My oldest Yorkie has arthritis. Some days are better than others but I have taken to giving her one half of a baby aspirin for the pain. This was recommended by my vet. It really helps and makes her much more comfortable.
Before you give anything to your Yorkie make sure you check with your vet. One thing I learned was that Tylenol was not safe for Yorkies and should not be given. You also have to be careful with how much you give your Yorkie as anything medicine can be deadly if overdosed.
I have found that baby aspirin is not as easy to find as one might think. The last time I bought a bottle for Surrobbie I got Bayer Chewable low does 81 mg. I give her just a half in her breakfast.
You can also buy aspirin that is made just for dogs. Check out DoctorDog.com for a variety of aspirin related products for your Yorkie.
For more information about giving your Yorkie aspirin check out School for Champions. However before giving your Yorkie anything ask your vet. It is better to be safe than sorry.