Depending on what the actual cause is, a corticosteroid like dex could help to immediately reduce swelling and stiffness. If its chronic, duralactin or similar might be your answer for preventative maintenance. Or, if he is related to Rice, you could order some antler spray

I have a bottle of duralactin left over from my old Lab. If its a chronic condition, and you want to give it a shot, PM your address.
Steve