I would check into supplementing with both glucosamine and chondroitin. I don't think it can really hurt them.
There are a lot of good quality dog foods now that have both added to their formulas as well. You might check with your vet but I've also heard that vitamin c helps. If your Yorkie doesn't want to take a supplement you might check into the dog foods and/or dog treats made with both supplements. Good luck,
Teresa