I have a friend that has a horse suffering from Navicular.

Does anyone have any experience with this condition?
This horse is primarily off in the left front...enough to give him a noticeable gimp, but not enough to slow him down. He is very hot under saddle and owner is not sure what is best for this guy. He is miserable not being worked and "light" riding is nearly impossible. He gets too worked up and wants to GO!!

Any thoughts and experience would be appreciated.