Knee pain down stairs is commonly caused by degenerative osteoarthritis of the knee, knee meniscal injury and synovial inflammation of the knee, as follows: First, degenerative osteoarthritis of the knee: in the case of elderly patients, most have degenerative osteoarthritis of the knee. Patients will show knee pain when going down stairs, and more severe pain when squatting, and relatively mild symptoms when walking on flat ground, even without any pain. The MRI can reveal a large area of patellofemoral articular cartilage exfoliation, subchondral bone sclerosis or cystic changes, joint cavity injection of sodium glass and exercise leg muscles will gradually relieve the symptoms; second, knee meniscal injury and knee synovial inflammation: If the patient is young, most of them have knee meniscal injury and knee synovial inflammation. Patients will have pain in the knee joint when going down the stairs, along with limited knee movement and significant inter-articular pressure and pain. An MRI will reveal the extent and location of the lesion, and the symptoms can be relieved with early treatment. Patients should take care to avoid joint injuries and cold, and to strengthen the leg muscles.