02/10/2024
Interesting
WHY DO KNUCKLES CRACK... and is it Safe?
“What’s known with certainty is that the cracking happens when the space between joints is increased, by bending or pulling. This creates a pressure vacuum within the synovial fluid, as it’s called, and dissolved gases form an air bubble. What scientists don’t know is whether the sound is caused by the bubbles forming or collapsing.
Problem is, it’s hard to get inside a knuckle and watch what’s happening, but researchers did the best they could in a 2015 study, using an MRI machine. They concluded that the pop is made by air rushing into a cavity, forming a bubble.
Another group of scientists, using a mathematical model in 2017, argued that the collapse of a bubble would produce a sound consistent with what we actually hear.
Either way, the air bubbles help explain why most people can’t usually crack the same joint twice without a delay: The air must build back up (or dissolve back out, depending on which explanation is correct). There’s also room in all this for a partial crack, scientists say, which sometimes allows for a second cracking right away.
THE BRAIN SEEMS TO GET A KICK OUT OF IT
The force produced by these bubbles may activate sensory receptors in the joint, which some experts believe causes the satisfaction people derive from cracking their knuckles,” says Branden Daubel, physical therapist in UT Health Austin’s Musculoskeletal Institute. “These receptors send information about where your joint is in space to your brain, and your brain gives you a little hit of dopamine because it loves information.”
BUSTING THE ARTHRITIS MYTH
Importantly, and contrary to what Mom said, knuckle cracking does not seem to cause arthritis. A large study way back in 1975 found no greater risk for arthritis in older people who were lifelong, habitual knuckle-crackers. The finding was confirmed by a smaller 2011 study.
One study is hands-down the most interesting, however. Donald Unger, MD, conducted his own 50-year-long experiment. At least twice a day, he cracked the knuckles of his left hand only—more than 36,000 times in all, as described by Steve Mirsky in Scientific American. Then Unger published a study on the results in 1998, indicating that he’d suffered no arthritis, and there were no noticeable visible differences in his two hands.
As long as knuckle cracking doesn’t cause you pain, there's no reason to worry, says Alexander Soneru, MD, an orthopedic surgeon with Loyola Medicine.
“Parents frequently tell me that their child cracks their knuckles,” Soneru notes. “I tell them that they may not like the sound, but they shouldn’t worry about negative effects, such as arthritis, down the road.” Robert Britt
HOW DO YOU THINK THIS RESEARCH APPLIES TO OTHER SYNOVIAL JOINTS?
