Finally, scientists unveiled the science behind the mystery of cracking knuckles. In a study led by Dr. Robert Boutin, radiology professor at University of California Davis, researchers used ultrasound imaging to see what happens when people crack their knuckles.
"It's extremely common for joints to crack, pop and snap," Boutin said in a statement. "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."
For the study, the researchers recruited 40 participants - 23 men and 17 women with ages ranging from 18 to 63 years old. Thirty of them had been cracking their knuckles habitually, sometimes up to 20 times a day, while 10 of them had never cracked their knuckles.
The participants were told to crack the base of their fingers, called the metacarpophalangeal joint, while the researchers took audio and visual recordings in addition to the ultrasound imaging. Their fingers were examined for range of motion, grip strength and laxity before and after the experiment.
The researchers saw that the recordings of the knuckle crackings coincided with the appearance of flashes of light near the base of the fingers in the ultrasound images 94 percent of the time.
"There have been several theories over the years and a fair amount of controversy about what's happening in the joint when it cracks," Boutin said. "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."
So what did the cracking sound indicate - the bursting of a bubble or the creation of a bubble? Boudin theorized it was the latter, although he emphasized the need for more research to confirm this, according to The Washington Post.
Knuckle cracking appeared to have no immediate harmful physical effect on the study participants. Upon examination, their range of motion, grip strength and laxity were almost the same as those who did not crack their knuckles. Boutin said future studies are needed to determine any long-term effect.
The results of the study were presented Tuesday at the annual meeting of the Radiological Society of North America.
