Avascular necrosis also called Osteonecrosis refers to a condition which results from lack of blood supply to bone tissue leading to bone death. Blood flow to the bone may be adversely affected from damage to the blood vessels, blockage by air or fat embolism in the blood vessels or by inflammation of the walls of the blood vessels. Though it can affect any bone, the ends of the thighbone (femoral heads) and shoulder are most commonly involved. Avascular necrosis is most common in young men below 50 years of age. Injury to the bone is the main cause of avascular necrosis. Pain and stiffness are the most common symptoms associated with avascular necrosis.