What is knuckle cracking? Are there any harmful effects?

Some say that Knuckle Cracking can cause Arthritis. But I don't believe this. I have a habit of cracking my knuckles or any other joints on my body like my neck, toes, wrists, etc. I mostly do this when my hands or fingers get tired of writing or typing. I do like the sound it produces and also I feel a little more relaxed after cracking my joints. Some do this cracking joints during massages and other therapeutic purposes I think. I see many people doing this thing too. I first learned how to crack my knuckle when I was still grade 5, my classmate thought me on how to crack my knuckles. He said that it produces a pop because of the bones cracking. But after I did some research, I knew that the popping sound is produced because of synovial fluid rapidly collapses that causes a sharp sound.

How about you? What do you think about cracking joints or knuckles? Do you think that this can cause arthritis or any kinds or illnesses? It's up to you guys to decide.

The whole arthritis thing is just an old wive's tale, and has no truth to it. There are 3 MAIN types of arthritis, which is osteoarthritis, rheumatoid arthritis, and gout.

Osteoarthritis is simply due to age and natural wear/tear. It is where the synovial fluid in your joints lessens over time, and causes your bones to grind into each other. It is a natural thing that knuckle popping does not cause or even been shown to worsen/speed up.

Rheumatoid arthritis is an immune system disorder. Your body is attacking its own body tissue. No definite known cause, but possibly genetically inheritable. Again, nothing to do with joint popping. 

Gout is simply when uric acid ends up in the joints and crystallizes. Nothing to do with joint popping. 

There have been absolutely no published PEER REVIEWED study that has been able to link joint popping to any forms of arthritis. In your joints, you constantly get little pockets of air trapped in the synovial fluid (squishy cushion for your joints). The popping you hear is simply those air bubbles escaping like air in bubble wrap. The difference between syovial fluid and bubble wrap is that the fluid doesn't have a hole when the air is squeezed out. It just closes up because it is fluid-like. So crack away.

rcarter2 :  Just a weird thought I had... I was trying to picture this even though it's been posted here on vizzed many times.  So I was imagining the air escaping the joints and..... where does it go?!?!  O.o  I mean... does it somehow get absorbed by your other tissues?  Does it escape through your pores some how?  (Being silly, but... seriously... where does it go?!)

That was a really creepy image in my head....

Singelli : I think I get exactly what you are picturing. Our body is filled with blood, so if a bubble escapes the synovial fluid, you might be picturing a bubble just in your blood now. Is that kind of what you picture? If so, I see where that question would come from. But in reality, blood is simply in your blood vessels. Quite a bit of the makeup of your body is not filled with fluids, but just air (a lot of hollow spaces). So picture the bubble wrap thing again. When you pop bubble wrap, the air inside is just released into the surrounding air. Same thing with this. It just gets released and mixed around the air trapped in your body. In a way, our body is like a bubble already. So the bubble in your synovial fluid is just a bubble inside of a larger bubble. Pop the smaller bubble, and the air just mixes around like normal. 

But one thing to remember is that you don't just get extra air in your body floating around. The air that builds up in your joints is air that was already in your body in the first place. It just got packed in and trapped in a little spot. So releasing it just makes that trapped air go wherever it would go when it wasn't trapped before.

rcarter2 :  I actually wasn't picturing it going into blood vessels. hehe. I was actually picturing the air being pushed between the muscles around the bone, and I was kinda wondering where it went from there. However, It was kind dumb for me not to consider where the air came from in the first place. LOL When I first started reading your response, I just imagined someone getting more and more air inside of their bodies as they cracked their knuckles, and then wondering if that air escapes your body with the way your skin 'breathes' or maybe even through... ahem... gas. ROFL

I can't believe I didn't consider the origins of the air! That makes so much more sense. So essentially, when you crack your knuckles/ spine whatever, you're actually just rearranging your body's air and pushing it back where it came from. Der. haha

So how does the air build up in the first place? Do extra active people get more bubbles in their joints and thus feel the need to crack their joints more often?

EDIT: It'd be kinda creepy if I or anyone else imagines are bodies are just full of blood.  I mean... like a blood balloon? Ew.....

Singelli : It helps to remember that air is just a bunch of different individual atoms going all over the place in whatever direction. Air does not exist as a clump/bubble/ but just a large void of billions of trillions of individual atoms going their own directions. Atoms being the smallest whole building block of matter, it is no problem for individual atoms to move their way around muscle. But synovial fluid is borderline liquid. As apposed to solid, liquid state has a lot more energy and the atoms making up things in liquid state move around a lot more and a lot faster. So the air travels through that mess of atoms in semi-liquid state. But as it gets in there, it is harder to get out due to having atoms bumping into you at all sides. So those atoms in gas state get trapped. Get enough of them within close proximity to each other, and they attract, forming larger bubbles. Because of that attraction of the atoms in gas form and the properties of sime-solid fluid, the bubbles can be sqeezed out.

As of what I know, knuckle cracking won't cause any harmful effects, like arthritis, but what I think I heard (I might be wrong though) it might even just help you prevent from getting arthritis, but I don't know.

Singelli :
rcarter2 :

He did a great job describing the popping. Fun fact #1) I thought it was neat that the guy who proved you can't get arthritis from cracking your knuckles won a Nobel prize for it. He cracked the knuckles on one hand but not the other for like 50+ years and didn't get arthritis in either hand.

To help with the air/fluid/joint analogy, let's go back to the synovial joint concept. The synovial joint, like rcarter2 explained very well, is a sac that sits within a joint to help the bones glide without touching each other. If the synovial sac shrinks and bones rub on bones, it becomes very painful, and this is the definition of osteoarthritis. 

Now, this sac is supposed to be a definite size and isn't really supposed to get larger. If the sac gets stretched out, the volume in it now becomes a little larger, and this extra volume is filled with air. The synovial fluid surrounds the air, causing bubbles within it, and when these bubbles pop, you get the CRACK sound. Picture something like a latex glove or a balloon. If you push your finger into it, you can create a new pocket that is now filled with your finger. Remove your finger, and the tension in the balloon will snap back to give the balloon it's original shape. Think of that snapping back as the cracking sound your joint makes when the bubbles pop. Let me know if that description helps, or just confused you more.

And for your second question, the body is able to absorb free air and does it all the time. Whenever laparascopic surgery is done (for gallbladder, appendix, hernias, etc...) we pump air into the abdominal cavity and use that air pressure to push all the vital organs and vessels out of the way so we can operate more safely. The patient is bloated that day, but air is re-absorbed in a day or two. Fun Fact #2) the scrotum will appear inflated with this as well, and will also reduce back to normal size after the air is re-absorbed. Multiple body cavities are integrated, and only a nerd/dork like me finds this stuff fascinating/awesome.