Is simultaneous posterolateral tibial plateau fracture with ACL injury a special pattern of ALRI of the knee joint? A finite element analysis

Abstract

Background The simultaneous posterolateral tibial plateau fracture (PTPF) with anterior cruciate ligament (ACL) injury has posed a great challenge to both orthopedic trauma and sports medicine surgeons. This study investigated the biomechanical mechanism of simultaneous PTPF with ACL injury and demonstrated the consistency with anterolateral rotatory instability (ALRI) of the knee.Methods A healthy male volunteer’s right knee CT and MRI images were imported into Mimics software to reconstruct a three-dimensional geometric model of bone, ligament, meniscus and cartilage. The PTPF were simulated at posterior half of the lateral tibial plateau (LTP) and lateral meniscus posterior horn (LMPH). Three PTPF depression angles were set at 5°, 10° and 15°. Finite element analysis (FEA) was conducted to observe the displacement of bone and meniscus, ACL strain and LTP stress at 0°and 30° knee flexion with vertical and tibial internal rotation loading, in ACL intact and deficient knee.Results For ACL intact knee, FEA showed vertical loading at 0° knee flexion led to abnormal displacements of lateral femoral condyle and LMPH. At 30° flexion, axial 10Nm tibia internal rotation loading resulted in more LTP anterior displacement and ACL strains. The stress of LTP concentrated abnormally on anterolateral part at 0° flexion and posterolateral LTP at 30° flexion. All above parameters tended to increase with the enlargement of depression area and depression angle. In ACL deficient knee, axial 10Nm tibia internal rotation loading led to even more LTP anterior displacement and LTP articular stress at 30° flexion than ACL intact knee, with a tendency of aggravating with increasing depression area and angle.Conclusion Simultaneous PTPF with ACL injury has common flexion valgus and tibial internal rotation injury mechanism with ALRI and should be treated as a special pattern of ALRI. Clinically, high grade PTPF associated with ACL injury should be addressed by concomitant PTPF reduction and ACL reconstruction to fully restore LTP articular congruence and knee stability.