If you go online to smartpak, you can actually talk to a rep. The smartflex 1 is about 20 per month but with an old injury I would reccomend smartflex III but it's alot more expensive.
Why don't you start out with something that is around 20-30 per month (Just go to your local feed store) and see if there is a difference. I would say about 2 weeks before you see anything. You may not have to do anything super special, especially if he's not currently on anything. Just a little kick may make the difference.
Another thing is, if you can keep him out 24/7 with a shelter then do that over a stall. When they have stiffness issues, movement is better.
Stick to pellets if he's a picky eater because he can pick around the specific pellets that have the powder on it where if you throw pellets in his feed and shake it up they'll be spread out and the taste will be lost....
"Be a best friend, tell the truth, and overuse I love you
Go to work, do your best, don't outsmart your common sense
Never let your prayin knees get lazy
And love like crazy"