Science & Technology

What is it that makes your knuckles crack ?

By T.K. Randall
April 16, 2015

Image: AI-generated (Midjourney) 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

Tags: Knuckle, Cracking