An In Vitro Robotic Assessment of the Anterolateral Ligament, Part 1 Secondary Role of the Anterolateral Ligament in the Setting of an Anterior Cruciate Ligament Injury

Background: Recent investigations have described the structural and functional behavior of the anterolateral ligament (ALL) of the knee through pull-apart and isolated sectioning studies. However, the secondary stabilizing role of the ALL in the setting of a complete anterior cruciate ligament (ACL) tear has not been fully defined for common simulated clinical examinations, such as the pivot-shift, anterior drawer, and internal rotation tests. Hypothesis: Combined sectioning of the ALL and ACL would lead to increased internal rotation and increased axial plane translation during a pivot-shift test when compared with isolated sectioning of the ACL. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen human cadaveric knees were subjected to a simulated pivot-shift test with coupled 10-Nm valgus and 5-Nm internal rotation torques from 0 degrees to 60 degrees of knee flexion and a 5-Nm internal rotation torque and an 88-N anterior tibial load, both from 0 degrees to 120 degrees of knee flexion via a 6 degrees of freedom robotic system. Kinematic changes were measured and compared with the intact state for isolated sectioning of the ACL and combined sectioning of the ACL and ALL. Results: Combined sectioning of the ACL and ALL resulted in a significant increase in axial plane tibial translation during a simulated pivot shift at 0 degrees, 15 degrees, 30 degrees, and 60 degrees of knee flexion and a significant increase in internal rotation at 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, 90 degrees, 105 degrees, and 120 degrees when compared with the intact and ACL-deficient states. Based on the model results, ALL sectioning resulted in an additional 2.1 mm (95% CI, 1.4-2.9 mm; P < .001) of axial plane translation during the pivot shift when compared with ACL-only sectioning, when pooling evidence over all flexion angles. Likewise, when subjected to IR torque, the ACL+ALL-deficient state resulted in an additional 3.2 degrees of internal rotation (95% CI, 2.4 degrees-4.1 degrees; P < .001) versus the intact state, and the additional sectioning of the ALL increased internal rotation by 2.7 degrees (95% CI, 1.8 degrees-3.6 degrees; P < .001) versus the ACL-deficient state. Conclusion: The results of this study confirm the ALL as an important lateral knee structure that provides rotatory stability to the knee. Specifically, the ALL was a significant secondary stabilizer throughout flexion during an applied internal rotation torque and simulated pivot-shift test in the context of an ACL-deficient knee.