Hopefully not an infection, but if it is, don’t waste time trying to treat it with the prosthetic in place as my surgeon originally tried. Six weeks with temporary IV PIC line for massive antibiotic doses every eight hours seemed to work, but three days after they stopped the infection was back. I was sent to Mayo and after a long surgery to remove the prosthetic and put in a temporary plastic spacer, went through the same six week PIC line therapy which then worked. Waited a couple of months to be sure the infection was gone and then a final surgery to put in a new permanent prosthetic. All has been well since including a TKR on my other knee. It’s a rare complication, but it does happen.