The role of the anteromedial and posterolateral bundles of the anterior cruciate ligament in anterior tibial translation and internal rotation

Background: A rupture of the entire fibers of the anterior cruciate ligament leads to knee instability due to increased anterior tibial translation and increased internal tibial rotation. The influence of isolated deficiency of the anteromedial or posterolateral bundle of the anterior cruciate ligament on the resulting knee kinematics have not yet been reported. Hypothesis: Transection of the anteromedial bundle will lead to increased anterior tibial translation at 90 degrees. Transection of the posterolateral bundle will show an increased anterior tibial translation as well as a combined rotatory instability at 30 degrees. Study Design: Controlled laboratory study. Methods: Kinematics of the intact knee were determined in response to a 134-N anterior tibial load and a combined rotatory load of 10 N(.)m vaigus and 4 N-m internal tibial rotation using a robotic/universal force moment sensortesting system. Subsequently, the fibers of the anteromedial and posterolateral bundle were resected in an alternating order and the new translation in response to the same external loading conditions measured. Statistical analysis was performed using a 2-way ANOVA test. Results: Transection of the anteromedial bundle increased anterior tibial translation at 600 and 901 of knee flexion significantly. Isolated transsection of the posterolateral bundle increased anterior tibial translation in response to 134-N anterior load at 30o of knee flexion significantly and resulted in a significant increase in combined rotation at 0 degrees and 30 degrees in response to a combined rotatory load compared with the intact knee and isolated resection of the anteromedial bundle. Conclusion: The anteromedial and posterolateral bundles stabilize the knee joint in response to anterior tibial loads and combined rotatory loads in a synergistic way. Clinical Relevance: The results of the current study suggest that, from a biornechanical point of view, it may be beneficial to reconstruct both bundles of the anterior cruciate ligament to better restore normal anterior tibial translation and combined rotation.