Stubborn's posted is almost 3 year ago, hopefully the problem has been resolved. And hopefully , even more, he had a full knee replacement, for each knee. As with a hip replacement, fairy fast and common procedure now days. In Stubborn's case, the only logical option. His injury is/was well beyond Ultrasound.
Only trouble is going through a airport security checkpoint. You can explain about the mental they detected, on their scanner, but it will be to deaf ears. Know a 72 year old lady, who was searched and questions for 2 hours, because of just it. Good Luck.