Osteoarthritic knee cartilage. Coloured scanning electron micrograph (SEM) of cartilage from the knee of a patient suffering from osteoarthritis. This disease causes the wasting of the cartilage that normally reduces friction between moving bones. The surface of the cartilage has become roughened, making it less effective at lubricating the joint, which may result in pain and stiffness. Painkilling drugs can treat the pain, and weight loss reduces pressure on the joints. In serious cases the knee joint may be replaced surgically. Magnification unknown.