An artificial joint for full knee replacements typically has a curved metal component shaped like the lower end of the femur, states the American Academy of Orthopaedic Surgeons. The femoral component is also grooved along the center to enable kneecap motion. A dome-like component covers the back of the kneecap, or patella, and is fitted to its shape. A flat metal component with a plastic upper lining covers the top of the tibia bone and may include a protruding stem.
Partial knee replacement systems, such as the DePuy Sigma high-performance device, usually allow doctors to install individual components, depending on which parts of the knee are deteriorated, according to Healthline. Surgeons can choose from a variety of mechanical designs and material compositions based on factors such as patient age, degree of physical activity and the required surgical skills. For example, a common choice for seniors is a traditional fixed-bearing system in which the femoral component rolls smoothly over the polyethylene-capped tibial component. This system works for adults who do not require extra rotational capabilities needed for an active lifestyle while still providing a 20 to 50 percent increase in range of motion.
Surgeons may recommend a mobile-bearing system for younger or active patients, notes Healthline. The polyethylene insert above the metal tibial cap rotates in short increments for increased flexibility, but this option is only suitable for people with adequate soft tissues to support the prosthesis and prevent dislocation.