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TECHNICAL BRIEFS

Finite Element and Experimental Cortex Strains of the Intact and Implanted Tibia

[+] Author and Article Information
A. Completo, J. A. Simões

Departamento de Engenharia Mecânica, Universidade de Aveiro, 3810-193 Aveiro, Portugal

F. Fonseca

Faculdade de Ciências da Saúde, Universidade da Beira Interior, 6201-001 Covilhã, Portugal

J Biomech Eng 129(5), 791-797 (Feb 22, 2007) (7 pages) doi:10.1115/1.2768382 History: Received January 08, 2007; Revised February 22, 2007

Finite Element (FE) models for the simulation of intact and implanted bone find their main purpose in accurately reproducing the associated mechanical behavior. FE models can be used for preclinical testing of joint replacement implants, where some biomechanical aspects are difficult, if not possible, to simulate and investigate in vitro. To predict mechanical failure or damage, the models should accurately predict stresses and strains. Commercially available synthetic femur models have been extensively used to validate finite element models, but despite the vast literature available on the characteristics of synthetic tibia, numerical and experimental validation of the intact and implant assemblies of tibia are very limited or lacking. In the current study, four FE models of synthetic tibia, intact and reconstructed, were compared against experimental bone strain data, and an overall agreement within 10% between experimental and FE strains was obtained. Finite element and experimental (strain gauge) models of intact and implanted synthetic tibia were validated based on the comparison of cortex bone strains. The study also includes the analysis carried out on standard tibial components with cemented and noncemented stems of the P.F.C Sigma Modular Knee System. The overall agreement within 10% previously established was achieved, indicating that FE models could be successfully validated. The obtained results include a statistical analysis where the root-mean-square-error values were always <10%. FE models can successfully reproduce bone strains under most relevant acting loads upon the condylar surface of the tibia. Moreover, FE models, once properly validated, can be used for preclinical testing of tibial knee replacement, including misalignment of the implants in the proximal tibia after surgery, simulation of long-term failure according to the damage accumulation failure scenario, and other related biomechanical aspects.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Tibia with locations of strain gauges. Bone strains were measured with four gauges glued at the posterior (P0, P1, P2, and P3) and six gauges glued at the anterior-medial (AM1, AM2, and AM3) and lateral (L1, L2, and L3) sides of the tibia.

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Figure 2

Instrumented intact (left) and implanted (right) tibia

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Figure 4

Comparison of the FE and mean experimental principal strains for each gauge location for a vertical force applied on the medial (1160N) and lateral (870N) condyles (superimposition principal was used to determine the experimental strains): (a) intact tibia model, (b) reconstruction with standard implant, (c) reconstruction with noncemented stem, and (d) reconstruction with cemented stem. The gauge locations are named as defined in Fig. 1.

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Figure 3

FE models built and used to simulate the experiments: (a) FE model of a composite intact tibia, (b) FE model of a composite reconstruction with standard implant, (c) FE model of a composite reconstruction with cemented stem, and (d) FE model of a composite reconstruction with noncemented (press-fit) stem

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Figure 5

The graphs show the linear regression results for the strains in (a) intact femur model, (b) reconstruction with standard implant, (c) reconstruction with noncemented stem, and (d) reconstruction with cemented stem

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