My knee. On the right - bone on bone! Surprisingly I have not had a replacement as many do. I decided to start walking every day at a good pace for thirty minutes. It was a little rough for awhile but the more I walked the better it got. I have went from waking at night in severe pain, hardly able to get in and out of the car, to no pain at all. It is just a little stiff and slightly sore on occasion.