dog hind quarters

Question
I have a mixed breed dog that weights about 15 pounds.  He is getting old (about 15 years).  Lately he seems to be stiff in his hind quarters but has never seemed to have any pain related to it.  Late this afternoon (Friday of course)his back legs are not working most of the time.  He tries to get up and can't.  If I stand him up on all fours, he just sits his butt back down.  He did walk one time when I was outside with him and other times I just know he did because he was in a different location than when I saw him earlier.  I will be taking him to the vet, but just wondered if you had any suggestions?

Answer
This is probably a degenerative condition of the muscle and nerves in addition to arthritis; however, he could have a herniated disc for which steroids could benefit him.  In addition, I would recommend starting him on high doses of Glucosamine and MSM to help lubricate the joints.