Bending knee ringing may be physiological ringing, may also be trauma, arthritis, chondromalacia patella and other pathological causes. 1. Physiological popping: mostly seen in teenagers, exercise more people, due to the negative pressure in the joint cavity caused by the knee joint activities, the patient may appear to be bending the knee occasionally ringing. 2. Trauma: due to trauma caused by knee meniscus, cruciate ligament and other tissues of the injury, the patient in the bending of the knee joint pulling the corresponding tissues, can appear pain, knee ringing and other symptoms. 3. Arthritis: commonly seen in osteoarthritis caused by degenerative changes in the knee joint, as well as arthritis caused by rheumatism and rheumatoid arthritis, these diseases can cause wear and tear of the cartilage in the knee joint, resulting in uneven joints and joint effusion, and the patient can experience ringing in the knee when bending the knee joint. 4. Chondromalacia patella: due to various reasons caused by the patella articular surface cartilage stripping, resulting in uneven knee joint surface, in the bending of the joint surface and the femoral joint friction, which can cause knee ringing. Bending knee ringing may also have other reasons, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.