Impact of Tibial Component Coronal Alignment on Knee Joint Biomechanics Following Fixed-bearing Unicompartmental Knee Arthroplasty: A Finite Element Analysis

Objective Unicompartmental knee arthroplasty (UKA) has indicated a higher rate of revision than total knee arthroplasty (TKA). The success of UKA depends on UKA component alignment, fixation, and soft tissue integrity. The purpose of this study was to investigate the effects of different tibial component alignments in the coronal plane on the stress distribution in UKA. It was hypothesized that the stress distribution would approach native knee when the tibial component was neutrally positioned. Methods The left legs from two healthy volunteers were considered to represent the geometric native knee models. All bones within the knee joint were extracted from the three-dimensional (3D) computed tomography (CT). MRI was used to generate cartilage, menisci, and four major ligaments. The UKA components were virtually implanted in the medial compartment of the knee model using MIMICS. A total of five different configurations of UKA tibial obliquity in the coronal plane (neutral, 3 degrees varus, 6 degrees varus, 3 degrees valgus, and 6 degrees valgus) were adopted and investigated. Subject-specific inhomogeneous material properties of bones were used in the finite element analysis (FEA) model. The von Mises stress in the tibia platform and proximal tibia, and the load distribution between the medial and lateral compartments were extracted and compared among the five different configurations. Results The inhomogeneous material properties of the trabecular bone were closer to real physics than traditional homogeneous methods. Neutral and 3 degrees varus alignments of the tibial component in the coronal plane have better stress distribution between medial and lateral compartment as healthy knee models, and less stress-shielding effects than other UKA configurations. The stress pathway under the medial tibia platform in neutral and 3 degrees varus UKA configurations was similar and more obvious than the other three UKA configurations. Notably, the stress of the medial tibia platform in the 3 degrees varus UKA models was more homogenous than the neutral UKA configuration. The 6 degrees varus, 3 degrees valgus, and 6 degrees valgus UKA models had higher stress at the location of anterolateral and posterolateral tibia platform than other UKA configurations. Conclusion Neutral or 3 degrees varus positioned in the coronal plane for the tibial component could be the optimal alignment for UKA. Excessive varus or valgus obliquity in the coronal plane lead to significant differences in bone stress transfer and load distribution in the knee, and increase the risk of UKA failure.