I am a retired nurse and my advice is do everything they tell you to,I had both done but not at once,only thing I can say is make sure they check and have the right size of knee replacement on my last one they just about goofed but doctor caught it. I needed a large and they sent a small. I had some discomfort last year and had fallen so went to see my O.surgeon and he couldn't believe it was over 20 years. I can't kneel also the doctor told me not too.
good luck and let us know how you do.