Why Knuckle Pop?

“What is that sound we hear when we crack our knuckle?”

I remember my son asking me this, couple of years ago…

I had asked this very same question when I was a kid. That time, I got different answers. Some
said its bones sliding over…some said they don’t know…Some said its a bad habit…Some, told me that it would lead to arthritis and hence asked me to not to do that. But what is the reality?
Instead of telling what not it is, it is better we understand what it is. Simply put, that sound is coz of some gas bubble (mostly nitrogen, oxygen and carbon dioxide) bursting.

Knuckle is a joint and just like any other joint its covered by a capsule form which is called synovial capsule. Inside this capsule there is some fluid called synovial fluid. The major function of this fluid is lubrication. There are many gases dissolved in this fluid. When we crack a knuckle, we stretch the capsule that creates a low pressure inside the joint which results in a vacuum and some already dissolved gas gets released. This vacuum then gets filled by these gases which then form a bubble and finally bursts (at the peak of we applying the pressure to crack) resulting into that funny sound. It take some time for the process of gas getting dissolved in the synovial fluid again and hence we cant crack a knuckle immediately.

Now the ‘what is not’ part. As I mentioned earlier, some people even told me its coz of the ends of two bones touching and slipping over and hence it will lead to arthritis. As far as the bones touching part is concerned, it is wrong. Will it lead to arthritis? As of now, we can’t say. Coz nobody has done a solid study which resulted in sufficient data to prove it. But the health pro people thinks that habitual knuckle cracking can lead to some damage to tendons or ligaments (this can further lead to arthritis, depending on many other factors like age, nature of work etc - a possibility, since that is the case with knee joints ).

I remember, when I was practicing Karate, during the warm-up stretches we used to interlink our fingers and stretch the hand forward resulting in knuckle cracking. Why we do this is coz this makes that joints little more lose and thus flexible. This is not believed to be harmful.