I too learned that cracking knuckles releases gas from your joints but I don't think that is all that it does. Over the years I have cracked my pinky and ring finger joints only, because they are the only ones that ever needed to be. I have noticed that these knuckles (pinky and ring finger) have swolen to 2-3 times the size of the others on my hand. There is also a little stiffness in these knuckles as well. That doesn't mean that I think those who crack their knuckles will develop RA. It means that those gene pools who are susceptible to RA may develop earlier signs with knuckle cracking (just my opinion).