Not only is the knee the largest joint in the human body, it is also the most complicated, according to Inner Body. The knee is a hinge joint that is formed to move only on one axis.
The knee is reinforced with both internal and external ligaments to give it a wide range of motion. It is strong and durable enough to support the body's weight with only slight reinforcement from other bones. It acts as a shock absorber due to fibrocartilage that is between the femur and tibia. This fibrocartilage protects the bones when running or doing other flexion activities.