that is unreasonable to expect MSM to come in and magically fix a problem that has been present for such a long time.
Yep, arthritis is a degenerative disease. It's easy to forget that means that it gradually gets worse and slowly destroys the joint -- loss of cartilage and joint lubrication, even bony changes. It's not just a symptom that you "turn off" but rather a disease process that gets worse over time. The goal should be to "turn off" the inflammation to the extent that you can do so, slow the disease process, and if you're lucky, relubricate the joint so it hurts less.
Because it's a disease process, it's often most responsive to "multi-modal" treatment:
-anti-inflammatory nutrition and supplements (often several different things, not just one),
-physical therapy and/or regular, gentle low-impact exercise,
-and sometimes RX meds, acupuncture, or cold laser
Most vets (and human doctors) who pay close attention to this disease find that patients who are doing a combination of these things over the long term experience more relief than the ones who try just one thing...and that makes it impossible to say for sure what's helping. My own vet is pretty sure they're all helping synergistically, as he sees such a difference in outcomes in the "all of the above" group of patients vs. the "just one thing" group.
My strong preference is to start arthritic dogs on Adequan therapy (RX only) as soon as one knows about the arthritis. Adequan moves through the synovial fluid into the joint and lubricates it, preventing loss of cartilage -- in a some cases, it may even spur the body to produce more cartilage. This slows down the degenerative process and can buy the joint more pain-free years, and it can even "heal" inside the joint, at least temporarily. In about half of dogs, it has a powerful anti-inflammatory effect comparable to an NSAID, even though it's not a pain drug. It pairs well with anti-inflammatory nutrition and many supplements too.
However, the dogs only keep the benefit as long as they're on it. Other than the cost and hassle, and the pain of getting an injection, it doesn't have any bad long-term side effects that I've ever heard of, and I've had all my personal dogs on it, plus most of the rescue's foster dogs over 8.
Adequan is a name brand of polysulfated glycosaminoglycan (PSGAG). You can read about it here:
There are some other PSGAG products that are significantly cheaper, used by some vets off label for clients who find Adequan prohibitively expensive (Ichon is an example).
If the vet does the injections, they run about $50 per injection for a big dog. If you do them with your vet's permission at home, it may cost half that. The loading dose is 8 injections at 2 per week for 4 weeks, and you don't typically see benefits until around week 3. The maintenance dose after that is usually monthly, but some dogs with severe arthritis need it every two weeks.
My last elderly dog with pretty bad hip arthritis went from barely shuffling behind me on his walks to trotting at a good clip in 3 weeks. He was better on Adequan (plus good supplements), without any pain meds, than he ever was on pain meds alone. We always knew when he was nearing the need for another shot (for him, about 2 weeks), as he started slowing down again, then when he got his injection, he perked up and started moving well again. It was like magic for him.
I would also look into Natural Eggshell Membrane as a supplement (there are several excellent threads discussing it and linking to a study showing its benefit) -- and maybe Collagen II/Hyaluronic Acid and/or curcumin/turmeric, in addition to the MSM and other things Carmen mentioned.
I also strongly recommend investing in a set of xrays to definitively diagnose whatever is going on in the joint...and even the spine too. When doing hip xrays, I ask the vet to try to get a good image of the spine too, as sometimes we find things there that are unexpected (back problems instead of hip problems). Also, while it's true that arthritis is the most "likely" reason for his issues at this age, there are some other things that need to be ruled out. When my oldster (who already had hip arthritis) developed lameness in his elbow too around age 11, the vet and I both thought it was probably just more arthritis showing up there. We almost didn't xray because we were so sure that was so very likely. We ran a set of xrays "just in case"....and it was osteosarcoma (bone cancer). It came out left field and wasn't anything anyone suspected in that dog. So...your dog probably has arthritis, but xray him anyway!