Knuckle cracking

Dear Alice,

What makes the "popping" sound when your knuckles are cracked?

Dear Reader,

“Pop” goes your knuckle. The sound you’re hearing when you try to catch some tension relief is your joints either being pushed back into or out of their normal position. Which might not sound so good, but rest assured, these cracks and pops are common and aren’t cause for much concern unless there’s pain or swelling involved.

Joints can be found all over the body — fingers, shoulders, knees, just to name a few. When they’re manipulated or extended in any way, like through knuckle cracking, they tend to pop for three main reasons:

  • Passing gas: The synovial fluid that acts as a lubricant within joints contains nitrogen, oxygen, and carbon dioxide gases. Stretching the joint capsule triggers this gas to quickly release, forming tiny bubbles that make a “pop” sound.
  • Movin’ and groovin’: Manipulating your fingers causes your joints to move and your tendons to reposition. This shuffle may fire off a “snap” sound as it moves out of or back into its original place.
  • Rough patches: Joint cracking may also rough up smooth cartilage and create sharpened edges within the joints. The sound you hear might be from these jagged surfaces rubbing up against each other during the cracking.  

While there is plenty of research on the origin of the knuckle “pop”, there is limited information on the long-term effects of cracking. That being said, there is some research that suggests that making your knuckles snap, crackle, and pop isn’t associated with arthritis (contrary to popular belief). One such study using radiography to test for arthritis among 50 to 89 year olds showed no association between knuckle cracking and hand arthritis among study participants.

Whatever the reason for cracking knuckles may be — for the sense of relief it may bring, habit, or both — joints sounding off aren’t cause for alarm unless you experience pain, swelling, or your joint becomes locked or stuck. If you experience any one of those scenarios, seeking the advice of a health care provider is recommended. Overall, knuckle popping is not harmful and if it eases tension, it’s safe to get crackin’!

Last updated Aug 20, 2015
Originally published May 19, 2005