When we squat and get up, we often hear a “clucking” sound in the knee joints; when we break our fingers, we hear the joints of our fingers “clucking”. So, why do our joints rattle? What causes these sounds? In fact, the mechanisms and causes of these two sounds are different. The sound we make when we break our fingers is due to the fact that the knuckle has reached its limit of motion. The joint is normally filled with lubricating fluid and encapsulated by the joint capsule.
When we move the knuckle that way, intentionally or unintentionally, the gas dissolved in the lubricating fluid spontaneously separates from the solution and forms a small bubble, thus causing a squeezing sound. It is not until the gas is reabsorbed by the fluid that this sound can be made again. The rumor that breaking fingers will make the joints thicker and larger is still worth further exploration. On the other hand, the sound made by the knee joint when we squat and get up is a short sound, caused by the sudden stretching and shifting of the fibers that connect the muscles to the bones —- tendons when the joint is moving under weight. Because the tendon moves back and forth with the movement of the joint, it can make a continuous sound without intervals.