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Questions and answers from
Harvard Medical School

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.

— Howard LeWine, M.D.

Q: Why do people become more forgetful as they age?

A: It’s common to have moments of forgetfulness about where we put the keys, why we walked into a room, or what an object is called. This reflects age-related changes in thinking skills. Over time we can expect a decline in all areas of brain function, with the exception of vocabulary.

Memory involves three processes: encoding, recording and retrieval. The brain receives and encodes (takes in) new information; the brain then records (stores) the information; finally, the brain retrieves information when you need it.

Many brain regions are involved in this process. For example, the cerebral cortex — the large outer layer of the brain — acquires new information as input from our senses. The amygdala tags information as being worthy of storage. Nearby, the hippocampus stores memories. And the frontal lobes help us consciously retrieve information.

Many people notice a difference in memory starting in their 50s. That’s when age-related chemical and structural changes can begin in brain regions involved with memory processing, such as the hippocampus or the frontal lobes. These changes may slow processing speed, making it hard to recall familiar names or words.

Other factors may be at play as well. Working memory — a mental scratch pad that allows us to use important information throughout the day — is susceptible to depression, anxiety and stress. And a lack of sleep can affect the brain’s retention and use of information.

Here are some tips to make the most of the way your memory works now.

• Repeat what you hear out loud, such as someone’s name, an address or a new idea. Repetition increases the likelihood you’ll record the information and be able to retrieve it later. With each repetition, your brain has another opportunity to encode the information, so the connections between brain cells are reinforced.
• Make notes to remind you of people you need to call, errands to run, and appointments to make/keep. We are much better at recognition than recall. With recognition, such as reading a list, you have additional hooks or hints that help you find the information you’re looking for.
• Divide information into chunks. It’s easier to store little bits through working memory. For example, if you’re trying to memorize a speech, focus on getting only one sentence or idea down at a time, not the whole speech in one take.

— Robert H. Shmerling, M.D.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School.

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, visit www.health.harvard.edu.

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