Causes of joint clicking include physiologic and pathologic. Generally speaking, joint popping without redness, swelling, pain and activity limitation are physiological, such as stretching, knee joint instability. Common pathologic causes include degeneration of articular cartilage, meniscus injury, joint free body and so on. 1. Physiological popping sound: it is the tendon and bone rubbing against each other in the process of movement to produce popping sound. It is also possible that the patella of the knee joint is not in the completely suitable anatomical position, and the patella and femur will hit each other during flexion and extension to produce popping sound. 2. Degeneration of articular cartilage: mainly due to strain, trauma, osteoarthritis and other factors, the articular cartilage is subjected to a long time and a large load, the chondrocytes gradually apoptosis, the cartilage surface is not smooth. The rough cartilage surface rubs against each other when the joints are active, thus producing a popping sound. The decrease of estrogen level in menopausal women will also lead to degeneration of articular cartilage. 3. Meniscus injury: After meniscus injury, the surface flatness of meniscus decreases and the neighboring articular cartilage wears out, or the meniscus enters the joint space after tearing, thus generating popping sound. 4. Joint free body: the causes include exfoliative chondritis, cartilage fracture, chronic wear and tear, trauma, synovial osteochondromatosis and so on. The free body moves during joint activity and produces a popping sound. Physiologic joint popping does not require special treatment and patients should not worry too much. Excluding the symptoms caused by physiological factors, it is recommended to go to the regular hospital in time, by the doctor to clarify the cause of the disease, and then give targeted treatment.