Upon knee revision if plastic and metal particles are found from worn out prosthesis is there cause for concern?

If I understand your: Question, yes it would be a cause of concern; but i hope when the surgeon found the plastic/metal debris, called wear products, he would have cleaned the knee joint out, before implanting the revision prosthesis. That would be one of the reasons for performing the revision surgery. I hope I have answered the question you asked, otherwise write again. Thanks.

Expected: Not really, as wear debris is usually found at the time of revision surgery. Metal debris being present suggests metal against metal contact with the original implant which often requires more extensive surgery than if the only issue is plastic debris.