What Causes Itchiness After Knee Replacement Inspite Of Taking Gabapentin And Hydrocodone?

I had total knee replacement surgery 7 weeks ago and have had trouble with itching. It occurs mostly both legs, back and arms. It is worse at night. I was on hydrocodone for 5 weeks and Gabapentin for 6 weeks. I stopped taking the Gabapentin 2 days ago. Still itching. I am concerned that I have an allergy to the metal implant. How would I know?Thanks