Wow, you could be right then. Have they looked specifically for this? In my experience, doctors, ESPECIALLY in the ER, are complete idiots who believe everything is "all in your head". Trust your gut and force them to check for what you believe he's dealing with. Remind them that it's coming out of your pocket, not theirs. If they don't act satisfactorily, ask for another doctor.
Either way, going to a chiropractor still sounds like a good idea to me.