Pelvic Fractures

Pelvic fractures are a common orthopedic injury in small animals, typically resulting from high-energy trauma such as vehicular accidents or falls. The pelvis is a ring-like structure composed of the ilium, ischium, pubis, and acetabulum, which together form the pelvic canal and provide attachment for the hindlimbs. Fractures can involve one or multiple segments, and may be classified as stable or unstable based on the integrity of the pelvic ring. Surgical management is indicated for fractures that cause significant pain, instability, or compromise the pelvic canal, leading to potential obstipation or neurological deficits. The goal of surgical intervention is anatomical reduction and rigid stabilization to restore normal pelvic dimensions, preserve joint function, and allow early return to weight-bearing.

The primary cause of pelvic fractures in dogs and cats is blunt trauma, most commonly from motor vehicle accidents, falls from heights, or kicks from large animals. Less common causes include gunshot wounds, bite wounds, and pathological fractures due to neoplasia or metabolic bone disease. The pelvis is particularly vulnerable to trauma due to its superficial location and the transmission of forces from the hindlimbs to the axial skeleton. The ilium, being the largest and most weight-bearing component, is frequently fractured, often with concurrent fractures of the pubis and ischium. Acetabular fractures are less common but can lead to degenerative joint disease if not anatomically reduced. In young animals, the growth plates of the ilium and ischium are weak points, making physeal fractures more likely. Iatrogenic fractures can occur during excessive manipulation or surgical approaches to the pelvis, especially in osteoporotic bone.

Pelvic fractures account for approximately 20-25% of all fractures in dogs and cats. They are most commonly seen in young to middle-aged animals, with a slight male predominance, likely due to increased roaming behavior. There is no strong breed predisposition, but large-breed dogs may be overrepresented in vehicular trauma. Cats are also commonly affected, often from falls (high-rise syndrome). Working dogs, such as those used for hunting or police work, may have a higher incidence due to increased exposure to trauma. Concurrent injuries are common, including thoracic trauma (pneumothorax, pulmonary contusions), abdominal trauma (uroabdomen, hernias), and other orthopedic injuries (e.g., sacroiliac luxation, femoral fractures). The presence of multiple injuries significantly impacts the overall morbidity and mortality.

The pelvis forms a rigid ring, and a fracture of one segment is often accompanied by a fracture or luxation of another segment to disrupt the ring. The biomechanical forces causing pelvic fractures include direct impact, axial loading, and shearing forces. The ilium, being the main weight-bearing bone, often fractures in a transverse or oblique pattern. Acetabular fractures can be classified according to the scheme of the AO/ASIF, with the most common being those involving the dorsal acetabular rim, which are critical for weight-bearing. Fractures of the pubis and ischium are often minimally displaced and may not require surgical fixation. However, displacement of the pelvic canal can lead to narrowing, causing obstipation or dystocia. Neurological deficits can occur due to trauma to the sciatic nerve, which runs caudal to the acetabulum, or the lumbosacral trunk. Additionally, trauma can cause hemorrhage into the pelvic canal, leading to hypovolemic shock. The inflammatory response to fractures includes local edema, hematoma formation, and activation of osteoclasts and osteoblasts for healing. In unstable fractures, excessive motion can delay healing and lead to nonunion or malunion.

Intrinsic factors include age (young animals have open physes, making them more prone to physeal fractures), breed (some breeds may have conformational differences in pelvic shape), and body condition (obesity may increase the risk of trauma due to reduced agility). Metabolic bone diseases such as nutritional secondary hyperparathyroidism or osteogenesis imperfecta can weaken bone, predisposing to fractures. Extrinsic factors include environmental hazards (e.g., roads, heights), owner management (e.g., allowing animals to roam), and prior orthopedic conditions that alter gait and increase fall risk. In working dogs, high-intensity activities may increase exposure to trauma. Additionally, iatrogenic factors such as improper handling during anesthesia or surgery can cause fractures in osteoporotic bone.

Clinical signs of pelvic fractures include acute onset of hindlimb lameness or non-weight-bearing, pain on palpation of the pelvis, crepitus, and swelling. Animals may be reluctant to stand or walk, and may adopt a crouched posture. There may be visible deformity or asymmetry of the pelvic region. Neurological deficits can manifest as proprioceptive deficits, reduced withdrawal reflex, or urinary/fecal incontinence if the cauda equina is involved. In cases of pelvic canal narrowing, signs of obstipation (straining to defecate) may be present. Concurrent injuries may cause additional signs such as dyspnea (pulmonary contusions), abdominal pain (uroabdomen), or shock. On physical examination, careful palpation of the pelvis may elicit pain and crepitus, but should be performed gently to avoid further displacement. Neurological examination is essential to assess sciatic nerve function, including deep pain perception.

Differential diagnoses for pelvic fractures include: 1) Sacroiliac luxation, which often occurs concurrently but can be isolated; 2) Hip luxation (coxofemoral luxation), which presents with a shortened limb and greater trochanter displacement; 3) Femoral head/neck fractures, which may mimic acetabular fractures; 4) Spinal fractures or disc disease, which can cause similar neurological deficits; 5) Pelvic neoplasia (e.g., osteosarcoma), which may present with pathological fracture; 6) Osteomyelitis, which can cause bone lysis and pain; 7) Myopathy or neuropathy (e.g., lumbosacral stenosis) causing hindlimb weakness; 8) Soft tissue trauma (e.g., muscle contusions) without fracture. Definitive diagnosis is made via imaging, but clinical signs and palpation can help differentiate.

The diagnostic workup for a suspected pelvic fracture begins with a thorough history and physical examination, including assessment of the cardiovascular and respiratory systems to identify life-threatening concurrent injuries. After stabilization, orthopedic and neurological examinations are performed. Radiography is the primary imaging modality, with ventrodorsal and lateral views of the pelvis. Additional oblique views may be needed to assess the acetabulum. If the patient is unstable, a single lateral view may be obtained initially. Advanced imaging such as computed tomography (CT) is increasingly used for complex fractures, providing 3D reconstructions that aid in surgical planning. CT is particularly useful for assessing the sacroiliac joint and pelvic canal dimensions. In cases with suspected neurological involvement, magnetic resonance imaging (MRI) may be indicated to evaluate the spinal cord and nerve roots. Exploratory surgery may be necessary if there is a suspicion of concurrent abdominal or thoracic injury. The diagnostic algorithm should be systematic to avoid missing concurrent injuries.

Laboratory findings in pelvic fractures are often nonspecific but may reflect concurrent trauma. A complete blood count may show anemia due to blood loss, or leukocytosis due to stress or infection. Serum biochemistry may reveal elevated muscle enzymes (creatine kinase) due to muscle trauma, and liver enzymes if there is concurrent hepatic contusion. Blood gas analysis may show metabolic acidosis due to shock or tissue hypoperfusion. Coagulation profiles (PT, aPTT, platelet count) are important to assess for coagulopathy, especially if there is significant hemorrhage. In cases of suspected uroabdomen, a urinalysis and creatinine measurement in abdominal fluid may be performed. Synovial fluid analysis is not typically indicated unless there is a joint effusion. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated but are not specific.

Radiography is the mainstay for diagnosing pelvic fractures. Ventrodorsal and lateral views are standard. The ventrodorsal view allows assessment of the ilial wings, acetabulum, and pubis, while the lateral view is useful for evaluating the sacrum and sacroiliac joint. Oblique views may be needed to better visualize the acetabulum. In cases of suspected sacroiliac luxation, a ventrodorsal view with the beam centered on the sacrum is helpful. Computed tomography (CT) provides superior detail and 3D reconstructions, which are invaluable for surgical planning, especially for complex acetabular fractures. CT can accurately measure pelvic canal diameter and detect subtle fractures. Magnetic resonance imaging (MRI) is reserved for cases with neurological deficits to assess nerve root compression. Ultrasonography may be used to evaluate the bladder and urethra for concurrent injury. Fluoroscopy can be used intraoperatively to guide reduction and implant placement.

Cytology and histopathology are not typically performed for pelvic fractures unless there is a suspicion of an underlying pathological process such as neoplasia or infection. If a bone biopsy is obtained during surgery, histopathology can differentiate between osteosarcoma, chondrosarcoma, and other tumors. In cases of osteomyelitis, culture and sensitivity of bone samples are essential. Joint fluid analysis may be performed if there is a concurrent joint effusion, but it is not routine. In general, the diagnosis of pelvic fractures is based on imaging, and tissue sampling is reserved for atypical cases.

Treatment of pelvic fractures can be conservative or surgical. Conservative management is reserved for minimally displaced, stable fractures that do not compromise the pelvic canal or joint function. This involves strict cage rest, analgesia, and supportive care. However, most pelvic fractures benefit from surgical stabilization to achieve anatomical reduction and early return to function. Surgical options include: 1) Internal fixation with plates and screws for ilial and acetabular fractures. For ilial fractures, a lateral approach is used, and a plate (e.g., 2.0-3.5 mm dynamic compression plate or locking plate) is applied to the lateral surface. Acetabular fractures require a dorsal approach to the hip joint, and a plate is contoured to the dorsal acetabular rim. 2) Sacroiliac luxation is treated with lag screws placed from the ilial wing into the sacral body. 3) Pubic and ischial fractures are often not fixed unless they cause pelvic canal narrowing. 4) External skeletal fixation may be used for highly comminuted fractures or as a temporary stabilization. 5) In cases of severe acetabular fractures with poor prognosis for joint function, femoral head and neck excision (FHNE) may be considered. Postoperative management includes pain control, antibiotics, and restricted activity for 6-8 weeks. Physical rehabilitation is important to regain muscle mass and joint mobility.

The prognosis for pelvic fractures is generally good to excellent with appropriate surgical intervention. For ilial fractures, the success rate is high, with most animals returning to normal function within 3-4 months. Acetabular fractures have a more guarded prognosis due to the risk of degenerative joint disease, but anatomical reduction and rigid fixation can lead to good outcomes. Complications include implant failure, infection, nonunion, malunion, and sciatic nerve injury. The presence of concurrent injuries, such as spinal trauma or uroabdomen, worsens the prognosis. Negative prognostic indicators include severe comminution, delayed surgical intervention, and postoperative infection. With proper management, the overall complication rate is low, and most animals regain acceptable limb function.

Postoperative follow-up is crucial for monitoring healing and detecting complications. Sutures are typically removed 10-14 days after surgery. Radiographs are taken immediately postoperatively to assess reduction and implant placement, and then at 4, 6, and 8 weeks to evaluate bone healing. Activity is restricted to short leash walks for the first 4 weeks, with gradual increase over the next 4 weeks. Physical therapy, including passive range of motion exercises and swimming, may be initiated after 2 weeks. Long-term follow-up at 6-12 months may be recommended to assess for degenerative joint disease, especially after acetabular fractures. Owners should be advised to monitor for signs of pain, lameness, or neurological deficits.

Pearls: 1) Always assess the entire pelvic ring; a fracture of one segment often indicates another injury. 2) Use a lateral approach to the ilium, preserving the gluteal muscles. 3) For acetabular fractures, achieve anatomical reduction to prevent DJD. 4) Use lag screws for sacroiliac luxation, ensuring proper placement into the sacral body. 5) Consider FHNE for severely comminuted acetabular fractures in small dogs and cats. Pitfalls: 1) Failing to identify concurrent injuries (e.g., uroabdomen, pneumothorax) can be fatal. 2) Inadequate exposure can lead to poor reduction and iatrogenic nerve damage. 3) Over-tightening screws can cause bone necrosis. 4) Not addressing pelvic canal narrowing can lead to obstipation. 5) Early weight-bearing without adequate stabilization can cause implant failure.

Perioperative antimicrobial prophylaxis: Cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery. Postoperative antibiotics are not routinely needed unless infection is present. Analgesia: Opioids such as hydromorphone 0.05-0.1 mg/kg IV or IM q4-6h, or fentanyl CRI at 2-5 mcg/kg/hr. NSAIDs such as carprofen 2.2 mg/kg PO q12h or meloxicam 0.1 mg/kg PO q24h, but avoid in patients with renal or gastrointestinal issues. Local anesthesia: Epidural with morphine (0.1 mg/kg) and bupivacaine (0.5-1 mg/kg) can provide excellent analgesia. Muscle relaxants: Methocarbamol 15-20 mg/kg PO q8h may be used for muscle spasms. Chondroprotectants: Polysulfated glycosaminoglycan (Adequan) 4.4 mg/kg IM twice weekly for 4 weeks may be considered for joint health. For patients with head trauma, mannitol 0.5-1 g/kg IV over 20 minutes may be used. Always adjust dosages based on patient status and concurrent medications.

Several studies have evaluated the outcomes of pelvic fracture management. A retrospective study by DeCamp et al. (1991) reported that surgical stabilization of ilial fractures resulted in excellent functional outcomes in 90% of dogs. Another study by Kaderly et al. (1995) found that acetabular fractures treated with open reduction and internal fixation had a good to excellent outcome in 75% of cases, with the main complication being DJD. A more recent study by Vnuk et al. (2004) compared conservative versus surgical treatment of pelvic fractures and found that surgical treatment led to faster return to function and fewer complications. The use of locking plates has been shown to provide superior stability in comminuted fractures (Koch et al., 2008). For sacroiliac luxation, a study by Tomlinson et al. (1999) demonstrated that lag screw fixation provides excellent outcomes. The AO Veterinary Expert Group has published guidelines for the management of pelvic fractures, emphasizing the importance of anatomical reduction and stable fixation. Overall, the evidence supports surgical intervention for most pelvic fractures to achieve optimal outcomes.