Consider the marvelous physics of the human knee. The largest hinge joint in the body, it has two rounded bones held together by ligaments that not only swing like a door, but also roll and glide over each other, allowing the knee to flex, extend, and balance.Consider the marvelous physics of the human knee. The largest hinge joint in the body, it has two rounded bones held together by ligaments that not only swing like a door, but also roll and glide over each other, allowing the knee to flex, extend, and balance.[#item_full_content]