Avascular necrosis (AVN), also known as osteonecrosis, is a condition in which poor, temporary, or permanent loss of blood supply to an area of bone leads to the cellular death of the components of bone, including the marrow. From Wikipedia, the free encyclopedia: "Although it can happen in any bone, avascular necrosis most commonly affects the ends (epiphysis) of long bones such as the femur, the bone extending from the knee joint to the hip joint. Other common sites include the upper arm bone, knees, shoulders, and ankles. The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times. Avascular necrosis usually affects people between 30 and 50 years of age; about 10,000 to 20,000 people develop avascular necrosis each year. Orthopaedic doctors most often diagnose the disease. Avascular necrosis cut short the football and baseball careers of star athlete Bo Jackson." http://en.wikipedia.org/wiki/Avascular_necrosis I gathered that the Wikipedia article above was taken, at least in part from the website address given below. This interesting and easy to follow information is not copyrighted. You are encouraged to print and distribute all the copies you'd like: http://www.niams.nih.gov/hi/topics/avascular_necrosis/AvasNec.pdf Hope this helps.