What Really Happens When You Crack Your Knuckles

Don’t worry—you’re not actually cracking anything.

Whether you crack your knuckles daily on purpose or every once in a while by accident, Canadian scientists decided to investigate what, exactly, is taking place inside your hand each time that cracking or popping-like sound occurs.

“It’s what we call the ‘Pull My Finger’ research,” lead author Greg Kawchuk, PhD, a professor in the Facility of Rehabilitation Medicine at the University of Alberta, tells Yahoo Health.

“However, there’s no cracking in the sense since nothing’s breaking. People have just traditionally used that word to describe the sound because that is what it sounds like. So clearly there is a sound being produced, and what we’ve been able to do is look inside the joint and see what’s going on inside there.”

Watch a knuckle crack from the inside. Note the quick flash that happens after the joint pops. Researchers can’t explain what’s going on there — yet. (Video: University of Alberta)

And here’s what Kawchuk and his team discovered, which was published in the journal PLOS One: With the help of an MRI video and an avid knuckle-cracking participant (a chiropractor was also a fellow researcher on this study, who Kawchuk described as “like having the Wayne Gretzky of knuckle cracking on our team”), they found that in every instance, the cracking and joint separation was associated with the rapid creation of a gas-filled cavity within the synovial fluid, a super-slippery substance that lubricates the joints.

“It’s a little bit like forming a vacuum,” says Kawchuk. “As the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created and that event is what’s associated with the sound.”

Their findings differ from previous conclusions where at one time scientists believed a vapor bubble formation was the cause, where others stated this audible reaction was caused by collapsing bubbles.

So is this the same activity that takes place inside the neck or back, for example, when someone is having a session with a chiropractor? “We do believe it is the same thing,” says Kawchuk. “The process that we described in this finger experiment happens in a type of joint called the synovial joint. And it’s surely possible that this can happen in any other synovial joint, which can be found all over the body, like in the back, the neck and even in the toes. So it can happen during a therapeutic procedure or maybe just from moving a certain way.”

Yet not all crackling sounds coming from the body can be explained using this theory. “It is different than those cases where sometimes you’ll have a joint sound that is repetitive,” he explains. “Like if you move your wrist a certain way and you’ll hear a click. Then you’ll do it again right away and you’ll hear the click — that’s probably two things rubbing over each other. But what we’re talking about is the kind of crack that takes about 15 to 20 minutes for the gaseous cavity to go back into the solution of the joint fluid before you can do it again.”

Kawchuk adds that there is also no evidence that suggests cracking your knuckles can lead to premature arthritis or joint issues. “So we can’t say that it’s good for you, but it certainly isn’t bad for you, according to the latest information that is available.”

And as far as someone’s knuckles getting bigger due to a knuckle-cracking habit, Kawchuk has his own opinion about how this false theory may have come about. “The more and more I talk to people around the world, I think this story has persisted over time from those who find it so repulsive — they’re just trying to find a way to make their friends or their family stop!”

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