Hi. Welcome to Bike Forums. You might want to try posting your question in the 'Training & Nutrition' forum or the 'General Cycling Discussion' forum. I'm not an expert on stationary bikes, however when you get properly fitted for a regular bike, they look at, and adjust, the geometry of the frame, footwear & position of foot on pedal (if you use clipless pedals), etc. This can correct many issues including knock knee.