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Implementing a mechanical testing methodology for assessing the flexure stiffness of healed mouse femurs
Assessing the mechanical properties of healed mouse femurs with three point bending tests poses a challenge due to certain test artifacts. Implementation of an experimental, imaging and computational approach will allow accurate determination of these properties.
One of the commonly used metrics of post fracture healing quality assessment is the 3 point bending test. The healed femur is loaded in a traditional 3 point bending manner and the resulting flexure modulus is compared to the flexure modulus of the contra-lateral femur. While this approach is commonly seen in the literature, there are a few issues that can induce error in the results. Firstly, the cross sectional area of the femur cannot be well approximated by an ellipse, nor by a constant cross section throughout the exposed test area. Secondly, when there is a short moment arm there is a risk of significant shear effects, and thirdly, indentation into the bone and distortion of the bone’s cross section can affect results. Several authors have assessed these errors and proposed error correction factors [1, 2]. One of these studies was performed in our lab several years ago and consisted of a comprehensive experimental – computational comparison [1]. This work made several suggestions for improvement of this methodology to achieve more accurate results. We aim to implement these suggestions to develop a mechanical testing framework for our healed mouse femurs to improve our quantification of fracture healing.
[1] G.H. van Lenthe, R. Voide, S.K. Boyd, R. Muller, Tissue modulus calculated from beam theory is biased by bone size and geometry: Implications for the use of three-point bending tests to determine bone tissue modulus, Bone 43(4) (2008) 717-723.
[2] J.L. Schriefer, A.G. Robling, S.J. Warden, A.J. Fournier, J.J. Mason, C.H. Turner, A comparison of mechanical properties derived from multiple skeletal sites in mice, J Biomech 38(3) (2005) 467-475.
One of the commonly used metrics of post fracture healing quality assessment is the 3 point bending test. The healed femur is loaded in a traditional 3 point bending manner and the resulting flexure modulus is compared to the flexure modulus of the contra-lateral femur. While this approach is commonly seen in the literature, there are a few issues that can induce error in the results. Firstly, the cross sectional area of the femur cannot be well approximated by an ellipse, nor by a constant cross section throughout the exposed test area. Secondly, when there is a short moment arm there is a risk of significant shear effects, and thirdly, indentation into the bone and distortion of the bone’s cross section can affect results. Several authors have assessed these errors and proposed error correction factors [1, 2]. One of these studies was performed in our lab several years ago and consisted of a comprehensive experimental – computational comparison [1]. This work made several suggestions for improvement of this methodology to achieve more accurate results. We aim to implement these suggestions to develop a mechanical testing framework for our healed mouse femurs to improve our quantification of fracture healing.
[1] G.H. van Lenthe, R. Voide, S.K. Boyd, R. Muller, Tissue modulus calculated from beam theory is biased by bone size and geometry: Implications for the use of three-point bending tests to determine bone tissue modulus, Bone 43(4) (2008) 717-723.
[2] J.L. Schriefer, A.G. Robling, S.J. Warden, A.J. Fournier, J.J. Mason, C.H. Turner, A comparison of mechanical properties derived from multiple skeletal sites in mice, J Biomech 38(3) (2005) 467-475.
The aim of this work is the implementation of the work done by Van Lente et al. [1] on our current setups. The project will consist of; experimental testing using a Zwick compression tester to conduct 3 point bending test, micro computed tomography (μCT) imaging to assess the geometry of the specimens and implementation of the experimental setup in our micro finite element (microFE) code using out computational frameworks developed internally. The intention is to create a framework that allows complete assessment of the bending stiffness of healed femurs.
[1] G.H. van Lenthe, R. Voide, S.K. Boyd, R. Muller, Tissue modulus calculated from beam theory is biased by bone size and geometry: Implications for the use of three-point bending tests to determine bone tissue modulus, Bone 43(4) (2008) 717-723.
The aim of this work is the implementation of the work done by Van Lente et al. [1] on our current setups. The project will consist of; experimental testing using a Zwick compression tester to conduct 3 point bending test, micro computed tomography (μCT) imaging to assess the geometry of the specimens and implementation of the experimental setup in our micro finite element (microFE) code using out computational frameworks developed internally. The intention is to create a framework that allows complete assessment of the bending stiffness of healed femurs.
[1] G.H. van Lenthe, R. Voide, S.K. Boyd, R. Muller, Tissue modulus calculated from beam theory is biased by bone size and geometry: Implications for the use of three-point bending tests to determine bone tissue modulus, Bone 43(4) (2008) 717-723.
Graeme Paul
Email: graeme.paul@hest.ethz.ch
Telephone: +41 44 633 2162
Graeme Paul Email: graeme.paul@hest.ethz.ch Telephone: +41 44 633 2162