By Howard J. Bennett

If you’re a kid, chances are you either crack your knuckles or know someone who cracks theirs. If you’re a parent, chances are you get the willies if you see someone cracking his knuckles. You may also worry that the knuckle-cracker (or should that be knucklehead?) will get arthritis if he repeatedly engages in this behavior.

First, you need to know a bit about your knuckles, the common name for the joints in your fingers. A joint is a place where two bones come together to allow movement. The bones that make up a joint are held together by tough, flexible tissue called ligaments.

Joints are also covered with a capsule. A special type of liquid called synovial fluid is contained within the capsule. Synovial fluid acts as a lubricant for the cartilage and bone. The synovial fluid also contains dissolved gas.

When a person stretches a joint to crack his knuckles, he creates negative pressure within the capsule. That vacuum allows more dissolved gas to enter the capsule as a bubble. When the gas bubble bursts, you hear the characteristic popping sound that we all know and some of us love. The reason you can’t re-crack your knuckles immediately is because the joint isn’t “loaded” until more gas dissolves within the synovial fluid.

So, does knuckle-cracking cause harm? In most cases, no—unless you count grossed-out friends and parents.

Kids crack their knuckles for two main reasons. First, some find that their joints feel a bit looser after they’ve been cracked. That is particularly true for older kids and teenagers who crack the joints in their necks or backs. Unfortunately, the effect is temporary, which invariably leads to more cracking. Second, kids often get attention when they crack their knuckles. This encourages them to do it more often even if the attention is negative: “Timmy, that is so gross!”

Although cracking your joints will not lead to arthritis, overzealous cracking can injure the ligaments that support those joints. That usually results in mild pain, which will resolve if the knuckle-cracker takes a break from his noisy hobby. In severe cases, it can weaken one’s grip by loosening the tendons that attach muscle to bone.

So the next time your parents are worried that you’re going to end up with arthritic hands, you can read them this story to put their minds at rest. Then again, it might be a good idea to leave your knuckles alone and get some exercise.

© 2012 Howard J. Bennett. All Rights Reserved.
(First published in the Washington Post 2/23/09.)

For more KidsPost articles and lots of other cool stuff,
please visit Dr. B’s website at  www.howardjbennett.com.