Researchers have finally resolved the mystery as to why the popping sounds occur when we crack our knuckles paving way for further studies into whether there are any therapeutic benefits or harms of joint cracking.
An international team of researchers led by the University of Alberta used MRI video to determine the act inside finger joints, and observed for the first time, that the cause is a cavity forming rapidly inside the joint. Lead author, Professor Greg Kawchuk, said that the study they call “pull my finger study” shows very clearly in the MRI what happens when someone`s finger is pulled.
Fingers of Nanaimo chiropractor Jerome Fryer, who had approached Kawchuk about the new knuckle-cracking theory and could continuously crack his knuckles, were inserted one at a time into a tube connected to a cable that was slowly pulled until the knuckle joint cracked. MRI video captured each crack in real time, occurring in less than 310 milliseconds.
In every instance, the cracking and joint separation was associated with the rapid creation of a gas-filled cavity, like forming a vacuum, within the synovial fluid, a super-slippery substance that lubricates the joints.
Kawchuk said “as the joint surfaces suddenly separate, there is no more fluid available to fill the increasing joint volume, so a cavity is created and that event is what`s associated with the sound.”
Cracking knuckles a sign of healthy joints?
More than settling a scientific curiosity, the findings pave the way for new research into the therapeutic benefits or harms of joint cracking, explained Kawchuk, a PhD in bioengineering and expert in spinal structure and function.
Scientists have calculated that the amount of force at work when you crack your knuckles has enough energy to cause damage to hard surfaces, yet research also shows that habitual knuckle cracking does not appear to cause long-term harm. Those conflicting results are something Kawchuk and his team plan to investigate next.
“The ability to crack your knuckles could be related to joint health,” said Kawchuk, who believes this work could have implications for other joints in the body, including the spine, and help explain why joints become arthritic or injured.
In addition to solving the riddle of finger cracking, the team’s data revealed the presence of a white flash that appears just before cracking. No one has observed it before, says Kawchuk, an occurrence he believes is water suddenly being drawn together just before the joint cracks. Kawchuk said he’d like to use even more advanced MRI technology to understand what happens in the joint after the pop, and what it all means for health.
“It may be that we can use this new discovery to see when joint problems begin long before symptoms start, which would give patients and clinicians the possibility of addressing joint problems before they begin.”