The Complimentary Contributions of the Anterolateral Ligament and the Lateral Meniscus to the Control of Rotational Knee Laxity

OBJECTIVES: Anatomical studies consistently describe an anatomical connection between the anterolateral ligament (ALL) and the lateral meniscus. The aim of this study was to investigate the role of the ALL and lateral meniscal posterior root (LMPR) in internal rotational (IR) control in the ACL deficient knee. METHODS: Sixteen cadaveric knees were potted into a hip simulator proximally and a six degree of freedom load cell distally. Positional data for femur and tibia were collected using a navigation system. Testing was performed in 15° increments from extension to 90° of flexion under a 5 Nm internal rotational torque. Specimens were tested in the intact state and after division of the ACL (ACL-), before randomization to division of the ALL (ALL-/M+) or LMPR (ALL+/M-), and finally after division of the remaining structure (ALL-/LMPR-). A one-way ANOVA was performed for each sectioning condition at each knee flexion angle (α = 0.05). RESULTS: In extension, there was no significant increase in IR after division of the ACL. After division of the LMPR, there was a significant increase in IR compared to the intact state of 2.93° (p<0.05). Division of the ALL caused only a small increase in IR compared to the intact state (0.87°, NS). Division of the ALL after the LMPR caused no additional increase in IR. At 30° flexion, division of the ALL caused a greater magnitude increase in IR when compared to the intact state than division of the LMPR (4.04° vs 1.32°), although neither reached statistical significance. At 45° flexion, division of the ALL increased IR compared to the intact state by 10.92° (p<0.05), whilst IR caused by division of the PRLM did not reach significance. This pattern of ALL dominance was maintained at 60° and 75° of knee flexion, where the increase in IR was significant compared to both the intact and ACL deficient states. DISCUSSION: The ALL and LMPR demonstrate complimentary roles in the control of internal rotation, with the meniscal root more important near extension and the ALL beyond 30° of flexion. These results do not support anatomical ALL reconstruction for control of the pivot shift. LMPR repair may improve stability and have benefits for chondroprotection.