There are many herbs that appear to be beneficial for arthritis as well. This is a whole other story. A few of these herbs include yucca, devils claw, alfalfa as well as various chinese herbal formulas. One chinese herbal formula for arthritis for dogs is currently being evaluated at the University of Guelph Veterinary School in Ontario Canada. I'll let you know the results when that is completed.
Regular exercise is extremely beneficial also.
Exercise helps keep muscles, tendons and ligaments strong and in condition and improves mobility and range of motion. You want to be careful to give enough exercise but not too much. A good general rule of thumb is to do enough that your dog enjoys it and is out frequently but not too much that they are stiff and ache all over afterwards. Shorter more frequent walks and play time or swimming throughout the day are better than one long one. In addition, acupuncture, and chiropractic can be very beneficial for arthritic dogs, not only in relieving pain but in increasing circulation to the muscles and joints and improving overall health.