Maybe there is a difference of terminology of some sort but the head of the rib certainly can slip off the fossa of the spine. That is called dislocation of a rib at least sometimes. I've had it a few times. A chiropractor puts it (or them) back. It goes from a very sharp pain at every breath to kinda sore for a couple of hours or a day or so. I don't know what a dr would say it is; I never went to a dr for that.Well the doc said there’s nothing broken and that dislocated ribs weren’t actually a thing ...