Knee flexion anatomy. Artwork of a frontal (anterior) view of the bones and some of the cartilage and ligaments of an extended (left) and flexed (right) knee joint. The knee joint is where the upper leg bone (femur) articulates with the two lower leg bones, the tibia (left) and fibula (right). The ends of the bones are covered in pads of cartilage (white), with ligaments (white) holding the joint together. The ligament shown here is the transverse ligament, between the two menisci (lateral and medial). The knee-cap (patella) is not shown.