by Marcin Gornsiewicz, M.D.
Entwine your fingers together and then bend them back. Do you hear the popping sound? Chances are you do. We have all done and heard it before, and some kids do it all the time just for fun or to make their parents crazy. Knuckle cracking is a common habit. Where is the noise coming from? To understand it, you need to know a bit about joint anatomy.
Joints are divided into fixed and movable ones. Most of the joints in our face are fixed, and the joints between the vertebrae of the back allow only slight movement. In contrast, other joints such as the ones in the hands, wrists, arms and legs are very flexible. The bones that make up a joint are held together by ligaments, which are like tough cords or straps. Joints are covered by a capsule, a thin, fibrous sac containing a special type of liquid called synovial fluid. This fluid acts as a thick, clear lubricant, helps the joint move smoothly and contains nutrients for the adjacent bone surfaces. A variety of gases are continuously dissolved in this fluid including oxygen, nitrogen, and carbon dioxide.
When you stretch or bend your fingers, the bones of the joints are forced apart. The stretching of the capsule increases the volume of space between the tissues and lowers the pressure inside the joint. This creates a vacuum which is filled by the gas. The bubbles that are formed quickly expand and then burst, creating the cracking or popping sound. It takes a while (up to 30 minutes) until the gases return to synovial fluid, which explains why the knuckles can’t be re-crack immediately.
Some people can’t crack their knuckles. They are not able to relax enough to allow the bones to separate. Others can crack almost every joint in their body.
Kids crack their knuckles for two main reasons: First, it just feels good as cracking stimulates certain nerve endings and the muscles surrounding the joint relax. The joints feel more loose immediately thereafter. Second, kids realize that cracking produces a funny noise, and they often get attention. That encourages them to do it even more often. Overtime, they are not even aware they are cracking their knuckles until somebody tells them. It becomes a subconscious nervous habit.
So is knuckle cracking safe? Does it lead to arthritis? Several studies have shown no evidence that cracking knuckles causes any damage, such as arthritis, to the joints. However, people who continue to crack their joints for a very long time can develop local inflammation of ligaments. This can lead to swelling of the hands and slightly reduced grip strength. Perhaps the biggest problem is that it can become an annoying habit and can make people around insane.
Here are some recommendations if you have a kid who pops and cracks his/her joints every other minute. Try to ignore it as much as possible. Nagging and complaining about it is more likely to make it worse. Keep your children occupied. Keep their hands busy. Encourage them to stretch their hands and fingers rather then crack them, to take up a new hobby like crafting and drawing. Most importantly be patient. It will go away with time.
Dr. Marcin Gornisiewicz graduated with an MD degree from the Medical School of Warsaw in Warsaw, Poland. He completed residency training in internal medicine at Saint Barnabas Medical Center in Livingston, New Jersey. He completed fellowship training in rheumatology at the University of Alabama at Birmingham in Birmingham, Alabama. He joined Rheumatology Consultants, PLLC (rheumatologyconsultants.org) in 2002. He is board certified in Rheumatology.