The Medicine Cabinet: Ask the Harvard Experts
Q: People keep telling me to stop cracking my knuckles. Does it cause arthritis?
A: Knuckle cracking is a common behavior enjoyed by many. It can become a habit or a way to deal with nervous energy; some describe it as a way to “release tension.” For some, it’s simply an annoying thing that other people do.
Despite how common it is, there has been considerable debate regarding where the noise comes from. Fortunately — at least for those of us who are curious about it — knuckle cracking has been the subject of a fair amount of research.
The “cracking” of knuckle cracking seems to be produced by increasing the space between finger joints. This causes gas bubbles in the joint fluid to collapse or burst. It’s a bit like blowing up a balloon and then stretching the walls of the balloon outward until it pops.
The reason you can’t crack the same knuckle or joint twice right away is that it takes some time for the gas bubbles to accumulate again in the joint.
Cracking the knuckles is probably harmless. Although there have been occasional reports of dislocations or tendon injuries from overly vigorous knuckle cracking, such problems seem very much to be the exception and not the rule.
One of the most convincing bits of evidence suggesting that knuckle cracking is harmless comes from a California physician who reported on an experiment he conducted on himself. Over his lifetime, he regularly cracked the knuckles of only one hand. He checked x-rays on himself after decades of this behavior and found no difference in arthritis between his hands. A larger study came to a similar conclusion.
The origin of most joint noises, such as popping sounds or cracking of the knees when squatting, is uncertain. They may come from the kneecap rubbing on the bones below, or a tendon sliding across an irregular surface. However, in the absence of pain, swelling, or other joint symptoms, these sounds are probably nothing to be concerned about, and there is no reliable way to silence them.
If you want to crack your knuckles, it’s unlikely to cause you harm. But if you want someone else to stop cracking their knuckles, you’ll need a better reason than telling them they’re ruining their joints.
(Robert H. Shmerling, M.D., is Associate Professor of Medicine at Harvard Medical School and Clinical Chief of Rheumatology at Beth Israel Deaconess Medical Center in Boston. For additional consumer health information, please visit www.health.harvard.edu.)
