Hmm, my Amber had spinal issues, but it wasn't arthritis. It was because he was hyperthyroid. The calcium built up deposits and fused 2 vertebrae. It showed up on the x rays. The space between the discs should look like a horse head in profile. In that one spot, the shape was quite different. It meant he couldn't jump up onto things the way he used to do. Once we got the hyperthyroid under control, the situation did not get any worse, but there was no way to improve it, either. I gave him 5 mg Prednisone daily for some pain relief.

I have always worried that the Prednisone caused his renal failure, but the vet insists that was from the hyperthyroid.

Let us know what you learn from the x rays.

I just did a quick search on Google, I put in feline arthritis (no quotes around the words.) Lots of sites came up. Looks like they can take glucosamine and chondroitin as humans due. You just need the right dosage. So you may want to look at a few of those sites so you have some questions ready for the vet when you pick up Louie and learn what the x rays show.