Avascular necrosis (AVN) or Osteonecrosis is death of bone tissue that occurs when healthy stem cells in a bone die off, become sick, or are too few in number to keep up with normal wear and tear. The single most common cause of osteonecrosis is use of oral steroids like Prednisone that in high doses stunt your body’s natural healing ability. While oral steroids can reduce swelling, they are frequently given in such high doses that they can cause cells that help to maintain your bone to actually die off or become stunned.