Fun story: Last time I flew, the scanner detected the surgical plate in my right shoulder. The TSA agent saw the diagram and put his hand on my left shoulder before letting me walk.
The cause? I was in Hawaii, wearing a backpack. If you didn't know, their airports are mostly open-air. Of course, Hawaii is pretty warm and it was humid, so I was sweaty on my shoulders where the straps were.
Win for security (theater).