Believe it or not, I've already had 2 knee replacements. One of them has failed, the appliance went bad and is totally out of kilter. It only lasted 5 years, not the expected 15-20 years. So it needs to get completely done again, what they call a revision: cut, take out the old, and put in a new one, hopefully anchored in the bones a bit better. Thanks for the tip Dave.