Avascular necrosis is an infarction of bone that is associated with (1) long-term corticosteroid use, such as in patients with systemic lupus erythematosus (most common cause), (2) sickle-cell disease, (3) trauma, (4) Legg-Perthes disease, or (5) Kienbock disease involving the scaphoid (navicular) bone. OsgoodSchlatter dis ease is a localized inflammation that produces pain in the tibial tuberosity at the point of attachment of the patellar tendon, which results in prominence of the tibial tuberosity that persists throughout life. It usually occurs during the pubertal growth spurt and is not an example of avascular necrosis.