I agree totally with what the others have said - have him evaluated as a driving prospect, and that driving is not that hard on the joints. Driving horses can stay actively working and sounder a lot longer than riding horses. One big thing with driving is that they are balancing themselves- whereas a poor rider that carries their weight more to one side, or more to the front, or more to the back, will force the horse to compensate for the imbalance by shifting his weight. In driving, there is no weight on the back, so the horse can carry his own body quite evenly, and help keep him sounder longer.
So, driving ? Yes!
I’m confused about the true problem. You said your equine orthopedic could not tell what what wrong from the “ultrasound”… this doesn’t make sense to me.
Surely the vet did xrays? or someone, right?? Ultrasounds are not used as diagnostic tools for bone problems. U/S are for soft tissue diagnosis.
If the question is calcification of the hock, that would be diagnosed with xrays, or even a bone scan should you go that route.
If your well known equine orthopedic didn’t do xrays, no wonder he couldn’t tell what was wrong.
Arthritic hocks can fuse together as calcium deposits build up. The hock itself is comprised of 5 bones, 3 of which are smushed together in the middle like packed rice cakes. The spaces between those bones can fuse due to arthritis. The hock will have limited motion for a long time while the joint actively fuses, and it can cause soreness and lameness while it’s happening, but often, once fused, a hock can still function, and the horse can still have a working career. I’ve known horses with fused hocks that were still jumpers (JUMPERS - not hunters!).
Joint injections may help. Living on glucosamine/MSM joint supports may also help.
I’d personally be getting a second opinion on the horse either way before ending his career.
Good luck!