterns of fracture have been investigated² and it has been shown that:

 The pelvic floor is fractured in 90% of cases.

 Sacroiliac luxation is present in 60% of cases and is bilateral in 27% of these.

 Ilial body fractures are present in 48.5% of cases.

 Sacral wing fractures are present in 2% of cases.

The most common combination of fractures is an ilial body fracture with concomitant pelvic floor fractures with/without a contralateral sacroiliac luxation.

Due to the high force required to fracture the pelvis, additional injuries are seen in a large number of cases. Thoracic trauma is common and is reported in up to 30% of cases. Urinary tract trauma is also seen, more commonly in dogs than in cats. Lumbosacral plexus damage is reported in 13.9% of cases³ and is most common in cases with sacroiliac luxation with pronounced cranial displacement or in cases with an ilial fracture.

Initial Assessment

Physical examination starts with a simple visual assessment of the patient. Assessing the respiratory pattern and general demeanour of the patient is important, given the high incidence of additional injuries. A detailed examination of the respiratory system, including thoracic compliance and thoracic auscultation, should be performed. The body wall should be assessed carefully for any evidence of rupture, and the abdomen palpated carefully, noting particularly the presence/absence, size, and turgidity of a palpable bladder. A rectal exam may be performed, noting the presence of any sharp bony fragments in the area, the degree of pelvic canal narrowing, and the presence of anal tone.

A detailed neurological examination should be carried out, including:

 Observation of ambulation, looking for evidence of paresis, plantigrade stance, and tail movement

 Pelvic limb postural reactions

 Segmental reflexes, including withdrawal reflex, patellar reflex, perineal reflex

 Assessment of bladder function

 If concern exists regarding a potential tail pull injury, tail nociception and perineal nociception should also be assessed

The initial workup required for each cat prior to management of the pelvic fractures varies depending on case presentation. For the majority of cases, the tests below are appropriate to provide a minimum database:

 Thoracic radiography

 Abdominal radiography or ultrasonography

 Urinary contrast study

 Haematology and serum biochemistry

When to Repair?

While stabilisation of the patient takes precedence, if surgery is to be performed, every effort should be made to stabilise pelvic fractures within five days of injury, as delaying beyond this time can lead to significant difficulties in achieving accurate fracture reduction. High-quality radiography is generally sufficient to allow classification of fractures and planning of management, but in particularly complex cases with acetabular and sacral fractures, computed tomography can be beneficial. Fractures of the pelvis are divided into sacroiliac luxation, fractures of the body of the ilium, acetabular fractures, pelvic floor fractures, and fractures of the pelvic margin (ilial wing or ischial tuberosity). The decision for conservative or surgical treatment largely depends upon whether the weight-bearing components of the pelvis are affected, whether there is significant pelvic canal narrowing, and whether there is evidence of neurological injury.

It is important to preserve the weight-bearing axis of the pelvis by repairing fractures or luxations of the sacroiliac joint, ilial body, and acetabulum. Repair of these three structures usually allows an animal to bear weight on the affected limb soon after surgical stabilisation. Repair of these areas also minimises the risks of malunion, delayed union, and pelvic canal narrowing. Fractures of the non-weight-bearing elements of the pelvis (the pelvic floor, ilial wing, and ischium) can often be treated conservatively; however, there are exceptions to this.

Other indications for surgical intervention, regardless of the bone affected and configuration, include:

 Patient is non-ambulatory after 3 days of conservative management

 Extreme pain, which can indicate nerve entrapment or severe instability

 Fractures of the ischial tuberosity which are clinically disabling

Why to Repair?

Many veterinarians believe that most pelvic fractures can be managed conservatively; however, no long-term studies have been performed to support this. While many cases will do well with conservative management, there are several potential benefits to performing surgical stabilisation in appropriate cases, including:

 Early stabilisation alleviates pain associated with the injury and allows the patient to return to function earlier.

 In cases of neurological entrapment, surgery will allow identification of the area of compromise and release of the affected nerve.

 In cases where multiple injuries are present, particularly affecting multiple limbs, surgery will facilitate recovery.

 In cases with pelvic canal narrowing, surgery will re-establish the pelvic canal so as to avoid constipation, obstipation, and potentially development of megacolon.

Conservative Treatment

Conservative treatment is applicable for cases where:

 There is less than 45% pelvic canal narrowing

 The patient is ambulatory

 The patient is not unduly painful

 There are financial concerns

Patients should be confined to a cage for 6 weeks, with short walks on the lead for toilet purposes only, and restricted to activity indoors for another 3–6 weeks. Cages should be well padded with dirty bedding changed promptly. If the patient becomes soiled or wet, regular and frequent bathing and drying should be performed to prevent scalding and pressure sores.

Appropriate analgesia is essential to improve overall wellbeing, to encourage early weightbearing, and to allow physiotherapy where appropriate. While opioids can be used while the patient is in the hospital, NSAIDs, tramadol, gabapentin, codeine, and amantadine are all appropriate analgesic options following discharge, as long as the patient has no systemic contraindications.

Inability or unwillingness to get up can result in urinary retention and obstipation, and in these cases gentle manual expression of the bladder or placement of an indwelling urinary catheter and use of faecal softeners or enemas may be required. It is important to prompt owners to carefully monitor urination and defaecation when the patient is discharged. Many of these patients, particularly cats, will not groom themselves, so grooming and general nursing care are also important.

Physical therapy can be of great assistance in these patients in terms of maintaining muscle mass and range of motion and encouraging weightbearing. A balanced physical therapy plan is important, as different exercises achieve different end results. For example, passive range-of-motion exercises are important in maintaining range of motion, but will not assist with maintaining muscle mass. Rehabilitation should be started as soon as comfort level allows with cryotherapy and passive range-of-motion exercises. Sling therapy can also be started early, which can have positive psychological benefits for the patient, as it enables them to be in a more normal position and to start some assisted active exercise. Water treadmill or hydrotherapy can be considered if the patient will tolerate this. Radiographs should be repeated and osseous union confirmed prior to allowing a gradual return to normal activity.

References

1.  Houlton JEF, McGlennon NJ. Castration and physeal closure in the cat. Vet Rec. 1992;131:466–467.

2.  Bookbinder PF, Flanders JA. Characteristics of pelvic fracture in the cat. Vet Comp Orthop Traumatol. 1992;5:122–127.

3.  Bohmer E. Beckenfrakturen and luxationen bei der Katze. Munchen: Ludwig-Maximilians-Universitat; 1985.