The service life of knee prosthesis varies from about 15 to 20 years. For elderly people, joint replacement between the ages of 65 and 80 is generally the most appropriate and can solve the problem in one replacement. Knee replacement in the elderly is mainly for severe osteoarthritis or rheumatoid arthritis. In some patients with severe symptoms, despite their young age, the age of knee replacement can be advanced if knee flexion and extension are severely limited, affecting their lives, or if the pain is so unbearable that the only way to stop it is with pain medication. We have knee replacements around 30 years of age, mainly for juvenile rheumatoid arthritis with severe deformities.