Likelihood of spinal fusion?

Hi,

I just recently found out that fusion of the spine and/or ribs is a possible result of ankylosing spondilitis. Neither of my rheumy docs mentioned this to me, so I was pretty shocked when I discovered this doing research online.

Does anyone know what the likelihood of this is? Is it very common for people with AS, or is it a rarity? Is there an estimated percentage of how many will have this happen? If it does happen, is it a long slow process over years?

I know that I don't have any sign of it developing so far, as none showed up on my recent x-rays. But when I asked my current rheumy about it, she dismissed it with an "Oh, that's not going to happen to you." I never take that as an answer anymore as it seems I am always one of the exceptions, getting the rare things that doctors tell me I can't possibly have and I'm tired of it. I asked her why it wouldn't happen to me and her reply was because I would've gotten AS in my twenties if it was going to happen. (My AS symptoms started when I was in my thirties.) This seemed like BS to me, a quick way to allay my fears, but of course I don't know.

Can anyone enlighten me, please? Thanks.