Avascular necrosis occurs when blood flow to a bone is interrupted or reduced. Reduced blood supply can be caused by:
Joint or bone trauma. An injury, such as a dislocated joint, might damage nearby blood vessels. Cancer treatments involving radiation also can weaken bone and harm blood vessels.
Fatty deposits in blood vessels. The fat (lipids) can block small blood vessels, reducing the blood flow that feeds bones.
Certain diseases. Medical conditions, such as sickle cell anemia and Gaucher's disease, also can cause diminished blood flow to bone.
For about 25 percent of people with avascular necrosis, the cause of interrupted blood flow is unknown.