BEFORE you let anyone put a new knee (or hip for that matter), into your body find out what it is made of and get yourself tested for any allergic reaction. Yes, I learned this the hard way. I was deathly allergic to the Cobalt Chromium knee the VA put in. My body was rejecting that knee before I was off of the operating table.
It took 6 months and ultimately firing the original surgeon {head of the department}, to convince the VA something was desperately wrong - swollen, warm to the touch, pain off the charts despite struggling through excruciating pain with all of the physical therapy.
Eight months after the first surgery they cut my leg off again and put in an Oxinium knee {Google it}, with better but not great results. While severe allergic reactions are rare you DO NOT want to be that guy.... trust me!
:E