It’s referred to as the “pull my finger” study, so you know it’s good.
Scientists have found that a bubble forms in your joint fluid when you crack your knuckles.
With the help of a colleague who volunteered for his knuckles to be cracked, the team 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.)
Vox / Via youtube.com
Here you can see the subject get his finger pulled in an MRI, shown in slow-motion video.
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.
RehabMedicineUofA / Via youtube.com
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
It's still a bit unclear whether it's bad for your joints or not.
Disney / Via imgbuddy.com