Femoral component alignment in unicompartmental knee arthroplasty leads to biomechanical change in contact stress and collateral ligament force in knee joint

In recent years, the popularity of unicompartmental knee arthroplasty (UKA) has increased. However, the effect of femoral component positioning in UKA continues to invite a considerable debate. The purpose of this study involved assessing the biomechanical effect of mal-alignment in femoral components in UKA under dynamic loading conditions using a computational simulation. A validated finite element model was used to evaluate contact stresses in polyethylene (PE) inserts and lateral compartment and force on collateral ligament in the femoral component ranging from 9A degrees of varus to 9A degrees of valgus. The results indicated that contact stress on the PE insert increased with increases in the valgus femoral alignment when compared to the neutral position while contact stress on the lateral compartment increased with increases in the varus femoral alignment. The forces on medial and lateral collateral ligaments increased with increases in valgus femoral alignments when compared to the neutral position. However, there was no change in popliteofibular and anterior lateral ligaments with respect to the malpositioning of femoral component. The results of the study confirm the importance of conservation in post-operative accuracy of the femoral component since the valgus and varus femoral malalignments affect the collateral ligament and lateral compartment, respectively. Our results suggest that surgeons should avoid valgus malalignment in the femoral component and especially malalignment exceeding 9A degrees, which may induce higher medial collateral ligament forces.