Journal
BONE
Volume 43, Issue 4, Pages 717-723Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.bone.2008.06.008
Keywords
tissue modulus; biomechanical testing; finite element analysis; mouse; femur
Categories
Funding
- Roche Research Foundation [RRF 76-2004]
- ETH [TH 00124/41-2631.5]
- Swiss National Science Foundation [FP 620-58097.99, PP-104317/1]
- Swiss National Supercomputing Centre (CSCS)
- Jackson Laboratory, Maine, USA
- ETH Zurich, Switzerland
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Current practice to determine bone tissue modulus of murine cortical bone is to estimate it from three-point bending tests, using Euler-Bernoulli beam theory. However, murine femora are not perfect beams; hence, results can be inaccurate. Our aim was to assess the accuracy of beam theory, which we tested for two commonly used inbred strains of mice, C57BL/6 (B6) and C3H/He (C3H). We measured the three-dimensional structure of male and female B6 and C3H femora (N=20/group) by means of micro-computed tomography. For each femur five micro-finite element (micro-FE) models were created that simulated three-point bending tests with varying distances between the supports. Tissue modulus was calculated from beam theory using micro-FE results. The accuracy of beam theory was assessed by comparing the beam theory-derived moduli with the modulus as used in the micro-FE analyses. An additional set of fresh-frozen femora (10 B6 and 12 C3H) was biomechanically tested and Subjected to the same micro-FE analyses. These combined experimental-computational analyses enabled an unbiased assessment of specimen-specific tissue modulus. We found that by using beam theory, tissue modulus was underestimated for all femora. Femoral geometry and size had strong effects on beam theory-derived tissue moduli. Owing to their relatively thin cortex, underestimation was markedly higher for 136 than for C3H. Underestimation was dependent on Support width in a strain-specific manner. From our combined experimental-computational approach we calculated tissue moduli of 12.0 +/- 1.3 GPa and 13.4 +/- 2.1 GPa for B6 and C3H, respectively. We conclude that tissue moduli in murine femora are strongly underestimated when calculated from beam theory. Using image-based micro-FE analyses we could precisely quantify this underestimation. We showed that previously reported murine inbred strain-specific differences in tissue modulus are largely an effect of geometric differences, not accounted for by beam theory. We suggest a re-evaluation of the tissue properties obtained from three-point bending tests, especially in mouse genetics. (c) 2008 Elsevier Inc. All rights reserved.
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