Loss of range is also telling, yet some loss can be due to stiffening tendons and ligaments and does not necessarily mean fusion has occurred. I think the most accurate predictor of future fusion is signs of vertebral degeneration and bone growth on a current xray or MRI. In other words, if it is already happening then it will most likely keep happening.
I have loss of range in my neck only. My last x-rays 3 months ago showed a perfectly normal spine, neck included.
I don't know what's causing the neck stiffness, probably a lot of combined stuff, inflammation, muscle spasm and so on.
Can stiffening tendons or ligaments be "un-stiffed"? I've been that way for about 3-4 years now with no progression, good or bad. I stretch every day. It seems to be wee-bit better after two months on Enbrel but still about only half normal ROM on both sides (strangely, on the left side I can push it to almost normal ROM).
It sucks. I'd just like to keep what I have for as long as I can. I'm 27 now. I don't want to end up with a totally frozen neck too young. In my 40's I don't care, but before that it just attracts unwanted attention.