You have probably been exposed to this concept at least once; the practice of intentionally twisting, compressing, and bending joints in order to produce an audible sound, often known by the onomatopoeias ‘crack’ and ‘pop’. The most obvious example of joints that make this sound when manipulated are those of fingers and hands, but other joints include jaws, wrists, toes, elbows, ankles, and the vertebrae of the spinal column.
There are a few theories on why joints pop when you twist them, but the prettiest girl at the ball is cavitation, that is, the formation and collapse of a void.
Synovial joints, such as the fingers have, have cavities between the cartilage between the bones, those cavities are filled with a fluid that acts as a lubricant amongst other things. Anyhow, when the joint is manipulated, the surface of the bones are pulled apart which lowers the pressure inside the joint cavity, the reduced pressure allows dissolved gasses escape and form bubbles, the bubbles quickly collapse and produce pops
Despite what I was told by a particularly terrifying woman as a child, the claim that cracking your knuckles will cause the development of arthritis is unsubstantiated by any evidence. On the topic of long term effects, chronic knuckle crackers tend to have laxer grip strength and hand swelling, this however is offset by the chance that lax ligaments are simply more likely to cavitate. So it’s unknown whether people who crack get lax, or if people who are lax are more likely to crack in order to relieve pressure.
I never believed it, but she was still scary.