Healthy knee joint. False-colour computer enhanced gamma scan (scintigram) of a human knee joint seen in side view. At top (blue), the thigh femur bone is positioned horizontally and connects at the knee joint to the tibia shin bone (blue, lower centre). The articular surfaces of these bones meet in cartilage (red), and the joint is united by ligaments (yellow). This image shows the dis- tribution of a radioactive tracer technetium-99m, injected into the subject & which concentrates in bone. Radiation is recorded by a gamma camera. Bone scanning is frequently used in screening for secondary disease in cancer patients. Cancerous bone would appear as brighter hot spots"."