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Knuckle Cracking

December 10, 2015

Cracking your knuckles sets off a tiny “firework explosion” in the joint.



BOB HIRSHON (host):Knuckle fireworks. I’m Bob Hirshon and this is Science Update.

[sound of  knuckles cracking]

The sound of knuckles cracking is distinctive and, to some, cringe-worthy. But what goes on inside the joint is less well known. To find out, University of California, Davis radiologist Robert Boutin took ultrasound images of knuckles being cracked.

ROBERT BOUTIN (University of California, Davis):

When that crack occurred there was something that looked like a tiny firework explosion going off in the joint. And it was pretty impressive.


The explosion was likely caused by dissolved gas in the joint fluid being liberated and coming out of solution. Cracked joints displayed no differences in swelling or strength, but had increased range of motion compared to joints that weren’t cracked. The study, presented at the Radiological Society of North America meeting, didn’t evaluate long-term effects, but the only detrimental short-term effect seems to be annoying those nearby.  I’m Bob Hirshon, for AAAS, the science society.

Watch a video sonogram of what happens when knuckles crack

KC pre_post(RSNA Fig) (2)