Finite Element Analysis of Fixed-bearing Unicompartmental Knee Arthroplasty: Coronal Alignment of the Tibial Component under Physiological Alignment

<title>Abstract</title> <p> <bold>Background</bold> : To investigate the influence of tibial component varus and valgus angles on knee joint biomechanics in fixed-bearing unicompartmental knee arthroplasty (FB-UKA) with physiological mechanical alignment of the lower limb. <bold>Methods</bold> : A normal knee joint model was established and validated. Nine simulation conditions were created based on the physiological mechanical alignment of the lower limb, with the tibial component positioned at neutral (0°), and varus/valgus angles of 3°, 6°, 9°, and 12° in the coronal plane. The peak von Mises stress and maximum principal strain were analyzed across different regions, including the superior surface of the polyethylene (PE) bearing, the cartilage surface of the lateral compartment, and the cancellous and cortical bone surfaces beneath the tibial component. <bold>Result</bold> : In the FB-UKA model, a tibial component valgus angle exceeding 3° significantly increases the peak von Mises stress and maximum principal strain on the anteromedial proximal cortex. During tibial component varus alignment, changes in the peak von Mises stress and maximum principal strain within the cancellous bone are initially minimal; however, as the varus angle continues to increase, stress levels approach the yield threshold, which may lead to bone resorption and prosthetic loosening. Furthermore, a further increase in the valgus angle exacerbates the load on the contralateral compartment, potentially accelerating the progression of contralateral osteoarthritis. <bold>Conclusion</bold> : This study demonstrates that in FB-UKA models with physiological limb mechanical alignment, static analysis results are significantly influenced by the position of the tibial component. We recommend that, as long as the global hip-knee-ankle (HKA) is not malaligned, the coronal alignment of the tibial component can be safely targeted between neutral and mild varus. This strategy may help reduce the risk of complications and improve implant survivorship. </p>