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Research Papers

A Cadaverically Evaluated Dynamic FEM Model of Closed-Chain TKR Mechanics

[+] Author and Article Information
Joel L. Lanovaz1

College of Kinesiology, University of Saskatchewan, 87 Campus Drive, Saskatoon, SK, S7N 5B2, Canada

Randy E. Ellis

School of Computing, Queen’s University, Kingston, ON, K7L 3N6, Canada; Department of Mechanical and Materials Engineering, Queen’s University, Canada; Human Mobility Research Centre, Queen’s University, Canada

1

Corresponding author.

J Biomech Eng 131(5), 051002 (Mar 20, 2009) (11 pages) doi:10.1115/1.3078159 History: Received October 25, 2007; Revised December 12, 2008; Published March 20, 2009

Knowledge of the behavior and mechanics of a total knee replacement (TKR) in an in vivo environment is key to optimizing the functional outcomes of the implant procedure. Computational modeling has shown to be an important tool for investigating biomechanical variables that are difficult to address experimentally. To assist in examining TKR mechanics, a dynamic finite-element model of a TKR is presented. The objective of the study was to develop and evaluate a model that could simulate full knee motion using a physiologically consistent quadriceps action, without prescribed joint kinematics. The model included tibiofemoral (TFJs) and patellofemoral joints (PFJs), six major ligament bundles and was driven by a uni-axial representation of a quadricep muscle. An initial parameter screening analysis was performed to assess the relative importance of 31 different model parameters. This analysis showed that ligament insertion location and initial ligament strain were significant factors affecting simulated joint kinematics and loading, with the contact friction coefficient playing a lesser role and ligament stiffness having little effect. The model was then used to simulate in vitro experiments utilizing a flexed-knee-stance testing rig. General model performance was assessed by comparing simulation results with experimentally measured kinematics and tibial reaction forces collected from two implanted specimens. The simulations were able to reproduce experimental differences observed between the test specimens and were able to accurately predict trends seen in the tibial reaction loads. The simulated kinematics of the TFJ and PFJ were less consistent when compared with experimental data but still reproduced many trends.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 3

A representative patella coordinate system (for right side specimen). The x and y axes were obtained using the major and minor axes of an ellipse fit to the anterior view and aligned to the mid-plane of the patella

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Figure 4

FEM model of the experimental setup showing the representations of the main flexed-knee-stance testing rig components; insert shows a closer view of the TKR component models and the cable element representations of the ligaments

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Figure 5

Experimental (Exp) and simulated (Sim) TFJ angular kinematics for the right and left knee specimens; V-V angles (top panel) and I-E rotation angles (bottom panel) are expressed with respect to the TFJ F-E angle

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Figure 6

Experimental (Exp) and simulated (Sim) PFJ angular kinematics for the right and left knee specimens; PFJ F-E angles (top panel), tilt angles (middle panel), and spin angles (bottom panel) are expressed with respect to the TFJ F-E angle.

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Figure 7

Experimental (Exp) and simulated (Sim) tibial reaction forces for the right and left knee specimens; M-L forces (top panel), A-P forces (middle panel), and axial forces (bottom panel) are expressed with respect to the TFJ F-E angle

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Figure 8

Experimental (Exp) and simulated (Sim) tibial reaction moments for the right and left knee specimens; F-E moments (top panel), V-V moments (middle panel), and I-E moments (bottom panel) are expressed with respect to the TFJ F-E angle

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Figure 2

Bone-based coordinate systems used for the femur (top row) and the tibia (bottom row). The reference models (based on standard sawbones) are shown. Surface models of the specimens, derived from CT scans, were fit to the reference models to obtain specimen-specific coordinate systems.

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Figure 1

The flexed-knee-stance testing rig assembly used in this study. A schematic (A) shows the mechanical joints representing the hip and ankle degrees of freedom. The specimen is shown mounted in the rig (B) with the following components labeled: a. motor assembly, b. quadriceps clamp, c. femur dynamic reference body (DRB) used to track kinematics, d. patellar DRB, e. tibial DRB, f. tibial load cell.

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