Biomechanical Evaluation of Loading Variability and Bone Quality in Total Knee Arthroplasty: A Finite Element Sensitivity Study

While total knee arthroplasty (TKA) is highly successful, wear, primary fixation stability and structural failure remain significant challenges, particularly in patients with diverse kinetic profiles and compromised bone. This study evaluates a fixed-bearing cruciate-retaining TKA prosthesis under extreme load variability in healthy and osteoporotic bone. Finite element simulations utilized ISO-standardized baseline gait cycle, scaling independently axial forces, antero-posterior forces, and rotational torque to 50% and 200%. Polyethylene insert stress, tibial stress, and bone–implant micromotion were evaluated to assess structural safety, load transfer, and primary stability. Kinetic variability directly influenced the stress magnitude and load transfer. Insert load distribution revealed a compartmental split (medial side bearing 47.6% to 60.9%) sensitive to force orientation and translational load magnitudes (axial and shear), but totally independent of rotational torque magnitude. While reduced bone quality did not significantly affect overall polyethylene stresses, it directly impacted primary stability. Osteoporotic conditions nearly doubled the total baseline interface micromotion (from 19 µm to 37 µm) and exhibited an absolute maximum of 63 µm under 200% axial load scaling. These findings highlight the necessity of definition of model parameters for careful preclinical planning for patients with compromised bone quality regarding prosthesis selection, fixation method and alignment.