i had my knee done Feb 20 2014. one month to the day I was walking down stairs and "pop" i feel and was in more pain than ever. I completely tore my quadracept muscle, back into surgery the next day. I have been working hard in PT and 2 weeks ago bought a Specialized Crosstrail Disk. I am averaging 6 miles a day. some swelling but I am staying with it. I love it. As a kid I lived on my bike and now I am back after quite a few decades.