Ischemic necrosis of the femoral head is caused by the destruction and interruption of blood flow in the femoral head and the development of cystic changes in the femoral head, which leads to the collapse of the femoral head and the involvement of the cartilage of the hip joint surface, while osteoarthritis of the hip joint is caused by the lesion of the cartilage of the femoral head joint surface first and then the involvement of the internal femoral head, which leads to cystic changes in the femoral head. The treatment of both femoral head necrosis and hip osteoarthritis is the same in advanced stages, and both require joint replacement surgery. However, the diagnosis of these two diseases needs to be differentiated from each other in two aspects: First, from the aspect of medical history, femoral head necrosis is mostly seen in young adults, with a history of hormone use, heavy alcohol consumption or trauma, while hip osteoarthritis is mostly seen in elderly patients. Secondly, from the X-ray film, the early stage of femoral head necrosis is characterized by small or interrupted bone texture of the femoral head, uneven bone density, cystic and hardened femoral head, the joint gap is normal at this stage, and the femoral head becomes flat and collapsed at a later stage, and the joint gap can become narrower; the joint gap becomes narrower in the early stage of hip osteoarthritis, and the joint surface of the acetabulum and femoral head appears less smooth or wavy at the same time. The bone surface corresponding to the narrowing of the gap often has irregular osteosclerosis, and the head of the femur is mushroom-shaped. The osteophytes at the edge of the acetabulum form dense triangular bone masses or long curved strips that cover the outwardly enlarged head of the femur. The main clinical symptoms of hip osteoarthritis are joint pain and inflexible joint movement. Physical examination shows joint swelling, fluid, muscle atrophy; creaking sound during active and passive joint activities, and varying degrees of activity limitation and muscle spasm. Some older adults also have thickening of the distal interphalangeal joints. The causes of secondary osteoarthritis include: congenital abnormalities of the joint; trauma; acquired unevenness of the joint surface; poor joint alignment due to extra-articular deformity; joint instability; and medical factors, such as long-term inappropriate use of corticosteroids. The main symptoms of femoral head necrosis are manifested in the following five points: 1. Pain. Pain can be intermittent or persistent, increased after walking activities, sometimes for rest pain. The pain is mostly pins and needles, dull pain or soreness and discomfort, often radiating to the groin area, inner thigh, posterior hip and medial knee, with numbness in the area. 2.Joint stiffness and activity limitation. The affected hip joint flexes and extends unfavorably, has difficulty squatting, cannot stand for a long time, and walks with a duck walk. The early symptoms are limited abduction and external rotation activities. 3.Crippling. Progressive shortening limp, due to hip pain and femoral head collapse, or late onset of hip subluxation. Intermittent claudication often occurs in the early stage, and is more obvious in children. 4. Physical signs. Local deep pressure pain, pressure pain at the stopping point of the adductor muscle, positive 4-word test, positive Gaja s sign, positive Allis sign test. Abduction, external rotation or internal rotation activities are limited, the affected limb may be shortened, muscle atrophy, and even signs of subluxation. Sometimes the axial impulse pain is positive. 5.X-ray performance. The bone texture is thin or interrupted, and the femoral head is cystic, sclerotic, flattened or collapsed. Early and late pain manifestation of femoral head necrosis The first conscious symptom of femoral head necrosis is pain, which is around the hip joint, inner thigh, anterior side or knee. In the early stage, the pain is vague, dull or intermittent, and the pain is aggravated by more activities and can be relieved or reduced by rest. However, there are some cases of persistent pain, whether it is from exertion or rest, or even from lying in bed. Moreover, the pain gradually increases. At this time, although there is no obvious abnormal morphological change on the X-ray, the hip joint has different degrees of functional limitation. For example, the patient’s hip joint on the affected side is limited in abduction and rotation, and cannot squat in place. In the advanced stage, the femoral head collapses, fractures and deforms, and some of them may cause hip dislocation, and the pain at this time is directly related to hip joint activities and weight bearing. Pain is caused by bony friction in the joint when moving, but when the head and socket are not rubbing against each other at rest, the pain is not obvious. Therefore, the pain is aggravated by walking and activity, and the pain is stopped or reduced by moving. In short, the early stage is mainly pain with functional limitation; the late stage is mainly functional impairment with pain. There is an essential difference between femoral head necrosis and hip osteoarthritis. The former is ischemic necrosis, which develops from the inside out, while osteoarthritis is mostly degenerative, which develops from the outside in.