When the knee joint is damaged and cannot be repaired, as is typical with some forms of arthritis, a total knee replacement may provide relief from pain and restricted movement. Approximately 581,000 knee replacements are performed each year in the United States. Most patients who undergo a total knee replacement are 60-80 years old, but surgeons evaluate patients individually based on pain and level of disability, not age. Many different types of materials are currently used in total knee replacement surgery. Most replacements consist of three components: a femoral piece made of metal, a tibial piece made of durable plastic held in a metal tray, and a patellar piece also made of durable plastic. Total knee arthroplasty can restore patients to their previous level of function, but recovery requires a significant amount of exercise and therapy post-surgery.