What can cause inflammaiton on the back of the leg behind the knee?

See an orthopedist: Swelling in a leg /knee can be commonly seen from knee related problems, with or without injuries and medical causes such as poor circulation, inflammation, and constriction from a brace or cast. However, sometimes you can get a clot in your leg that can cause swelling in the calf. Go to er immediately to rule out a clot as this can be be fatal if left untreated.