Legg-Calvé-Perthes disease is a childhood condition in which the blood supply to the head of the femur is temporarily disrupted, causing the bone to die (osteonecrosis). Over months to years, the bone gradually regenerates, but the shape of the femoral head can be permanently altered, leading to long-term hip problems if the condition is not managed appropriately.
Legg-Calvé-Perthes disease is the childhood form of femoral head osteonecrosis — the same fundamental process of bone death from disrupted blood supply that occurs in adults as avascular necrosis (AVN) of the hip, though the causes, course, and remodeling potential differ substantially between children and adults. Some children are initially diagnosed with transient synovitis before Perthes disease becomes apparent — a recognized relationship that underscores the importance of follow-up imaging when synovitis symptoms persist or recur. Without appropriate treatment, the deformed femoral head that results from severe Perthes disease leads to early hip osteoarthritis in adulthood, often requiring hip replacement at a relatively young age.
Causes
Idiopathic avascular necrosis.
The precise cause of Perthes disease remains incompletely understood. It is fundamentally caused by a temporary interruption of blood flow to the growing femoral head — the capital femoral epiphysis — leading to ischemic bone death. What triggers this vascular interruption is not definitively established, but proposed mechanisms include coagulation abnormalities that predispose to small vessel thrombosis (elevated factor V Leiden, protein C or S deficiency), repetitive trauma causing vascular damage, venous hypertension within the femoral head, and synovial inflammation elevating intra-articular pressure and compromising blood flow. The condition is almost certainly multifactorial, with genetic susceptibility intersecting with environmental triggers. Following the ischemic event, the body mounts a reparative response — resorbing the dead bone and replacing it with new bone — but if the femoral head is not mechanically protected during this vulnerable remodeling phase, it deforms under the load of weight-bearing.
Risk factors.
Perthes disease typically affects children between ages 4 and 10, with a peak incidence around age 5–6. It is four to five times more common in boys than girls. Low birth weight, short stature (children with Perthes tend to be in the lower growth percentiles), second-hand smoke exposure, hyperactivity, and a prior history of transient synovitis are recognized risk factors. A family history is present in approximately 10% of cases, suggesting a genetic component. Bilateral involvement occurs in 10–15% of patients, and when bilateral, the two hips are typically at different stages of disease.
Symptoms
The classic and most common presentation is a painless limp in a young child — the child walks with an antalgic or Trendelenburg gait without appearing distressed, which often delays parental concern and medical evaluation. When pain is present, it is typically a dull, intermittent ache in the groin, thigh, or knee — the referred knee pain pattern is well-recognized and can mislead clinicians into focusing on the knee rather than the hip. Symptoms develop gradually over weeks to months, rarely acutely. Hip range of motion becomes progressively restricted, especially hip abduction and internal rotation, as the synovial inflammation and femoral head deformity develop. Some children are initially diagnosed with transient synovitis and improve temporarily before Perthes disease becomes radiographically apparent — the two conditions share the early presentation of hip effusion and limited motion, making follow-up essential when synovitis does not fully resolve.
Diagnosis
X-rays are the initial imaging study and are essential for staging the disease once it is established. Early findings include a small, dense femoral epiphysis, subchondral fracture (crescent sign), and widening of the medial joint space. Later findings include fragmentation, collapse, and eventually reossification. However, X-rays are frequently normal in the earliest stage of the disease, when intervention is most impactful. An MRI is the most sensitive imaging modality for early Perthes disease, demonstrating decreased perfusion and bone marrow signal change within the femoral head before any X-ray changes develop. MRI precisely quantifies the extent and location of femoral head involvement — the most important prognostic factor — assesses cartilage integrity, identifies associated hip joint effusion, and is essential for surgical planning. The lateral pillar classification, which measures the degree of lateral femoral head involvement on X-ray during the fragmentation stage, is the most widely used prognostic grading system and directly guides treatment decisions.
Classification
Perthes disease progresses through four classic radiographic stages, though MRI allows detection and characterization before the radiographic stages are apparent.
- Stage 1 (Initial/avascular): Interruption of blood supply with early bone death. X-rays may show subtle findings — mild epiphyseal density, slight joint space widening — or appear normal. MRI demonstrates avascular change before X-ray findings develop. Duration: several months.
- Stage 2 (Fragmentation): The necrotic bone is resorbed and fragments. This is the most vulnerable stage for femoral head deformation under weight-bearing load. X-rays show fragmentation and collapse. Duration: 1–3 years.
- Stage 3 (Reossification): New bone is progressively deposited and the femoral head begins to heal and remodel. The shape that the femoral head takes during this stage largely determines the long-term outcome. Duration: 1–3 years.
- Stage 4 (Healed/residual): The final shape of the femoral head is established. Outcomes range from a near-spherical head (excellent prognosis) to a flattened, enlarged, or aspherical head (coxa magna or coxa plana) with high risk of early arthritis.
Treatments
The fundamental goals of treatment are to preserve hip range of motion, maintain the femoral head centered within the acetabulum (containment) so that the socket can mold a rounder shape during healing, and minimize the long-term deformity that predisposes to early arthritis. Treatment is individualized based on age at onset, extent of femoral head involvement, and the stage and progression of disease.
Conservative care: In younger children — generally under 6 years — and those with less than 50% femoral head involvement (lateral pillar A and B), the remodeling potential of the growing hip is sufficient that observation with activity modification, physical therapy to maintain abduction and internal rotation range of motion, and anti-inflammatory medications for painful flares often produces excellent outcomes. Protected weight-bearing during painful phases reduces stress on the compromised femoral head. The key principle is maintaining range of motion — a stiff hip in Perthes leads to a deformed femoral head.
Containment strategies.
Maintaining the femoral head within the acetabulum during the critical fragmentation and reossification stages allows the socket to serve as a mold, promoting a rounder healing shape. Hip abduction bracing (Petrie casting or Scottish Rite orthosis) was historically the primary containment method but has largely fallen out of favor due to poor compliance and limited evidence of superiority over surgical options in older children. Maintaining full abduction range of motion through dedicated physical therapy remains an important conservative containment strategy at all ages.
Surgery.
Surgical containment is recommended for older children — generally over age 8 — and those with greater than 50% femoral head involvement (lateral pillar B/C or C), where the remodeling potential alone is insufficient to produce a round femoral head. Proximal femoral varus osteotomy redirects the femoral head more deeply into the acetabulum by angulating the femur, improving containment and distributing load more evenly across healthy cartilage. Pelvic (Salter or triple) osteotomy redirects the acetabulum to provide better coverage of the deformed femoral head. Both approaches have demonstrated good outcomes in appropriately selected patients. After surgery, a structured rehabilitation program restoring range of motion and strength is essential.
Long-term outlook.
Most children with Perthes disease — particularly those who develop the condition before age 6 — recover with good hip function and relatively spherical femoral heads. Children who develop the condition after age 8, or those with extensive lateral pillar involvement, are at significantly elevated risk for femoral head deformity (coxa magna), femoroacetabular impingement from the enlarged head, and early hip osteoarthritis in adulthood — sometimes requiring hip replacement in their 30s or 40s. Long-term radiographic monitoring into adulthood is appropriate for patients with residual deformity.
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