Influence of Anterior Cruciate Ligament Bundles on Knee Kinematics

Abstract

Background The synergistic functions of the anteromedial and posterolateral bundles of the anterior cruciate ligament in restraining anterior laxity are known. Cadaveric experiments have also suggested different functions of the 2 bundles in controlling a combined rotatory load simulating the pivot shift. Hypothesis The posterolateral bundle is important in controlling the coupled tibial axial rotation laxity occurring during clinical laxity tests performed in vivo, particularly the pivot-shift maneuver. Study Design Cohort study; Level of evidence, 2. Methods Twenty-one patients underwent navigated 2-bundle anterior cruciate ligament reconstruction. The navigation was additionally used to measure the knee kinematics in response to the anterior drawer test (performed at 90°), Lachman test (performed at 20° of flexion), and pivot-shift test. Two sequential reconstruction protocols were used to assess the contribution of the anteromedial and posterolateral bundles to restraining tibial translations and coupled axial rotation occurring with the manually performed clinical laxity tests. Results Anterior tibial translation during the anterior drawer test was better restrained by anteromedial bundle reconstruction than by posterolateral bundle reconstruction. Conversely, posterolateral bundle reconstruction better restrained anterior tibial translation during the Lachman test. Both bundles contributed to the control of anterior laxity during the pivot shift. However, the posterolateral bundle was more important than was the anteromedial bundle in controlling the tibial rotational component (posterolateral bundle reconstruction caused a 53% reduction in tibial rotation laxity compared with a 42% reduction with anteromedial bundle reconstruction, P < .0001). Conclusion This study provides objective, in vivo data about how the anteromedial and posterolateral bundles act differentially to stabilize the knee, particularly during the pivot shift. The posterolateral bundle was important in controlling not only anterior laxity toward knee extension but the rotational component of the pivot shift.