Gross MRI scan of knuckle cracking helps boffins figure out how it works

Researchers at the University of Alberta said the knuckle cracking does not come from the bursting of a gas bubble, as previously believed.


NSFW    An MRI video released as part of a study published Wednesday in the PLOS ONE medical journal shows the knuckle joint separating and creating a bubble of gas in the synovial fluid between the bones.

Led by Professor Greg Kawchuk researchers at the University of Alberta found the cracking sound is caused by the rapid separation of the joint, rather than the previously-believed breaking of the bubble.

The study backed up previous research indicating joint cracking does not damage the body or lead to arthritis. All of the joints in the body are surrounded by connective tissues, ligaments and synovial fluid.

Synovial fluid is a clear, thick liquid that contains dissolved gasses. When joints, such as the ones between finger bones are pulled apart as a person cracks his or her knuckles, the volume increases between the joints, lowering the pressure inside the synovial fluid and causing the gases within it to burst.
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