How did you know when your knee was bad?
It was the hip. And basically recurring intermittent pain. I saw the DR about 3 years ago and he x-rayed and said at the time that I was going to be due a new hip at some point, use it up as long as you can until your body tells you it's time. Over those years, the pain became more frequent until this past ski season, when I decided I was going to get it replaced at the end of this March.