What Causes Itchy Rash On Knee And Ankle Post Total Knee Replacement?

Hi! I am 5 five weeks out from total knee replacement. About one week after surgery, I noticed a itchy rash on some spots where the bandages were on my knee. Not a big problem, except it would seem to dry up, then come back again. I have not used any soaps different from before surgery. About a week ago, the rash went to my left ankle( leg which TKR was performed). It would get real bumpy, seem to dry up, them flare again. It has since spread to my right ankle, and is moving up my left leg. Thoughts?