Ask A Scientist

Why do your bones (joints) crack?

Asked by: Camryn Rose Hovancik
School: Thomas Jefferson Elementary School (BSD)
Grade: K
Hobbies/Interests: Dolls, Drawing, Reading, Playing with friends Family: Mom (Kellie), Dad (Gerald), Brother (Logan) and dog (Cooper)

Answer from Alison Dura

Clinical Lecturer, Binghamton University

Professional interests: Inpatient medical-surgical care, pharmacology, health systems, health promotion
Family: Husband, two daughters
Interests/hobbies: Vocaland instrumental music, reading, travel

I'm sure you've watched and heard friends "cracking" or "popping" their knuckles, back, neck, or other joints. Maybe you've even done it yourself. Or, maybe you've noticed a crackling or creaking sound when you bend, stand, or sit. This crunching sound is call "crepitus," from Latin.

Fortunately, these noises are not anything to worry about. And interestingly, no one really know exactly what causes this odd sound/experience. There are probably several causes, and a person might experience any one of them at different times. Sometimes the ligaments that connect bones to other bones snap or rub over the bumps in your bones while you move. Sometimes a tendon, which connects muscle to bone, snaps around a joint during movement. One of the most popular explanations has to do with the gases normally dissolved in join fluids. The body's joints are naturally "cushioned" by a small amount of this fluid so that they move smoothly. This joint fluid normally has small amounts of oxygen, carbon dioxide, and nitrogen dissolved in it, not unlike the carbon dioxide dissolved in soda. When a joint is forecefully stretched by pushing or pulling, gas bubbles can escape from the fluid and collapse or "pop." This causes the sound you hear. A person often can't "re-crack" the joint again until the gas is absorbed back into the fluid. Then the process can happen again. That's why a person can't make joints "pop" again for a little while.

Now, if the crepitus also comes along with pain, swelling, or a feeling of getting "stuck or caught," then there might actually be a problem that should be examined. Otherwise, there's no evidence that shows that cracking your joints causes arthritis or any other problem. It might annoy the people around you, but it won't damage anything!

Last Updated: 3/1/17