Knee joints. Coloured X-ray of healthy knee joints. Bone is green and and flesh is beige. This joint, known as a hinge joint, is the largest in the body. It is formed where the femur (thigh bone, upper bone) meets the tibia (shin bone; thicker lower bone). The fibula (calf bone; thiner lower bone) runs parallel to the tibia. Cartilage (not seen) lines the gap between the femur and tibia, reducing friction and providing protection.