I Had Total Knee Replacement Eight And A Half Months

I had total knee replacement eight and a half months ago. The surgery went well and I have mad progress, so much so that I have been walking better now than I had for eight years. In the past few days, however, the back of the lower leg has been sore. What could that possibly be? By the way, years ago I had DVT, which is why I was kept under Coumadin for almost two months after the knee surgery. That was on the recommendation of the orthopedic surgeon as well as the hematologist.