Femoral head necrosis is a pathological evolutionary process that initially occurs in the weight-bearing area of the femoral head, with damage to the trabecular structures of the necrotic bone under stress, i.e., microfracture and subsequent repair process for the damaged bone tissue. The causes of osteonecrosis are not eliminated, the repair is not perfected, and the process of injury-repair continues, leading to structural changes in the femoral head, femoral head collapse, deformation, joint inflammation, and functional impairment. Femoral head necrosis certainly causes pain, joint movement and weight-bearing walking dysfunction. Signs and symptoms The most common symptom is pain, which is located in the hip joint, proximal thigh, and may radiate to the knee. The pain can be caused by inflammatory lesions of necrotic tissue-repair or high pressure within the inflammatory lesion and can manifest as constant pain, resting pain. Osteochondral collapse deformation leading to traumatic arthritis, or there is chronic injurious pain in the area of muscle-ligament attachment around the hip joint. Restriction of hip movement, especially rotational movement, or painful and short limp. Etiology There are two causes of femoral head necrosis: one occurs when the femoral neck fracture is poorly repositioned and healed, and the weight-bearing trabeculae in the femoral head turn to the weight-bearing area to carry less stress and develop stress injury, so necrosis always occurs after the patient’s fracture heals and walks with weight. The other type of necrosis is a disease of the bone tissue itself, such as osteonecrosis caused most commonly by chronic alcoholism or glucocorticoid use, along with impaired regeneration and repair of the bone tissue. It also includes osteonecrosis of the femoral head epiphysis, the growth center of the femoral head during the developmental growth period in children, also known as osteonecrosis of the femoral head in children and flattened hip. Diagnosis Early X-rays may have no positive findings, and with progression, there is disruption of bone trabeculae in the weight-bearing area, interruption, and later cystic degeneration and entrapment sclerosis of the subchondral bone of the femoral head. As the lesion progresses and repair is impaired, linear translucent areas appear in the lesion area, surrounded by sclerotic bone, showing crescentic signs. X-ray can determine the extent of the lesion and exclude other lesions of the bone, which has the advantages of simplicity, convenience, economy and wide application, and is still used as the basic examination method for femoral head necrosis. MRI can detect osteonecrosis foci at an early stage and can make a diagnosis before abnormalities are found on X-ray. The T2-weighted image shows high signal, which is characteristic of the repair response caused by necrosis of bone and bone marrow, and is characterized by acute inflammatory pathological changes such as bone marrow edema, local congestion, and exudation, etc. The T1-weighted image is mostly low signal. The T1-weighted image is a crescent-shaped, well-defined, inhomogeneous signal. If the T2-weighted image shows a moderate slightly high signal surrounded by a heterogeneous slightly low signal, it shows a typical bilinear sign, and the location is basically consistent with the striped osteosclerosis of CT. Treatment Etiologic treatment is the key to terminate the progression of the lesion and make it possible to get on a benign regression track. For example, for alcohol and hormone intoxication, the first and second leading causes of the disease in China, measures are taken to abstain from alcohol and to end the use of glucocorticoids. Protecting the necrosis that has occurred and at the same time promoting bone regeneration and lesion tissue repair through a biological response to make the repair as complete and effective as possible, restoring the weight-bearing capacity and preventing the femoral head from deforming and collapsing. Therefore the second key treatment lies in reducing weight bearing, walking, and decreasing the load on the weight bearing area of the femoral head to avoid microfractures and collapse of the weakened bone tissue. Patients are encouraged to do load-reducing exercises, such as cycling and swimming. It is difficult to intervene with drugs in the necrotic lesion of the femoral head because of the tissue reaction and the attenuated osteogenic regenerative capacity, which is difficult to enhance by drugs. For patients with osteonecrosis of the femoral head that has not yet collapsed, the following surgical procedures can be used: simple core decompression, core decompression + bone graft, various types of osteotomy, etc. For patients with collapsed or deformed femoral head with long term pain and dysfunction, artificial hip arthroplasty is feasible, which is a mature surgery with positive results and high success rate.