Ischemic necrosis of the femoral head is a pathological process in which partial or complete ischemia of the femoral head occurs due to different reasons, resulting in necrosis of bone cells, bone marrow hematopoietic cells and fat cells. As the body has the natural ability to repair the necrotic area, while new bone cells grow with new blood vessels to the necrotic area and form new bone, the necrotic bone trabeculae will be gradually absorbed. During this process, the mechanical properties of the bone are significantly weakened, and normal weight-bearing can cause the femoral head to collapse and deform. The affected hip will show clinical symptoms, mainly pain and activity impairment. Traumatic ischemic necrosis of the femoral head: 1. Fracture of the femoral neck: When there is displacement of the fracture in the femoral neck capsule, there are different degrees of tearing of the supporting vessels. If the fracture is severely displaced, all the supporting blood vessels can be destroyed, and the femoral head loses almost all its blood supply, and the degree of ischemic necrosis is very serious. 2.Hip dislocation: After dislocation of the femoral head from the acetabulum, the round ligament is ruptured and the hip capsule is torn to varying degrees. The internal and external vessels of the femoral neck, which form the vascular ring at the base of the femoral neck, can be distorted, stretched, compressed or even ruptured. If the dislocation is not reset in time, the blood supply to the femoral head may be affected by secondary thrombosis of the above vessels. Ischemic necrosis of the femoral head in adults: Ischemic necrosis of the femoral head in adults or non-traumatic ischemic necrosis of the femoral head can be complicated by a variety of internal and external diseases. The pathogenesis of this disease is not fully understood, and the following diseases can be considered as high-risk factors related to the development of ischemic necrosis of the femoral head. 1, hyperadrenocorticism or exogenous corticosteroid increase: clinically it is common to see patients with systemic lupus erythematosus, psoriasis, heavy bronchial asthma, and other patients due to long-term or intermittent high doses of adrenocortical steroids (hereinafter referred to as steroids) and ischemic necrosis of the femoral head. It is difficult to determine the relationship between the dose and duration of application and the onset of the disease. The history of steroid application accounts for 30%–50% of female patients, about 50% are bilateral, and the prognosis is the worst, especially for lupus erythematosus. 2, alcoholism: the incidence of ischemic necrosis of the femoral head in long-term alcoholics is between 10-20%. In these patients, the incidence of pancreatitis, fatty liver, malnutrition and neglect of trauma is higher. 3, decompression disease (diving disease): McCallum census of workers, found that the incidence of osteonecrosis is 20%, and later in sea divers and collection of shellfish divers found in this disease. When working in deep water, divers inhale compressed air, their blood and tissues contain high concentrations of nitrogen. When divers quickly surfaced and decompressed, the solubility of nitrogen in the body quickly decreased and released as free nitrogen. Because nitrogen is easily soluble in fat, it tends to accumulate in the fatty bone tissue, causing internal and external blockage of the intramedullary vessels and leading to bone ischemia and necrosis. Similarly, a similar situation can arise when a high-altitude pilot rises rapidly from normal atmospheric pressure to a low-oxygen environment. 4, Gaucher disease: this disease is also known as cerebrolysin lipid disease, a disorder of lipid metabolism, for autosomal recessive inheritance. The main cause is the accumulation of cerebrosides in the reticular cells and the formation of Gaucher cells to squeeze the capillaries in the medulla, which reduces or blocks the blood supply in the medulla and causes necrosis and resorption of bone trabeculae. Skeletal lesions can be seen in the lower femur. The systemic symptoms include hepatosplenomegaly, skin hyperpigmentation, and macularity of the bulbar conjunctiva. 5. Sickle cell disease is a hereditary abnormal hemoglobinopathy caused by structural abnormalities of red blood cells, mostly in blacks, with the highest incidence in Nigeria and Guinea, and more common in females. The red blood cells become sickle-shaped, long semilunar, or otherwise deformed, losing the flexibility and deformability of the normal red blood cells so that they cannot pass through the junction of blood vessels and sinuses, resulting in intravascular infarction, often accompanied by increased blood consistency, stagnant blood flow, bone marrow fibrosis, narrowing of the marrow cavity, and bone infarction, resulting in extensive bone necrosis and sclerosis. Ischemic necrotic lesions can also involve the humeral head, vertebral body and long bones. 6.Radiotherapy: When radiotherapy is given to female cervical cancer, the pelvic area is the area of concentration of radiation for many times. In addition to directly killing bone marrow cells and bone cells, high-dose irradiation can also cause intraosseous arteritis, which can lead to ischemic necrosis of the femoral head due to luminal narrowing or occlusion at a later stage. Ischemic necrosis of the femoral head can also be seen in gout, Cushing’s syndrome. Cartilage malnutrition, iron toxicity, diabetes mellitus, mucopolysaccharide metabolic disease, pancreatitis, hemophilia, burns, pregnancy, ochreosis, chronic kidney disease, vascular sclerosis, erythrocytosis, occlusive vasculitis, hypothyroidism, etc. Most scholars believe that this disease is the result of ischemic necrosis of the epiphysis, which is a series of changes caused by changes in the mechanical properties of the epiphysis during the resorption of necrotic bone and the formation of new bone. The exact cause of epiphyseal ischemia of the femoral head is not known. The disease occurs in children between 4 and 8 years of age, when the blood supply to the femoral epiphysis is mainly from the lateral epiphyseal artery. The blood supply to the epiphysis is mainly from the lateral epiphyseal artery at this age, which can be compressed by increased pressure in the joint capsule due to synovitis. The incidence of epiphysitis in children with transient hip synovitis is less than 10% and is therefore not recognized by most scholars. Other factors associated with the development of this disease include trauma, development, weight, genetics, and endocrine factors.