Bone death. Coloured X-ray of a frontal view of the knee of a 78 year old patient with severe osteonecrosis (bone death). At top is the femur (thigh bone), at bottom is the tibia (shin bone), with the smaller fibula to its right. The dead area of tissue is brown (centre left). 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.