Hi, new member.

I have similar problems with my knee (dislocated knee cap, torn ligaments, etc) so I also invested in an elliptical trainer (Horizon E1200). I have used the elliptical twice a day, 30 minutes per session. I recently decided that I wanted to do a triathlon, and felt pretty confident that I could run, considering that I was kicking butt on the elliptical...... didn't work out that way :-)

Long story short, the elliptical can not and does not take the place of running. In fact, I got really used to exercising on the elliptical and found myself having to constantly vary the intensity just to break into a sweat (some cardio workouts, some power with high resistance, etc).

I think it has helped with my cardio though.... but not a substitute for running.