Tibial Strains and Tray-Bone Micromotions After Total Knee Arthroplasty: Computational Studies Evaluating the Tibial Fixation

Cemented and cementless fixation in total knee arthroplasty (TKA) have been successfully used for decades. As the number of younger and more active patients treated with TKA continues to increase, long-term implant survivorship is of increasing importance. One of the most common complications and hence the reason for revision is mechanical loosening (23.1% of all revised TKA). The loosening mechanisms have been proposed for different fixation types. For cemented fixation, bone remodeling after surgery is regulated by the changes in strain energy density (SED). The recruitment of osteoclasts and osteoblasts is controlled by SED-related signals. Insufficient stimuli can promote bone resorption, which causes implant loosening. For cementless fixation, the initial fixation of cementless tibial trays is crucial to bony ingrowth onto the porous surface, as the micromotion magnitudes exceeding 150 μm may inhibit bone formations and cause implant loosening. However, the critical parameters influencing SED distributions and tray-bone micromotion are not fully understood. Finite element models have been commonly used to estimate the SED and micromotion, which typically cannot be measured experimentally. However, the challenge that has limited the use of computational modeling in clinical practice is model validation. Any poorly characterized input would directly influence the accuracy of the resulting outputs and cause validation failure. The purpose of this work is to create an experiment to finite element analysis pipeline for investigating the sensitivities of common TKA factors to the tibial SED and tray-bone micromotion. Specifically, the first study developed an experimental-computational validation framework for predicting tibial micromotion and bone deformation. The validated models were utilized for the subsequent application studies. The second study investigated the influence of five common TKA factors on tibial strain energy density. The third study assessed the impact of seven common TKA factors on the tray-bone interface micromotion. Physiological conditions were considered for both bone models and boundary conditions used in each study. Therefore, the conclusions were more clinically meaningful. There were clear recommendations for optimizing the post-operative SED distribution and minimizing the interface micromotion to improve the tibial fixation. The research framework presented in this dissertation could be used as a benchmark for investigating critical parameters influencing implant fixation stability. The computational models presented in this dissertation could be used for pre-clinical assessment and further implant development