Joint clicking is common for the following reasons: first, articular cartilage damage, joint trauma and osteoarthritis can cause articular cartilage damage, cartilage exfoliation, joint flexion and extension activities when the rough cartilage surface friction with each other, can cause a foreign sound in the joint. Second, meniscus injury, the meniscus surface flatness decreases after the tear of the meniscus inside and outside the joint, which will wear with the adjacent articular cartilage, resulting in a strange sound in the joint, in addition, the meniscus tear into the joint space, which can appear in the joint flexion and extension activities, and at the same time manifest as joint noise. Third, joint free body, cartilage fragments can be formed in the joint free body, free body in the joint flexion and extension activities will move, resulting in joint noise.