DEAR DOCTOR K:

My husband cracks his knuckles constantly. Aside from the fact that I find it annoying, I'm also worried that it's bad for him. Can knuckle-cracking lead to arthritis or other problems?

DEAR READER:

That "popping" noise that irritates you so much when your husband cracks his knuckles may well be music to his ears. But for those who don't crack their knuckles, the appeal can be hard to understand. And, like you, some of my patients (spouses of habitual knuckle-poppers) have wondered what causes the sound and whether it's harmful.

I passed on your question to my colleague Dr. Robert Shmerling, an arthritis specialist. This is what he told me. The "pop" of a cracked knuckle is caused by bubbles bursting in the fluid that lubricates your tendons and joints, called synovial fluid.

When the bones are pulled apart, it stretches the joint capsule that contains the synovial fluid. This decreases pressure inside the capsule, which causes the little gas-filled bubbles in the synovial fluid to burst.

Like you, many people assume that knuckle-cracking can lead to arthritis. Although it may seem a logical connection, it hasn't been proven. One study comparing rates of arthritis between habitual knuckle-crackers and people who didn't crack their knuckles found no difference in the rates of arthritis between the two groups. But it is true that chronic knuckle-crackers were more likely to have swollen hands and reduced grip strength.

I've heard stories of people suffering injuries as a result of trying to crack their knuckles. It may be that these people were overly vigorous or didn't know their own strength. But such reports are quite rare.

While knuckle-cracking can be annoying to others, it seems to be harmless. The same is generally true of other joint-related noises such as popping, crackling or snapping, as long as no pain accompanies it.

However, there are some red flags to look for. Does your husband have pain and a grinding sound when he flexes his knuckles? Do any of his fingers lock or give way? Does he hear a sudden "pop" and feel pain when using his hands? Any of these red flags could be a sign of a more serious problem that may need medical attention.

I once had two patients, a husband and wife, who were having marital strife. They'd been married 15 years. I asked the wife what was causing the problem in their marriage. She answered, "My husband." When I pressed for a little more detail, she first listed his carelessness with money and his unwillingness to do work around the home. But numbers 3 and 4 were his constant popping of the joints in his hands and his tendency to chew ice loudly. These little annoyances had made it to near the top of her list.

So, your husband is probably not harming himself by cracking and popping his knuckles. But if he's driving you up the wall, by all means ask him to stop -- at least when you're around.

(Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.)

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