What Causes Itchy Rash Around Incision Post Knee Replacement?

I had tkr jan 27,2015. Itchy rash started arouund areas where bandage was placed. 2 week exam. Blistery rash on incision and about 1 inch around. Rash spreads to both lower limbs and continues to cause sever itching. On 4th week post surgery steroids given for eight days. On 7th day rash again appears on incision mostly on left side. I am allergic to cheap jewelry and buttons. Could I be having an allergic reaction to the metal in the kne replacement device?