Joint “Fireworks” Captured with Ultrasound Imaging
Finally, the mystery is solved! Ultrasound imaging has revealed that when you crack your knuckles, you’re actually creating a gas bubble between the bones of the pulled joints, which is what is producing that “crack” sound. Even more interesting is that, in addition to the “crack”, a flash of light is also being created about 10 milliseconds after the sound. Radiologist Robert Boutin of the University of California, described the bright flash seen with the ultrasound like a “firework exploding in the joint”.
“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.”
The research, which tested 40 participants of varying age and gender, used an ultrasound sonograph to record video images and static images of the participants while they cracked their knuckles. The images were then reviewed by two radiologists, who found that the flashes of light created provided evidence of audible cracking in 62 of the 400 joints imaged with the ultrasound scanner, with 94% specificity.
In addition, physical examinations of each participant also found that those 30 who regularly cracked their knuckles did not appear to have sustained joint issues, despite years of the habit.
“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,” Boutin said.
This was the first study of its kind, and the results were recently presented at the annual meeting of the Radiological Society of North America (RSNA).
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