In my case, not even the surgeon knew until he opened me up for a revision and found a lot of pus. Pre operative blood test showed no infection. In addition to the pain, the old device began to fall apart. He put in a spacer, but the bone continued to deteriorate, and later when he put in the new device, he had to work to attach the patella ligaments.
I had both MRSA and klebseilla, which respond only to a few newer antibiotics.
Good luck with yours.