What's behind this and does it lead to arthritis or other joint problems?
How are joints cracked?
Manipulating your joints, such as the knuckles, or the vertebrae of the neck and back, can produce a high-pitched popping sound. People generally push, pull or twist their joints into unusual positions. For example, to crack a knuckle, you can bend your finger backwards (extension), forwards (flexion), pull it away from the hand (distraction) or twist it (torsion). Tendons snapping over bony prominences or scar tissue can also generate a loud popping sound. In snapping hip syndrome, the hip flexor tendon snaps over the lesser trochanter of the hip.
Why do people crack their joints?
Knuckle cracking, like nail biting, may develop as a response to anxiety or stress. Once started, It can become a very difficult habit to break. On a positive note, many people feel looser and more relaxed after cracking their joints. When joints are popped, Golgi tendon organs are stimulated, which causes the muscles around the joint to relax.
What causes the cracking sound in the joints?
The actual mechanism is still uncertain, but there are a few theories. The most popular explanation is synovial fluid cavitation. When you manipulate your joint, you stretch your joint capsule. As the volume increases, the pressure in the joint cavity decreases, according to the ideal gas law. When the pressure is low enough, bubbles (nitrogen or carbon dioxide) in the joint fluid will cavitate or burst. This is thought to produce the popping sound. Tendons and ligaments can also cause snapping sounds. They can slide over bony prominences and "snap" back into place. Sometimes, snapping is caused by adhesions, or scar tissue, being broken down. Ligamentous laxity, in those who are "loose-" or "double-jointed," may also be associated with an increased tendency to cavitate and crack. In this case, their bones may actually be sliding in and out of joint.
What are the consequences of cracking joints?
So far, no study has conclusively shown that cracking joints will lead to arthritis. Raymond Brodeur, in a published study in the Journal of Manipulative and Physiological Therapeutics, found no correlation between joint cracking and arthritis. However, chronic knuckle-crackers can potentially have damage to their joint capsules. The only other consequence would be perhaps comments or odd looks from friends or bystanders!