What Causes Pain And Swelling In Thighs After Surgery?

My son broke his femur skiing 7 months ago. He had surgery and a metal rod was inserted. His recovery went well untill just a few days ago. For no reason his thigh started to swell and hurt. He went to the E.R. and was told that x-rays show that everything looks good however there is a prominent screw. An appointment has been made with an orthopedic surgeon for a week from now. In the meantime the pain is much worse and has spread to the knee and the calf. There is a lot of swelling and he is unable to walk. What is going on?

Worried Mother