Before you have that knee replaced have a conversation with your surgeon about what he will be replacing it with. Then be sure you are not allergic to the material in the new knee. Admittedly it is along shot that affects very few but...
You do NOT want to be that guy, trust me!
The VA put in the standard Cobalt Chromium knee used by most hospitals and I was deathly allergic to Cobalt {rare} and Nickel - not so rare. My body was rejecting that knee before I was off of the operating table. It took six months to convince the VA that I had a serious problem and have may leg cut off a second time and a ceramic knee replacement put in. First surgery was 17 days at the VA hospital and the second 14 more followed by months of PT.
Just sayin...