Arthritis

Hi guys....it's been a while here for me, I've been so busy with work.....hope everyone is doing well.
I popped in a few onths ago asking about Arthritis for my Boxer Rusty, I decided to go with Syn-Flex (liquid Glucosamine) and also ading MSM and Ester-C powder, it seems to help, but he is getting really bad and I wanted to check in before I bought another batch to see if anyone had any more suggestions that would be better. He is getting so bad and we have so many stairs where we live and if I don't get to him before he hits the stairs he falls and it kills me. He is ashamed that I have to help him, so I made a game of helping him up the stairs and then he gets a treat, otherwise he hides for hours till he thinks I have forgotten...poor baby, I hate to see him go through that. I would like to know what has worked for everyone else and why so that I can make a good decision on what to get for him. I will also be adding Sea Salt and ACV to his water.
Just for a background....the vet says that his back knees are so bad that if he were able to have it, he would be a great candidate for knee replacement...that's how bad it is.

Thanks for any advice, it's greatly appreciated.

Hope you all are happy and healthy,
Jenni Tweet