In daily life, many people find that their knee joints often “click”, especially when squatting and going up and down stairs. People are worried that there is something wrong with their knee joints. This “click” sound, in fact, is the popping of the knee joint, is the sound of gas vibration in the knee joint cavity. Normal human knee joint, sudden extension and flexion of the knee, the joint cavity gas flow, negative pressure, there will be this popping sound. It is usually not accompanied by pain, or functional limitations. In this case, we can live a normal life without intentionally reducing knee activities, do not have to worry. However, if the knee joint joint in addition to the “click” sound, accompanied by knee joint redness, swelling, pain, limited activities, then it may be the knee joint problems. With the degeneration of the knee joint, injury, articular cartilage will wear, soften, lose elasticity, or even rupture, peeling, subchondral bone sclerosis, osteophytes, meniscus and ligament damage, the formation of the knee joint pain and activity limitation. At this point, it is necessary to pay attention to the need to go to the hospital in a timely manner to avoid delaying the condition.