X-ray examination is the most common and basic diagnostic method. Since the femoral head is a spherical structure, it is usually required to take double hip orthogonal frog films. The dynamic X-ray can also indicate the regression of necrosis and judge the treatment effect. MRI is currently the most sensitive and accurate method for diagnosing femoral head necrosis and is considered the “gold standard” for diagnosis. It can not only detect early necrosis of the femoral head, even if the patient has no symptoms, but also more accurately determine the extent of necrosis, the state of repair after necrosis, and reflect many changes that cannot be shown on X-rays, such as the presence of edema in the bone marrow and the presence of fluid in the joint cavity. In addition, MRI can be considered a non-invasive test because there is no X-ray radiation. The disadvantage is that it is more expensive than X-rays, and it is not suitable when metal is present in the body. CT is particularly sensitive to bone and can detect even the slightest collapse of the femoral head, so it can be considered a good tool for detecting early collapse of the femoral head. Isotope or nuclide scans (ECT) are used to determine changes in blood circulation by detecting differences in the degree of radioactive element accumulation in different tissues of the body. In a typical ECT of femoral head necrosis, a decrease in the concentration of radioactive elements in the femoral head can be found, indicating a decrease in the blood supply to the femoral head. Although ECT is not as sensitive as MRI in diagnosing femoral head necrosis, it can be of special value when the presence of metal in the body makes MRI inappropriate, or when understanding multiple early necrosis throughout the body.