My late BC had bad arthritis but she was coming up for 15. She was on glucosamine which helped in the earlier stages but not so much as she got really old.
She also went on Metacam and that didn't seem to make a difference either.

My current 13yrs old BC has been on glucosamine as a maintenance measure since she was about 7 and it has kept her in good order but she too has got a bit of arthritis now in one of her forelegs. Metacam didn't seem to make any difference on her either.
I know there are other things but metacam is supposed to be one of the better ones.

My uncle commented that nothing seems to really help with arthritis. It's such a shame old dogs end up with it so often. It tends to be one of the biggest killers of old dogs, especially larger ones, when it causes their legs to go.

I think putting Jess on Glucosamine when she was about 7 was the best thing because it does more good in preventing damage to start with that trying to rectify joint damage already done.

There might be other treatments available. I know my vets have mentioned there are quite a lot of different things you can try. Good luck.