What did I do to my back?

I was dead lifting at the high school today and when i went up on the 4th rep, i felt a sort of tearing in my back (in the middle of it, but to the right of the spine) and it hurt really bad and i groaned involuntarily. I can't bend over now, it hurts really bad. Even sitting down hurts. There's no visible swelling on the spot by the way. What did i do to it?