Why do joints crack? © Getty Images

Why do joints crack?

Snap, crackle and pop! Scientists have found out why knuckles make those cringe-inducing cracking sounds.

Asked by: Steve Shaw, Durham


A 2015 study at the University of Alberta, Canada took real-time MRI images of finger joints as they cracked. The researchers found that as the surfaces of the cartilage pull away from each other, they create a site for a tiny bubble of dissolved gas (mostly CO2) to form in the joint’s lubricating fluid. The sudden expansion of the bubble creates the popping sound.


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