I'd put money that your lack of ability to fuse is related to that overage in the steroid nasal spray. It must be playing havoc not only with your cortisol balance, but with your calcium levels. (Wonder if this would be picked up on a CBC, or whether it would take more sophisticated calcium ion testing.)

In any case, this is serious--a person such as you, of a "certain age", as they say, and not being a large person to begin with, is definitely at risk for other bone loss from such an ovedosing, beyond the fact that it likely leached calcium that might have been available for fusion.

(Being the type of person I am, I always wonder if you've got a malpractice case here . . .)