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TECHNICAL PAPERS: Joint/Whole Body

Comparison of Deformable and Elastic Foundation Finite Element Simulations for Predicting Knee Replacement Mechanics

[+] Author and Article Information
Jason P. Halloran, Sarah K. Easley, Paul J. Rullkoetter

 University of Denver, Department of Engineering, 2390 S. York, Denver, CO 80208

Anthony J. Petrella

 DePuy, a Johnson & Johnson Company, Biomechanical Testing and Analysis, 700 Orthopaedic Drive, Warsaw, IN 46581

J Biomech Eng 127(5), 813-818 (May 20, 2005) (6 pages) doi:10.1115/1.1992522 History: Received October 07, 2003; Revised May 20, 2005

Rigid body total knee replacement (TKR) models with tibiofemoral contact based on elastic foundation (EF) theory utilize simple contact pressure-surface overclosure relationships to estimate joint mechanics, and require significantly less computational time than corresponding deformable finite element (FE) methods. However, potential differences in predicted kinematics between these representations are currently not well understood, and it is unclear if the estimates of contact area and pressure are acceptable. Therefore, the objectives of the current study were to develop rigid EF and deformable FE models of tibiofemoral contact, and to compare predicted kinematics and contact mechanics from both representations during gait loading conditions with three different implant designs. Linear and nonlinear contact pressure-surface overclosure relationships based on polyethylene material properties were developed using EF theory. All other variables being equal, rigid body FE models accurately estimated kinematics predicted by fully deformable FE models and required only 2% of the analysis time. As expected, the linear EF contact model sufficiently approximated trends for peak contact pressures, but overestimated the deformable results by up to 30%. The nonlinear EF contact model more accurately reproduced trends and magnitudes of the deformable analysis, with maximum differences of approximately 15% at the peak pressures during the gait cycle. All contact area predictions agreed in trend and magnitude. Using rigid models, edge-loading conditions resulted in substantial overestimation of peak pressure. Optimal nonlinear EF contact relationships were developed for specific TKR designs for use in parametric or repetitive analyses where computational time is paramount. The explicit FE analysis method utilized here provides a unique approach in that both rigid and deformable analyses can be run from the same input file, thus enabling simple selection of the most appropriate representation for the analysis of interest.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

FE meshes for (a) PCR femoral component, (b) PCS femoral component, and corresponding (c) unconstrained insert, (d) semiconstrained insert, and (e) PCS insert

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Figure 2

Input load and motion profiles for Stanmore knee simulator are, flexion angle, axial load (a), anterior-posterior load, and internal-external torque (b)

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Figure 3

Applied loading and available (unconstrained) degrees of freedom for the FE model of the Stanmore knee wear simulator

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Figure 4

Nonlinear true stress-true strain UHMWPE material model (17)

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Figure 5

AP displacement for the semiconstrained PCR (a) and unconstrained PCR (b) devices using linear, nonlinear, and optimized EF and fully deformable representations

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Figure 6

IE rotation for the semiconstrained PCR (a) and unconstrained PCR (b) devices using linear, nonlinear, and optimized EF and fully deformable representations

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Figure 7

Peak contact pressure throughout the gait cycle for the semiconstrained PCR (a), semi-constrained PCS (b) and semiconstrained PCR (c) devices using linear, nonlinear, and optimized EF and fully deformable representations

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Figure 8

Contact pressure distribution for the semiconstrained PCR insert from deformable (a) and optimized rigid EF (b) representations at 15% of the gait cycle (on the same scale)

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Figure 9

Predicted contact area for the semiconstrained PCR device using linear, nonlinear, and optimized EF and fully deformable representations

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Figure 10

Linear, nonlinear, and optimized pressure-overclosure relationships for each insert type

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