Let me start by stating, "I know what you mean by your doc not being able to give you a straight answer!" My rheumatologist has more "I don't knows" than I can believe.
I take it that you had Xrays showing deteriorated cartilage and fusion of the ankle.
Yes, the ankle can fuse and given time could fuse completely. The ankle is a joint, and I believe that the ankle, like the wrist and spine, can self fuse as well. (ankyloses, which is joint immobility or fixation happening when the cartilage and bone are deatroyed by RA).
The ankle fusion can also extend to the supprt structures of the bones, tendons, ligaments and thus joint instability and deformity can occur.
What I would recommend:
Be sure that your rheumatologist knows how unhappy you are! You're in pain and that's not good! There's a lot of pressure demands on your ankle and the pain needs to be addressed. The pred, MTX and celebrex are good...but you can add additional pain management. Talk it over with the doc about a stronger pain med (he might not Rx an opioid, so you might have to see your primary care physician for one). And also, it might be a good idea to talk about a DMARD/Biologic like Enbrel, Humira or Remicade. To try to prevent other joints from fusing.
Ankle-foot orthotics will aid in some measure of foot and leg support by preventing dorsiflexion and inversion of the ankle (basically ankle deformity in other words). I would say it can't hurt to try one! It would reduce pain by providing proper alignment. My best advise would be to get a consult with an occupational therapist or an orthopedic doctor or orthopedic surgeon, and they can give you the best route to take further.
I can only imagine how many conflicting views you'll hear from your docs about this. Rheumatics is an art! I try to remember that at each appt! And many times we have to try one thing after another until something works.
But definitely take action on PREVENTING further fusions. Have you considered the TNF meds like Humira and such?
I hope this made some sort of sense! Pain and immobiltiy are big issues regarding the ankles. So there are some options here and things to look into.
I'm not sure if there is a surgical approach to this or not.
If I can offer any more input on this I'll post it for you!
Take good care,