Osteon interfacial strength and histomorphometry of equine cortical bone

Abstract

The interfacial strength of secondary osteons from the diaphysis of the Thoroughbred equine third metacarpal was evaluated using the fiber pushout test. The pushout was performed on 300-500 microm sections of 4x4x15 mm bone blocks machined from four anatomic regions of the cortex. Pushout strength was evaluated from proximal to distal location within the diaphysis on four osteon types classified under polarized light on adjacent histologic sections from each block. The shear strength of the interfaces were estimated from shear lag theory. Differences were found in the interfacial strength of osteons based on appearance under polarized light with bright field having the highest interfacial strength (40.3 MPa). The lowest strength was found in the dark field osteons (22.8 MPa). The dorsal region had the highest shear strength and toughness compared to all other regions. The cement line and interlamellar interfaces are similar in strength, but exhibit regional dependence--specifically, the palmar region strength is less (17.5 MPa) than the osteon interlamellar interfaces (30.4 MPa) and osteon type dependent (alternating significantly weaker than other types). Histomorphometry revealed significant regional differences (p<0.0001) in osteon area fraction among the four osteon types as well as differences in the osteon diameter (p=0.01), with dorsal regions having larger osteons (170 microm) than the palmar region (151 microm). Fatigue life and fracture toughness of Haversian bone are reported in the literature to be regionally dependent and are known to be associated with osteon pullout--an osteon interfacial phenomenon. Therefore, the results presented in this study are important to further the understanding of the mechanisms of fragility and damage accumulation in cortical bone.

Cortical bone histomorphology of known‐age skeletons from the Kirsten collection, Stellenbosch university, South Africa

“…Variables such as collagen fiber orientation, osteon shape, and intra‐cortical porosity (i.e. resorption spaces and Haversian canals) have all been linked to the mechanical competency of bone tissue (Sevostianov and Kachanov, 2000; Goldman et al, 2003, 2014; Bigley et al, 2006; Skedros et al, 2013, 2007). Counts and measurements along with regionally‐specific concentrations of microstructural features may reflect different adaptations to bone strain (Rose et al, 2012).…”

A review on recent advances in numerical modelling of bone cutting

“…The cortical bone can be properly modelled as a rate dependent transversely isotropic material (Reilly and Burstein, 1975;Yoon and Katz, 1976) thus this tissue can be considered analogous to a fiber reinforced composite material as has been demonstrated in different contributions in the literature; see for instance Guo et al (1998), Hogan (1992), Katz et al (1984), and Bigley et al (2006).…”

The influence of anisotropy in numerical modeling of orthogonal cutting of cortical bone

“…This means that the assumption of mechanically isotropic bone tissue is a strong simplification of the problem. The cortical bone can be properly modelled as a rate dependent transversely isotropic material [33,34], thus the cortical bone tissue can be considered analogous to a fibre reinforced composite material [35][36][37][38]. Based on this analogy, the osteon acts as the fibre with the matrix being interstitial bone consisting of old osteon fragments.…”