Arthritis of the knee. Coloured X-ray showing a joint affected by chondrocalcinosis. In this condition, crystals of calcium pyrophosphate are deposited in soft tissues such as cartilage, the connective tissue found in joints. In this case, deposits (green) have formed in the cartilage of the knee. They have fused to the knee cap (patella, far right) causing severely reduced movement of the joint. The degeneration of the joint has triggered synovial chondromatosis, the formation of fragments of cartilage and bone in the fluid-filled space in the joint. The bones of the leg are shown in red.