Hi Nick,
Firstly, I assume you're actually talking about the DIP (distal interphalangeal joint), as that's the one that hyperextends when you crimp.
Did the physios do a proper assessment or just have a quick look and decide there was nothing they could do?
When you say it doesn't move, is that when you try to move it itself, or when you use your other hand to move it?
Where do you live?
Joe