kneeASME2008 - Dong Zhao Department of Mechanical &...

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Dong Zhao Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL 32611 Hideyuki Sakoda Nakashima Medical Division, Nakashima Propeller Co., Ltd., Japan W. Gregory Sawyer Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, FL 32611 Scott A. Banks Benjamin J. Fregly 1 e-mail: fregly@u±.edu Department of Mechanical & Aerospace Engineering, Department of Biomedical Engineering, Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL 32611 Predicting Knee Replacement Damage in a Simulator Machine Using a Computational Model With a Consistent Wear Factor Wear of ultrahigh molecular weight polyethylene remains a primary factor limiting the longevity of total knee replacements (TKRs). However, wear testing on a simulator ma- chine is time consuming and expensive, making it impractical for iterative design pur- poses. The objectives of this paper were Frst, to evaluate whether a computational model using a wear factor consistent with the TKR material pair can predict accurate TKR damage measured in a simulator machine, and second, to investigate how choice of surface evolution method (Fxed or variable step) and material model (linear or nonlin- ear) affect the prediction. An iterative computational damage model was constructed for a commercial knee implant in an AMTI simulator machine. The damage model combined a dynamic contact model with a surface evolution model to predict how wear plus creep progressively alter tibial insert geometry over multiple simulations. The computational framework was validated by predicting wear in a cylinder-on-plate system for which an analytical solution was derived. The implant damage model was evaluated for 5 million cycles of simulated gait using damage measurements made on the same implant in an AMTI machine. Using a pin-on-plate wear factor for the same material pair as the implant, the model predicted tibial insert wear volume to within 2% error and damage depths and areas to within 18% and 10% error, respectively. Choice of material model had little in±uence, while inclusion of surface evolution affected damage depth and area but not wear volume predictions. Surface evolution method was important only during the initial cycles, where variable step was needed to capture rapid geometry changes due to the creep. Overall, our results indicate that accurate TKR damage predictions can be made with a computational model using a constant wear factor obtained from pin-on- plate tests for the same material pair, and furthermore, that surface evolution method matters only during the initial “break in” period of the simulation. f DOI: 10.1115/1.2838030 g Keywords: dynamic contact simulation, computational wear prediction, knee simulator machine, total knee replacement, biomechanics Introduction Wear of ultrahigh molecular weight polyethylene remains a pri- mary factor limiting the longevity of total knee replacements f 1 g .
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kneeASME2008 - Dong Zhao Department of Mechanical &...

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