The effect of bone plasticity models on simulations of primary fixation in total knee arthroplasty

Predictions of primary fixation in total knee arthroplasty (TKA) can aid in implant design, optimizing long-term survival. Finite element (FE) simulations are commonly used to assess micromotions at the bone-implant interface during daily activities, requiring accurate computational models. A key factor is the material model used to simulate bone properties. This study evaluated two plastic material models—Isotropic Crushable Foam (ICF) and softening Von-Mises (sVM)—for predicting primary fixation in femoral TKA components. Mechanical tests on human femoral trabecular bone samples under cyclic loading were replicated using FE simulations with ICF and sVM models. These models were then applied to FE simulations of three femoral TKA reconstructions, representing patients aged 57, 73, and 90 years. The ICF model replicated the gradual plastic deformation observed in experiments, unlike the sVM model, and more closely matched the permanent deformation of bone samples. In primary fixation simulations, micromotions at the bone-implant interface averaged 27 µm with ICF and 17 µm with sVM. While both predictions fall within acceptable ranges, the ICF model, as a pressure-dependent material model, more accurately replicates experimental energy dissipation and plastic deformation patterns, closely mirroring human bone's plastic behavior. This makes it better suited for simulating implant-bone interface micromotions in primary TKA fixation.