It was pretty obvious that my cat had arthritis and my vets didn't feel that we needed xrays to diagnose it. I gave her a supplement, Cosequin, twice a day. It was a sprinkle capsule that I mixed into her wet food. She also had a treat that had glucosamine in it as well. There was a heavier duty medicine, I can't remember the name, but I have it around the house somewhere, but she was only able to have it for a short period of time becuase my cat was ill and had kidney problems and that particular medicine is harder for the kidneys to process. But that isn't a problem for healthy cats, my cat was just very elderly.
There are also heated pads for bedding that can help bring comfort to the joints. I saw them online, but never used them.