There isn't probably a whole lot you can do. He is probably really straight and the stress has caused fluid build up. There are some supportives you can do though. Make sure he has plenty of bedding wherever you keep him. I would leave him loose so he can move around the pen (as opposed to keeping him tied in 1 spot all day) Make sure he gets turned out evey night if possible to move around. You can run cold water over his hocks and also put some of that gel stuff that is like icy hot but its for livestock. Usually horses. Absorben or something.
Good luck with him.