Patients with knee pain at the age of 50 have several common causes: first, osteoarthritis of the knee joint, mainly degenerative changes in inflammation, the patient will have joint pain, walking on a flat road, walking up and down stairs have pain symptoms, at the same time there will be swelling of the joint and limited movement, moving the joint will be obvious joint friction sound, taking X-rays can confirm the entire knee joint there are joint space narrowing, joint overload, and joint surface sclerosis. This can be confirmed by X-rays. Second, patellofemoral arthritis, also known as chondromalacia patellae, if the patient does not have joint pain when walking, but has joint pain when walking up and down stairs or squatting, in most cases it is patellofemoral arthrosis. If cartilage damage occurs on the joint surface, the patient will experience localized joint pain when walking up and down stairs or squatting, along with limited joint movement.