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.