
The Cause of the Knuckle-Cracking Sound - mhb
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0119470
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matthewrhoden1
I know there isn't anything to worry about, thanks to that one guy popping his
knuckles in one hand for 60 years (quick google:
[http://geekologie.com/2015/03/taking-one-for-the-team-man-
cr...](http://geekologie.com/2015/03/taking-one-for-the-team-man-cracks-
knuck.php)) but the description in this article made me not want to pop mine
anymore. :(

~~~
lgas
There's only nothing to worry about if you don't mind reduced grip strength:

[http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1004074/pdf/annr...](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1004074/pdf/annrheumd00439-0036.pdf)

~~~
vanderZwan
Err... that doesn't look like a proven causal relation to me?

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logfromblammo
In short, the knuckle popping sound is more akin to quickly pulling your boot
out of sucking mud--with the ensuing "schlorp" sound--than pricking a balloon
with a pin and its more acoustically similar "pop". When joints pull apart,
the joint fluid is viscous enough that gases cannot immediately rush in to
fill the gap. That creates a pressure differential, and when the fluid finally
gives way, the rapid formation of a gas bubble makes an audible popping or
cracking noise.

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morganvachon
Very interesting. In my "old age" (38 next month) I've found that my ankles
and knees have begun popping or cracking with regularity. I can rotate my
right foot in a circular motion and it will pop just below the top of the
ankle on every single downstroke no matter how many times I do it. My knees
have begun popping every time I stand up and usually when I stretch them out
under a desk or table. Five years ago this didn't happen, and I'm actually
more active today than I was back then.

I've often wondered if the "gas bubble" theory was only partially correct, as
there are different kinds of pops and cracks with different sounds and
sensations (including pain).

~~~
andegre
In my old age also (36), one of my ankles pops every time going up (not down)
stairs. I also, crack my knuckles, fingers, neck numerous times throughout the
day. It's more of a habit now, versus "feeling" anything.

I'd love to know, in laymans terms, the repercussions to doing this. As far as
I could gather from the article, it doesn't sound like any long-term effects.

One other question I have, though, is why is it "easier" to crack these parts
over time? The more I do it, the easier it is to repeat in the future. Am I
just creating this space, and making it easier to "fill" with every
"distraction", as the article called it?

~~~
rosser
Dr. Donald Unger won the 2009 Ig Nobel for demonstrating (N=1) that knuckle-
cracking doesn't lead to arthritis, by cracking the knuckles of one hand daily
for 60 years, and never cracking those of the other.

[http://tech.mit.edu/V129/N41/ignobels.html](http://tech.mit.edu/V129/N41/ignobels.html)

~~~
andegre
Like I said, for someone that does this NUMEROUS times a day, that is some
EXTREME self-control to be able to only do it to one hand that long.

~~~
Crito
When I don't crack my knuckles regularly, they start to feel extremely stiff
and experience a dull pain. There is no way I'd be able to stop myself from
cracking one of my hands for that long. That really is extraordinary self-
control.

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Jun8
Mini Ask HN: Do you find it rude to crack one's knuckles in business meetings?
I sometimes do this and wonder if it's bad form.

~~~
Raphmedia
I know a woman that cannot stand it. Doing it in internal meetings will get
you a beating. If you were to do it in a business meeting where she was the
client, she would probably never speak to you again and take the business
elsewhere.

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dschiptsov
In my own experience joints clicking is strongly related to chronic
dehydration (abbusive gren teas/strong coffee drinking) coupled with physical
activity.

When I avoid coffeinated drinks and related excessive water loss but
continuing some active physical exercise the effect is almost disappear. It is
"lubrication" issue.)

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aluhut
Unfortunately my girlfriend still hates the sound...

I crack in my back and neck before sleeping. It helps. It may go pretty bad if
I already have some kind of pain so I don't do that anymore. I wish I could
teach my girlfriend to do it properly so she could fix me but well...she hates
it ;)

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mullingitover
Given that the cracking is cavitation bubbles, it's kinda surprising that it
wouldn't be doing damage. You just have to look at metal ship propellers that
are worn from cavitation damage to see how cavitation bubbles can eat away at
things.

~~~
stouset
Consider how many cavitation bubbles a propeller has to deal with in its
lifetime, versus a typical knuckle.

~~~
ars
I wouldn't discount it so fast, tuna have damage to their tail because of
cavitation.

[http://www.newscientist.com/article/dn13553-dolphins-swim-
so...](http://www.newscientist.com/article/dn13553-dolphins-swim-so-fast-it-
hurts.html)

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astazangasta
Crack your knuckles if you cracked your knuckles while reading this story. I
cracked mine.

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symfoniq
So what does it mean if your joints don't pop? I'm unable to induce it, and it
happens very rarely by chance. However, my wife pops her knuckles (and other
joints) all the time.

~~~
sfeng
Seems like it would be slightly loser ligaments which allow you to move your
joints apart enough to create the empty spaces. Or, possibly, a different
tension profile which causes your wife's joints to suddenly open while yours
open more gradually.

~~~
agumonkey
After trying for a while, I finally 'managed' to do it any time I wanted to,
now that I stopped it doesn't happen anymore. I'd second the stretched
ligament theory.

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abalone
tl;dr it's from creating cavities not popping bubbles.

Not creating and popping them, but rather that's the sound of creation.

~~~
erikb
Thanks. Can you explain it in simpler English please? I'm not native and
googling for "cavity" results in pictures of teeth with holes not ankles. If I
transfer "hole" to the topic of ankle I don't see the difference between the
bubble and the hole theory.

~~~
corysama
Think about bubbles in a bottle of carbonated soda. Before you open the
bottle, the carbonation is a liquid inside of the water because of the
pressure inside the bottle. When you open the bottle, the pressure drops and
the carbonation converts to a gas and becomes bubbles.

But, imagine if instead of opening the bottle, you just somehow reduced the
pressure then quickly increased it back to what it originally was. The
carbonation would go from liquid -> gas -> liquid very quickly. CO2 bubbles
would form then collapse.

Converting from liquid to gas is not a special property of CO2. There are
liquids in your joints that will convert to gas if you drop the pressure.
That's what happens for an instant when you crack your knuckles. What you are
hearing is the bubbles of gas collapsing as the gas converts back to liquid.

~~~
Crito
What they actually found in this MRI study is that the bubbles stick around
for several minutes, slowly dissolving back into the fluid. They don't
immediately collapse as you would expect. The sound seems to come from the
very rapid expansion.

The time it takes for the bubbles to dissolve again seems to be responsible
for the "cool-down" period that you experience between cracks.

