How much previcox where you giving him and how often?
My one gelding has hock, stifle, ringbone issues and arthritis. We had him on 1/2 a previcox everyday.
Since you have already done body work and chiro, you might want to look into homeopathic. I put my horse on a cycle(took about a year) but now he is no longer on previcox daily, only gets it when he’s having a bad day(which is maybe once every 2-3 months).
I was at my wits end and was debating putting him down because he was always limping and just seemed miserable. I found an animal communicator who was able to pinpoint his pain more for me and was able to help me with which remedies to use for his issues. This might be something you could look into. She also gave me peace of mind, knowing he wasn’t ready to give up. And yes I was very questionable about this being legit, but when she told me something that I did not know about, only my mom knew about. I knew it was legit.(he told her that he really liked these chewy cookies he was getting. I had never given him anything chewy, turns out my mom was giving him these little trail bite cookies that are pretty chewy in the mornings when she’d go out to put masks on)
Good luck. I know your frustration.
"Take the time it takes, so that it takes less time."
"Expect a lot, accept a little, reward often."