The ACL is one of the four primary stabilizing ligaments of the knee. It limits the movement of the tibia with respect to the femur when subjected to flexion, extension and rotation.

As shown in Figure 32.1: Human Knee Components, the ACL attaches to the knee-end of the femur (at the back of the joint) and passes down through the knee joint to the front of the flat upper surface of the tibia. It passes across the knee joint in a diagonal direction.

The primary objective of this simulation is to investigate the behavior of the ACL in relation to the movement of the femur; therefore, a section of the ACL is constructed. The femur is modeled as a rigid surface. The length of the ACL is specified as 31 mm. The ACL is assumed to exhibit visco-anisotropic hyperelastic behavior. Several analyses are performed to simulate various femur movements.

The ACL has no stress-free state. At all knee flexions, stress is present in the ligament.[2] The precise experimental distribution of the stress field is unknown; therefore, the simulation is performed without prestressing the ACL.

A constant strain rate is applied with displacement at the top of the ACL, while the lower part is fixed at the bottom. The behavior of the ACL under knee flexion of 45 degrees and rotation of 11.25 degrees is also examined.