Think back to the last party you attended that had balloons. Some were stuck to the ceiling, and some had fallen down to the floor. You just started to connect with old friends or make new ones, when all of a sudden: “POP!” Some jerk purposely stomped on a balloon.
I offer this imagery by way of introducing the knuckle crack. I’m not saying that knuckle cracking is as obnoxious as the party animal who popped the balloon, though some folks do find knuckle cracking annoying (consider yourself warned, habitual knuckle crackers).
But if you recognize how loud that pop is from the balloon at the party, that will help you understand what exactly is happening within the cracked knuckle.
When you hyperextend any joint—that is, when you bend a joint back past 180 degrees—the space inside the joint expands. The expansion creates a vacuum, sucking out dissolved gases from joint fluid to make a big bubble inside the joint.
Expand the joint a touch more or flex the joint, and this bubble pops, leading to the “POP!” of the cracked knuckle. Now, this “POP!” isn’t quite as loud as its cousin the party balloon, but those party balloons are big, and knuckles are small, so just be thankful for the “POP!” that you get.
So joint space expands, bubble forms to fill vacuum, then bubble pops and that is how knuckle cracking works.
Now back to the question: Does knuckle cracking cause damage to the joints? No.
So far, numerous studies have demonstrated that folks classified as “habitual knuckle crackers” are no more likely to develop joint problems such as arthritis than those of us who abstain from this habit.
When you think about how knuckle cracking works, it makes sense that an air bubble popping wouldn’t do too much damage to bones and joint spaces.
However, if you’re at a party and your knuckle cracking draws unwanted attention, you can always divert the attention by popping a balloon.
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Dave Margolius is a physician in San Francisco, California. He is originally from Cleveland, Ohio, and attended Brown University for undergrad and med school. He is currently doing his residency in internal medicine at UCSF. His main interests are in health policy, improving primary care, and healthcare for all.