Just cant imagine this happening. When I had knee surgery several years ago, the doctor came in and circled the knee in question with a magic marker and had me agree with the markings. Every person that approached me there after asked me if the knee circled was the knee that would be worked on. I even think the janitor approached me with the same question.
Just before I was put under the anesthesiologist asked me to point to the offending knee.
I work in a hospital for a living. I was not being paranoid. In one of the local hospitals (not mine) they took out the wrong kidney on a patient. That meant he had no functioning kidneys and was on dialysis until he died.
The Janitor!
I
I sure hope you checked afterwards to make sure the correct knee was still circled.