I. Overview Femoral head necrosis, also known as ischemic necrosis of the femoral head, is usually caused by interruption or impairment of blood supply to the femoral head, resulting in death of bone cells and bone marrow components and subsequent repair, which then leads to structural changes of the femoral head, collapse of the femoral head and joint dysfunction. Femoral head necrosis can be divided into two categories: traumatic and non-traumatic. The former is mainly caused by hip trauma such as femoral neck fracture and hip dislocation, while the latter is mainly caused by alcoholism and glucocorticoid application in China. Diagnostic criteria Main criteria: 1. Clinical symptoms, signs and history: arthralgia mainly in the groin, hip and thigh area, limited internal rotation of the hip joint, history of hip trauma, history of glucocorticoid application and history of alcoholism. 2.X-ray changes: femoral head collapse without joint space narrowing; sclerotic zone with demarcation within the femoral head; translucent zone of subchondral bone. 3.Nuclear scan shows a cold zone in the hot zone within the femoral head. 4, T1-weighted phase of MRI of femoral head shows banded low signal or T2 phase with bilinear sign. 5.Bone biopsy shows more than 50% osteocyte vacuolation sockets in the trabeculae and involves multiple adjacent trabeculae with bone marrow necrosis. Secondary criteria: 1. X-ray shows collapse of the femoral head with narrowing of the joint space, cystic degeneration or speckled sclerosis in the femoral head, and flattening of the traumatic part of the femoral head. 2.Nuclear scan shows hot or cold areas. 3, MRI shows banding type with homogeneous or heterogeneous low signal intensity without T1 phase. Two or more major criteria are met for diagnosis. Meeting one major criterion, or the number of positive secondary criteria is greater than or equal to four (including X-ray multiple criteria), the diagnosis is possible.