Cracking knuckles feel so satisfying but the "cracking" sound has always been a mystery, until today. Researchers found that a gas bubble between the bones of the flexed joints creates the sound.
Interestingly, researchers not only "cracked open" the mystery of the cracking sound. Using an ultrasound imaging, they also found a flash of bright light that happens 10 milliseconds after the cracking sound. Researchers from the University of Califorina, Davis likened the flash of light to fireworks exploding in the flexed joints.
Led by radiologist Robert Boutin, a team of researchers recorded 40 people, 23 men and 17 women, cracking their knuckles simultaneously via ultrasound imaging. The participants ranged between 18 to 63 years old. Ten of the participants said they do not crack their knuckles while 30 said they do it regularly. These 30 participants said they crack their knuckles approximately 20 times daily for years and they were found to have healthy joints. The evidence suggests that for people without joint problems, knuckle cracking doesn't appear to be causing damage.
"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," said Boutin.
Over the years, there had been several theories as to what really happens when people crack their knuckles, apart from that satisfying release. Boutin and his colleagues said the brief bright light and cracking sound come from the pressure changes related to the gas bubble between the joints.
Dr. William Palmer from the Massachusetts General Hospital explained that the gas bubble is formed from dissolved gas. This gas, which is suspended in fluid, acts as joints' lubrication. When a person cracks a knuckle or stretches the fingers, the action results in a negative pressure which extracts the gas out.
"You're yanking on a joint, and then suddenly the seal is broken," said Palmer, who is the director of musculoskeletal imaging and intervention at Massachusetts General Hospital.
Boutin added that these tiny bubbles of gas merge into one large bubble. The cracking sound comes from tiny bubbles of gas crashing into one another. The team stressed that no evidence of swelling or decrease in grip strength was found in regular knuckle crackers compared to people who don't share the habit.
The research was presented at the Radiological Society of North America's annual meeting in Chicago prior to its publication in a peer-reviewed journal.
Photo : Guian Bolisay | Flickr
