Summary
This biomechanical investigation highlights the complex interplay between tibial slope and meniscal function and their influence on rotational kinematics.
Abstract
Background
Increased posterior tibial slope is a recognised risk factor for both Anterior Cruciate Ligament (ACL) injury and failure after ACL reconstruction. The medial and lateral tibial slopes differ, and the relative importance of each slope remains unclear.
It has been proposed that with an increased lateral tibial slope, axial load will cause the lateral femur to slide down the slope and pivot around the concave medial compartment, causing external rotation of the femur in relation to the tibia and increasing forces in the ACL. Further, the menisci have been proposed to contribute to the functional tibial slope, and loss of the lateral meniscal root has been shown to allow increased internal tibial rotation under torque.
The aim of this study is to assess the impact of increasing lateral compartment tibial slope and lateral meniscal root lesions on the rotational kinematics of the knee under an axial load. Our hypothesis was that increased tibial slope would cause increasing internal tibial rotation under load, and that this increase would be magnified with meniscal deficiency.
Methods
8 cadaveric knee specimens were prepared. A posterior closing wedge osteotomy was performed and secured with an external fixateur, allowing the slope in the lateral compartment to be increased by up to 10°. The potted specimens were placed into an Instrom machine and tested under 200N of axial compression with 0°, +5°, and +10° of posterior tibial slope, at 0°, 15° and 30° of flexion, and with the meniscal root intact and released. An optical system was used to measure internal tibial rotation under load for each condition.
Results
With increasing tibial slope in the meniscus intact state here was a trend towards increased internal rotation in extension and at 15° of knee flexion. Release of the meniscal root resulted in increased internal rotation in extension for the +5° and +10° slope conditions, and at 15° flexion for the +5° slope condition compared to the meniscus intact state. Increasing slope by 5° and 10° with the meniscal root released also caused an increase in internal rotation in extension compared to the anatomical slope.
Conclusion
Increased lateral tibial slope and loss of the lateral meniscal root causes increased internal rotation under axial loads at low flexion angles, and increased lateral plateau bony slope causes increased internal rotation in the meniscal root deficient state in extension.
The interplay between tibial slope and meniscal function and their influence on rotational kinematics is complex. Further study is required to determine if the meniscus contributes to the functional tibial slope, acts as a restraint to rotation, or both.