There Are No Kinematic Differences Between Inframeniscal and Suprameniscal Anterolateral Ligament Injury in the Anterior Cruciate Ligament-Deficient Knee.

Background: Previous research demonstrated that the attachment of the anterolateral ligament (ALL) to the lateral meniscus is stiffer and stronger in its tibial attachment than its femoral attachment. How this relates to anterolateral knee stability and lateral meniscal function is unknown.

Hypothesis/purpose: The hypothesis was that the ALL acts as a peripheral anchor to the lateral meniscus, aiding in anterolateral rotatory stability, and that the inframeniscal fibers of the ALL will provide greater anterolateral rotatory stability because of their greater tensile properties. The purpose was therefore to compare the difference in kinematics of the anterior cruciate ligament (ACL)-deficient knee between the infra- and suprameniscal ALL-sectioned states.

Study Design: Controlled laboratory study.

Methods: Eight paired fresh-frozen cadaveric knees were tested in a 5-degree of freedom loading jig under the following loading conditions: 5-N·m internal rotation at 15° incremental angles of flexion and combined 5-N·m internal rotation moment, 10-N·m valgus moment, and 88-N anterior translation force representing a pivot shift test at 0°, 15°, and 30° of flexion. The knees were tested under intact, ACL-deficient, and ACL-/ALL-deficient conditions, with the pairs of knees being randomized to either supra- or inframeniscal ALL sectioning. Resultant joint kinematics and tibiofemoral translations were measured and compared with a 2-way mixed repeated measures analysis of variance.

Results: Internal rotation increased by 3° after sectioning of the ACL at 0° of knee flexion ( P = .035). At 45° of knee flexion, internal rotation increased significantly by 2° between the ACL-deficient and the ACL-/ALL-deficient conditions ( P = .049). Secondary kinematics of valgus and anterior translation were observed in response to the 5-N·m load after ACL and ALL sectioning. Analysis of the pivot shift showed increases in tibiofemoral translation after sectioning of the ACL, with further translations after sectioning of the ALL. No differences were observed between supra- and inframeniscal ALL sectioning under any of the loading conditions.

Conclusion: An injury to the ALL, coexisting with ACL deficiency, results in only minor increases in knee joint patholaxity. No differences in pivot-shift kinematics or tibiofemoral rotations were observed between the supra- and inframeniscal sectioning of the ALL in the ACL-deficient knee.

Clinical Relevance: Tears of the midbody and/or posterior root attachment of the lateral meniscus are often observed at the time of ACL reconstruction. Increased anterolateral rotatory laxity has been observed in both lateral meniscus- and ALL-deficient states in combination with an ACL injury. While no significant functional relationship was found between the ALL and lateral meniscus, ALL sectioning did result in increased knee joint patholaxity, as demonstrated by composite tibiofemoral rotations.