Left Behinds

The anti-andrewsullivan.com. Or, the Robin Hood (Maid Marian?) of bright pink Blogger blogs.

Thursday, April 06, 2006

Awesum sciense III

What happens when you crack your knuckles.

Some scientists wanted to learn more about knuckle cracking, so they actually stuck a sensitive microphone onto a finger. They found that there wasn't just one single sound when you cracked a finger joint - there were actually two separate sounds. The joint space is the space between the bones. There is a liquid in this space [the synovial fluid], and there are ligaments on each side, holding the bones together. As you pull on the joint, you first drop the pressure in the joint space - and the ligaments get sucked in. Once this pressure gets low enough, a bubble pops into existence - making a popping sound, which is the first of the two sounds.

Now this bubble has a certain size - on average, about 15% of the now-bigger joint space. Because the joint space suddenly has a bubble in it, the liquid, just as suddenly, pushes on the ligaments - snapping them back to their original position. This snapping back of the ligaments is the second sound.


healthy-joint

And now you know. (Image source here.)

3 Comments:

  • At 2:39 AM, Blogger Solomon Grundy said…

    But is it true that cracking your knuckles gives you arthritis?

     
  • At 2:42 AM, Blogger Antid Oto said…

    Is joint cracking harmful? If you are feeling pain when your joints pop, than you should seek a health care professional. In terms of knuckle cracking, some studies show that knuckle cracking does not cause serious harm. Other studies show that repetitive knuckle cracking can do some damage to the soft tissue of the joint. It may also lead to a weak grip and a swelling hand.

    (Second link.)

     
  • At 10:25 AM, Blogger Solomon Grundy said…

    Yuck! I have never been a knuckle cracker, and there's why.

     

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