Femoral head necrosis in children is also known as osteochondritis of the femoral head and Legg-Calve-Perthes disease. It mainly involves the hip joint in children and causes osteonecrosis due to reduced blood supply to the femoral head. [It is idiopathic and its etiology is unclear. It may be related to abnormalities in the human fibrinolytic system or deficiencies in human iron, c-protein, and S-protein. [Differential diagnosis] Bilateral hip involvement needs to be excluded from other causes, such as renal disease. Cretinism, multiple epiphyseal dysplasia, systemic application of hormones, history of hemoglobin, etc. [The disease usually occurs in children aged 4 to 8 years, with a male to female ratio of 4:1, but it can also occur in children younger than 2 years or older than 12 years. 10% of patients have bilateral onset, with delayed skeletal development and painless limping. The disease can be self-limiting, with a natural course of about 2-4 years. 1.Onset period Early stage of the disease, sclerosis of the femoral head. 2. Fracture phase The femoral head appears to be “fractured”. Subchondral fracture (Salter’s sign) is a sign of the beginning of this period, accompanied by necrotic bone resorption. 3.Re-ossification phase The beginning of healing is indicated by the union of fragments at the “fracture” of the femoral head. 4.Healing phase The reossification process is completed and the femoral head returns to its pre-onset density, but the deformity still remains.