It might be arthritis but there are other causes for limping. There could be something in the paw or a cut. There could be a ligament or muscle strain or tear. Sometimes there is a subluxation in the back. Your veterinarain might be able to determine the cause. I would try the homeopathic PROMAXOL to reduce the pain and inflammation. I would split the dose and give a half dose twice daily on the breakfast and supper food. If need be you can extra half doses between meals, too. I also like to give PROBIOTICS and OMEGA 3,6,9 to support the body which is especially helpful if you are dealing with a chronic condition like arthritis.