Prompt diagnosis of ischemic necrosis of the femoral head allows for early treatment of osteonecrosis, which may lead to a good early outcome. The diagnosis of ischemic necrosis of the femoral head is mainly supported by medical history with high-risk factors, clinical symptoms and imaging data. 1. Medical history: Among all the diagnostic criteria, medical history is one of the most important criteria. The occurrence of ischemic necrosis of the femoral head often has a high risk factor associated with osteonecrosis, such as the history of hormone use, alcohol abuse, history of hip trauma fracture, these high risk factors together account for 90% – 95% of all osteonecrosis. A focus should be placed on exploring an associated risk factor at the time of initial diagnosis. If there are no such high-risk factors, do not consider ischemic necrosis of the femoral head in the first place. 2. Symptoms and signs: The most common clinical symptom is deep pain in the ventral sulcus, which can be mild and severe at times and relieved after rest. Signs seen on physical examination may not be noticed in the early stage or only when the hip joint is internally rotated, the range of motion is reduced, and the characteristic pain-resistant gait appears. When the femoral head has collapsed, there may be a popping sound (cracking sound) when there is a necrotic fragment, and the most common sign is increased pain and limited activity when the hip joint is rotated internally. 3, imaging seen: (1) radiological study is necessary for the diagnosis of osteonecrosis, radiographs are still the first choice in diagnosis. Appropriate anteroposterior and frog lateral views are necessary. Radiographic changes in the femoral head usually occur several months after the onset of disease and include cystic changes, sclerosis or crescentic signs. The crescent sign arises from subchondral collapse of the necrotic portion. (2) Technetium 99 bone scan is used in high-risk patients with negative X-rays. However, recent studies have shown that the value of bone scans is limited, as they are often misleading with 25-45% false negatives in cases that have been confirmed by MRI or histologic evaluation. (3) MRI has become the standard for the diagnosis of osteonecrosis. The sensitivity and specificity are 99%. single concentration lines on T1-weighted images are the interface between normal and ischemic bone tissue, while double concentration lines on T2-weighted phases are indicative of hypervascular granulation tissue. (4) CT scans and planimetric calculations can demonstrate the collapse of the femoral head. However, they are rarely applied because of their high cost and high-dose X-ray exposure. (5) Functional assessment of bone, including direct measurement of bone marrow pressure, venography and tissue biopsy. Because of its invasive nature and the high accuracy of MRI it is not widely used nowadays.