A group of scientists were interested in some of people’s habit of cracking their knuckles and performed a series of ultrasound scans on the hands of these people to better understand the mechanism behind it. And the findings suggest that finally science explains the popping sound of knuckle cracking.
Sonograms of people who love cracking their finger joints showed that the act creates a bright fire-work-like flash in the joints. Scientists were puzzled by the wince-inducing sound of the cracking, but their investigation provided them with an explanation,
Both the flash and the sound are caused by a bubble of gas created within the joints during cracking. But until now, science couldn’t tell whether teh sound was triggered during the bubble’s formation or explosion.
Dr. Robert Boutin, radiology expert with the University of California Davis Health System, explained that his team was able in a world’s first to match ultrasounds with audio.
Boutin noted that he and his fellow researchers heard the sound before the flash, therefore it is not generated by the bubble exploding. Instead it is emitted when the gas bubble forms. The research team also found that it takes 10 milliseconds for the flash to appear after we hear the sound.
The study results were presented Dec. 2 at the annual gathering of the Radiological Society of North America. Nevertheless, the study isn’t yet peer-reviewed, so its conclusions are not final.
According to the study’s background data, up to 50 percent of people crack their knuckles. Researchers noted that many patients are concerned that their habit, which sometimes helps them relieve stress, may induce long-term harm to their joints.
The study involved 40 adults with the average age of 35.5, who were asked to stretch their fingers 400 times in total. About 30 participants admitted that they crack their knuckles regularly. During the experiment scientists witnessed 62 cracks.
Study investigators reported that they saw a bubble of gas forming during the cracking and a fire-work-like flash on ultrasound scans.
Boutin explained that scientists worldwide were divided over what happens when people crack their finger joints. The recent findings show that the popping sound and the flash are linked to a change in the pressure of the liquid that lubricates joints.
The team explained that whenever a person cracks his or her knuckles an abrupt change happens in that pressure which draws out the gas into tiny bubbles that milliseconds later create a larger bubble. The popping sound is generated when the tiny bubbles collide into one another to create the larger bubble.
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