Avascular necrosis occurs when the tissue in the joints literally die when the blood supply is cut off to the bones. This can be a temporary blood supply loss or a permanent loss. Causes of avascular necrosis can include alcoholism, steroids, or blood disorders.
In the early stages of avascular necrosis, pain only occurs when pressure is put on the joint. However, as the necrosis worsens the pain is present even while resting the joint. In many cases, the blood supply is lost permanently and the damage tissue must be removed and replaced with a hip replacement.