Two of mine have had FCEs.
The first was Cora. It happened in the middle of the night--she was suddenly restless and panting and would not settle. She lost the use of the right side of her body, which, in conjunction with her not-yet-healed broken leg, made her a one-legged dog. She did have deep pain response, so the vet was hopeful. Steroids were not used because she'd been on an NSAID. She eventually regained most of her mobility on the right side, but the broken leg never fully healed--it turned out to be OS.
The second was Cal. She was playing in the living room, then started pacing and panting, settling only for a few seconds at a time. She lost the use of her right hind leg, which was already wobbly. Even though she'd been on an NSAID, she was given an injection of Dex, plus stomach protection meds. A couple of days later, something went very wrong with the front leg on the same side. X-rays were clear, so it must have been a sprain. More Dex was administered, plus antibiotics in case it was an infection. The FCE leg recovered more quickly than the sprain, and, in fact, is better than it was before the FCE. I half-jokingly suggested to my vet that the piece of cartilage that broke off might have been what was bothering her before; no way to know though.
Just by-the-by, both diagnoses were based on observation, not MRIs. Neither went to rehab. And the change in treatment reflected what the vets had heard at the last conference they'd attended.