Decoded: What causes knuckle cracking sound

New York: Next time when your kid asks you to "pull his finger," also tell him the secret behind the distinctive popping sounds that are heard while cracking knuckles. Settling a decades-long debate about what happens when you crack your knuckles, an international team of researchers led by the University of Alberta have found that the cause is a cavity forming rapidly inside the finger joint.

Scientists have debated the cause of joint cracking for decades, dating back to 1947 when British researchers first theorised vapour bubble formation as the cause. That was put in doubt in the 1970s when another team of scientists instead fingered collapsing bubbles as the cause. To find an answer, the team asked acclaimed chiropractic physician Jerome Fryer to volunteer for the test.

MRI video captured each crack in real time -- occurring in less than 310 milliseconds. 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. The ability to crack your knuckles could be related to joint health.