It isn't the actual artificial knee that is infected its the tissues and muscle around the knee. You see the body recognizes things that are put in the body as invaders, so it sends out the white blood cells out to attack and kill the invader. When it can't the wbc's continue to get more and more which by now has turned into an infection. Alon of people have metal placed within the body and their body just can't handle it after a while. So this is where your Dr comes in to perscribe an antibiotic to kill the infection whether it be my mouth, injections or iv's. Please rate my answer