If you're somebody who likes to crack your knuckles before tackling a tough task, listen up. A study led by researchers at the University of Alberta has cracked the secret behind the popping sound knuckles make when they're cracked.
The secret to the sound is a momentary, vacuum-like gap formed in the lubricating synovial fluid between the finger and knuckle bones. When the joints are pulled apart too far, a momentary gas-filled gap forms in between, triggering the sound.
Lead author and U of A professor Greg Kawchuk says the "pull my finger" study could lead to future breakthroughs in joint health, including better analysis of spinal injuries, knee problems and other joint difficulties.
"It may be that we can use this new discovery to see when joint problems begin long before symptoms start," Kawchuk said in a statement.
Kawchuk's international team of scientists used MRI scans to watch a knuckle crack in super-slow motion. A video of the MRI shows a momentary pocket of darkness between the knuckle and finger bones as they are pulled apart.
"You can actually see very clearly what is happening inside the joints," said Kawchuk.
The MRI also revealed a brief flash of white just before the cracking sound occurs. Kawchuk says no one has ever observed that flash before, and he hopes to analyze it further with more powerful MRI machines in the future.
Scientists say the force generated by knuckle-cracking is enough to damage a hard surface. However, medical research has found no ill effects in people who indulge their knuckle-cracking habit.
Kawchuk says the study findings will form the basis of further research into joint health and arthritic pain.
"The ability to crack your knuckles could be related to joint health," he said.
Kawchuk is an expert in spinal structure and function with a PhD in bioengineering.
The study is published in the April 15 edition of the journal PLOS ONE.
