Osteonecrosis. False-colour computed tomography (CT) scan of a posterior view of the knee joint, showing osteonecrosis (bone tissue death) of the tibia bone. At top (red) is the head of the femur where it meets the tibia (brown) of the lower leg; the fibula is a thin bone at left of the tibia. Osteonecrosis has occurred on the head of the tibia (at centre, yellow & black egg-shape). Bone tissue death may result from infection after bone injury. Usually it is due to impaired blood supply to the bone, which may occur in disorders such as sickle- cell anaemia, diabetes, Cushing's syndrome. It is sometimes seen in cases of renal failure, associated with corticosteroid treatment.