Introduction

Fractures of the pelvis are divided into sacroiliac luxation, fractures of the ilial body, acetabular fractures, pelvic floor fractures, and fractures of the pelvic margin. 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.

The two hemipelves are connected to each other via the pelvic floor. In some cases, fracture reduction and stabilisation of one hemipelvis can result in adequate reduction of the contralateral side. However, the pelvic floor is damaged in 90% of cases, and bilateral injuries with concurrent fractures of the pelvic floor result in marked instability of both hemipelves, often necessitating bilateral fracture or luxation repair. If bilateral surgeries are to be performed, the side where anatomic reduction is most important is performed first. If unilateral neurological deficits are evident, the affected side should be operated first to prevent further nerve entrapment during manipulation of the contralateral side.

Fractures of the Ilium

Ilial fractures can be divided into simple transverse, long oblique, and comminuted, with long oblique and comminuted being most common. The caudal fragment tends to displace medially and ventrally.

The most common form of fixation for ilial fractures is bone plating, but lag screw fixation, pins and wires, and external skeletal fixation (ESF) have all been used. The cortices of the ilium are very thin, particularly in the ilial wing, and this contributes to the high incidence of screw loosening following ilial fracture stabilisation using bone plates. There are four ways to reduce this:

 Position the plate along the ventral border of the ilium

 Insert cranially located screws across the sacroiliac joint into the sacrum

 Use of locking plates and screws

 In cats, because the ilium is straighter, it is possible to apply the plate along the dorsal surface

A lateral approach to the ilium with roll-up of the gluteal muscles is suitable for lateral plating, placement of lag screws, or use of pins and wires. For dorsal plating, either a lateral or a dorsal approach can be used. For fractures in close proximity to the acetabulum, a cranial approach to the hip joint can be combined with the lateral approach if necessary.

The caudal fragment normally has to be levered up in a lateral and dorsal direction, but care must be taken to ensure that the sciatic nerve and lumbosacral plexus are not damaged. If the coxofemoral joint is intact, this can sometimes be achieved by placing bone-holding forceps on the greater trochanter and using this as a leverage point.

The plate is contoured to the lateral surface of the ilium and positioned along the ventrolateral border. A minimum of three screws should be placed in both the cranial and caudal fragments. The use of T-plates or L-plates can facilitate this where the caudal fragment is short. Alternatively, double lateral plating can be performed. For dorsal plating, a plate length is selected which allows placement of at least three screws both cranially and caudally, and the plate is contoured with a slight concave bend. When placing the screws over the acetabulum, the drill bit is aimed to exit the medial cortex of the pelvis.

Fractures of the Acetabulum

Acetabular fractures are demanding to treat since any displacement of the articular surface must be perfectly reduced and rigidly immobilised to ameliorate development of degenerative joint disease. Plate osteosynthesis is the most widely applied stabilisation method. If anatomic reconstruction or adequate stability is not achievable, such as in severely comminuted fractures, femoral head and neck excision may be necessary.

There are many different approaches to the acetabulum. For exposure of simple fractures affecting the cranial portion, the craniolateral approach to the hip is generally adequate. For fractures of the middle or caudal acetabulum that only require a short plate or a pin and tension band wire, a dorsal intergluteal approach may be sufficient. For comminuted or caudal fractures where greater exposure is needed, an osteotomy of the greater trochanter or gluteal tenotomy is required.

The most challenging part of the surgery is often fracture reduction. The caudal fragment tends to distract and rotate ventrally. Placing a K-wire or bone-holding forceps on the ischial tuberosity helps with manipulation of the caudal fragment. If the caudal fragment is attached to the round ligament, then manipulation of the greater trochanter and hip joint may also assist. In order to maintain reduction during application of definitive fixation, a temporary K-wire can be placed across the fracture, or pointed reduction forceps can be used.

Simple acetabular fractures may be immobilised with lag screws and/or K-wires and a figure-of-eight tension band. The dorsal aspect of the acetabulum has a strong tension aspect such that large implants are not required. However, most acetabular fractures are best stabilised using reconstruction plates or specially designed acetabular plates positioned dorsally. Perfect plate contouring is necessary when using non-locking technology to retain anatomic reduction, and screws are directed ventromedially so as not to penetrate the articular surfaces. Locking plates have advantages in acetabular fracture repair in that accurate plate contouring is less critical, monocortical screws may be used, and they provide better stability when only two screws can be engaged per segment. However, most locking plate constructs do not allow direction of the screws away from the articular surface. For simple transverse fractures, shorter plates can be used with two screws cranial and caudal to the fracture. For oblique or multifragmentary fractures, longer plates are required.

Sacroiliac Luxation

Since the sacroiliac joint essentially connects the pelvic limb to the axial skeleton, these injuries can be very disabling. Minimally displaced sacroiliac luxations can be treated conservatively, especially if they are unilateral, and this has been reported to result in almost complete recovery within six weeks.¹ A general rule is that displacement of <50% of the length of the joint allows conservative treatment. The degree of instability of the ilium is also important, as assessed by palpation, normally with the patient sedated or anaesthetized. Cases with marked instability are generally associated with more discomfort and are less likely to respond promptly to medical management. Internal fixation is recommended for cases with bilateral sacroiliac luxation, marked instability, those with complex injuries and involvement of the contralateral limb, and those with medial displacement of the contralateral hemipelvis.

Following accurate reduction, the most commonly used stabilisation method is insertion of a lag screw from the lateral surface of the ilial wing across the sacroiliac joint into the sacral body. The screw must enter the body of the sacrum rather than the thin ventral sacral wing, and it must pass ventral to the neural canal. Other methods include insertion of a positional screw from a ventroabdominal approach, ESF, transilial pins, transsacral screws, tension band techniques, and transilial bolts.

The dorsolateral approach to the sacrum and ilial wing is the best approach for lag screw fixation, as it allows the best visualisation of the sacroiliac joint. The lag screw should penetrate at least 60% of the width of the sacrum to prevent screw loosening.^2,3 It is important to know the regional anatomy and to follow anatomical guidelines for placement of these screws, as the size of the area for safe screw insertion is small (<0.5 cm² in a cat).

The patient should be positioned either in sternal or lateral recumbency. A dorsolateral approach to the sacroiliac joint is performed and the luxation is visualised. The wing of the ilium can be carefully ventrally depressed using a Hohmann retractor to enhance visualisation of the sacral body. A thread hole is drilled into the sacral body with the entrance point located just cranial to the crescent-shaped hyaline cartilage and slightly dorsal to the geometric centre of the sacroiliac joint. The hole is drilled perpendicular to the long axis of the sacrum across at least 60% of sacral width. The thread is then cut. A glide hole is drilled from lateral to medial through the ilial wing. The hole is located slightly ventral to the centre of the ilial wing height and at a distance of 60–70% of the sacral tuber length. The exit point on the medial aspect of the ilium can also be identified as the palpably slightly irregular articular surface. The screw length is premeasured from preoperative radiographs to a minimum of 60% of sacral width. The screw is inserted from lateral through the ilial wing until it emerges on the medial surface. The luxation is then reduced, and the screw advanced into the predrilled hole in the sacral body. Sacroiliac luxations can also be treated in a minimally invasive fashion in facilities that have access to intraoperative fluoroscopy.⁴

Pelvic Floor Fractures

The pelvic floor is fractured in 90% of patients with pelvic fractures. In the vast majority of cases, stabilisation of concurrent fractures/luxations of the weight-bearing axis results in sufficient stability and allows healing of pelvic floor fractures without specific treatment. Occasionally it is necessary to stabilise a debilitating fracture of the tuber ischii with a tension band technique. In very rare circumstances, when the pattern of injuries renders the pelvis extremely unstable, repair of pelvic floor fractures may be considered. Symphyseal separations can be repaired with hemicerclage wires while plate osteosynthesis is necessary for fractures of the pubis and ischium.

References

1.  Denny HR. Pelvic fractures in the dog: a review of 123 cases. J Small Anim Pract. 1978;19:151–166.

2.  Burger M, Forterre F, Waibl H, et al. Sacroiliac luxation in the cat. Part 2: cases and results. Kleintierpraxis. 2005;5:287–297.

3.  De Camp CE, Braden TD. Sacroiliac fracture-separation in the dog: a study of 92 cases. Vet Surg. 1985;14:127–130.

4.  Maturello DM, Dejardin LM, Guiot LP, et al. Comparison of open reduction versus minimally invasive surgical approaches on screw position in canine sacroiliac lag-screw fixation. Abstract presented at 42nd annual conference of the Veterinary Orthopedic Society. Sun Valley, ID, USA; 2015.