Avascular necrosis (AVN) [also known as osteonecrosis, bone necrosis, bone infarction, aseptic necrosis, and ischemic necrosis] is a condition that results from a significant loss of blood supply to an area of bone tissue. The most common areas affected are the hip, knee, spine, shoulder and wrist. Loss of circulation causes the bone tissue to die, and in extreme cases can result in the collapse of a segment of bone. When the surface of a joint is involved, it may lead to rapidly progressive osteoarthritis.Avascular necrosis may be the result of trauma, which interrupts blood supply, as in AVN of the head of the femur (hip joint) after fracture of the neck of the femur. Other causes include the use of systemic steroids as well as certain inflammatory diseases. The exact mechanism for loss of circulation in these circumstances is not well understood.