Security machines at most airports will go off after hip and knee replacement surgery. There have been some rare occasions where the patients told me that they did not set off the airport security (which makes me worry about the quality of the machines at those airports!).
A doctor’s note about hip or knee replacement surgery will not help because anybody can carry that note. If you set off alarm set airport security, the security personnel will usually use a “wand” to ensure safety of the airport. In the earlier days we used to give a card with the patient’s name and the name of the joint that was replaced. However, carrying operative note or this card or a doctor’s note is not helpful. Although if the patients wanted one, we will be happy to give it to them.