Avascular necrosis (AVN), also called osteonecrosis, bone infarction, aseptic necrosis, and ischemic bone necrosis, is cellular death (necrosis) of the bone due to interruption of the blood supply. Without blood, the bone tissue dies and the bone collapses. If avascular necrosis involves the bones of a joint, it often leads to the destruction of the joint articular surfaces.

For more information check out;

• https://en.wikipedia.org/wiki/Avascular_necrosis
• http://www.avncharity.org.uk/