Assessment and management of pelvic fractures in dogs and cats (Proceedings)

Pelvic fractures are common, representing 20-30% of fractures in small animals. They are most commonly seen in young, healthy dogs and cats subsequent to being hit by car. Concurrent injuries to vital organs are very common, and should be addressed before definitive fracture management. Not all fractures require surgical correction, and many can heal well with conservative management. Appropriate assessment and management of pelvic fractures requires an understanding of the anatomy and biomechanics of the pelvis.

Presentation and Physical Examination

Patients with pelvic fractures may present with a mild to non weightbearing lameness. In some cases, they may be non-ambulatory. They typically present with a trauma history and almost always have a second injury, whether orthopedic or soft tissue. While pelvic fractures are painful and can result in significant blood loss, their stabilization comes second to treatment of immediately life-threatening injuries.

A thorough physical examination to rule out thoracic and abdominal injury is imperative. A minimum database of thoracic radiographs, complete blood count, serum chemistry, and urinalysis are also indicated. Some concurrent injuries are obvious on initial presentation. Others may be more insidious and may not be diagnosed until later in the hospitalization and recovery period, when they become more apparent. These include pulmonary contusions, diaphragmatic hernia, and urinary tract trauma. Urinary tract trauma is particularly common with pelvic fractures, and has been reported in over ⅓ of cases. A palpable bladder on physical examination or a visible bladder on abdominal radiographs do not necessarily rule out urinary tract trauma. If physical signs, urinalysis or serum chemistry suggest urinary tract compromise, further imaging by contrast studies or ultrasound may be indicated.

Physical examination of the pelvis should include assessment of pelvic symmetry, of the patient's ability to stand, of sacroiliac instability, and of pain on direct palpation. A rectal examination should be performed to assess for rectal perforation or pelvic canal narrowing. The hindlimbs should be evaluated for concurrent fractures, and the stifle and tarsus assessed for palpable instability. This is especially true for any animal that is non-ambulatory.

A complete neurologic examination is indicated, as peripheral nerve and nerve root injuries are common with pelvic fractures. Intact cutaneous sensation to the medial and lateral digits can help confirm integrity of the femoral and sciatic nerves and their spinal nerve roots. Use caution when interpreting myotactic reflexes and proprioceptive testing in pelvic trauma patients. Apparent deficits may musculoskeletal rather than neurologic injury. Trauma to sacral nerve roots may cause urinary incontinence. While incontinence may not be immediately apparent on examination, evaluation of perineal sensation, perineal reflex, and tail tone can help to evaluate sacral and caudal nerve roots. Fortunately, most neurologic deficits seen with pelvic fractures are transient. However loss of perineal sensation, anal tone, or hindlimb deep pain sensation are cause for cause for concern over recovery. This should be conveyed to the owner at initial evaluation.

Anatomy and Fracture Appearance

In conjunction with the sacrum, the pelvis forms a 'box-like' structure. It consists of the paired bones of the ilium, acetabulum, ischium, and pubis. Single pelvic fractures are rare; damage and displacement at one point of this structure usually requires displacement at a second point. The exceptions to this are: fractures of the medial acetabular wall, certain pelvic fractures in young animals, and ischial tuberosity fractures.

Treatment Planning

The decision to treat pelvic fractures surgically or medically is based on a combination of radiographic evaluation, physical examination findings, and client/patient factors. Because it is surrounded by a significant muscle mass, the pelvis is a good biological environment for fracture healing. Even displaced fractures that are managed medically rarely proceed to non-union. Nonetheless, in many cases surgery is indicated to maximize functional outcome, relieve discomfort, and accelerate return to activity.

A systematic review of radiographs is important for planning treatment. Ventrodorsal and lateral radiographs typically are sufficient, but cross-sectional imaging may be helpful, especially in examining the acetabulum and sacrum. When evaluating radiographs, particular attention should be paid to the weight bearing segment- the path that transfers weight bearing forces form the hindlimb to the spinal column. The weight bearing segment includes the femoral head/neck, acetabulum, ilium, sacroiliac joint, and sacrum. Fractures in the weight bearing segment are candidates for surgical repair. Those for which surgery is especially indicated are:

• acetabular fractures

• significantly displaced ilial fractures

• sacroiliac luxations which are unstable or are displaced >50%

• fractures with significant narrowing of pelvic canal

• weightbearing segment fractures in dogs with multiple limb fractures or bilateral pelvic fractures

Some non-weight bearing segment fractures may be candidates for surgery. These include pubic bone fractures with concurrent ventral abdominal hernia, and ischial tuberosity fractures.

In contrast, medical management is indicated for most pubic and ischial fractures. Other fractures for which medical management may be indicated are:

• minimally displaced ilial fractures

• minimally displaced sacroiliac luxations

• fractures with minimal pelvic canal narrowing

• longstanding fractures (>2weeks)

Surgical Management

In sacroiliac (S-I) luxations, the ilium is typically displaced craniodorsally as compared to the sacrum. The luxation is usually approached from dorsally, with the patient in lateral recumbency. This can be altered if bilateral repair is necessary (sternal recumbency) or approach to the ipsilateral ilium is needed (ventral approach). Caution should be taken with the approach and fracture manipulation, to avoid iatrogenic neurotrauma. Knowledge of the local anatomy is essential. Repair is performed by lag screw fixation of the ilium to the sacrum. The ilium is reflected ventrally and the threaded hole is drilled in the sacral body, just cranial to the c-shaped cartilage of the S-I joint. The glide hole is drilled in the ilium, based on landmarks on the lateral aspect of the ilium. S-I luxations can also be repaired using a closed technique with fluoroscopic guidance. Bilateral repairs can be achieved by repeating the technique on the contralateral side, or by placement a trans-ilial rod. Principle complications of S-I stabilization include implant failure, misdirection during screw placement, and nerve damage.

Ilial body fractures most often appear as oblique fractures, with the fracture line extending from cranioventral to caudodorsal. The ischium commonly is displaced medially, narrowing the pelvic canal. The ilium is approached laterally, by elevation of the gluteal muscles from ventral to dorsal. Reduction is achieved by a combination of traction, levering, and use of bone holding forceps. Most ilial fractures are stabilized by plate fixation. The plate should be precontoured to match the concavity of the cranial ilium, to create sufficient lateralization of the caudal segment and avoid pelvic narrowing. Ideally, three screws are placed on each side of the fracture. The principle complication with ilial fracture fixation is screw loosening/pullout and loss of reduction. Penetrating the sacrum with one of the cranial screws adds stability to the plate fixation and may diminish the risk of pullout of the cranial screws. In principle, long oblique fractures can be repaired using ventrodorsally directed lag screws or K-wires with hemicerclage wiring. However, in practice the large muscle mass and relatively narrow target for implant placement makes these techniques difficult.

Acetabular fractures are one of the most challenging fracture repairs in the canine. Their articular nature dictates precise anatomic reduction and rigid fixation to minimize the development of degenerative joint disease. Achieving this can be difficult due to the lack of exposure and poor visualization even with a maximal approach. Typically, either a dorsal approach with greater trochanteric osteotomy, or a caudal approach is used, depending on fracture location. Achieving reduction and maintaining reduction during plate placement is the most difficult aspect of the surgery. This can be facilitated by manipulation of the caudal segment via a separate approach to the ischial tuberosity, or by manipulation of the greater trochanter of the femur, provided the round ligament is still intact in the caudal segment. Once reduced, alignment can be maintained by Kirschner wires or pointed bone-holding forceps. Alternatively, use of mandibular reduction forceps has been described for achievement and maintenance of reduction. Fixation can be achieved using a variety of bone plates. Standard bone plates are challenging to contour to the dorsal acetabular rim, and may result in loss of anatomic reduction once applied. Location-specific acetabular plates require less contouring but remain a challenge to apply without loss of alignment. Stabilization using composite fixation of screws, orthopedic wire, and polymethylmethacrylate has been described. It exhibits similar biomechanical properties as plate fixation and may result in diminished loss of alignment during application. Newer technology locking plates and screws may have an application in acetabular fracture management as well. Principle complications of acetabular fracture fixation include implant failure, degenerative joint disease, and fracture malunion.