1, gas escapes, and there is joint fluid in the joint, which plays a lubricating role. The fluid contains oxygen, nitrogen and carbon dioxide. When the joint is squeezed, after the joint capsule expands and contracts, the gas is released quickly, forming bubbles and noises. This mechanism prevents the joint from being squeezed again, because the gas cannot be squeezed again until it returns to the joint fluid.

2. Joint, tendon and ligament movement. During exercise, the tendon moves slightly from its original position and then returns to its original position. This process will also be accompanied by sound.

3, cartilage loss, after arthritis, a rough surface appears because of the loss of smooth cartilage, and there will be noise when rubbing.

The first two points are physiological joint sounds, and the last point is abnormal. Generally speaking, knee joint ringing is normal and does not need treatment. What really needs attention is that when the knee bends, there is not only noise, but also pain; Or joint ringing accompanied by swelling, in both cases, see a doctor as soon as possible.