I would try Promaxol to reduce the pain and help healing to begin. Promaxol would be a good choice for your dog. It contains the stronger LM potencies. After improvement is seen then you can switch over to Arthro-IonX. In addition it is helpful to give digestive enzymes with each meal, MSM, probiotics, and fish oil. The oligotherapeutic mineral base found in the IONX products helps the body to better utilize the other nutritional substances given for a synergistic response and faster healing.
Also be sure to give sufficient fresh water that is free of chlorine and fluoride. If you can gradually phase into a grain free diet that can be helpful too.
The other thing that is sometimes beneficial is to have a certified veterinary chiropractor check for spinal alignment and make any corrections as necessary. Hopefully you will be able to slowly decrease the pred dose, but when someone has taken it for a long time, the body becomes dependent on it. You will need to work with your veterinarian on this so you don't hurt your dog.
Please let us know how you progress or if you have any other questions. I can offer more suggestions depending upon the responses you see.