The worry does eventually go away. It's perfectly natural to worry after this surgery. I mean, new body part, foreign object, all the cautionary advice and articles... it's a wonder we don't stress ourselves silly. I'm not particularly fretful, but for the first months I worried about nearly everything. I caught a cold... was the fever sign of infection? One of my knees hurt especially much one morning... was the implant loose? Misaligned? I developed a mysterious rash at six months... was it a metal allergy? I react to cheap earrings. Maybe that was it!!! It wasn't. It was quite something else and I never ended up with any of the things I worried about.
Getting a new knee is very much like getting an infant. We don't know what is happening with it and we have to guess what's going on. Is the baby sick, or just hungry? What does it need to make it stop crying? When in the name of mercy will it ever grow up?
So eventually the worry does stop. It stops when we realize the knee is actually doing very well. When we feel less pain. When it begins to bend better (finally!) and we start to walk normally again, and return to a more normal life. After a while you will not worry about it at all because you won't even think about it; it becomes just a knee and you will love it.