I've had serious problems with my left knee for about five years now. I've had surgery twice and am scheduled for a third time next month. It used to almost make me cry when I think about how much I missed riding. I gained a ton (65 lbs) of weight and got in crappy shape.
Now I'm riding with one leg. The left leg just sits on a peg and my right leg does all the work in a fixed gear. 100 miles per week for the last two weeks, getting in better shape and loosing weight.
I LOVE TO RIDE!!!