The causes of femoral head necrosis are many and complex, so it is difficult to be detected. Even if one is aware of it, it is likely to treat some symptoms as other diseases, such as lumbar disc herniation, rheumatism, etc., resulting in the development of complete necrosis of the femoral head and even paralysis. Therefore, patients should have an understanding of the causes of femoral head necrosis to achieve early prevention and early detection and treatment. Femoral head necrosis is also known as ischemic necrosis of the femoral head, non-traumatic ischemic necrosis of the femoral head, idiopathic ischemic necrosis of the femoral head and so on. The femoral head is the two bones that support the upper part of the body, the specific location is below the pelvis, where the pelvis has an acetabulum on one side, the two femoral heads are exactly the same as the acetabulum, playing the role of supporting the upper body. The cause of femoral head necrosis is the increase of pressure in the femoral head, the femoral head bone tissue can not get the normal blood supply from the artery, so that the bone cells, bone marrow, hematopoietic cells, other cells in the femoral head tissue necrosis. Femoral head necrosis is a disease that develops gradually over a long period of time, from intermittent pain in the early stage to persistent pain, and then from pain to muscle spasm and restricted joint movement, and in the late stage, the femoral head collapses and most of them cannot move or walk, resulting in disability and limpness and loss of the ability to take care of themselves. Ischemia of the femoral head is the main cause of necrosis. Necrosis is caused by impaired arterial blood supply, poor venous reflux, or increased intramedullary pressure. What are the causes of femoral head necrosis? Mainly as follows: a. Intraosseous factors The abnormal red blood cells of hemoglobinopathy, the nitrogen emboli of decompression disease, alcoholism and the fat emboli produced by the pancreas can block the microvessels in the bone, leading to ischemic necrosis of the femoral head. In addition, the accumulation of abnormal erythrocytes in Gaucher’s disease, metastatic tumors, and the increase in volume of bone marrow contents caused by hormone-induced hypertrophic adipocytes can lead to increased pressure in the bone marrow cavity and impaired microcirculation, eventually causing necrosis. Second, extra-osseous factors Trauma-induced fracture and compression of the femoral head vessels, vasculitis, arteriosclerosis-induced vascular obstruction, Raynaud’s disease, decompression disease and sympathetic neuroreflex-induced vascular spasm can directly or indirectly lead to ischemic necrosis of the femoral head. Various pathogenic factors inside and outside the bone can increase the intramedullary pressure, which in turn increases the resistance to blood flow, leading to ischemia, cellular degeneration and necrosis, edema, etc. The edema of the tissues further increases the increased intraosseous pressure, forming a series of vicious circles, especially the continued weight-bearing of the affected limb, which increases the pressure of the ischemic femoral head and will accelerate the necrosis of the bone and lead to the fracture of the bone trabeculae and the collapse of the femoral head. Third, traumatic femoral head necrosis For example, femoral neck fractures, sprains, falls, bruises, hip dislocations and other reasons, because of untimely treatment or no treatment, it is likely that femoral head necrosis will occur. Hip fractures such as acetabular fracture, femoral neck fracture, and intertrochanteric fracture can endanger the blood supply to the femoral head. Once femoral head necrosis occurs, failure to detect and treat it in time will aggravate the condition of fracture patients. Therefore, patients with hip fracture should master reasonable methods to prevent the occurrence of femoral head necrosis. Fourth, non-traumatic femoral head necrosis such as hormonal drug overuse (resulting in osteoporosis, arterial vascular obstruction, so that bone cells, bone marrow cells gradually necrosis); long-term excessive alcohol consumption; decompression disease; rheumatism (often combined with ankylosing spondylitis and rheumatoid arthritis); osteoporosis (due to changes in the internal structure of bone tissue, partial degeneration of bone trabeculae, bone blood circulation is blocked, easy to cause femoral head necrosis); systemic diseases of blood (hemoglobinopathy, maritime anemia, Gaucher disease, hemophilia, inflammatory arteritis, stenosing arteritis, etc.); obesity, etc. For osteonecrosis of the femoral head, the most desirable treatment is in the early stage of its onset. At present, the examination method that can detect femoral head necrosis in early stage is magnetic resonance imaging (MRI). According to the research, it is proved that MRI can detect signal abnormality 7 days after the occurrence of femoral head necrosis. If effective measures are taken quickly, collapse of the femoral head can be prevented and the function of the joint can be preserved. Therefore, patients must go to a regular orthopedic hospital for examination and treatment in a timely manner once femoral head necrosis is detected.