The knee and hip joints are the largest joints in the human body. Arthritis of the knee or hip is one of the most common conditions, resulting in progressive disability and affecting common activities such as walking, standing, or simply getting out of a chair. Total knee replacement is a rapidly-growing procedure.Initially, knee replacement was intended for patients in their late 60s and 70s. Recent improvements to the prosthesis and overall surgical technique have enabled the procedure to be performed on patients in their 50s as well as their 80s and 90s. Each year, over 600,000 primary total knee replacements are performed in the United States. Total hip replacement has been around in various forms for many years. The technique and the material used have evolved over the years.These newer techniques allow for more durable prosthesis, which will more readily tolerate the demands of the younger, more active patient.