How To Treat Severe Osteoarthritis In Legs?

I have severe Ostoarthrits in both knees. I walk with a cane. I am looking into knee relacements. After knee replacements, will be get back my mobility and strength in my legs. I have been active all my life and I cannot do anything. I am 65 years old and in pretty good health otherwise. Also, if you have OA can you get RA as well. Thank-you for your time. Regards, Mary-Ann Coolich