Is there a race track near by? If there is one, I would suggest calling the race track to see what vet they use. Those guys are generally experts in lameness and can suggest whatever techniques can be done to save an animal (if that is an option for you). They won't sugar coat it and they are pretty good at giving clear diagnosis.
I took my gelding to a racetrack about an hour and a half away when he injured himself. The local vet diagnosed and treated a stifle injury. While I'm not so sure that wasn't part of the problem, it turned out to be a fractured pelvis. These guys work with leg injuries daily and can call things really easily.
Good luck. I hope you find a way to make whatever decision.