The femoral transverse axis about which the tibia extends and flexes is the most distal and posterior (Green line). The femoral transverse axis about which the patella extends and flexes is more proximal and anterior (Violet line). The longitudinal axis about which the tibia externally and internally rotates on the femur passes through the medial femorotibial compartment (Yellow line). All three axes are either perpendicular or parallel to the joint lines (Blackline).