Animation 5: Demonstration of the response of the model ACL to movement of the tibia backwards and forward relative to the femur at a fixed flexion angle

With the unloaded knee flexed to 50°, all but the anterior fibres of the ACL are slack. When the tibia is pushed backwards 5 mm from the neutral position, the anterior fibre slackens and all other fibres slacken further. When the tibia is pulled forwards 5 mm from its neutral position, ACL fibres are progressively tightened and stretched to bear load. A 5 mm anterior translation tightens and stretches about half the model ACL.