The incidence is 5 times higher in boys than in girls, and the common age of onset is 4-8 years. It seems that the younger the age of onset, the better the prognosis. The disease begins with the child calling knee pain – hip pain, walking inconvenience or limp, the affected hip can not flexion and extension, internal retraction. Parents often mistake this for a sprain and do not pay attention to it, delaying the course of the disease and causing the femoral head to flatten – “flat hip”. Trauma mainly causes damage to the blood vessels around the femoral head in children, and after the blood vessels are damaged, the epiphysis of the femoral head loses blood flow, resulting in ischemic osteonecrosis of the femoral head epiphysis. Main manifestations: a. Knee pain and walking limp for no reason. 2. While the knee joint is painful, press the area around the hip joint with your hand and there are pressure points when you press. 3.Let the child lie in a flat position and lift the affected limb upward, but there is pain in the hip joint when it does not reach 45 degrees. Four, do the “4” experiment. Put the affected limb on the healthy side of the thigh in a 4-character shape, knee to the hip joint pain. Clinically, for cases with limp for more than one week, it is recommended to perform pelvic plain film examination. If necessary, CT or MRI examination is required for confirmation. In some difficult cases, diseases such as tuberculosis of the femoral head or osteoblastoma need to be excluded. Treatment: fixation by an abductor brace and regular check-ups.