What is osteonecrosis of the femoral head, what is the diagnostic basis of osteonecrosis of the femoral head and its differential diagnosis This is what many patients want to know, here to give you an introduction. Definition of ONFH: Combining the criteria of the International Association for Research in Bone Circulation (ARCO) and the American Academy of Orthopaedic Surgeons (AAOS), ONFH is defined as: ONFH is a disease caused by the death of bone cells and bone marrow components and subsequent repair due to interruption or impairment of the blood supply to the femoral head, which subsequently leads to structural changes in the femoral head, femoral head collapse, and joint dysfunction. Diagnostic criteria Main criteria 1. Clinical symptoms, signs and medical history: hip pain mainly in the groin, hip and thigh area, limited internal rotation of the hip joint, history of hip trauma, history of corticosteroid application, history of alcoholism, history of deep water work, history of high snow disease, history of HIV infection, history of autoimmune disease and high coagulation and low fibrous solubility disease, etc. 2.X-ray changes: femoral head collapse without joint space narrowing; sclerotic zone in the femoral head with demarcation; subchondral bone with trans-x-ray zone (crescent sign, subchondral fracture). 3.Nuclide scan: it shows that there is a cold area in the hot area of the femoral head, i.e., the center of the femoral head has decreased radioactivity and the periphery has increased radioactivity, showing “fried noodle circle”-like changes. 4.MRI of femoral head: T1-weighted phase shows banded low signal (banded type) or T2-weighted phase has bilinear sign. 5.Bone biopsy: shows osteoblastic vacuolation of trabeculae >50%, and involves adjacent trabeculae, with bone marrow necrosis. Secondary criteria 1. X-ray: femoral head collapse with narrowing of the joint space, cystic or speckled sclerosis in the femoral head, and flattening of the external upper part of the femoral head. 2.CT: disappearance of the “asterixis sign” in the femoral head in cross-section. 3.ECT: nuclear bone scan shows cold or hot areas. 4.MRI: Band type with homogeneous or heterogeneous low signal intensity without T1 phase. The diagnosis can be confirmed by meeting 2 or more of the main criteria. If 1 major criterion is met, and the number of positive secondary criteria is ≥4 (including at least one positive radiographic change), the diagnosis is possible.