Osteonecrosis occurs 12 hours after the blood supply to the femoral head is interrupted, but it takes at least two months, if not longer, to see the changes in the femoral head on X-ray. The X-ray manifestation of femoral head necrosis is increased bone density, which shows that the color of the femoral head becomes whiter on the X-ray. Increased bone density is the manifestation of new bone formation after osteonecrosis, not osteonecrosis itself, and the femoral head necrosis can be divided into four stages according to the X-ray examination, as follows: 1. Subchondral lysis stage: the femoral head is intact in shape and the hip joint gap is normal, but a 1 2, femoral head repair phase: the femoral head is intact, the joint gap is normal, but the bone density under the femoral head weight-bearing area is increased, and the surrounding lamellar hypodensity area or cystic changes can be seen; 3, collapse phase: the subchondral bone in the femoral head weight-bearing area is flattened, brittle and collapsed to varying degrees, the femoral head loses its round and smooth shape, the subchondral bone density The femoral head loses its round and smooth shape, the subchondral bone density increases, and the joint gap is of normal width; 4. Femoral head dislocation stage: the femoral head is severely collapsed, the femoral head becomes flattened, the outer upper part is not covered by the acetabulum, which also bears pressure and is a residual protrusion, the femoral head will be displaced to the outer upper part, and the joint gap may become narrow.