Design and validation of bending test method for characterization of miniature pediatric cortical bone specimens

Orthopaedic and Rehabilitation Engineering Center, Department of Biomedical Engineering, Marquette University, Milwaukee, WI 53201-1881, USA.
Proceedings of the Institution of Mechanical Engineers Part H Journal of Engineering in Medicine (Impact Factor: 1.33). 02/2013; 227(2):105-13. DOI: 10.1177/0954411912463868


Osteogenesis imperfecta is a genetic disorder of bone fragility; however, the effects of this disorder on bone material properties are not well understood. No study has yet measured bone material strength in humans with osteogenesis imperfecta. Small bone specimens are often extracted during routine fracture surgeries in children with osteogenesis imperfecta. These specimens could provide valuable insight into the effects of osteogenesis imperfecta on bone material strength; however, their small size poses a challenge to their mechanical characterization. In this study, a validated miniature three-point bending test is described that enables measurement of the flexural material properties of pediatric cortical osteotomy specimens as small as 5mm in length. This method was validated extensively using bovine bone, and the effect of span/depth aspect ratio (5 vs 6) on the measured flexural properties was examined. The method provided reasonable results for both Young’s modulus and flexural strength in bovine bone. With a span/depth ratio of 6, the median longitudinal modulus and flexural strength results were 16.1 (range: 14.4–19.3) GPa and 251 (range: 219–293) MPa, respectively. Finally, the pilot results from two osteotomy specimens from children with osteogenesis imperfecta are presented.
These results provide the first measures of bone material strength in this patient population.

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    • "We examined the response of cortical bone under flexural loading by means of three-point bending tests. For this type of test, we followed the standard ASTM D790 [59] , generally used for unreinforced plastics but also adopted for bone tissue [21,37]. We cut rectangular specimens (50 Â 8 Â 4 mm), where the length of the specimens corresponds to the main axis of the osteons (seeFig. "
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    • "Several papers study mechanical properties of children's bone by uniaxial bending (Currey and Butler, 1975; Jans et al., 1998; Davis et al., 2012; Agnew et al., 2013; Berteau et al., 2013; Albert et al., 2013a, 2013b, 2014), compression (McPherson et al., 2007; Ohman et al., 2011) or ultrasonic characterization (Berteau et al., 2012, 2013). Some even study mechanical properties at the tissue level by nanoindentation (Fan et al., 2006; Weber et al., 2006; Albert et al., 2013a,2013b; Imbert et al., 2014). However, most of these studies were conducted on only a few samples, because of the scarcity of specimens for laboratory testing. "

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