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Scientists Cracked Some Joints In An MRI To See What Really Happens

It's referred to as the "pull my finger" study, so you know it's good.

Posted on April 17, 2015, at 2:32 p.m. ET

Scientists have found that a bubble forms in your joint fluid when you crack your knuckles.

Vox / Via youtube.com

With the help of a colleague who volunteered for his knuckles to be cracked, a team of University of Alberta researchers gave each of his fingers a good pop while hooked up to an MRI.

(In case that sounds torturous, the study's lead author Greg Kawchuk referred to him as the "Wayne Gretzky of knuckle cracking" in a release, so he does it all the time.)

Here you can see the subject get his finger pulled in an MRI, shown in slow-motion video.

RehabMedicineUofA / Via youtube.com

The new PLOS ONE study re-affirms the notion of a vapor bubble forming that was first theorized in the 1940s. That idea was later doubted after scientists did another study in 1971 and said it was the bubble collapsing.

This is another view, where you can see the cavity forming.

Your joints are lubed with what's called synovial fluid, and when you crack your knuckles, your joints separate and create more space. Essentially, there's not enough of that fluid to fill the gap. And so that gas-filled bubble appears — and what's behind that satisfying pop that you hear right before your mom tells you to please stop.
Kawchuk et al. / Via journals.plos.org

Your joints are lubed with what's called synovial fluid, and when you crack your knuckles, your joints separate and create more space. Essentially, there's not enough of that fluid to fill the gap.

And so that gas-filled bubble appears — and what's behind that satisfying pop that you hear right before your mom tells you to please stop.

It's still a bit unclear whether it's bad for your joints or not.

Disney / Via imgbuddy.com

Specifically, if that cracking can lead to damage or arthritis.

"Certainly there has been no evidence to support the concept that knuckle-cracking is a cause of osteoarthritis in the hands," Dr. Stephen Kennedy, a hand, wrist, and elbow surgeon and assistant professor at the University of Washington, wrote in an email. "It is much more likely due to other genetic and environmental factors."

So err on the side of listening to your annoyed parents — or keep cracking your way to bliss.

  1. What do you think of knuckle-cracking?

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    I do it all the time — it's so satisfying!
    Correct
    Incorrect
    I do it sometimes
    Correct
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    I've never purposely done it but I don't mind when others do it
    Correct
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    I've never purposely done it and the sound of it makes my skin crawl
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What do you think of knuckle-cracking?
  1.  
    vote votes
    I do it all the time — it's so satisfying!
  2.  
    vote votes
    I do it sometimes
  3.  
    vote votes
    I've never purposely done it but I don't mind when others do it
  4.  
    vote votes
    I've never purposely done it and the sound of it makes my skin crawl

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