Ischemic necrosis of the femoral head is no longer an uncommon disease. Since many of the patients are young adults and the treatment period is long, people are already aware of this disease. So how to carry out radiological examination in the clinic is reasonable? First of all, it must be understood that although femoral head necrosis is relatively common, it is not something that can be acquired casually, most of them have predisposing factors and known causes. The most common ones are hip trauma, long-term alcohol consumption, hormone use, etc. In addition to trauma, other causes of necrosis do not have painful symptoms in the early stages. Ordinary X-ray examination is not easy to find osteonecrosis. Second, once there are symptoms of hip pain and the above-mentioned high-risk factors, there is a reason to conduct a simple X-ray examination. If there is no obvious problem, symptomatic treatment can be carried out and observed. It is possible to repeat the examination 3 months after the first examination. Note that the same X-ray film, experienced doctors can detect osteonecrosis early, that is, easy to miss the diagnosis. Third, if ordinary X-ray film did not find osteonecrosis, and after the evidence of treatment and can not relieve or eliminate the symptoms, it is necessary to carry out high-level examination, more practical is the magnetic resonance examination. It is sensitive to the early diagnosis of osteonecrosis up to 100%, but the cost is higher. If the pain has been present for more than 3 months and the MRI is fine, there is little chance of osteonecrosis. It is important to note that if the diagnosis has been confirmed, MRI is not necessary. It is often seen in the clinic that some patients take out the MRI film for many times, which is a waste. Fourth, CT is not as sensitive as MRI for early diagnosis of femoral head necrosis, so it is not a recommended test for suspected cases. For patients who have been diagnosed, especially those who receive hip preservation treatment, if you suspect that the femoral head has early collapse and deformation, you can have a CT scan, which can detect the deformation and collapse of the anterior side of the femoral head, while ordinary X-ray films are not easy to detect the early deformation. Once the collapse and deformation of the femoral head is detected, it is redundant and wasteful to perform CT scan again. 5. For patients undergoing hip preservation treatment, the most simple, practical and inexpensive test is x-ray examination. Pay attention to the preservation of each stage of the film, dynamic observation of the series of X-rays, which is meaningful to judge the treatment effect and prognosis. Sixth, to suspect other diseases, such as tumor rheumatism and other diseases easily misdiagnosed as osteonecrosis, magnetic resonance CT and isotope scan have more differential diagnostic significance. Seven, the early stage of femoral head necrosis is easy to be missed and misdiagnosed. For example, misdiagnosis as lumbar spondylosis, misdiagnosis as knee arthrosis, etc.