I am scheduled for a knee joint replacement. Because I am younger than the average patient, 55 years old, I am told I may need a second operation years later when certain parts wear out. Which part will most likely wear out?

A knee replacement is made of metal and plastic components. Both components have the potential to fail, but the plastic component
usually wears out and fails first. The plastic component is also known as polyethylene. It serves as a spacer between the metal components, which are applied to the tibia and femur. The polyethylene plastic component acts as a bearing surface between the metal components. Like a car tire, the plastic component undergoes a slow progress wear creating small particles of plastic debris. This plastic debris within the joint can stimulate inflammation and might cause loosening of the metal components. The initial prototype knee replacements have a 10- to 12-year average age of survival. Many factors influence the wear rate, such as level of activity, age and body weight. The newer knee replacements are expected to have better resistance against wear. Thus, the newer components are felt to have more longevity.