Influence of bone stress relaxation and abrasion on micromotions in uncemented femoral knee implants: A finite element study

Aseptic loosening is the primary cause of revision in cementless total knee arthroplasty, emphasizing the importance of reliable primary fixation. Pre-clinical evaluations are crucial for understanding fixation mechanics. Finite element (FE) models typically use linear elastic bone properties, which inadequately represent bone behavior. Incorporating bone plasticity increases realism but tends to underestimate micromotions at the bone-implant interface compared to experiments, likely due to the exclusion of viscoelasticity and abrasion. This study assessed whether including bone stress relaxation and abrasion improves micromotion predictions at the bone-implant interface of an uncemented femoral knee implant. Experimental micromotion data from five components implanted in cadaveric femora were compared with cadaverspecific FE models assigned elastic, plastic, or plastic-viscoelastic bone properties with varying virtual abrasion.Stress relaxation had minimal impact on micromotions, which remained lower than experimental values. Introducing bone abrasion increased micromotions across all models. For the plasticviscoelastic model with 0.75 mm abrasion, predicted micromotions (53.0 ± 43.0 µm) closely matched experiments (53.1 ± 42.3 µm), though simulations failed to converge for two specimens due to limited bone-implant contact. These findings highlight the importance of incorporating bone abrasion into FE models and the need to further refine simulations addressing bone plasticity, friction, and abrasion simplifications.