Marc, is it a front or hind leg that's lame?
We use a multimodal approach to osteoarthritis in our dogs - dietary management, nonsteroidal antiinflammatory pain relief, neutraceuticals, life-style changes and stem cell therapy. When used concomitantly these approaches should synergize and provide the best control of symptoms. For example, he might show considerable improvement if you add fish oil to his diet. The omega-3 fatty acids in fish oil are anti-inflammatory. I use the cost-effective generic human fish oils and dose them at 20 mg/lb daily of the EPA in the fish oil. You'll find the amount of EPA on the label of the fish oil product.
Avoid flax oil because it is poorly bioavailable to dogs. They can't metabolize it properly.
If you prefer, there are diets that are extremely high in omega-3 fatty acids. Hill's Prescription Diet j/d is one such diet.
Many vets feel that injections of Adequan (polysulfated glycosaminoglycan) work better than oral neutraceuticals such as glucosamine/chondroiton sulfate or the over the counter Cosequin or prescription Dasequin (please see here: http://www.amazon.com/Nutramax-Cosequin-PLUS-Chewable-Tablets/dp/B003ULL1NQ/ref=sr_1_1?s=pet-supplies&ie=UTF8&qid=1432474254&sr=1-1&keywords=cosequin). Adequan is injected into him weekly for a number of weeks at his vet's discretion. You can read more about Adequan here: http://www.adequancanine.us/
Regenerative stem cell therapy has come into its own and is now available for addressing osteoarthritis in dogs . Please see Vet-Stem's website here for more information:***@******.*** The regenerative stem cells are created from his fat cells and are capable of differentiating into a variety of tissue types including tendon, ligament, bone, cartilage, and muscle and have been proven to reduce pain and inflammation.
We have to suspect that just as in people, geriatric osteoarthritis in dogs is painful. If a prescription nonsteroidal antiinflammatory drug (NSAID) such as carprofen or meloxicam isn't sufficient for controlling pain, please consider adding a well-tolerated narcotic such as tramadol to these therapies mentioned above. All of these drugs are available from his vet. Aspirin dosed at 10 mg/lb with food every 12 hours can be helpful in a pinch.
Weight reduction is essential. The less weight his joints need to carry, the better.
Please respond with the additional information and further questions or concerns if you wish.