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Research Papers

Increased Conformity Offers Diminishing Returns for Reducing Total Knee Replacement Wear

[+] Author and Article Information
Benjamin J. Fregly1

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611-6250; Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611-6131; and Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL 32611-2727fregly@ufl.edu

Carlos Marquez-Barrientos

Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611-6131

Scott A. Banks

Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611-6250; Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611-6131; and Department of Orthopaedics and Rehabilitation, University of Florida, Gainesville, FL 32611-2727

John D. DesJardins

Department of Bioengineering, Clemson University, Clemson, SC 29634-0905

1

Corresponding author. Present address: Department of Mechanical and Aerospace Engineering, University of Florida, 231 MAE-A Building, P.O. Box 116250, Gainesville, FL 32611-6250.

J Biomech Eng 132(2), 021007 (Jan 29, 2010) (7 pages) doi:10.1115/1.4000868 History: Received September 24, 2008; Revised October 01, 2009; Posted December 21, 2009; Published January 29, 2010; Online January 29, 2010

Wear remains a significant problem limiting the lifespan of total knee replacements (TKRs). Though increased conformity between TKR components has the potential to decrease wear, the optimal amount and planes of conformity have not been investigated. Furthermore, differing conformities in the medial and lateral compartments may provide designers the opportunity to address both wear and kinematic design goals simultaneously. This study used a computational model of a Stanmore knee simulator machine and a previously validated wear model to investigate this issue for simulated gait. TKR geometries with different amounts and planes of conformity on the medial and lateral sides were created and tested in two phases. The first phase utilized a wide range of sagittal and coronal conformity combinations to blanket a physically realistic design space. The second phase performed a focused investigation of the conformity conditions from the first phase to which predicted wear volume was sensitive. For the first phase, sagittal but not coronal conformity was found to have a significant effect on predicted wear volume. For the second phase, increased sagittal conformity was found to decrease predicted wear volume in a nonlinear fashion, with reductions gradually diminishing as conformity increased. These results suggest that TKR geometric design efforts aimed at minimizing wear should focus on sagittal rather than coronal conformity and that at least moderate sagittal conformity is desirable in both compartments.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 3

Phase one tests: wear volume as a function of changes in medial sagittal conformity when coronal and sagittal conformity on the lateral side are 0. In the legend, “mcc” indicates the medial coronal conformity, while “fcr” indicates the femoral coronal radius in mm.

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Figure 4

Phase one tests: wear volume as a function of changes in medial sagittal conformity when coronal and sagittal conformity on the lateral side are 0.5. Lines are the same as in Fig. 3.

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Figure 5

Phase two tests: wear volume as a function of changes in sagittal conformity of the nominal design when medial sagittal conformity was varied and lateral sagittal conformity was held constant.

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Figure 6

Phase two tests: wear volume as a function of changes in sagittal conformity of the nominal design when lateral sagittal conformity was varied and medial sagittal conformity was held constant. Lines are the same as in Fig. 5.

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Figure 7

Phase two tests: wear volume as a function of changes in sagittal conformity of the nominal design when medial and lateral sagittal conformity were varied together. Lines are the same as in Fig. 5.

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Figure 1

Computational model of a Stanmore knee simulator machine constructed in Pro/MECHANICA MOTION showing idealized femoral and tibial articular geometry from one of the tests. Multiple time frames over the gait cycle are displayed to illustrate the predicted motion of the components during a dynamic simulation.

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Figure 2

Wear scars and depths (in mm) predicted by the computational model for the implant geometry and simulation shown in Fig. 1

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