How It Works - - SCIENCE MYTHS -

Knuckle crack­ing in­volves pulling apart the joints by stretch­ing or bend­ing them, which de­creases the pres­sure in the fluid be­tween them. This causes dis­solved gases in the fluid to form bub­bles, which then burst with a char­ac­ter­is­tic crack. Leg­end has it that this causes os­teoarthri­tis, where the car­ti­lage cov­er­ing the ends of the bones be­comes thin and rough­ens. But this leg­end isn’t true.

In 1998, Dr Don­ald L Unger wrote a let­ter to the editor of Arthri­tis and Rheuma­tol­ogy. He had been crack­ing the knuck­les of his left hand at least twice a day for 50 years, with his right hand act­ing as the con­trol. He had com­pared both hands for ev­i­dence of arthri­tis and found none, but he did con­fess that his study wasn’t enough to de­bunk the myth.

How­ever, a larger study later ap­peared in the Journal of the Amer­i­can Board of Fam­ily Medicine. The team quizzed 215 peo­ple aged 50–89 about their knuckle-crack­ing habits and looked at X-rays of their hands. The re­sult? There was no dif­fer­ence be­tween those who cracked and those who didn’t.

Os­teoarthri­tis is caused by wear to the car­ti­lage that cov­ers the joints

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