Change in porosity is the major determinant of the variation of cortical bone elasticity at the millimeter scale in aged women

Abstract

At the mesoscale (i.e. over a few millimeters), cortical bone can be described as two-phase composite material consisting of pores and a dense mineralized matrix. The cortical porosity is known to influence the mesoscopic elasticity. Our objective was to determine whether the variations of porosity are sufficient to predict the variations of bone mesoscopic anisotropic elasticity or if change in bone matrix elasticity is an important factor to consider. We measured 21 cortical bone specimens prepared from the mid-diaphysis of 10 women donors (aged from 66 to 98 years). A 50-MHz scanning acoustic microscope (SAM) was used to evaluate the bone matrix elasticity (reflected in impedance values) and porosity. Porosity evaluation with SAM was validated against Synchrotron Radiation μCT measurements. A standard contact ultrasonic method was applied to determine the mesoscopic elastic coefficients. Only matrix impedance in the direction of the bone axis correlated to mesoscale elasticity (adjusted R(2)=[0.16-0.25], p<0.05). The mesoscopic elasticity was found to be highly correlated to the cortical porosity (adj-R(2)=[0.72-0.84], p<10(-5)). Multivariate analysis including both matrix impedance and porosity did not provide a better statistical model of mesoscopic elasticity variations. Our results indicate that, for the elderly population, the elastic properties of the mineralized matrix do not undergo large variations among different samples, as reflected in the low coefficients of variation of matrix impedance (less than 6%). This work suggests that change in the intracortical porosity accounts for most of the variations of mesoscopic elasticity, at least when the analyzed porosity range is large (3-27% in this study). The trend in the variation of mesoscale elasticity with porosity is consistent with the predictions of a micromechanical model consisting of an anisotropic matrix pervaded by cylindrical pores.

A multiscale analytical approach for bone remodeling simulations: Linking scales from collagen to trabeculae

“…Actually, the micromechanical representation depicted in Fig. 2 also holds for the latter, as was evidenced by various studies reporting satisfactory agreement between respective model predictions and corresponding experimental results [7,57,58].…”

Ultrasonic evaluation of intact, healing and osteoporotic long bones

“…X-ray computed tomography was used in (Moilanen et al 2007) to establish more realistic 3D geometries of the human radius cortical bone and ultrasonically determine the thickness based on a guided wave analysis. Other numerical studies focus on the evaluation of cortical microstructure, porosity and anisotropy using QUS , Grimal et al 2013, Granke et al 2011, Bourgnon et al 2014. In , Grimal et al 2013) SAM images of the human femoral neck were used to study the interaction of ultrasound with cortical microstructure, porosity and thickness.…”

“…FAS velocity calculations were performed and it was observed that: (a) the FAS velocity is sensitive to cortical porosity changes, while it is not affected by cancellous bone properties and the inhomogeneous nature of the cortical bone mineralized matrix, (b) the FAS velocity decreases as the porosity increases, while it increases as the cortical thickness and pores' diameter increase. A 3D micromechanical model was developed in (Granke et al 2011) consisting of an anisotropic matrix with cylindrical pores to investigate the bone matrix and porosity. Porosity assessment using SAM was validated against Synchrotron Radiation μ-CT measurements.…”

“…It was shown that, for the aged women, the elastic properties of the mineralized matrix do not indicate large variations among different samples. Also, it was reported that alterations of the intracortical porosity reflect most of the variations of mesoscopic elasticity, at least when the analyzed cortical porosity is large (Granke et al 2011). with different sizes of pores (Potsika et al 2016a) More recently, in (Potsika et al 2016a) we presented a parametric and systematic computational study on ultrasound propagation in cortical bone models with different porosities.…”

A critical assessment of the in-vitro measurement of cortical bone stiffness with ultrasound

“…Most of the knowledge on the stiffness of cortical bone, which is an orthotropic or transverse isotropic material (Ashman et al, 1984;Rho, 1996;Orías et al, 2009;Rudy et al, 2011) has been obtained through the measurement of ultrasonic bulk wave velocity (BWV) ex vivo along different anatomical directions using cuboid specimens. Since the method was introduced to measure bone in the 1960's (Lang, 1969), and until recently, this technique has been applied to assess bone elasticity and relate it to age (Lefèvre et al, 2015), anatomical location (Orías et al, 2009;Schwartz-Dabney and Dechow, 2002) or others bone properties such as microstructure (Granke et al, 2011) and extravascular bone tissue properties (Baumann et al, 2012). …”