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Here’s what actually happens when you crack your knuckles

Never mind cancer or AIDS: what we really want medical researchers to be concentrating on is things like this.

In the first study of its kind, radiographers at the University of California have taken a closer look at what exactly is going on when you crack your knuckles.

Using the latest ultrasound technology, the researchers recorded simultaneous audio, video and images of 40 adults - 30 with a history of regular cracking and 10 without - as they attempted to crack the knuckle at the base of each finger - also known as the metacarpophalangeal joint (MPJ). In addition, orthopaedists evaluated each participant for grip strength, range of motion and laxity of each MPJ.

Robert Boutin, Professor of radiology at the University of California, explained: "It’s extremely common for joints to crack, pop and snap. We were interested in pursuing this study because there’s a raging debate about whether the knuckle-cracking sound results from a bubble popping in the joint or from a bubble being created in the joint." 

Using a transducer, a sonographer recorded 400 MPJs, as well as static images before and after each knuckle crack, which occurred in 62 cases.

Professor Boutin said, "What we saw was a bright flash on ultrasound, like a firework exploding in the joint. It was quite an unexpected finding."

He continued: "There have been several theories over the years and a fair amount of controversy about what’s happening in the joint when it cracks. We’re confident that the cracking sound and bright flash on ultrasound are related to the dynamic changes in pressure associated with a gas bubble in the joint."

But which comes first - the cracking sound or the flash of light? More research is needed apparently.

And is it bad for you? Examinations saw no pain, swelling or disability in the knuckle-crackers, and no difference in laxity or grip strength.

Prof Boutin said: "We found that there was no immediate disability in the knuckle crackers in our study, although further research will need to be done to assess any long-term hazard – or benefit – of knuckle cracking."

Let's be honest, that's not really cleared up anything has it?

Well done science.

(Image: Shutterstock)