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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Available from: John Robert Jameson, Oct 01, 2015
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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. "
    Computer Methods in Biomechanics and Biomedical Engineering 08/2014; 17 Suppl 1(sup1):60-1. DOI:10.1080/10255842.2014.931116 · 1.77 Impact Factor
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    ABSTRACT: Osteogenesis imperfecta (OI) is a genetic disorder leading to increased bone fragility. Recent work has shown that the hierarchical structure of bone plays an important role in determining its mechanical properties and resistance to fracture. The current study represents one of the first attempts to characterize the 3D structure and composition of cortical bone in OI at the micron-scale. A total of 26 pediatric bone fragments from 18 individuals were collected during autopsy (N c =5) or routing orthopaedic procedures (N OI =13) and imaged by microtomography with a synchrotron light source (SRµCT) for several microstructural parameters including cortical porosity (Ca.V/TV), canal surface to tissue volume (Ca.S/TV), canal diameter (Ca.Dm), canal separation (Ca.Sp), canal connectivity density (Ca.ConnD), and volumetric tissue mineral density (TMD). Results indicated significant differences in all imaging parameters between pediatric controls and OI tissue, with OI bone showing drastically increased cortical porosity, canal diameter, and connectivity. Preliminary mechanical testing revealed a possible link between cortical porosity and strength. Together these results suggest that the pore network in OI contributes greatly to its reduced mechanical properties.
    Medical Imaging 2013: Biomedical Applications in Molecular, Structural, and Functional Imaging; 02/2013
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    ABSTRACT: Osteogenesis Imperfecta is a genetic disorder resulting in bone fragility. The mechanisms behind this fragility are not well understood. In addition to characteristic bone mass deficiencies, research suggests that bone material properties are compromised in individuals with this disorder. However, little data exists regarding bone properties beyond the microstructural scale in individuals with this disorder. Specimens were obtained from long bone diaphyses of nine children with osteogenesis imperfecta during routine osteotomy procedures. Small rectangular beams, oriented longitudinally and transversely to the diaphyseal axis, were machined from these specimens and elastic modulus, yield strength, and maximum strength were measured in three-point bending. Intracortical vascular porosity, bone volume fraction, osteocyte lacuna density, and volumetric tissue mineral density were determined by synchrotron micro-computed tomography, and relationships among these mechanical properties and structural parameters were explored. Modulus and strength were on average 64-68% lower in the transverse vs. longitudinal beams (P<0.001, linear mixed model). Vascular porosity ranged between 3-42% of total bone volume. Longitudinal properties were associated negatively with porosity (P≤0.006, linear regressions). Mechanical properties, however, were not associated with osteocyte lacuna density or volumetric tissue mineral density (P≥0.167). Bone properties and structural parameters were not associated significantly with donor age (p≥0.225, linear mixed models). This study presents novel data regarding bone material strength in children with osteogenesis imperfecta. Results confirm that these properties are anisotropic. Elevated vascular porosity was observed in most specimens, and this parameter was associated with reduced bone material strength. These results offer insight towards understanding bone fragility and the role of intracortical porosity on the strength of bone tissue in children with osteogenesis imperfecta.
    Bone 06/2014; 66. DOI:10.1016/j.bone.2014.05.022 · 3.97 Impact Factor