Probably a good idea to see a vet if it has been going on for a while. Could be an arthrosis since it is only one leg. But could also be other things so best to have it looked at. I saw you posted about supplements, that is really important if this is arthrosis/arthritis so good thinking
Ingredients like glucosamine, chondroitin, omega 3 and antioxidants can do wonders. Easiest is probably to get a product that contains all of this so you get a proper dosage.
I have a dog with a knee that developed arthrosis. She got much better when I switched her on to joint specific vet diet, but if you are raw feeding or something then supplements can be an option.
I have also started my dog on treatments with a medicine called car
trophen (not the NSAID carprofen, a newer drug with more benefits and less side effects). This will slow down the deterioration and act as pain management, it works better when applied earlier rather than waiting until it's really bad so good to know about.
But first you should see a vet and make sure this is the problem. Will probably only need a quick x-ray to confirm if it is actually is arthrosis and then you'll know