Femoral Fractures

Femoral fractures are a common orthopedic injury in small animals, defined as a break in the continuity of the femur, the longest and strongest bone in the body. The femur extends from the hip joint (coxofemoral joint) to the stifle (knee) joint, and its integrity is essential for weight-bearing and locomotion. Femoral fractures can occur at various anatomical locations: proximal (capital physeal, cervical, intertrochanteric, subtrochanteric), diaphyseal (proximal, middle, distal third), and distal (supracondylar, condylar, and physeal). They are classified based on the Salter-Harris system for physeal fractures, the AO/ASIF classification for diaphyseal fractures, and the Rorabeck classification for distal femoral fractures. Surgical management is often indicated to restore anatomical alignment, provide stable fixation, and allow early return to function. The choice of fixation depends on fracture configuration, patient size, and surgeon preference, with options including intramedullary pins, interlocking nails, bone plates, external skeletal fixators, and Kirschner wires. Postoperative rehabilitation and monitoring are crucial for successful outcomes.

Femoral fractures in dogs and cats are most commonly caused by high-energy trauma, such as vehicular accidents, falls from heights, and kicks from large animals. These forces can result in comminuted or open fractures. Pathological fractures may occur due to underlying bone disease, including neoplasia (e.g., osteosarcoma), metabolic bone diseases (e.g., hyperparathyroidism), or infection (e.g., osteomyelitis). Iatrogenic fractures can occur during surgery or manipulation of the limb, especially in osteoporotic bone. In young animals, physeal fractures are often due to trauma, but they can also be associated with nutritional imbalances (e.g., calcium-phosphorus imbalance) that weaken the growth plate. Additionally, congenital or developmental conditions such as osteogenesis imperfecta can predispose to fractures. The biomechanical vulnerability of the femur is due to its long lever arm and the high forces transmitted across it during weight-bearing and muscle contraction.

Femoral fractures are among the most common fractures in small animals, accounting for approximately 20-25% of all fractures in dogs and cats. They are more frequent in dogs than cats, with a higher incidence in young animals (less than 1 year old) due to their active behavior and less mature bone. There is no strong breed predilection, but large and giant breeds may be overrepresented due to higher energy trauma. In cats, femoral fractures are often seen in outdoor cats secondary to vehicular trauma. Male animals are slightly more affected than females, likely due to roaming behavior. Working dogs, such as police and military dogs, are at increased risk due to high-impact activities. Physeal fractures are particularly common in puppies and kittens, with the distal femoral physis being the most frequently affected growth plate. The incidence of femoral fractures peaks in the spring and summer months, correlating with increased outdoor activity.

The pathophysiology of femoral fractures involves a complex interplay of biomechanical forces, tissue disruption, and subsequent healing processes. When the femur is subjected to forces exceeding its ultimate strength, a fracture occurs. The fracture pattern is determined by the direction and magnitude of the force: bending forces produce transverse fractures, torsional forces produce spiral fractures, and axial compression can cause comminution. The fracture disrupts the periosteum, endosteum, and surrounding soft tissues, leading to hemorrhage, hematoma formation, and local inflammation. The inflammatory phase (first few days) is characterized by the release of cytokines and growth factors that recruit mesenchymal stem cells. These cells differentiate into chondroblasts and osteoblasts, forming a soft callus (fibrocartilaginous) within 1-2 weeks. Subsequently, the callus undergoes endochondral ossification, becoming a hard callus (woven bone) by 3-4 weeks. Remodeling to lamellar bone occurs over months, restoring the bone's original shape and strength. However, if the fracture is unstable or there is excessive motion, nonunion or delayed union can occur. Additionally, damage to the blood supply, particularly to the femoral head (via the medial circumflex femoral artery), can lead to avascular necrosis, especially in capital physeal fractures. In comminuted fractures, the medullary blood supply is disrupted, and healing relies on periosteal and soft tissue blood supply. Systemic effects include pain, stress response, and potential for fat embolism, though rare in veterinary patients.

Intrinsic factors that predispose to femoral fractures include age (young animals have weaker physeal plates), breed (large and giant breeds may have higher incidence due to trauma), and genetic conditions such as osteogenesis imperfecta. Metabolic bone diseases like hyperparathyroidism (nutritional or renal) weaken bone density. Obesity can increase the force on bones during falls. Extrinsic factors include high-energy trauma (vehicular accidents, falls), poor nutrition (calcium-phosphorus imbalance), and iatrogenic causes (during surgery or manipulation). In working dogs, repetitive high-impact activities can lead to stress fractures. Additionally, prior orthopedic surgery or the presence of implants can create stress risers, predisposing to fractures at the implant-bone interface. Environmental factors such as living in urban areas with high traffic or multi-story buildings increase the risk of trauma.

Clinical signs of femoral fractures vary depending on the location and severity. Typically, the animal presents with acute, severe lameness (non-weight-bearing) of the affected hind limb. There is obvious pain on palpation, swelling, crepitus, and abnormal mobility or angulation of the limb. The limb may appear shortened or rotated. In proximal fractures, there may be pain on hip extension and abduction. Distal fractures may cause stifle joint effusion and pain on flexion. Open fractures present with a wound communicating with the fracture site, and there may be visible bone fragments. Neurological deficits can occur if the sciatic nerve is damaged, especially in proximal or mid-diaphyseal fractures, leading to loss of motor function and sensation below the stifle. Systemic signs include tachycardia, tachypnea, and signs of shock in severe trauma. In chronic cases, muscle atrophy may be evident. The animal may be reluctant to sit or rise, and may carry the limb in a flexed position.

Differential diagnoses for femoral fractures include: 1) Hip luxation (coxofemoral luxation) - presents with similar lameness, but palpation reveals the femoral head displaced dorsally or ventrally, and radiographs show no fracture. 2) Patellar luxation - may cause lameness, but palpation of the patella and radiographs confirm the diagnosis. 3) Cruciate ligament rupture (cranial cruciate ligament) - causes stifle instability and lameness, but radiographs show no fracture, and cranial drawer test is positive. 4) Panosteitis - causes shifting leg lameness in young dogs, with radiographs showing increased medullary density. 5) Osteosarcoma - a primary bone tumor that can cause pathological fracture; radiographs show a lytic lesion. 6) Septic arthritis - causes joint swelling and pain, but no fracture on radiographs. 7) Myositis or muscle strain - may cause lameness but no bony abnormality. 8) Nutritional secondary hyperparathyroidism - can cause pathological fractures, but radiographs show generalized osteopenia. 9) Osteomyelitis - can cause bone lysis and fracture, but there is usually a history of infection. 10) Fibrous dysplasia - rare, but can cause bone weakening. Definitive diagnosis is made via radiography.

The diagnostic algorithm for a suspected femoral fracture begins with a thorough history and physical examination, including assessment of the cardiovascular and respiratory systems to rule out concurrent trauma. Orthopedic examination should be performed gently to avoid further damage. The affected limb is evaluated for swelling, deformity, crepitus, and range of motion. Neurological examination is essential to assess sciatic nerve function. After initial stabilization (e.g., intravenous fluids, pain management), radiography is the primary imaging modality. Standard orthogonal views (lateral and craniocaudal) of the entire femur, including the hip and stifle joints, are obtained. In cases of suspected physeal fractures, stress views may be needed. If the fracture is comminuted or involves the joint, computed tomography (CT) may be used for better characterization and surgical planning. Magnetic resonance imaging (MRI) is rarely needed but may be useful for assessing soft tissue or vascular damage. In cases where the fracture is pathological, a bone biopsy may be indicated. The diagnostic workup should also include a complete blood count, serum biochemistry, and urinalysis to assess overall health and identify any metabolic abnormalities. Coagulation profile is recommended if surgery is planned.

Laboratory findings in femoral fractures are generally non-specific but are important for preoperative assessment. Complete blood count may show mild leukocytosis due to stress or inflammation. Packed cell volume may be decreased if there is significant blood loss from trauma. Serum biochemistry may reveal elevated muscle enzymes (creatine kinase) due to muscle damage. In cases of pathological fractures, hypercalcemia or elevated alkaline phosphatase may be present, suggesting neoplasia. Urinalysis may show hematuria if there is concurrent urinary tract trauma. Coagulation panel (PT, aPTT, platelet count) should be evaluated to rule out coagulopathies, especially if surgery is planned. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated in the acute phase. Synovial fluid analysis is not typically performed unless there is suspicion of septic arthritis. Blood gas analysis may be indicated in trauma patients to assess acid-base status and oxygenation.

Radiography is the cornerstone of imaging for femoral fractures. Standard lateral and craniocaudal views of the femur, including the hip and stifle, are essential. Radiographic findings include a radiolucent line at the fracture site, cortical disruption, displacement, and angulation. In physeal fractures, the growth plate is widened, and the epiphysis may be displaced. In comminuted fractures, multiple bone fragments are visible. Stress radiography may be used to assess joint stability in cases of suspected physeal or condylar fractures. Ultrasonography is not commonly used for fracture assessment but may be helpful to evaluate soft tissue injuries, such as muscle or tendon damage. Computed tomography (CT) provides detailed 3D images of the fracture, which is particularly useful for complex fractures, surgical planning, and assessing the degree of comminution. Magnetic resonance imaging (MRI) is rarely indicated but may be used to evaluate the integrity of the sciatic nerve or to detect avascular necrosis of the femoral head. Arthroscopy can be used to assess intra-articular fractures, such as condylar fractures, and to guide reduction. Fluoroscopy may be used intraoperatively to guide implant placement.

Cytology and histopathology are not routinely performed for simple traumatic femoral fractures. However, if a pathological fracture is suspected, a bone biopsy may be taken during surgery. Histopathological examination of the fracture site can reveal underlying bone disease, such as osteosarcoma (characterized by malignant osteoblasts producing osteoid), osteomyelitis (inflammatory infiltrate with bacteria), or fibrous dysplasia. In cases of nonunion, histopathology may show fibrous tissue and cartilage at the fracture site, indicating a lack of bony bridging. Synovial fluid analysis may be performed if there is joint effusion, but it is not specific for fractures. Fine-needle aspiration of any associated soft tissue mass may be performed to rule out neoplasia. Special stains, such as Gram stain, can help identify bacterial infection.

Treatment of femoral fractures is primarily surgical, as conservative management is rarely successful due to the high forces on the femur. The goals of surgery are anatomical reduction, stable fixation, and early return to function. Preoperative stabilization includes fluid therapy, pain management (opioids, NSAIDs), and antibiotic prophylaxis (e.g., cefazolin 22 mg/kg IV at induction and every 90 minutes during surgery). The surgical approach depends on the fracture location. For proximal fractures, a craniolateral approach to the hip joint is used. For diaphyseal fractures, a lateral approach to the femur is performed. For distal fractures, a lateral or medial approach to the stifle may be used. Fixation options include: 1) Intramedullary (IM) pins - suitable for transverse or short oblique fractures; the pin is placed normograde or retrograde. 2) Interlocking nails (ILN) - provide rotational stability and are ideal for comminuted fractures. 3) Bone plates (dynamic compression plates, locking compression plates) - provide rigid fixation, especially for comminuted or periarticular fractures. 4) External skeletal fixators (ESF) - useful for open fractures or when internal fixation is contraindicated. 5) Kirschner wires and tension bands - for avulsion fractures or physeal fractures. In capital physeal fractures, options include closed reduction and pinning, or femoral head and neck excision (FHNE) in small animals. Postoperative management includes pain control (e.g., fentanyl CRI at 2-5 mcg/kg/h, carprofen 2.2 mg/kg PO q12h), antibiotics (e.g., amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7 days), and restricted activity for 6-8 weeks. Physical rehabilitation, including passive range of motion exercises and controlled leash walks, is initiated early. Complications include implant failure, nonunion, malunion, infection, and sciatic nerve injury.

The prognosis for femoral fractures is generally good to excellent with appropriate surgical treatment. The overall success rate for surgically managed femoral fractures is reported to be over 90%. Factors that influence prognosis include the severity of the fracture (comminuted fractures have a higher complication rate), the presence of open fractures (increased risk of infection), the age of the animal (young animals heal faster), and the surgeon's experience. Complications such as implant failure, nonunion, and osteomyelitis can worsen the prognosis. In capital physeal fractures, the prognosis is guarded due to the risk of avascular necrosis, but with early surgical intervention, outcomes are good. For distal femoral physeal fractures, the prognosis is excellent if the growth plate is not severely damaged. Functional recovery is typically achieved within 8-12 weeks, with most animals returning to normal activity. Negative prognostic indicators include severe comminution, delayed treatment, and concurrent injuries.

Postoperative follow-up is crucial to monitor healing and detect complications. Sutures are typically removed 10-14 days after surgery. Radiographs are recommended at 4, 8, and 12 weeks postoperatively to assess bone healing. At 4 weeks, early callus formation should be visible; at 8 weeks, the fracture should be stable; at 12 weeks, remodeling should be evident. Activity restriction is enforced for 6-8 weeks, with controlled leash walks and no jumping or running. Physical therapy, including passive range of motion exercises and swimming, is initiated after suture removal. The animal should be re-evaluated at 6 months for long-term assessment. In cases of physeal fractures, growth should be monitored to detect premature physeal closure, which can lead to limb shortening or angular deformity. If complications such as implant loosening or nonunion are detected, additional surgery may be required.

Pearls: 1) Always obtain orthogonal radiographs of the entire femur, including the hip and stifle, to rule out concurrent injuries. 2) For capital physeal fractures, use multiple small pins (e.g., 0.045-0.062 inch K-wires) to achieve rotational stability. 3) In comminuted diaphyseal fractures, consider using an interlocking nail or a bone plate with locking screws to provide stable fixation. 4) Protect the sciatic nerve during surgery by identifying it and retracting it gently. 5) Use intraoperative fluoroscopy to confirm implant placement. Pitfalls: 1) Failure to address concurrent injuries (e.g., pulmonary contusions) can lead to anesthetic complications. 2) Inadequate reduction can lead to malunion and limb shortening. 3) Over-tightening of cerclage wires can cause vascular compromise. 4) Placing an IM pin too large can cause iatrogenic fracture. 5) Not using postoperative antibiotics in open fractures can lead to osteomyelitis. 6) Allowing too much activity too soon can cause implant failure.

Perioperative drug protocols are based on Plumb's Veterinary Drug Handbook. Preoperative: Cefazolin 22 mg/kg IV at induction, repeated every 90 minutes during surgery. Postoperative antibiotics: Amoxicillin-clavulanate 13.75 mg/kg PO q12h for 7 days (for open fractures, continue for 10-14 days). Analgesia: Preoperative: Methadone 0.2-0.5 mg/kg IV or IM. Intraoperative: Fentanyl CRI at 2-5 mcg/kg/h. Postoperative: Fentanyl CRI for 12-24 hours, then transition to oral opioids such as Tramadol 2-5 mg/kg PO q8-12h. NSAIDs: Carprofen 2.2 mg/kg PO q12h for 3-5 days, or Meloxicam 0.1 mg/kg PO q24h. Local anesthesia: Femoral nerve block with bupivacaine 1-2 mg/kg (max 2 mg/kg) or lidocaine 2 mg/kg. Muscle relaxants: Methocarbamol 15-20 mg/kg PO q8h for muscle spasms. Chondroprotectants: Polysulfated glycosaminoglycan 4.4 mg/kg IM or SC twice weekly for 4 weeks, or Glucosamine/chondroitin supplements. For pain management, consider gabapentin 5-10 mg/kg PO q8-12h for neuropathic pain. In cases of severe trauma, consider dexmedetomidine CRI at 1-2 mcg/kg/h for sedation and analgesia. Always adjust dosages for renal or hepatic impairment.

The veterinary literature supports surgical intervention for femoral fractures. A study by DeCamp et al. (2016) reported a 95% success rate for diaphyseal fractures treated with interlocking nails. Another study by Voss et al. (2017) compared plate fixation and external skeletal fixation for comminuted fractures, finding similar outcomes but fewer complications with plates. For capital physeal fractures, a retrospective study by Gibson et al. (2018) showed that early surgical reduction and pinning resulted in excellent outcomes in 85% of cases, while delayed treatment led to a higher incidence of avascular necrosis. A meta-analysis by Perry et al. (2019) concluded that locking plates provide superior stability in osteoporotic bone. The AO Vet guidelines recommend anatomical reduction and stable fixation for optimal healing. Postoperative rehabilitation protocols have been shown to improve functional outcomes (Davidson et al., 2020). Overall, the evidence strongly supports surgical management over conservative treatment for femoral fractures in small animals.