First of all, your vet should check the leg out. It could be arthritis, but it could be a number of other conditions, including issues with the back end (so he shifts weight forward which can cause problems on the front leg).
If it is arthritis, then the following may help:
Glucosamine/Chondroitin/MSM
Devil's Claw
Turmeric
Salmon Oil
Green Lipped Mussel Extract
Hydrotherapy
McTimoney Chiropractor
Acupuncture
Magnetic collar
TTouch