A few months back, I was stretching and trying to crack my back after a couple hours on the computer. But instead I think my sternum cracked. There was deep, muffled crack and instant pain where my sternum is. It hurt to move my arms to much for a couple days. The pain eventually went away and usually doesn't bother me until I'm running and breathing deep/rapidly. Then I can feel exactly where it cracked before and it starts to hurt again. I'm just wondering if its possible to actually crack your sternum (not nearby bones)?