The disease is known as flat hip and osteochondritis of the femoral head. The incidence is 1/10,000, about 4 times higher in boys than in girls, and about 10-15% of the cases are affected bilaterally. It is more common in children aged 4-12 years, but can develop from 18 months to skeletally mature teenagers. The pathological changes are synovitis and exudation, cartilage hypertrophy, osteonecrosis and collapse. The prognosis is poor. The most important factor affecting the prognosis is the degree of spherical shape of the femoral head at the time of bone maturation, and the shape of the femoral head is related to the age of onset, with the earlier the age of onset, the more spherical the femoral head is at the time of bone maturation. The prognosis of the disease is largely related to the age of onset of the child. According to the age of onset, there is an early pediatric group (0-5 years), an intermediate pediatric group (5-8 years), and a late pediatric group (8 years old and above), with the late pediatric group having the worst prognosis. The etiology is multifactorial, while the exact cause is not clear. Many findings suggest pathological changes in the blood vessels within the femoral head, associated with both arterial and venous systems. Another theory is the susceptible child theory, based on the fact that all children have abnormal growth and development, a history of trauma, excessive activity and other factors, as well as the sequelae of synovitis. Many children are not seen due to mild symptoms. The child often has a limp and sometimes complains of pain in the hip, knee and thigh. The main findings of the examination are limitation of hip movement (especially abduction and internal rotation) and mild atrophy of the thigh muscles. The limp is often detected by the parents. The lameness worsens with high activity, but can be relieved by rest. Secondly, the child has pain, which is limited to the hip, the front of the hip joint and the greater trochanter. Sometimes the pain may be misdiagnosed because it may spread to the knee. The pain is worse after activity or is more pronounced at night. The child or parent recalls a history of trauma (fall or sprain) several months ago, followed by limp and hip pain. The pain is relieved after a few days, but sometimes worsens and sometimes decreases. There were several delays before going to the clinic. Sometimes the child is more active than normal, runs and jumps more, and is sometimes smaller than normal child C, or overweight and immobile. For children in groups A and B with symptoms, the initial treatment is to reduce the amount of activity, use some anti-inflammatory drugs and short bed rest, traction, and reduce weight bearing, and for children in groups B and C with symptoms after the age of 6, once the joint has limited range of motion due to symptoms, they are treated with surgery and other inclusive therapies.