Forget unbendable arm -- I have unbendable back
I've contacted a couple of local Feldenkrais practitioners and we'll see what they have to say.
No, I haven't spoken to a chiropracter, or a doctor about it. A body psychotherapist I know believes it is long term muscle shortening caused by a desire to be "upright". The vertibrae are not fused -- you can clearly see the processes moving when I arch backwards. I do not suffer from any kind of back pain, nor ever have. People generally compliment me on my posture. They don't realize I don't seem to have a choice.
Thanks for all your advice. I expect it'll take months or years of gentle coaxing to fix. I just need a programme that'll work.