Salter-Harris Fractures

Salter-Harris fractures are a classification system for fractures involving the physis (growth plate) in skeletally immature animals. These fractures are unique to juvenile patients and represent a disruption of the endochondral ossification process. The classification, originally described by Robert B. Salter and W. Robert Harris in 1963, categorizes physeal injuries into five types (I-V) based on the anatomical location of the fracture line relative to the physis and epiphysis. Type I is a complete separation of the epiphysis from the metaphysis through the hypertrophic zone of the physis. Type II involves a fracture through the physis that extends into the metaphysis, creating a triangular metaphyseal fragment (Thurston-Holland fragment). Type III is a fracture through the physis that extends into the epiphysis, often involving the articular surface. Type IV is a fracture through the physis, metaphysis, and epiphysis, crossing the full thickness of the growth plate. Type V is a compression injury to the physis without an obvious fracture line, often leading to premature physeal closure. These fractures are clinically significant due to their potential to disrupt normal skeletal growth, leading to limb length discrepancies, angular limb deformities, and degenerative joint disease. Surgical management aims to restore anatomical alignment, preserve physeal function, and prevent long-term complications.

The primary etiology of Salter-Harris fractures is trauma, typically high-energy impact such as vehicular accidents, falls from heights, or kicks from large animals. The physis is biomechanically weaker than surrounding bone, ligaments, and tendons, making it a common site of failure in juvenile skeletons. In dogs and cats, the most frequently affected physis is the distal femoral physis, followed by the distal tibial, proximal humeral, and distal radial physes. The fracture occurs when forces exceed the tensile or shear strength of the physis, often during hyperextension or rotational stress. In some cases, iatrogenic trauma during difficult obstetric delivery or improper handling of neonates can cause physeal fractures. Additionally, pathological fractures can occur in the presence of metabolic bone diseases (e.g., nutritional secondary hyperparathyroidism, rickets) or neoplastic conditions (e.g., osteosarcoma) that weaken the physis. However, traumatic injury remains the overwhelming cause in clinical practice. The type of Salter-Harris fracture depends on the direction and magnitude of the force, with shear forces typically producing Type I or II, while compressive forces may lead to Type V injuries.

Salter-Harris fractures are most commonly diagnosed in dogs and cats between 4 and 10 months of age, coinciding with the period of rapid skeletal growth. The incidence is higher in large and giant breed dogs, such as Labrador Retrievers, Golden Retrievers, German Shepherds, and Rottweilers, due to their larger body mass and higher energy trauma exposure. Small breed dogs and cats are also affected but may present with lower-energy trauma. There is no significant sex predilection, although some studies suggest a slight male predominance due to increased roaming behavior and trauma risk. The distal femoral physis is the most commonly affected site, accounting for approximately 30-40% of all physeal fractures in dogs. Other common locations include the distal tibia, proximal humerus, distal radius/ulna, and proximal femur. In cats, the distal femoral and proximal tibial physes are frequently involved. Working and hunting dogs may have a higher risk due to increased activity and trauma exposure. The overall incidence of physeal fractures in juvenile dogs is estimated at 15-20% of all fractures, with Salter-Harris Type II being the most common type, followed by Type I and Type IV.

The pathophysiology of Salter-Harris fractures revolves around the unique structure of the physis, which is composed of distinct zones: resting, proliferative, hypertrophic, and provisional calcification. The hypertrophic zone is the weakest area, as the cartilage matrix is less mineralized and the cells are enlarged, making it susceptible to shear and tensile forces. In Type I and II fractures, the fracture line typically passes through the hypertrophic zone, sparing the germinal cells in the resting and proliferative zones, which are crucial for continued growth. This preservation of germinal cells often allows for continued growth if the fracture is properly reduced and stabilized. In Type III and IV fractures, the fracture line extends into the epiphysis, potentially damaging the articular cartilage and disrupting the blood supply to the epiphysis, which can lead to avascular necrosis and premature physeal closure. Type V fractures involve a compression injury that crushes the physis, often without visible displacement, leading to ischemic damage to the germinal cells and subsequent premature physeal closure. The systemic inflammatory response to trauma can also contribute to local edema, vascular compromise, and delayed healing. If left untreated or improperly managed, Salter-Harris fractures can result in malunion, nonunion, angular limb deformities, limb length discrepancies, and degenerative joint disease due to articular surface incongruity.

Intrinsic predisposing factors include age (skeletally immature animals), breed (large and giant breeds with rapid growth rates), and genetic predisposition to certain conformational traits that may increase stress on specific physes. Nutritional factors, such as excessive calcium or energy intake during growth, can lead to osteochondrosis and weakened physis. Extrinsic factors include high-energy trauma, such as vehicular accidents, which are more common in free-roaming or working dogs. Poor management practices, such as allowing young animals to engage in excessive jumping or strenuous exercise, can increase the risk. Prior orthopedic injuries or surgeries may also predispose to subsequent physeal fractures due to altered biomechanics. Additionally, iatrogenic factors, such as improper handling during obstetric procedures or overly aggressive physical therapy, can cause physeal injury. Metabolic diseases, including hyperparathyroidism and rickets, can weaken the bone and physis, making them more susceptible to fracture. Finally, the presence of underlying bone pathology, such as neoplasia or infection, can predispose to pathological fractures through the physis.

Clinical signs of Salter-Harris fractures vary depending on the location and severity of the fracture. The most common presentation is acute lameness, often non-weight-bearing, following a traumatic event. The affected limb may be held in a flexed or abnormal position, and there is obvious swelling, pain, and crepitus on palpation over the physis. In Type I fractures, the epiphysis may be completely separated, leading to instability and a palpable gap. Type II fractures often present with a visible or palpable metaphyseal fragment. Type III and IV fractures may involve the joint, resulting in hemarthrosis, joint effusion, and severe pain on joint manipulation. Type V fractures may present with minimal clinical signs initially, but progressive lameness and angular deformity develop over time due to premature physeal closure. Systemic signs such as tachycardia, tachypnea, and depression may be present if there is concurrent trauma. Neurological deficits may be observed if the fracture is near a peripheral nerve, such as the sciatic nerve in proximal femoral fractures. In open fractures, there may be visible bone exposure and signs of infection. A thorough orthopedic examination should include assessment of the entire limb, as multiple fractures may be present in polytrauma cases.

Differential diagnoses for Salter-Harris fractures include: 1) Physical separation without fracture (epiphysiolysis), which is essentially a Salter-Harris Type I injury but may be considered separately in mild cases. 2) Apophyseal avulsion fractures, such as avulsion of the tibial tuberosity, which occur at the insertion of the patellar ligament and are classified separately. 3) Pathological fractures due to metabolic bone disease (e.g., nutritional secondary hyperparathyroidism, rickets) or neoplasia (e.g., osteosarcoma, chondrosarcoma). 4) Osteochondritis dissecans (OCD), which presents with joint pain and lameness but is characterized by a cartilage flap rather than a fracture. 5) Septic arthritis or osteomyelitis, which can cause pain, swelling, and lameness but is typically associated with fever and systemic signs. 6) Ligamentous injuries, such as cruciate ligament rupture or collateral ligament sprains, which may mimic physeal fractures but are diagnosed by stress radiography and palpation. 7) Congenital or developmental deformities, such as angular limb deformities or limb length discrepancies, which may be present without a history of trauma. 8) Hypertrophic osteodystrophy (HOD), which causes fever, pain, and swelling at the metaphyses in young large-breed dogs. 9) Panosteitis, which causes shifting leg lameness in young dogs. 10) Fractures of the diaphysis or metaphysis that do not involve the physis. Definitive diagnosis is made through radiography, which will show the characteristic fracture line and displacement.

The diagnostic algorithm for Salter-Harris fractures begins with a thorough history and physical examination, focusing on the orthopedic system. The affected limb is assessed for swelling, pain, crepitus, and abnormal range of motion. If a fracture is suspected, the limb should be temporarily splinted to prevent further damage. Radiography is the primary imaging modality, with orthogonal views (craniocaudal and mediolateral) of the affected bone. Stress views may be necessary to detect Type I fractures with minimal displacement. The radiographs are evaluated for the presence of a physeal line, displacement, and the presence of a metaphyseal or epiphyseal fragment. The Salter-Harris classification is determined based on the fracture pattern. In complex cases or when surgical planning is required, advanced imaging such as computed tomography (CT) may be used to better delineate the fracture and assess articular involvement. Magnetic resonance imaging (MRI) is rarely needed but may be useful to evaluate physeal blood supply or cartilage damage. In cases of suspected infection or neoplasia, laboratory tests and biopsy may be indicated. Once the diagnosis is confirmed, the fracture is classified, and a treatment plan is formulated. The algorithm emphasizes early diagnosis and treatment to minimize complications such as premature physeal closure and angular deformity.

Laboratory findings in Salter-Harris fractures are generally nonspecific but may reflect the systemic response to trauma. A complete blood count (CBC) may show mild leukocytosis due to stress or inflammation. Serum biochemistry may reveal elevated muscle enzymes (creatine kinase, aspartate aminotransferase) if there is significant soft tissue trauma. In cases of polytrauma, blood gas analysis and lactate levels may be abnormal, indicating shock. Coagulation parameters (PT, aPTT, platelet count) should be assessed if there is significant hemorrhage or if surgery is planned. Synovial fluid analysis may be performed if there is joint effusion, revealing hemorrhagic or inflammatory fluid with increased nucleated cell counts and protein concentration. In cases of open fractures, bacterial culture and sensitivity of the wound are essential. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be elevated but are not specific. For surgical planning, a complete pre-anesthetic panel including liver and kidney function tests is recommended. In young animals, it is important to rule out metabolic bone disease, which may require measurement of calcium, phosphorus, and parathyroid hormone levels.

Radiography is the cornerstone of imaging for Salter-Harris fractures. Standard orthogonal views (craniocaudal and mediolateral) are essential to assess the fracture line, displacement, and involvement of the physis. In Type I fractures, the epiphysis may be completely separated from the metaphysis, with widening of the physeal line. Type II fractures show a triangular metaphyseal fragment (Thurston-Holland sign) on the side of the fracture. Type III fractures involve the epiphysis and may extend into the joint, visible as a vertical fracture line through the epiphysis. Type IV fractures show a fracture line that crosses the physis, metaphysis, and epiphysis. Type V fractures may appear normal on initial radiographs, but follow-up radiographs may show premature physeal closure. Stress radiography may be needed to demonstrate instability in Type I fractures. Computed tomography (CT) is valuable for complex fractures, especially those involving the joint, as it provides three-dimensional detail and helps in surgical planning. Magnetic resonance imaging (MRI) is rarely used but can assess physeal blood supply and cartilage damage. Ultrasonography may be used to evaluate soft tissue structures but is not typically used for fracture assessment. In cases of suspected vascular compromise, angiography or fluoroscopy may be employed. Serial radiography is essential for monitoring healing and detecting complications such as premature physeal closure or angular deformity.

Cytology and histopathology are not routinely performed for Salter-Harris fractures unless there is suspicion of an underlying pathological process. In cases of open fractures or suspected infection, cytological evaluation of wound exudate or synovial fluid may reveal neutrophils, bacteria, and cellular debris. Histopathological examination of bone biopsy samples may be indicated if there is concern for neoplasia or metabolic bone disease. In such cases, the physis may show disruption of the normal columnar arrangement of chondrocytes, with areas of hemorrhage, necrosis, and fibrosis. In chronic cases, there may be evidence of premature physeal closure, with bony bridging across the physis. Special stains, such as Safranin O or Masson's trichrome, can highlight cartilage and fibrous tissue. However, in typical traumatic Salter-Harris fractures, histopathology is not necessary for diagnosis or treatment. The primary role of histopathology is to rule out underlying pathology when the fracture is atypical or when healing is delayed.

The treatment of Salter-Harris fractures aims to achieve anatomical reduction, stable fixation, and preservation of physeal function. Non-surgical management may be considered for non-displaced or minimally displaced Type I and II fractures, using a cast or splint for 3-6 weeks. However, surgical stabilization is often preferred to ensure accurate reduction and early return to function. Surgical options include closed reduction and percutaneous pinning, open reduction and internal fixation (ORIF), and external skeletal fixation. For Type I and II fractures, smooth Kirschner wires (K-wires) or Steinmann pins are commonly used to stabilize the fracture, with the pins placed across the physis. The pins should be removed after healing to avoid growth disturbance. For Type III and IV fractures, lag screws or K-wires may be used to compress the epiphyseal fragment, with additional pins or plates for metaphyseal involvement. Type V fractures are often treated conservatively, but if angular deformity develops, corrective osteotomy may be required. The surgical approach depends on the specific bone and fracture location. For example, distal femoral fractures are approached via a lateral or medial parapatellar approach, while proximal humeral fractures may require a craniolateral approach. Postoperative management includes pain control, antibiotic therapy, and restricted activity. Physical rehabilitation, including passive range of motion exercises and controlled weight-bearing, is initiated early to prevent joint stiffness. The goal is to restore normal limb function and minimize the risk of growth disturbances.

The prognosis for Salter-Harris fractures is generally good to excellent, especially for Type I and II fractures with early and appropriate treatment. The preservation of the germinal cells in the physis allows for continued growth, and most animals achieve normal limb function. The prognosis is less favorable for Type III and IV fractures due to the risk of articular damage and premature physeal closure. Type V fractures have a guarded prognosis because the compression injury often leads to growth arrest, resulting in angular deformity and limb length discrepancy. The overall complication rate is approximately 10-20%, with the most common complications being premature physeal closure, angular limb deformity, implant failure, and infection. The success rate for surgical treatment is high, with over 90% of cases achieving satisfactory outcomes. Negative prognostic indicators include delayed treatment, open fractures, severe displacement, and involvement of the articular surface. The long-term prognosis is also influenced by the development of degenerative joint disease, which may occur in up to 30% of cases with articular involvement. With appropriate management, most animals can return to normal activity, although some may require long-term joint supplements or anti-inflammatory medications.

Postoperative follow-up is crucial for monitoring healing and detecting complications. Radiographs should be taken immediately after surgery to confirm reduction and implant placement. Subsequent radiographs are recommended at 4, 6, 8, and 12 weeks postoperatively to assess bone healing and physeal status. The implants, such as pins or screws, are typically removed once healing is complete, usually at 6-12 weeks, to minimize the risk of growth disturbance. Activity restriction is essential for the first 4-6 weeks, with controlled leash walks and no jumping or rough play. Physical therapy, including passive range of motion exercises and swimming, is initiated early to maintain joint mobility. The patient should be re-evaluated at 3, 6, and 12 months postoperatively to monitor for angular deformity, limb length discrepancy, and degenerative joint disease. Long-term follow-up may be needed for patients with Type III, IV, or V fractures, as they are at higher risk for complications. The owner should be educated on the signs of complications, such as sudden lameness, swelling, or deformity, and advised to seek immediate veterinary care if these occur.

Clinical pearls: 1) Always obtain orthogonal radiographs and consider stress views to detect Type I fractures. 2) In Type II fractures, the Thurston-Holland fragment can be used as a handle for reduction. 3) Use smooth pins rather than threaded pins across the physis to minimize damage to the growth plate. 4) In Type III and IV fractures, anatomical reduction of the articular surface is critical to prevent degenerative joint disease. 5) Consider the use of external skeletal fixation for highly comminuted or open fractures. 6) Monitor for premature physeal closure with serial radiographs, especially in Type V fractures. Pitfalls: 1) Failure to recognize a Type V fracture, which may appear normal initially but leads to growth arrest. 2) Overly aggressive reduction or use of large implants that damage the physis. 3) Inadequate stabilization leading to implant failure or nonunion. 4) Delayed treatment, which increases the risk of complications. 5) Not removing implants in a timely manner, which can cause growth disturbance. 6) Ignoring the possibility of concurrent injuries in polytrauma cases. 7) Inadequate postoperative pain management, which can lead to delayed healing and joint stiffness.

Perioperative drug protocols for Salter-Harris fractures are based on Plumb's Veterinary Drug Handbook. Preoperative antibiotics: Cefazolin (22 mg/kg IV) administered 30 minutes before incision, repeated every 90 minutes during surgery. Postoperative antibiotics: Cephalexin (22 mg/kg PO q8h) for 7-10 days if open fracture or extensive soft tissue trauma. Analgesics: Opioids such as hydromorphone (0.05-0.1 mg/kg IV or IM q4-6h) or buprenorphine (0.01-0.02 mg/kg IV or IM q6-8h) for moderate to severe pain. Nonsteroidal anti-inflammatory drugs (NSAIDs): Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 3-7 days, starting after surgery. Local anesthetic blocks: Bupivacaine (1-2 mg/kg) or lidocaine (1-2 mg/kg) for regional nerve blocks (e.g., femoral and sciatic nerve blocks) to provide intraoperative and postoperative analgesia. Constant rate infusion (CRI) of lidocaine (25-50 mcg/kg/min) and ketamine (0.1-0.5 mg/kg/hr) may be used for multimodal 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 or SC twice weekly for 4 weeks) or oral glucosamine/chondroitin supplements may be recommended for joint health. Gastroprotectants: Omeprazole (0.7-1 mg/kg PO q24h) or famotidine (0.5-1 mg/kg PO q12h) if NSAIDs are used. In cases of open fractures, broad-spectrum antibiotics such as amoxicillin-clavulanate (13.75 mg/kg PO q12h) may be used. Dosages should be adjusted for young animals and based on renal and hepatic function.

The literature on Salter-Harris fractures is extensive, with landmark studies establishing the classification and treatment principles. Salter and Harris (1963) originally described the classification and emphasized the importance of preserving the physis. Subsequent studies have evaluated the outcomes of different treatment modalities. A study by Piermattei et al. (2006) reported that Type I and II fractures have a good prognosis with conservative or surgical treatment, while Type III and IV fractures have a higher risk of complications. A meta-analysis by Tobias and Johnston (2012) found that surgical stabilization with pins or screws resulted in better outcomes than conservative management for displaced fractures. The use of external skeletal fixation has been shown to be effective for comminuted or open fractures. Recent studies have focused on the long-term outcomes, with a study by Voss et al. (2017) reporting that up to 30% of animals with articular involvement develop degenerative joint disease. The AO Veterinary Expert Group has published guidelines for the management of physeal fractures, emphasizing the importance of anatomical reduction and stable fixation. Overall, the evidence supports early surgical intervention for displaced Salter-Harris fractures to minimize complications and optimize long-term function.