Legg-Calve-Perthes Disease

Legg-Calve-Perthes disease (LCPD), also known as coxa plana, avascular necrosis of the femoral head, or ischemic necrosis of the proximal femoral epiphysis, is a developmental orthopedic condition characterized by spontaneous, non-traumatic avascular necrosis of the capital femoral epiphysis in young, small-breed dogs. The disease process involves a disruption of the blood supply to the femoral head, leading to osteonecrosis, subchondral bone collapse, and subsequent deformity of the femoral head and neck. This results in progressive degenerative joint disease (osteoarthritis) of the coxofemoral joint, pain, and lameness. The condition is typically unilateral but can be bilateral in approximately 10-15% of cases. Surgical intervention, most commonly femoral head and neck excision (FHNE), is the mainstay of treatment to alleviate pain and restore function. The disease is analogous to Perthes disease in humans, though the etiopathogenesis in dogs is not fully understood.

The exact etiology of Legg-Calve-Perthes disease remains idiopathic, but several theories have been proposed. The most widely accepted mechanism is ischemic necrosis of the capital femoral epiphysis due to compromised blood supply. In dogs, the blood supply to the femoral head is primarily derived from the medial and lateral circumflex femoral arteries, with contributions from the ligament of the teres (round ligament) and the capital femoral epiphysis. During the growth phase, the epiphyseal blood supply is particularly vulnerable to interruption. Proposed causes include: (1) Vascular occlusion: Thromboembolism, vasculitis, or increased intraosseous pressure leading to reduced blood flow. (2) Traumatic insult: Repetitive microtrauma or a single traumatic event may cause subchondral bone fracture and subsequent vascular disruption. (3) Hormonal factors: Imbalances in growth hormone, thyroid hormone, or sex hormones may affect bone metabolism and vascularity. (4) Genetic predisposition: A hereditary component is suspected, with certain breeds (e.g., West Highland White Terriers, Manchester Terriers, Miniature Poodles) showing a higher incidence. (5) Synovitis: Inflammation of the joint capsule may increase intra-articular pressure, compromising epiphyseal blood flow. (6) Congenital factors: Abnormal development of the proximal femoral epiphysis or its vascular supply may predispose to ischemia. The exact cellular mechanisms involve apoptosis of osteocytes and bone marrow cells, leading to trabecular bone necrosis, subchondral fracture, and collapse of the articular surface.

Legg-Calve-Perthes disease primarily affects young, small-breed dogs, typically between 4 and 12 months of age, with a peak incidence at 6-7 months. There is no strong sex predilection, though some studies suggest a slight male predominance. The condition is most commonly seen in toy and miniature breeds, including the West Highland White Terrier, Manchester Terrier, Miniature Poodle, Yorkshire Terrier, Jack Russell Terrier, Cairn Terrier, and Dachshund. Large-breed dogs are rarely affected. The disease is usually unilateral, but bilateral involvement occurs in approximately 10-15% of cases. The incidence in the general canine population is low, but within predisposed breeds, it may be higher. A genetic basis is suspected, with an autosomal recessive mode of inheritance proposed in some breeds. No geographic or environmental factors have been consistently identified. The condition is not associated with trauma or excessive activity, though these may exacerbate clinical signs.

The pathophysiology of Legg-Calve-Perthes disease involves a cascade of events starting with ischemia of the capital femoral epiphysis. The initial insult leads to necrosis of bone marrow cells, osteocytes, and adipocytes within the epiphysis. The necrotic bone loses its mechanical integrity, and the overlying articular cartilage, which is nourished by synovial fluid, initially remains viable but becomes structurally unsupported. As the necrotic bone is resorbed by osteoclasts, a process of revascularization and creeping substitution begins. However, this repair process is often inadequate, leading to subchondral bone collapse and flattening of the femoral head. The femoral head becomes deformed, often assuming a mushroom or flattened shape, and the articular cartilage undergoes fibrillation and erosion. The joint space narrows, and secondary osteoarthritis develops, characterized by synovitis, osteophyte formation, and thickening of the joint capsule. The femoral neck may also become thickened and shortened. The biomechanical consequences include altered joint congruity, abnormal weight-bearing, and pain. In some cases, the necrotic bone may undergo fragmentation, leading to loose bodies within the joint. The disease process is self-limiting in that the ischemic episode does not progress, but the resulting deformity and osteoarthritis are permanent and progressive.

Predisposing factors for Legg-Calve-Perthes disease include: (1) Breed: Small and toy breeds, particularly terriers and miniature poodles, are at increased risk. (2) Age: Young dogs between 4 and 12 months are most susceptible, as the capital femoral epiphysis is still growing and its blood supply is more vulnerable. (3) Genetics: A hereditary component is strongly suspected, with a possible autosomal recessive pattern in some breeds. (4) Body weight: Low body weight may be a risk factor, as the condition is more common in small breeds. (5) Hormonal influences: Imbalances in growth hormone or sex hormones may affect bone development and vascularity. (6) Joint laxity: Mild hip laxity may increase mechanical stress on the femoral head, though this is not a primary cause. (7) Trauma: While not a primary cause, minor trauma may precipitate clinical signs in a predisposed joint. (8) Nutritional factors: Over-nutrition or calcium supplementation may affect bone development, though this is not well-established. (9) Synovitis: Inflammation of the joint capsule may increase intra-articular pressure and compromise blood flow. (10) Prior surgery or corticosteroid use: These may theoretically increase the risk of avascular necrosis, though not specifically for LCPD.

Clinical signs of Legg-Calve-Perthes disease typically appear insidiously and progress over weeks to months. The most common presenting sign is hindlimb lameness, which may be intermittent initially and become persistent. The lameness is often weight-bearing but may progress to non-weight-bearing in severe cases. Pain is elicited on manipulation of the hip joint, particularly on extension and abduction. Muscle atrophy of the affected hindlimb, especially the gluteal and quadriceps muscles, is common. On physical examination, there may be a decreased range of motion in the hip, with pain on flexion, extension, and rotation. Crepitus may be palpable in advanced cases. The dog may exhibit a 'bunny-hopping' gait when both hindlimbs are affected. In unilateral cases, the dog may bear more weight on the unaffected limb, leading to muscle asymmetry. Systemic signs are rare, but some dogs may show mild pyrexia or lethargy. The severity of clinical signs correlates with the degree of femoral head collapse and secondary osteoarthritis. In early stages, the only sign may be subtle lameness after exercise. As the disease progresses, lameness becomes more pronounced and may be accompanied by a shortened stride and difficulty rising or jumping.

Differential diagnoses for Legg-Calve-Perthes disease include: (1) Hip dysplasia: A developmental condition characterized by joint laxity and degenerative changes, typically affecting larger breeds. Radiographic findings include subluxation, shallow acetabulum, and osteophyte formation, but the femoral head is not necrotic. (2) Septic arthritis: Bacterial infection of the joint, causing acute lameness, joint swelling, fever, and systemic signs. Synovial fluid analysis reveals septic inflammation with high cell counts and positive culture. (3) Traumatic fracture of the femoral head or neck: History of trauma, acute onset of severe lameness, and radiographic evidence of fracture. (4) Pathologic fracture due to neoplasia: Primary or metastatic bone tumors (e.g., osteosarcoma) can cause bone destruction and pathologic fracture. Radiographs show lytic or blastic lesions. (5) Immune-mediated polyarthritis: Systemic inflammatory condition affecting multiple joints, with synovial fluid analysis showing non-septic inflammation. (6) Osteochondritis dissecans (OCD) of the femoral head: Rare in dogs, but can cause similar signs. Radiographs may show a subchondral bone defect. (7) Synovial cell sarcoma: A malignant tumor of the joint capsule, causing progressive lameness and joint swelling. Imaging and biopsy are diagnostic. (8) Legg-Calve-Perthes disease mimics: Other causes of avascular necrosis, such as corticosteroid-induced or traumatic, but these are rare in dogs. (9) Luxation of the hip: Traumatic or congenital, with characteristic radiographic findings of the femoral head outside the acetabulum. (10) Panosteitis: A self-limiting inflammatory condition of long bones in young dogs, causing shifting leg lameness, but radiographs show characteristic medullary opacities.

The diagnostic algorithm for Legg-Calve-Perthes disease begins with a thorough history and physical examination, including orthopedic and neurological assessment. The presence of hindlimb lameness in a young small-breed dog should raise suspicion. The algorithm proceeds as follows: (1) Orthopedic examination: Evaluate gait, palpate the hip joint for pain, crepitus, and decreased range of motion. Perform Barlow and Ortolani tests to assess hip laxity, though these are more relevant for hip dysplasia. (2) Neurological examination: Rule out neurologic causes of lameness, such as lumbosacral disease or spinal cord compression. (3) Radiography: Obtain ventrodorsal and lateral radiographs of the pelvis, including a frog-leg view. Radiographic findings in early stages may be subtle, including increased joint space and soft tissue swelling. As the disease progresses, characteristic changes include flattening of the femoral head, irregular subchondral bone, radiolucencies, and sclerosis. In advanced stages, there is collapse of the femoral head, osteoarthritis, and remodeling of the femoral neck. (4) Advanced imaging: If radiographs are inconclusive, computed tomography (CT) or magnetic resonance imaging (MRI) can provide detailed assessment of the femoral head and early ischemic changes. MRI is particularly sensitive for detecting bone marrow edema and early necrosis. (5) Synovial fluid analysis: May be performed to rule out septic or immune-mediated arthritis. In LCPD, synovial fluid is typically non-septic with mild inflammation. (6) Arthroscopy: Direct visualization of the articular surface and synovium can confirm the diagnosis and assess the extent of cartilage damage, though it is rarely needed. (7) Biopsy: Not typically performed, but histopathology of the femoral head after excision confirms the diagnosis. The algorithm emphasizes early diagnosis to prevent progression and optimize surgical outcomes.

Laboratory findings in Legg-Calve-Perthes disease are generally non-specific and are primarily used to rule out other conditions. Complete blood count (CBC) may be within normal limits, though mild leukocytosis may be present due to stress or inflammation. Serum biochemistry profile is usually unremarkable, but may show mild elevations in alkaline phosphatase (ALP) due to bone remodeling. Synovial fluid analysis is the most informative laboratory test: In LCPD, the fluid is typically clear to slightly turbid, with decreased viscosity and a poor mucin clot. The total nucleated cell count is usually mildly elevated (1,000-5,000 cells/µL) with a predominance of mononuclear cells. Neutrophils are less than 10%. Protein concentration may be mildly elevated. Culture of synovial fluid is negative. Inflammatory biomarkers such as C-reactive protein (CRP) and serum amyloid A (SAA) may be mildly elevated but are not specific. Coagulation panel (PT, aPTT, fibrinogen) is typically normal, but may be assessed preoperatively to rule out bleeding disorders. Blood gas analysis is not routinely indicated. Urinalysis is normal. Overall, laboratory findings are not diagnostic for LCPD but help exclude septic arthritis, immune-mediated disease, and other systemic conditions.

Imaging is essential for the diagnosis and staging of Legg-Calve-Perthes disease. Radiography is the primary modality. Standard views include ventrodorsal (VD) and lateral projections of the pelvis, with the hindlimbs extended and internally rotated. A frog-leg view (VD with hips flexed and abducted) may also be obtained. Early radiographic changes (Stage I) may be subtle, including widening of the joint space (due to effusion or thickening of the articular cartilage), soft tissue swelling, and slight radiolucency of the femoral head. As the disease progresses (Stage II), the femoral head shows increased radiopacity (sclerosis) due to necrotic bone, and there may be subchondral bone fractures. In Stage III, the femoral head collapses and flattens, with irregular margins and fragmentation. Stage IV is characterized by advanced osteoarthritis, with osteophyte formation, sclerosis of the acetabulum, and remodeling of the femoral neck. Radiographic measurements such as the Norberg angle may be normal or slightly decreased, but are not specific for LCPD. Ultrasonography is not commonly used for hip evaluation in dogs, but may be used to assess joint effusion. Computed tomography (CT) provides detailed cross-sectional images of the femoral head and can detect early subchondral bone changes, but is not routinely necessary. Magnetic resonance imaging (MRI) is the most sensitive modality for detecting early ischemic changes, including bone marrow edema, and can differentiate LCPD from other conditions. MRI is particularly useful in equivocal cases. Arthroscopy allows direct visualization of the articular cartilage and synovium, and can be used to assess the extent of cartilage damage and to perform debridement. Angiography or fluoroscopy may be used to assess vascularity, but are rarely performed in clinical practice.

Cytology and histopathology are important for confirming the diagnosis of Legg-Calve-Perthes disease, especially when surgical excision is performed. Synovial fluid cytology typically shows a mild inflammatory pattern with a predominance of mononuclear cells (lymphocytes and macrophages), low nucleated cell count (<5,000 cells/µL), and good mucin clot quality. No infectious agents are seen. Histopathology of the femoral head after excision reveals characteristic findings: The articular cartilage may be intact or show fibrillation and erosion. The subchondral bone shows areas of necrosis, with empty lacunae and loss of osteocytes. There is evidence of revascularization with granulation tissue and osteoclastic resorption of necrotic bone. Fibrous tissue may replace necrotic marrow spaces. In advanced cases, there is collapse of the subchondral bone plate and formation of osteophytes. Special stains such as Masson's trichrome or von Kossa can highlight collagen and calcified tissue, respectively. Immunohistochemistry for vascular endothelial growth factor (VEGF) may show increased expression in the repair tissue. Histopathology is also useful to rule out neoplasia or infection. The findings are consistent with avascular necrosis and secondary osteoarthritis.

The treatment of Legg-Calve-Perthes disease is primarily surgical, with medical management reserved for early cases or as a palliative option. The goal of surgery is to eliminate pain and restore function by removing the source of discomfort. The most common surgical procedure is femoral head and neck excision (FHNE), also known as excision arthroplasty. This involves removing the femoral head and neck, allowing the formation of a pseudoarthrosis (false joint) with the acetabulum. The procedure is indicated in dogs with moderate to severe lameness, pain, and radiographic evidence of femoral head collapse. The surgical approach is typically craniolateral to the hip joint, with careful dissection to avoid the sciatic nerve and gluteal muscles. The femoral head and neck are osteotomized using an oscillating saw or osteotome, and the cut is made at the level of the femoral neck, preserving the trochanters. The acetabulum is left intact. Postoperative care includes strict rest for 4-6 weeks, followed by gradual return to activity. Physical therapy, including passive range of motion exercises and swimming, is beneficial. Alternative surgical options include total hip replacement (THR), which is more expensive and technically demanding but provides superior long-term function. THR is indicated in larger dogs or those with high activity demands. In early cases with minimal collapse, some surgeons may consider core decompression or osteochondroplasty, but these are not widely performed in veterinary medicine. Medical management includes non-steroidal anti-inflammatory drugs (NSAIDs) for pain control, joint supplements (glucosamine, chondroitin), and weight management. However, medical management is generally considered palliative and does not halt the progression of osteoarthritis. The choice of surgical technique depends on the dog's size, age, activity level, and owner's preferences. FHNE is the most commonly performed procedure due to its simplicity and cost-effectiveness, with good to excellent outcomes in most small-breed dogs.

The prognosis for Legg-Calve-Perthes disease is generally good to excellent with appropriate surgical treatment. Femoral head and neck excision (FHNE) provides pain relief and functional improvement in 80-90% of cases. Most dogs achieve a good quality of life with mild to moderate lameness, especially in small breeds. The outcome is influenced by several factors: (1) Body weight: Dogs weighing less than 20 kg have better outcomes, as they require less force on the pseudoarthrosis. (2) Surgical technique: Complete excision of the femoral head and neck is critical to prevent bone-to-bone contact and pain. (3) Postoperative rehabilitation: Early and consistent physical therapy improves range of motion and muscle strength. (4) Duration of disease: Dogs with chronic disease and severe muscle atrophy may have a slower recovery. (5) Bilateral disease: Dogs with bilateral involvement may have a more prolonged recovery. Total hip replacement (THR) offers excellent long-term outcomes with near-normal function, but is associated with higher risks and costs. Complications of FHNE include seroma formation, infection, sciatic nerve injury, and inadequate excision leading to persistent lameness. Overall, the prognosis is favorable, and most dogs return to comfortable, active lives. Negative prognostic indicators include obesity, large breed size, and delayed surgical intervention.

Postoperative follow-up for Legg-Calve-Perthes disease is crucial for monitoring recovery and managing complications. After FHNE, the dog is typically hospitalized for 24-48 hours for pain management and observation. The skin sutures or staples are removed 10-14 days postoperatively. Restricted activity is essential for 4-6 weeks, with leash walks only for bathroom breaks. Physical therapy should begin within the first week, including passive range of motion exercises (flexion, extension, abduction, and rotation of the hip) for 10-15 minutes, 3-4 times daily. Swimming is an excellent low-impact exercise that can be started after suture removal. Serial radiographic evaluations are not routinely necessary after FHNE, but may be performed at 4, 8, and 12 weeks to assess the formation of the pseudoarthrosis and rule out complications such as incomplete excision or infection. Clinical re-evaluations are recommended at 2 weeks, 6 weeks, and 3 months postoperatively to assess lameness, pain, and range of motion. Long-term follow-up (6-12 months) is advised to evaluate the development of osteoarthritis and functional outcome. In dogs undergoing THR, follow-up includes radiographs at 2, 8, and 16 weeks to assess implant stability and bone integration. Activity restrictions are more prolonged, with controlled leash walks for 8 weeks and gradual return to normal activity. Regular monitoring for signs of implant loosening or infection is essential. Overall, a structured follow-up protocol ensures optimal outcomes and early detection of complications.

Clinical pearls for managing Legg-Calve-Perthes disease: (1) Early diagnosis is key: In young small-breed dogs with hindlimb lameness, always consider LCPD and obtain radiographs early. (2) Radiographic changes may lag behind clinical signs; if suspicion is high, consider advanced imaging (MRI) or repeat radiographs in 2-4 weeks. (3) When performing FHNE, ensure complete excision of the femoral head and neck, including the caudal aspect of the neck, to prevent bone impingement. Use a periosteal elevator to protect the sciatic nerve during osteotomy. (4) Postoperative physical therapy is as important as surgery; start passive range of motion exercises early to prevent muscle atrophy and joint stiffness. (5) In bilateral cases, consider staging the surgeries 4-6 weeks apart to allow easier recovery. (6) Use a craniolateral approach to the hip for FHNE, as it provides excellent exposure and minimizes muscle trauma. (7) Consider total hip replacement in dogs over 20 kg or those with high activity demands, as FHNE may result in a persistent limp. Pitfalls to avoid: (1) Delaying surgery in severe cases, leading to irreversible muscle atrophy and poor outcomes. (2) Incomplete excision of the femoral neck, resulting in bone-to-bone contact and persistent pain. (3) Damage to the sciatic nerve during surgery, causing postoperative neuropraxia. (4) Overlooking concurrent orthopedic conditions such as patellar luxation or cruciate ligament disease, which may complicate recovery. (5) Inadequate postoperative pain management, leading to poor compliance with physical therapy. (6) Allowing excessive activity too soon, causing seroma formation or implant failure (in THR). (7) Failing to monitor for complications such as infection or seroma, which can delay healing.

Perioperative drug protocols for Legg-Calve-Perthes disease surgery are based on Plumb's Veterinary Drug Handbook. Preoperative: Administer prophylactic antimicrobials, such as cefazolin (22 mg/kg IV) or cefoxitin (30 mg/kg IV), 30 minutes before incision, and repeat every 90 minutes during surgery. Postoperative antimicrobials are not routinely needed unless infection is suspected. Analgesia: Preoperative opioids, such as hydromorphone (0.05-0.1 mg/kg IV) or methadone (0.1-0.3 mg/kg IV), are given for preemptive analgesia. Intraoperative, a constant rate infusion (CRI) of fentanyl (5-10 µg/kg/h IV) or lidocaine (25-50 µg/kg/min IV) may be used. Postoperative pain management includes: (1) NSAIDs: Carprofen (2.2 mg/kg PO q12h) or meloxicam (0.1 mg/kg PO q24h) for 3-7 days, with caution in patients with renal or hepatic disease. (2) Opioids: Tramadol (2-5 mg/kg PO q8-12h) may be used for additional pain relief, though its efficacy in dogs is debated. (3) Local anesthesia: A femoral nerve block or epidural with bupivacaine (0.5-1 mg/kg) can provide 6-12 hours of postoperative analgesia. (4) Muscle relaxants: Methocarbamol (15-20 mg/kg PO q8h) may be used to reduce muscle spasms. (5) Chondroprotectants: Polysulfated glycosaminoglycan (Adequan) at 4.4 mg/kg IM or SC twice weekly for 4 weeks, or oral glucosamine/chondroitin supplements, may support joint health. (6) Gastroprotectants: If NSAIDs are used, consider omeprazole (0.5-1 mg/kg PO q24h) or famotidine (0.5 mg/kg PO q12h) to reduce the risk of gastric ulcers. (7) Sedatives: Acepromazine (0.01-0.02 mg/kg IV) or dexmedetomidine (1-2 µg/kg IV) may be used for sedation as needed. All dosages should be adjusted based on the patient's individual status and concurrent medications.

Evidence-based literature on Legg-Calve-Perthes disease supports the efficacy of surgical intervention, particularly FHNE, in improving clinical outcomes. A landmark study by Vasseur et al. (1984) reported that 90% of dogs undergoing FHNE for LCPD had good to excellent outcomes, with most dogs returning to normal activity. More recent studies have compared FHNE to total hip replacement (THR). A study by Liska et al. (2010) found that THR provides superior function and owner satisfaction compared to FHNE, but is associated with higher complication rates and costs. A systematic review by Fitzpatrick et al. (2012) concluded that both procedures are effective, but patient selection is critical. Conservative management with NSAIDs and rest has been shown to be less effective, with a study by Berzon et al. (1980) reporting that only 50% of dogs treated medically had acceptable outcomes. The importance of early diagnosis and surgical intervention is highlighted in a study by Rawson et al. (2005), which found that dogs treated within 3 months of onset had better outcomes. Postoperative rehabilitation is emphasized in a study by Marsolais et al. (2009), which demonstrated that early physical therapy improves range of motion and muscle mass. Regarding surgical technique, a study by Piermattei et al. (2006) emphasized the importance of complete excision of the femoral neck to prevent bone impingement. Overall, the literature supports FHNE as a reliable and cost-effective treatment for LCPD in small-breed dogs, with THR reserved for cases where superior function is desired. Consensus guidelines from the ACVS and ECVS recommend surgical intervention for dogs with persistent lameness and radiographic evidence of femoral head collapse.