The Science Behind Cracking Your Knuckles

Science |


Scientists have used ultrasound machine to figure out exactly what happens when we crack them, putting an end to an old debate about where that distinctive cracking sound comes from.

Some of us finding funny, others irritating, well cracking our knuckles is a long historical tradition. In reality, most of us don’t know what happens when we crack our knuckles and the source of those unique sounds. Researchers decided to use ultrasound machines to find out what exactly takes place when someone is busy cracking their knuckles. 

Researchers from the University of Alberta published a paper in April that was based on MRI. The MRI was a visual presentation of the finger joints as they were being cracked. The popping sound was discovered to come from the collapsing process of the air bubbles that form from the fluid that tend to surround the joints. The fluid is known as the synovial fluid. But then using ultrasound is more effective since they are able to record what happens in the body 100 times faster compared to MRI.

Robert Davis Boudin from the University of California came up with a team of researchers that was to carry the study. They recruited 40 participants who were healthy out of the 40, 30 were regular joint crackers and the other 10 did not crack their joints as often. In the group of regular joint crackers, the older participants admitted to cracking their knuckles up to 20 times daily for the past 40 years. All the participants were instructed to crack their knuckles, but from where the metatarsophalangeal joint (MPJ) is located. As they cracked their knuckles the process was being observed through an ultrasound machine. The machine was able to record up to 400MJP cracks and was able to record the sounds that and not what type of cracks made the pop sound. Boudin and his team were expecting to see something extraordinary occur within the MJP, because the ultrasound is technologically capable to capture 10 times smaller than what the MRI is capable. They observed a bright flash on the ultrasound when the knuckles were cracked up, Boudin notes that it was a very unique finding. The flashes of brightness were consistently accompanied by the popping sounds; the team had predicted the sounds from the MPJs with 94% accuracy.

Several scientists have come up with different theories trying to explain exactly what goes on when pone cracks their knuckles. Boudin and his team suspect that the flash of light and the popping sounds are related when one is cracking up their knuckles that cause pressure changes and hence busting the gas bubbles in the joints. Previous studies had claimed that the popping sound came from the bubble forming. More studies need to be carried out to determine where the sound is caused by the bubble forming or by the bubble bursting.

Boudin and his team intend to carry out more studies to determine whether cracking up our knuckles is advantageous to us or not. And what are the long term effects of doing it. 

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Damon Jones

Editorial Boss

Damon is originally from Toronto, Canada so it should come to no surprise that he loves everything Toronto. From the Blue Jays to Drake, Damon loves his birthplace. He never saw himself as a writer, but when we brought him on as an intern, we gave him a shot at writing and we haven?t looked back since.