The role of the lateral extraarticular restraints in the anterior cruciate ligament-deficient knee

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Abstract
We measured the increases in tibiofemoral motion when lateral structures were sectioned in anterior cru ciate ligament-deficient knees of 20 unembalmed ca daveric whole lower limbs. Motion was measured with a six degrees-of-freedom electrogoniometer. The lateral structures investigated were the iliotibial band and mid- lateral capsule, lateral collateral ligament, and popliteus tendon and the posterolateral capsule. Cutting the anterolateral structures increased anterior translation and internal rotation, particularly in flexion. Increases in motions were highly variable, reflecting the variation in function in the lateral collateral ligament and posterolateral structures. Cutting the lateral collateral ligament produced small changes in anterior translation and external rotation and larger increases in adduction. Cutting the posterolateral structures produced small increases in external rotation. Large increases in exter nal rotation were found only if the lateral collateral ligament was also sectioned. The posterolateral struc tures act in concert with the lateral collateral ligament in restraining internal and external rotation. External rotation was affected at all flexion angles; internal ro tation was affected mainly in extension. Our results can be used in the diagnosis of complex knee ligament injuries. Findings of increased anterior translation in both flexion and extension and increased internal rotation at 90° of flexion are consistent with combined injury to the anterior cruciate ligament and the anterolateral structures. The anterior cruciate liga ment-deficient knee with significant posterolateral com promise (posterolateral structures/lateral collateral lig ament) would exhibit larger anterior translation in ex tension than in flexion, increased adduction, and increased external rotation in both flexion and exten sion.