http://www.huffingtonpost.com/2015/04/15/cracking-your-knuckles_n_7074354.html
There are two kinds of people in the world: Those who feel a great relief from cracking their knuckles, and those who squirm at just the thought of it. Scientists have long debated the the cause of joint cracking, and there’s a lot of confusion about whether or not it can damage the hand (the answer is: probably not!). Now, they’re finally beginning to settle the debate about what physically happens when someone says “pull my finger.” …
Fryer’s finger demonstration may help scientists better study joint problems, including arthritis and injury. Kawuck said in the statement that the findings have implications for new research into the therapeutic benefit — or harm — of cracking joints. At the moment, there is conflicting data in research…