Bone death. Coloured magnetic resonance imaging (MRI) scan of a side view of the knee of a 78 year old patient with severe osteonecrosis (bone death). Bone is blue and surrounding tissue is yellow. The bone at upper centre is the femur (thigh bone), with the tibia (shinbone) at lower centre. The dead area of tissue is brown (centre). The bone death results from a loss of blood flow to the area. The cause of the loss of blood flow is not known. The disease, which causes pain and swelling, is most common in women over 60 years of age. Treatment is with pain relief and exercise. In severe cases surgery may be needed to remove the dead tissue or replace the joint.