I have an artificial hip and both knees replaced. I always set off the metal detector. I wouldn't worry about it, its really no big deal. Just walk through, don't explain first or you might seem "suspicious". Then, when you set off the alarm, they will usually ask if you have anything in your pockets that might set off the alarm, such as coins, etc. This is the time to explain that you have a metal implant in your knee. You will then be directed to a screening area which is a glass enclosed area right next to the metal detector. You will be "wanded" then perhaps patted down, by a same-sex employee (or yeo can request one). You might be asked to remove your shoes, but I never have. It helps if you can wear shorts or a skirt so you can "expose" your knee, let them see there's nothing in your pant leg. However, don't worry about it. Its not a big hassle, the employees are polite, there's nothing demeaning or embarassing, its all over quick. I've never been asked for a doctor's note but it wouldn't hurt to have one. I have a card which says I have metal implants, however, there's no standard for such cards so they really can't accept them as "proof". Still, it wouldn't hurt to have one. Most of all, remember that security screeners "can't take jokes" that is, don't make any light-hearted remarks about how you'll probaby set off the alarm, maybe you'll look like you're carrying something, etc. Remember, they can't make such judgments and must take all remarks as serious. That's why I recommend not saying anything, just walk through, then explain if and when you "ding. Oh, and do allow extra time, at least 30 minutes extra on top of your airport time (I always get there 2 hours prior to flight time). Remember you have some special circumstances which might require more time. Don't worry, I've been traveling with metal implants for over 20 years and never had a problem. Don't worry about some posts you might have read (on this board and elsewhere) about problems with security. I really think such experiences are minor, and, in some cases, exagerrated. Really, its a common thing for people to have metal body implants and they are trained to handle it. You're not the first one! Good luck and have a great trip!