Knee bending and popping may be physiological popping, or it may be pathological popping caused by meniscus injury and other knee joint lesions, which need to be examined by a doctor to clarify the cause of the problem and be treated actively. 1. Physiological popping The first thing to consider is that the popping sound when bending the knee is caused by physiological factors. The knee joint is a large joint in the human body, and the joint cavity is usually in a completely closed state. Whenever the knee bends, there will be a change in the pressure in the cavity, and a slight popping sound can occur when the pressure is released, thus producing a physiological popping sound. 2. Pathological popping It may be caused by osteoarthritis or rheumatoid arthritis of the knee joint, or it may be caused by damage to the meniscus of the knee joint or chondromalacia patella. These lesions can lead to narrowing of the knee joint space and friction when the joint moves, resulting in popping when the knee is bent. Pathologic knee popping is usually accompanied by symptoms such as knee pain, swelling, and limitation of motion. When joint popping occurs and is accompanied by other uncomfortable symptoms, it is recommended to go to the hospital as soon as possible to get a clear picture of which disease is present, and to treat it accordingly, so as to prevent further aggravation of the condition, which may affect the quality of life.