Article
Influence of internal fixator stiffness on interfragmentary movement in healing murine femur fractures – A computational analysis
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Authors
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V. Pönnighaus
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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R. Steck
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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G. Chen
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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P. Krishnakanth
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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D. Epari
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
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M. A. Schuetz
- Queensland University of Technology, Institute of Health and Biomedical Innovation, Brisbane, Australia
| Published: | October 21, 2010 |
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Outline
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Objective: With the decoding of the mouse genome and the availability of mutated animals, the mouse has become an essential animal model for the study of molecular biological processes during fracture healing. However, until recently, there have been no experimental models available to study fracture healing under mechanically well defined and reproducible conditions. Therefore, two MouseFix™ murine fracture fixation implants, a flexible and a rigid plate, have been developed at the AO Research Institute (RISystems, Switzerland) which allow studying the influence of the mechanical environment (as defined by fixation stiffness) on fracture healing in the mouse. We have already established this murine fracture model in our group. For the interpretation of the results that are obtained with this experimental model, a complete mechanical characterisation of the fixation implants was necessary.
Methods: The characterisation was performed using validated Finite Element (FE) simulations. In these models, the plates were attached to PMMA cylinders, representing the mouse bones. Six different load cases were applied to the plate-cylinder constructs, namely axial compression, torsion and shear as well as bending in two planes. As the interfragmentary movement in the fracture gap has been shown to influence the course of fracture healing, this parameter was quantified in the simulations. For validation of the finite element simulations, the computed results of the global deformation behaviour of the plate-cylinder constructs were compared to the results of actual mechanical torsion tests performed on a custom-made testing device.
Results and conclusions: When the constructs were subjected to the same loads, the flexible plate was found to lead to significantly larger interfragmentary movements than the rigid plate with regard to axial compression (47-fold of the maximum interfragmentary movement of the rigid plate), torsion (18-fold), shear in two directions (34 fold and 47-fold) and out-of-plane (with respect to the plane formed by the fixation plate) bending (48-fold). During in-plane bending the flexible plate showed an interfragmentary movement similar to that with the rigid plate.
These results will greatly aid in the interpretation of the experimental results obtained with this animal model. Furthermore, this modelling approach allows for assessing the effect of future modifications of the plate design on the interfragmentary movement during the design phase, thereby reducing the number of experiments needed to find the optimized plate design for a given application.
