The effect of anterolateral ligament integrity on the tibia displacement and reaction forces of anterior cruciate ligament: A finite element model study

OBJECTIVE: Recent studies focused on rotational instability and remained positive pivot test in patients with anterior cruciate ligament (ACL) reconstruction. Clinical, radiological and biomechanical studies showed the importance of the anterolateral ligament (ALL) integrity. ALL is one of the stabilization structures against the internal rotation of the tibia under forces which was associated with Segond fracture previously. Even some authors claimed that ACL failure and risk of re-rupture increased if only ACL reconstruction performed in patients with simultaneous ALL injury. The aim of the study is to evaluate the importance of ALL on knee biomechanics during anterior drawer test and internal rotation forces with different flexion angles in terms of reaction forces on ACL and the amount of tibia displacement via finite element analysis. METHODS: Three dimensional (3D) solid model of knee joint and ALL injured models were constructed based on DICOM formatted computed tomography (CT) images. 0°, 15°,30°,45°,60°,75° and 90° flexion angles were applied respectively to reference models. Then varied anterior drawer and internal rotational forces were used to investigate the effect of ALL. ANSYS ®Version 17 was used in analyses and same boundary conditions were used in all models. RESULTS: In critical analyzing the all results; medial displacement and the amount of anterior drawer distance were increased in all ALL injured models when compared with references. Therewithal the rotational displacements were increased by increasing the knee flexion angle and rotational torque. But, it was not a significant change in the amount of displacement between the models with respect to anteroposterior displacement when the anterior drawer force was increased. CONCLUSION: ALL particular has an important role in the stability of the internal rotation occurs against the force and with increased contribution rate to the knee joint stability by increasing the knee flexion angle. But the reaction forces were not affected by ALL integrity. So this study do not support the previous studies which suggest simultaneously reconstruction of both ligaments to avoid re rupture of ACL in cases with ALL injured.