A group of scientists used ultrasound technology to analyse what happens when we crack our knuckles and got some rather unusual results.
"What we saw was a bright flash on ultrasound, like a firework exploding in the joint," Dr Robert D. Boutin, professor of radiology at University of California said in a statement.
"It was quite an unexpected finding."
Despite the dramatic footage the researchers found no evidence that knuckle cracking causes immediate damage to the joints.
The study, presented at the annual meeting of the Radiological Society of North America on Tuesday, recorded simultaneous audio and visual evidence of knuckles cracking.
The participants, who were all between the ages of 18-63, were asked to disclose their knuckle-cracking habits prior to the experiment. Some stated they had never intentionally cracked their knuckles while others admitted to doing it every day.
Dr Boutin and a colleague analysed the ultrasound footage and found that a bright light on the ultrasound correlated with an audible crack.
"There have been several theories over the years and a fair amount of controversy about what's happening in the joint when it cracks," he commented.
"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."
Boutin added that they found "no immediate disability" or "difference in laxity" among the people who regularly crack their knuckles involved in the study when compared to participants who never crack their knuckles.
However, he added that more research is needed on the topic.
This isn't the first study to find a "white light" on footage of knuckle-cracking.
A previous study published in the scientific journal PLOS ONE also stated that an unexpected white flash appeared on video footage of joints being cracked.
At the time, the researchers speculated that the flash may be caused be water being drawn to the joint.
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