What would you do about him??

I have a horse with athritic hocks. He is only 11 which is sad. I got him over a year ago. His so called family rode him hard and put him away wet if you get what I mean. Once they crippled him up, they had to get rid of him. In a nut shell, he basically has no cartilage anymore so you know what I'm getting at if you are experienced. Bute hasn't for a long time kept him comfortable. Injecting doesn't work and no supplements. Once bute no longer helps its pretty bad. I have hilly fields and he has been struggling to get up and down them now. Takes everything hes got to get himself thru the mud when it rains. It has been brought to my attention that it may be time for him. He would be the first horse I have had to have to put down. I have put clients horses down but never one of mine before. This may be why I'm hesitating. I just don't want to feel guilty cause hes perfectly healthy. What would you do? to be continued so hang on.......