Infection is based on blood tests like elevated white blood cell count, fever, pain & inflammation. Pain and inflammation also may occur due to hardware. The treating surgeon will always think about the safety of his patient so any diagnosis which does not confirm but point towards a cause will be over ruled as in your case as an infection. The abscess may also occur due to collection of sterile fluid so you cannot be sure it is infected or not. Well, as you were under good hands, orthopaedician there is nothing to worry as your belief in your operating surgeon is important. Take care!