Biomechanics of the goat three bundle anterior cruciate ligament

Introduction: The goat is a widely used animal model for basic research on the anterior cruciate ligament (ACL), but the biomechanical role of the different bundles [intermediate (IM), anteromedial (AM), posterolateral (PL)] of the ACL is unclear. Therefore, the aim of this study is to describe the biomechanical function of the different bundles and evaluate its use for a double bundle ACL reconstruction model. Materials and Methods: A CASPAR Stäubli RX90 robot with a six degree-of-freedom load cell was used for measurement of anterior tibial translation (ATT) (mm) and in situ forces (N) at 30° (full extension), 60°, 90° as well as rotational testing at 30° in 14 paired goat knees before and after each bundle was cut. Results: When the AM-bundle was cut, the ATT increased significantly at 60° and 90° of flexion (p<0.05). When the PL-bundle was cut, the ATT increased only at 30°. However, most load was transferred through the big AM-bundle while the PL-bundle shared significant load only at 30°, with only minimal contribution from the IM-bundle at all flexion degrees. Discussion: The observed biomechanical results in this study are similar to the human ACL observed previously in the literature. Though anatomically discernible, the IM-bundle plays only an inferior role in ATT and might be neglected as a separate bundle during reconstruction. Conclusions: The goat ACL shows some differences to the human ACL, whereas the main functions of the ACL bundles are similar.