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Science & Technology

What is it that makes your knuckles crack ?

April 16, 2015 | Comment icon 10 comments



Cracking your knuckles in public can prove unpopular. Image Credit: CC BY 2.0 Jaysin Trevino
Scientists have used an MRI scanner to solve the mystery of knuckle cracking once and for all.
For some people the cracking of the knuckles can be an appealing and stress-revealing process while for others even the mere thought of it can make them shudder and wince.

The exact mechanism through which the knuckles produce such a loud sound has been the subject of debate for several decades however the prevailing theory is that it is caused by the collapse of air bubbles that form within the synovial fluid of the joints.

Now in a renewed effort to get to the bottom of the mystery a team of scientists led by Professor Greg Kawchuk decided to use an MRI scanner to see exactly what was taking place within the knuckle joints at the moment that the cracking sound occurs.

To accomplish this chiropractor Jerome Fryer placed his hand under the machine with a special tube attached to his finger that exerted a pulling force until the knuckle cracked.
The results revealed that the formation of bubbles in the synovial fluid was indeed the cause.

"It's a little bit like forming a vacuum," said Prof Kawchuk.

"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."

The team also found no evidence to support the common notion that people with a regular knuckle cracking habit could damage the health of their joints in the long term.

"The data fails to support evidence that knuckle cracking leads to degenerative changes in the metacarpal phalangeal joints in old age," the scientists concluded. "The chief morbid consequence of knuckle cracking would appear to be its annoying effect on the observer."

Source: CNET.com | Comments (10)


Recent comments on this story
Comment icon #1 Posted by Foil Hat Ninja 7 years ago
Now that they've cleared this up, maybe they can get to work solving one of the truly great medical mysteries: pee shivers.
Comment icon #2 Posted by Lenore Graves 7 years ago
I hate the sound of knuckles cracking! The explanation just makes it sound so much worst!
Comment icon #3 Posted by paperdyer 7 years ago
I just wonder how much grant money this project got?
Comment icon #4 Posted by quasar_kid 7 years ago
It's bad for your joints, the fluid in between can't rejuvenate overtime and can lead to arthritis and other similar conditions.
Comment icon #5 Posted by stereologist 7 years ago
The article stated the following: The team also found no evidence to support the common notion that people with a regular knuckle cracking habit could damage the health of their joints in the long term. I have known for years what happens when knuckles crack. I don't understand what the purpose of the study was since this is well known.
Comment icon #6 Posted by Skeptic Chicken 7 years ago
I can't believe it. I heard of something before seeing it on UM! *fires celebratory confetti cannons*
Comment icon #7 Posted by Imaginarynumber1 7 years ago
It's bad for your joints, the fluid in between can't rejuvenate overtime and can lead to arthritis and other similar conditions. That is completely false and has been proven to be so. http://tech.mit.edu/V129/N41/ignobels.html
Comment icon #8 Posted by TripGun 7 years ago
I'll crack to that!!
Comment icon #9 Posted by Eldorado 7 years ago
Knuckle dragging is next.
Comment icon #10 Posted by Torviking 7 years ago
I find a 25lb lump hammer works great to crack knuckles, works on bonehead scientist skulls also. Will you people get real!


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