I know my dad has this hassle everytime he flys. he has a knee replacement. the usual pattern of events is this. He sets the maxchine off , he tells them he has an artificial knee. They either hand pat down or sweep with the portable thingy, then let him procede.
Only twice has he had problems , all in the UK ( BHX , I'm looking at you)
Once he had to show his scar , the other time the guy got very confused after the pat down and asked him " so is it on the inside then?"
