Hello, I would like to humbly add my two cents. My Frankie was limping oddly for a time and I kept taking him to the vet and they kept testing for Lyme - I live near Boston - so common. He always tested normal. My gut told me to take him to a chiropractor.
I did and within one visit, no more limping! Now when he limps, I get him adjusted. Now, this doesn't mean this is always the case. I can also say the Rimadyl as others have indicated, at least in my opinion as well, is not good for doggies - especially for a long time. I might ask for another drug - like Dermax - or something else for pain if your doggie is in pain. I give Frankie Traameel from the Health Food store - for ligment pain for people and okay for pets too! It is more holistic and natural.
One last thing I can mention - when I took Frankie to my naturopathic vet for the limping, he suggested no food with Chicken in it as that can cause imflammation in the body, muscles, joints, etc and this can irritate an injury or arthiritis or cause limping! Who knew?!
I hope this is helpful. I know it is frustrating to not have an answer on this but by following this I have found that Frankie only limps now after too enthusiatically jumping up on the door to chase away the mailman and jamming his front leg or hurting his back a bit!