1.What imaging examinations should be done in the early stage of suspected femoral head necrosis? How to carry out imaging examination scientifically? When patients have hip pain and the existence of osteonecrosis susceptibility factors, suspected femoral head necrosis, should choose MRI or isotope bone scan examination, can be early detection of osteonecrosis. Imaging should be selected scientifically when diagnosing or understanding the progression of osteonecrosis of the femoral head. Isotope bone scan can be used for screening of osteonecrosis of femoral head; MRI is the best means for early detection of osteonecrosis; once the manifestation of osteonecrosis appears in X-ray or CT, osteonecrosis of femoral head has progressed to at least stage II, and the progression of osteonecrosis of femoral head can be understood through them. 2, MRI in the diagnosis and treatment of osteonecrosis Nuclear magnetic resonance examination (MRI) is the gold standard for the diagnosis of osteonecrosis of the femoral head. Osteonecrosis has its specific manifestation in MRI images. When necrosis occurs in the outer superior region of the femoral head, bone repair begins at the interface between the necrotic area and normal bone, and new bone tissue is formed to cover the necrosis, thus producing a sclerotic rim. The abnormal signal characteristic of femoral head necrosis in T1 and T2-weighted phase is surrounded by a low signal band, which represents the aforementioned sclerotic rim. If this “linear sign” is present, the diagnosis of osteonecrosis can be established. As the repair process continues, a band of fibrous granulation tissue is formed on the medial side of the sclerotic margin, which appears as a high signal in the T2-weighted phase, and this “double line sign” is a characteristic MRI manifestation of osteonecrosis. MRI should be used to detect the presence of osteonecrosis, except in patients with unilateral osteonecrosis to determine whether necrosis occurs on the other side, and it is wrong to review MRI in the follow-up of the disease to understand the progress of the disease. 3, CT examination in the application of diagnosis and treatment of osteonecrosis CT examination is mostly used to understand the progression of osteonecrosis, according to its imaging performance to help choose the appropriate treatment method. The “asterisk sign” is a manifestation of lamellar repair of bone in the trabecular structure. The punctate low signal area or microfracture in the necrotic area indicates the early collapse of the femoral head and the progression of osteonecrosis to stage III. 4, the application of plain X-ray in the diagnosis and treatment of osteonecrosis Like CT examination, plain X-ray is used to understand the progression of osteonecrosis. Once the manifestation of osteonecrosis appears on the X-ray, it means that it has progressed to stage II. If the “crescent sign” appears, it is a sign of subchondral plate fracture and early collapse of the femoral head, indicating that it has progressed to stage III. When taking X-rays, the orthopantomogram of the pelvis and the froggy phase of both hips should be included, because only the froggy phase can detect the collapse of the femoral head in front of the necrosis. 5.When do you need to do X and CT examination After the diagnosis of femoral head necrosis is confirmed by MRI examination, X ray and CT examination should be done. In the follow-up of the disease, those who have the condition should review X-ray and CT examination every 3 months within 2 years. 6, bone scan examination in the diagnosis and treatment of osteonecrosis Bone scan early detection of osteonecrosis is highly sensitive, but the diagnosis of osteonecrosis still lacks specificity. Bone scan is suitable for patients suspected of multifocal osteonecrosis and failed to do MRI examination, or patients at high risk of osteonecrosis with persistent pain in the hip but no abnormality is seen in MRI. It is the characteristic sign of bone scintigraphy for the diagnosis of osteonecrosis when it is shown as the cold area in the hot area, i.e. the “fried bagel” sign. 7, the advantages and disadvantages of bone scan advantages: high sensitivity; disadvantages: poor specificity. 8, diagnostic imaging criteria Strictly speaking, the diagnosis of osteonecrosis requires pathological diagnosis, but in the clinical application is limited. MRI images can be seen as “linear sign” or “double line sign”, and the osteonecrosis lesion in the lipid suppression phase is high signal. 9, imaging on the prediction and significance of femoral head collapse According to the study of the natural course of femoral head necrosis, about 80% of patients with untreated femoral head necrosis will experience collapse of the femoral head joint surface within 1-3 years. Since non-traumatic osteonecrosis occurs mostly in middle-aged and young adults, the long-term outcome of artificial hip arthroplasty in these patients is still uncertain, so it is necessary to seek effective and efficient treatment to preserve the femoral head. Not all cases of osteonecrosis progress to collapse of the femoral head, and early diagnosis and prediction of whether the affected femoral head will collapse and non-operative treatment of those that do not progress can result in significant savings in medical costs and reduced patient suffering. The MRI data of femoral head necrosis is input into the computer, and the software system is used to perform 3D reconstruction to determine the site of necrosis in three dimensions and accurately calculate the volume of osteonecrosis, predict whether the femoral head will collapse, and individualize the simulation of hip joint load computer finite element analysis to determine whether the femoral head will collapse in the future.