What makes your knuckles crack, and is it as bad for you as my mother says

asks jaysway:

A. By 'crack', you mean when you lace your fingers together, turn your palms away from your body and bend your fingers back

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Q. Yes, when you get that strangely enjoyable cracking sound which makes other people wince. What causes it
A. Your knuckles produce the noise when bubbles burst in the fluid surrounding the joint.

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Q. Oh gross! How does that happen
A. Your joints are where two separate bones meet, and they are held together by connective tissues and ligaments. Each of your joints is surrounded by synovial fluid - a thick, clear liquid. When you bend your fingers to crack your knuckles, you are forcing the bones of the joints apart. As they stretch, the connective tissue capsule that surrounds the joint is also stretched. By stretching this, you are increasing its volume. If you remember your chemistry lessons, if you increase the volume you decrease�the pressure.

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This is getting complicated...
Well, you did ask. So as the pressure of the synovial fluid drops, gases dissolved in the fluid become less soluble, forming bubbles through a process called 'cavitation'. When the joint is stretched far enough, the pressure in the capsule drops so low that these bubbles burst, producing the crack that you hear.

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Q. How long does it take for these bubbles to go away again
A. About 25-30 minutes - in that time the gas will redissolve into the joint fluid, and you will not be able to crack your knuckles again until it is done.

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Q. So, does it harm you
A. There has been one in-depth study of knuckle cracking, published in the American Journal of Manipulative and Physiological Therapeutics. The study looked at 300 knuckle crackers for evidence of joint damage, and there was no apparent connection between joint cracking and arthritis. But there were other signs of damage.

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Q. What were they
A. People who crack their knuckles all the time were more likely to have soft tissue damage to the joint capsule and less grip strength.

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Q. So my mother is right
A. To an extent. There is some benefit to knuckle cracking, too. Manipulating joints on the body - any joints - relaxes the surrounding muscles and, in turn, makes you feel relaxed.

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By Sheena Miller

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