I have had trouble with mobility as well. I couldn't believe what was happening to me. I had the hardest time standing. I'd go from a sitting position to a count of 3 to stand up but I had to push myself off the couch or chair and lean forward so I wouldn't fall back down, plus it seemed to put less pressure on my knees. Then when I tried to walk, my left leg (sometimes its my right leg) would not want to move. It hurt too darn much! So I just held onto furniture and kind of dragged my leg. I had to stay kind of bent over too bc the pain of standing up straight was too much! I remember during one of those days I made my husband laugh bc I said, "I am Igor. What can I get for you Master?" I guess it was unexpected bc I had been complaining earlier. Luckily for me, that flare didn't last more than 10 days. When it moved it went to my rib on my right side, that was for just 4 or 5 days and then it moved to my jaw joints which lasted about 5 days and affected my throat and breathing. I think that scared my rheumy. My flares all involved major inflammation which just kept moving around until I got a steroid shot from my rheumy. It was like a miracle....sort of. I have been at a pain level of 1-3 for 3 weeks now, which is great but there always seems a price to pay for feeling better. I have insomnia and the steroid shot made it so much worse. The first or second night (can't really remember) I was up until 10 the next morning. Last night I fell asleep around 4:30am so I guess I'm getting closer to what was my normal.
Don't give up JeNee. Your flare will surely end. They say you have to move even though it hurts. Sometimes I want to say, "Yeah? Up yours!" But its true, even just gently straightening and bending your knees while on the couch or bed may help but I have never had a knee replacement so you may want to check with your doctor about what gentle exercises you can do while waiting for your knee replacement.
Best wishes for a day with less pain!