A hip disorder in children. Avascular necrosis causes pain, stiffness and limited range of motion in the affected hip joint. A child with this condition may limp. The condition is caused by the death of bone cells at the top of the thighbone due to a poor blood supply. It can result from an injury to the blood vessels that supply the femur. Taking a corticosteroid drug for an extended period or having sickle cell anemia increases the risk for developing avascular necrosis.