The question: I absentmindedly crack my knuckles all the time—could I actually be doing damage?
The expert:Pedro K. Beredjiklian, M.D., chief of hand surgery at The Rothman Institute
The answer: Probably not. And thank goodness, because were you really going to stop if the answer was "yes?"
But before we explain why, here's a quick anatomy refresher: Your hands contain lots of joints, points at which two (or more) bones meet. Ligaments connect the bones to each other, and a capsule that's filled with synovial fluid (your body's natural lube) surrounds the whole joint, Beredjiklian explains.
What you probably didn't know? When you push or pull your fingers to crack them, what you're really doing is stretching the capsule that surrounds the joint. That decreases the pressure inside the capsule, causing gasses that were dissolved in the synovial fluid (such as carbon dioxide, nitrogen, and oxygen) to release into the empty space to equalize the pressure. Like pulling a cork from a bottle of bubbly, that release is what makes your knuckles pop.
It feels so good because it simultaneously stretches the joint and stimulates its nerve endings for up to 30 minutes, which is about how long it takes for the gasses to dissolve back into the fluid before you're good to go for another round.
And no, the popping pressure doesn't cause arthritis.
In possibly the best proof of concept ever, Donald L. Unger, M.D. cracked the knuckles on his left hand—but never on his right—every day for more than sixty years, without any consequences. In 2009, he even won an Ig Nobel Prize (a parody of the Noble Prize) in medicine for that little self-study.
However, a few reports have linked knuckle cracking to sprain-type injuries and the formation of growths on the back of the joints, he says. But those problems are exceptionally rare and probably not reason enough to break your nervous habit.
Now, if the constant cracking makes your colleagues cringe, that's another story.
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