I have always thought that the knee was a faulty design if all of the things we do to it are considered. It's OK for walking, but running and making quick turns, twisting (whether intentionally or accidentally), jumping & landing, etc are all bad for that particular joint. That said, it's amazing that it can handle the loads presented and survive or, if a minor injury occurs, heal to the point on its own where the person isn't restricted from most typical activities.