He wanted to prove them wrong. So he did. Dr. Donald Unger was always told that cracking his knuckles would cause him to get arthritis. His parents and relatives would constantly remind Unger every time they heard that popping sound. So, he decided to put their theories to the test.

For the next 50 years, Unger cracked the knuckles on his left hand at least twice a day. He left his right hand alone to use as a control. At the conclusion of his experiment, not only did he not find arthritis in his left hand but he also found no significant difference between his two hands.

Unger received an Ig Nobel prize for his work, which is a satiric prize awarded to scientists in order to praise odd or trivial scientific achievements. Their purpose is to honor those whose achievements make people laugh and then think.

Why knuckles make that sound when popped has been long debated. Scientists were unsure of how and why it happened but there were theories. The prevailing theory up until 2015 was that the sound was caused by popping gas bubbles that formed in the fluid that lubricates a joint.

Then a study released in 2015 by an international team of researchers showed that that might not be the case. The researchers took an MRI video of someone cracking each of their knuckles to observe more precisely what happens. They found that it wasn’t gas bubbles, it was essentially a tiny vacuum forming in the space formed as the joint separates.

As someone pops their knuckle, the space between the two bones forming the joint gets larger. There is then not enough lubricating fluid to fill the space. The extra space is then filled by a gas filled cavity, similar to the idea of a vacuum. That formation is what is associated with the sound. The researchers, while thrilled with their findings, still acknowledge that there is more research that must be done.

A large portion of the public habitually cracks their knuckles for a variety of reasons. For some it is a nervous habit, for others it has a pleasurable release of tension. Regardless of why someone pops their knuckles, many who do still feel the threat of arthritis looming over them every time they hear that satisfying crack.

Fear not though, the research that has been conducted on the subject, alongside Unger’s experiment, has shown no relationship between knuckle cracking and the development of arthritis. That idea has been debunked as nothing more than an old wives’ tale. However, there has been some evidence that habitual knuckling cracking could lead to increased inflammation and decreased grip strength.

For those of us who are not going to quit cracking their knuckles any time soon, be content in the knowledge that it is relatively harmless. At least in its correlation to arthritis, long term knuckle cracking has not been shown to increase someone’s chances of developing arthritis. So continue to crack those knuckles and enjoying the sound they make when popped.

Emily Leclerc is a graduate student at Boston University pursuing her master’s degree in journalism. She hopes to be a science writer.

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