I have been diagnosed with avascular necrosis of my right hip. My doctor questioned me as to whether I have ever scuba dived or was a heavy drinker. What do these two things have to do with avascular necrosis?

Avascular necrosis of the hip refers to the death of bone cells in the head of the femur bone due to causes other than infection. In effect, the blood supply to the bone cells, which provide nutrients, is disrupted. One of the more common reasons is from a trauma, for example, a bad fall or a car accident. If you have no history of trauma, your doctor should look for other known sources of avascular necrosis, including alcoholism and use of steroids, such as Prednisone. Disease such as sickle cell anemia, leukemia and other blood abnormalities can cause sludging of the vascular network to the head of the femur. Excessive radiation treatment for a tumor in the pelvic area can also traumatize it. Scuba divers who get the ''bends,'' also known as caisson disease, can develop avascular necrosis.