It’s been a long day. You’re just home from work, and the whatever it is you do was tough today. You relax in your favourite chair or on your second favourite couch and stretch out your tired limbs. In return, you are greeted with a cacophony of snaps and crackles that would put the Rice Krispies mascots to shame. People tell you you’ll get arthritis, and that the sound is really gas bubbles popping in your joints. But is any of that true?
In short, no. It’s been shown conclusively that knuckle cracking has no correlation to developing arthritis. A study published in 2011 showed that the rate of arthritis was the same in people who cracked their knuckles than it was in those who did not. Unfortunately, other studies have shown that habitual knuckle-crackers have a higher rate of swollen joints and a weaker grip. So while the traditional rumour might be false, it seems that knuckle-cracking still isn’t an incredibly healthy option.
As for the cause, it’s a fairly recent discovery. In diarthrodial joints (which is a fancy way of saying joints where two bones interact, like your wrist, elbow, or knee) there is something called a joint capsule. This is a pocket of tissue that is formed around the joint, and inside this pocket is a lubricant as well as serving as a nutrient for the cells that live there. The fluid in the capsule also contains dissolved gasses, mainly nitrogen, which form bubbles that pop as you stretch your joint. The popping allows your knuckles to move a little further, which is why cracking your joints lets you stretch them a little more.
As for why such tiny bubbles of gas cause such a loud noise, scientists aren’t even sure. However, they do know why you can’t just endlessly crack your knuckles: the gasses need about 20 minutes to build up again before there’s enough to form a bubble. So next time you reach a little further for your phone and you hear your shoulder pop, don’t worry too much about what’s going on. It’s just bubbles of nitrogen and carbon dioxide quickly forming and popping in your joint capsule with such force that you can hear it quite clearly from a few feet away. So when someone complains about you cracking your knuckles, just throw some science back in their face.
Ian Mitchell is a pro-wrestling fan who also happens to be in the second year of the Professional Writing program. When not telling his friends about how he would run the WWE, he can be found playing video games, doodling, and writing a rules system for a pro-wrestling tabletop roleplaying game.