I had my knee replaced four years ago and I am so thankful that I did it. One thing no one mentioned during my pre-op visit was that the pain medication could cause depression. I was very blue and once I had the pain under control (needed to keep taking the pain medication so that I could do daily PT) I stopped the medication. But it took FIVE days to get it completely out of my system. I can't remember the name of the medication but I think it was a generic Vicodin. So I just wanted to add this in case.