I have had both knees rebuilt 3 and 4 years ago ( right and left respectively). I had my wife pushing me from the first day home after surgery ( 28 hours after I got over anaesthesia) She had picked up my new bike Speclized Roubaix pro. and had it sitting in the living room. My Ortho Dr. is a tri guy and he wanted me to be riding soonest. I sat on the bike with flat pedals at 2 weeks. The hard part for me was getting my leg around the bike just to get on the saddle. Long story short... I rode my first century post surgery, at 4 months. 10 1/2 hours and only 1200 feet of climbing, but a full 102 miles. Dr. said I will never run again unless a bear is chasing me. That's OK with me. This summer we did a hike across Scotland, and had only muscle pain. I did have to go for a new fitting on the bike as my legs are now the same length and about 1cm. longer than before. It is all good. Ride On.