Dear Martha,

Like many people, I have a bad habit of cracking my knuckles and consequently annoying others around me with the sound.  Just what IS that sound made from though?  I know I'm not really "cracking" the knuckles.  I've also heard that this will cause arthritis in later years.  Is this true?

--Matt, the nervous noisemaker

Matt,

You're in what some people call a vicious circle (or a vicious cycle--the rules on this one are relaxing). You feel nervous, so you crack your knuckles. Then you start worrying that you're bugging the people around you, and possibly setting yourself up for an old age plagued with bulgy knuckles and painful arthritis.

It's making me want to crack my knuckles out of sympathy.

I have good news and I have bad news.

The good news is that experts say that your habit doesn't cause arthritis. Nor does it enlarge joints or cause other significant musculoskeletal problems.

The sound you're hearing is actually two sounds (researchers put microphones up to knuckles to confirm this). The first sound happens when you pull your joint and create a bubble. The second sound is the bubble popping. Joints are where two separate bones meet. Ligaments and connective tissue hold them together, in kind of a bath of thick fluid. When you pull apart a joint, it creates extra space for the fluid. So, that first bubble forms. When the bubble appears, the liquid pushes back on the ligaments, snapping them back into place.

In a 1998 letter to the Arthritis and Rheumatism journal, Donald Unger, M.D., described the results of a very interesting 50-year experiment he'd conducted on his own hands. Every day during that time, he cracked the knuckles on his left hand at least twice. And, although the temptation must have been great to even things out, he left his right hand alone. After 50 years of this, he had no signs of arthritis in either hand. Also, both hands looked pretty much the same.

In a study involving more than one patient doctor, researchers looked at 300 long-term knuckle crackers (people who'd been doing it for at least 35 years). Their joints were a little swollen and their grip strength, which helps you open jars, was a little weaker. These things aren't major medical issues, so you have to decide whether popping your knuckles now is worth having a hard time with peanut jars later.

Here's the bad news: It is annoying. Next time the urge hits you, consider reading up on the anteater and the ape, the two animals that walk on their knuckles. Maybe it will inspire you to treat your own hands a little more kindly--or at least give you a different idea for something to do with your poor knuckles.

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