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TECHNICAL PAPERS: Bone/Orthopedics

A 3D Computational Simulation of Fracture Callus Formation: Influence of the Stiffness of the External Fixator

[+] Author and Article Information
M. J. Gómez-Benito, J. M. García-Aznar

Group of Structural Mechanics and Materials Modelling, Aragón Institute of Engineering Research (I3A), University of Zaragoza, María de Luna 3, 50008, Zaragoza, Spain

J. H. Kuiper

Institute for Science and Technology in Medicine, Keele University, Keele ST5 5BG, UK and Unit for Joint Reconstruction, The Robert Jones and Agnes Hunt Orthopaedic Hospital, Oswestry, Shropshire SY10 7AG, United Kingdom

M. Doblaré

Group of Structural Mechanics and Materials Modelling, Aragón Institute of Engineering Research (I3A), University of Zaragoza, María de Luna 3, 50008, Zaragoza, Spainmdoblare@posta.unizar.es

J Biomech Eng 128(3), 290-299 (Nov 09, 2005) (10 pages) doi:10.1115/1.2187045 History: Received January 27, 2005; Revised November 09, 2005

The stiffness of the external fixation highly influences the fracture healing pattern. In this work we study this aspect by means of a finite element model of a simple transverse mid-diaphyseal fracture of an ovine metatarsus fixed with a bilateral external fixator. In order to simulate the regenerative process, a previously developed mechanobiological model of bone fracture healing was implemented in three dimensions. This model is able to simulate tissue differentiation, bone regeneration, and callus growth. A physiological load of 500N was applied and three different stiffnesses of the external fixator were simulated (2300, 1725, and 1150Nmm). The interfragmentary strain and load sharing mechanism between bone and the external fixator were compared to those recorded in previous experimental works. The effects of the stiffness on the callus shape and tissue distributions in the fracture site were also analyzed. We predicted that a lower stiffness of the fixator delays fracture healing and causes a larger callus, in correspondence to well-documented clinical observations.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Scheme of cellular events in fracture healing (20)

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Figure 2

Finite element implementation

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Figure 3

Simplified geometry of the metatarsus (mm)

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Figure 4

Initial finite element model of the fractured metatarsus and the bilateral linear external fixator. Boundary conditions for (a) poroelastic analysis, (b) thermoelastic analysis, and (c) diffusion analysis.

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Figure 6

Osteoblast evolution (number of cells∕mm3) for fixators with stiffness of (a) 2300N∕mm, (b) 1725N∕mm, and (c) 1150N∕mm

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Figure 7

Evolution for the 2300N∕mm stiffness fixator of (a) stem cells (number of cells∕mm3), (b), chondrocytes (number of cells∕mm3), and (c) elastic modulus of the tissues (MPa)

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Figure 8

Final finite element meshes for the fixators (a) 2300N∕mm, (b) 1725N∕mm, and (c) 1150N∕mm

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Figure 9

Comparison between the frontal and sagittal planes for (a) periosteal callus size (P), and (b) time to complete bridging of the callus

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Figure 10

Axial stiffness evolution of the fractures fixed with fixators of different stiffness

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Figure 11

Evolution of the reaction force for different fixators: (a) 1150N∕mm, (b) 1725N∕mm, and (c) 2300N∕mm.

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Figure 5

(a) Average interfragmentary strain during fracture healing. (b) Interfragmentary strain along the outer fracture circumference in the 1750N∕mm stiffness fixator.

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