Impact of different alignment techniques in total knee arthroplasty (TKA): a biomechanical patient-specific analysis of severe varus knee during walking

Background: Total Knee Arthroplasty (TKA) is an orthopedic surgical procedure designed to replace a damaged or diseased knee joint with an artificial one, in order to relieve pain and restore patient mobility. The optimal alignment strategy for TKA is a topic of ongoing debate. The gold standard, Mechanical Alignment (MA), is aimed at restoring the neutral limb alignment and has led to excellent implant survival rates. However, many patients remain dissatisfied with functional outcomes. Consequently, patient-specific techniques such as Kinematic Alignment (KA) and Inverse Kinematic Alignment (IKA), aiming to restore the patient’s native joint line alignment, are gaining attention. For patients with severe deformities, selecting the appropriate alignment can significantly impact the outcomes. This study aims at analyzing how different alignment techniques affect knee biomechanics in a patient with severe varus deformity. Methods: CT images of a patient’s left knee with a 10.4-degree varus deformity were processed through an image processing software to generate 3D models of the femur, tibia and fibula. Following the surgical procedures of MA, KA, and IKA, appropriate surgical cuts are applied on the bone models. A Genus (Adler Ortho®) Fixed Bearing (FB), Posterior Stabilized (PS) prosthesis was virtually implanted for each configuration. The knee models, incorporating physiological and patient- specific soft tissue position were used to develop Finite Element Method (FEM) models to analyze the tibio-femoral kinetics and kinematics. Results: The kinematic analysis revealed similar trends across all models, though with variations in magnitude. The kinetic analysis showed more pronounced differences. The MA model exhibited higher contact area and stress concentration on the medial side of the insert, whereas the KA model demonstrated a more balanced distribution between the medial and lateral regions. The IKA model displayed the most pronounced deviations in both kinetic and kinematic outcomes compared to the other two models. These variations correspond to the different bone resection angles required by each alignment technique. Conclusions: The choice of alignment technique significantly affects patients with severe deformities. Therefore, surgeons have to thoroughly evaluate each case individually to determine the most suitable alignment strategy for optimal results.