Hello Morcottgirl and welcome to GN! I haven't had any knee or hip replacements (yet!) but a few years ago I had cartilage removed from my left knee. This was done with a spinal block, which is very similar to an epidural but is used for shorter and simpler procedures. It has the same effect, blocking all feeling from the lower half of the body, so there is no sensation whatsoever. I was conscious throughout and in fact watched the entire procedure on a monitor which they swivelled round for me! It was such an odd feeling because, since I couldn't feel anything that was going on, it was as if I was watching someone else's knee being operated on. The recovery is so much quicker - I had a nurse stay with me in the ante-room until my temperature had returned to normal (can't remember now why it drops) and then I was wheeled back to the ward, feeling none the worse for the whole procedure!
Good luck with your op 