Cecil explains the mechanics of knuckle cracking here: http://www.straightdope.com/classics/a2_305b.html
But what isn’t addressed is why it feels good. My hands have a nice relaxed feel about them afterwards.
Could there be some evolutionary advantage to knuckle cracking?
I know I love it, even though it annoy the hell out of my wife. She says it’ll cause arthritis, no matter how many articles I find disclaiming that.
She can makes her wrist and ankle bones crack by rotating them heavily. I think it’s the same process making the noise, but I’m not sure. I hope it is, so I can tell her that her ankle-cracking is as bad as my knuckle-cracking, if it’s bad at all.