I have a Westie who is having trouble with his back left leg - he sits on it more than the other side but doesn't seem to want to put weight on it for very long (could it be a weight problem) or arthitis - about 5 years old?
If your pet is not placing weight on the leg the problem is probably not arthritis. It could be a luxatting patella, ruptured cranial cruciate ligament or numerus other problems associated with the hind leg. I recommend a visit to the vet and an x-ray. Good luck, vetcare