The Biomechanical Role of the Anterolateral Ligament of the Knee in the Context of Anterior Cruciate Ligament Reconstruction

Introduction: Limited biomechanical data are available quantifying the biomechanical influence of the anterolateral ligament (ALL) in the anterior cruciate ligament (ACL)-reconstructed knee. Therefore, we posed 3 research questions: 1) Are loads borne by the ALL in the setting of ACL reconstruction different than the loads born by the ALL in the ACL-competent knee; 2) does ALL deficiency with ACL reconstruction alter knee kinematics and 3) does deficiency of the ALL change the loads carried by the ACL graft during simulated stability exams?

Methods: Eight fresh frozen human cadaveric knees were mounted to a robotic manipulator equipped with a universal force-moment sensor. Clinical Lachman, anterior drawer and pivot shift (15° & 30°) exams were simulated for intact ACL and ACL reconstruction with and w/o ALL.

Results: The average load carried by the ALL in ACLR knee were not significantly differed from the native knee in Lachman and pivot shift tests (p>0.05) but was 8.6 ± 8.8 N higher (p=0.041) in the anterior drawer test. Under applied rotatory loads, a 1.8 ± 1.5° larger increase in internal rotation was observed in ALL-deficient knees compared to ALL-intact knees at 30° flexion (p=0.011). Increased graft loads were observed in every test with the greatest increase in graft load being 19.0 ± 12.9 N (p=0.004) in response to applied rotatory loads at 30° flexion.

Discussion: The reconstruction restores the motions of the native knee closely enough that the ALL does not carry higher loads during most clinical exams. However, in particularly lax individuals or in the presence of an imperfect ACL reconstruction, there might be an increased role of the ALL in stabilizing internal rotation and this may increase loads on the ACL graft during applied rotatory loads at 30° flexion