The knee joint consists of the distal thigh bone (femur) and the proximal lower leg bone (tibia), with the kneecap (patella) in front. The bone surfaces of the components of the normal knee joint are covered with a smooth, pliable layer of clear cartilage that allows the joint to move freely. When diseases such as osteoarthritis and rheumatoid arthritis occur in the knee joint, the articular cartilage degenerates and peels away, bringing the bone beneath the cartilage into direct contact with the bone, resulting in severe pain. In addition, the joint may become deformed, bone fragments may form, stiffness may occur, difficulty in daily walking and going up and down stairs, and joint pain may be felt even when sitting or lying down. If pain is not relieved by pain medication, reduced activity, or the use of crutches, an artificial joint replacement may be considered. By removing the worn cartilage surface and wrapping it with a metal surface, artificial knee arthroplasty can effectively relieve pain, correct deformities, and help patients resume daily activities, which is currently the most effective means of treating advanced arthritis and one of the most important technological breakthroughs in the field of orthopedics in the 20th century. In recent years, with the rapid advances in prosthetic materials and surgical techniques, the results of arthroplasty have improved significantly, and it is now commonly performed at home and abroad, with approximately 580,000 knee replacements performed in the United States each year. Since artificial knee replacements are so effective, is it true that the earlier the surgery is performed, the better the results will be? For most diseases, the earlier an effective treatment is used, the better the outcome usually is. Unlike the artificial knee joint, which has a certain lifespan, it usually wears out and loosens about 15-20 years after surgery, just like a car tire that wears out after a certain number of miles and needs to be replaced. However, revision surgery is more difficult and the postoperative results are inferior to the first surgery, so it is usually only used for a small number of patients who have failed surgery. In younger patients, the joint wears out more quickly due to greater and more intense joint activity; and the life expectancy of younger patients exceeds the life expectancy of the prosthesis, making revision surgery inevitable. Therefore, for a long time, most physicians believed in the “once in, always in” principle and believed that the appropriate age for joint replacement should be 55 years or older. As a result, some patients with knee degeneration under the age of 55 were denied artificial knee replacements because they were “too young”. However, in recent years, with advances in artificial joint materials and surgical techniques, the longevity and postoperative outcomes of artificial joints have improved significantly. Some young patients who have undergone total knee replacement for a severely disfigured rheumatoid arthritic knee have also achieved good long-term outcomes. In the past, pain relief was the main purpose of knee replacement, but in modern life, patients, especially young patients, are more concerned about the function of the joint after arthroplasty, not only to meet the needs of daily life, but also to be able to engage in sports and leisure activities, believing that “Quality of life is more important than quantity of life. (Quality of life is more important than quantity of life.) Therefore, as long as young patients have reasonable expectations of postoperative outcomes, understand that vigorous joint activities can accelerate joint wear, and learn to use artificial joints properly in sports and leisure activities, they should be encouraged to choose artificial joint replacement in order to improve their quality of life and enjoy a rich and colorful life.