What did the do Xray on when you took him to the vet? His legs or his spine? Since they are telling you that they don't see anything in the Xray and offered the steroid I think you should give it a try to see if the issue goes away. He might have an injury that you are not able to see on Xray. Did they offer any pain meds as well? If you don't see improvement after the steroid is finished then your next trip should be to a specialist.
__________________ “Never argue with a fool, onlookers may not be able to tell the difference.”  Mark Twain |