Cartilage: The thin smooth protective lining of the bone inside the joint. It is responsible for smooth movement, shock absorption, and nutrition of the joint. Chrome Cobalt: A material (alloy) frequently used to make artificial components. CPM Machine: A device that comfort- ably supports the leg, while continuously bending the knee. Hence CPM - Continuous Passive Motion. Dislocation: This occurs if the hip pops out of the socket. The hip will need to be replaced into its normal position under anesthetic. Femoral Prosthesis: The artificial component that replaces the head of the femur (thigh bone). Femur: The thigh bone. The upper end forms the hip joint. Methyl Methacrylate: The "cement" used to pro- vide firm fixation of an implant within the bone. Osteoarthritis: Wear and tear changes in a joint. The cartilage lining surface becomes worn away, causing pain and stiffness. Patella: The kneecap. PMMA: This stands for poly- methyl-methacrylate. It is the cement used to bond the knee replace- ment in the bone. Press Fit: The tight fit of a metal prosthesis into bone. This improves fixation and the probability that bone will grow into the prosthesis. Prosthesis: A metallic or plastic device that provides an artificial substitute to replace the removed bone. Thrombosis: A blood clot in the veins. This may occur in the legs or pelvis following major surgery. Tibia: The leg bone. The long bone between the knee and the ankle. Titanium: An essentially pure metal that is more flexible than chrome cobalt. It is more commonly used in non- cement hip replacements. Total Hip Replacement: The operation in which the upper part of the thigh bone and its socket are replaced by an artificial joint. Total Knee Replacement: The operation in which a diseased knee joint is replaced by an artificial joint.