I had a tibial plateau fracture in June of 2009. It involved the cartilage of my knee. I have moderate osteoarthritis as a result. I also have a partial tear of the MCL and PCL resulting in instability of my knee. Cycling has been the best rehab. It has greatly strengthened my knee and helped build up my legs from severe muscle wasting from being bedridden. I haven't had any setbacks. But I know a great deal about bike fit so I can avoid further aggravating my knee. I also spin at a relatively high cadence.