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 Canine Probiotics with each meal, Omega 3,6,9, MSM, and vitamin C daily. (We carry the first two and the other two you can get at a health food store.) In older dogs I also use Geri-Form a choline supplement. 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. You might also look at a harness by Guardian Gear. It has handles so you can help stabilize the dog if it is slippery out. In the past I have seen it sold by PetEdge, a groomers catalog. I have had Bernese Mt. Dogs and so I know how difficult it can be helping large dogs stay mobile.
Please let us know how you progress or if you have any other questions. If you do these things and it also appears that the nerves are also affected, let me know and I can make some suggestions for that.