I've been out of the horse game for a few years.  I've got a 21 year old horse that I plan on legging back up and trail riding on, and doing some casual team roping.  He's been used in the summer time.  He does have a knee chip, but it doesn't seem to bother him.  I doubt he'd pass a vet check (what 21 year old would?) but he's sound enough and feels good and should look pretty good in the spring when he's slicked off.  He's on a feed through joint supplement currently.  But I'd like to add an injectable, just to keep him feeling good and maintain where he's at. 

What intramuscular injection would you do for joint health for his situation?  Adequan loading dose? Just glucosamine?

Thanks for the help!

For a horse that age with some issues, I would use Pentosan. Adequan is great for prevention or maintaining joint health. Pentosan is cheaper Abbas works great!