Are Distributions of Secondary Osteon Variants Useful for Interpreting Load History in Mammalian Bones?

Abstract

Background/Aims: In cortical bone, basic multicellular units (BMUs) produce secondary osteons that mediate adaptations, including variations in their population densities and cross-sectional areas. Additional important BMU-related adaptations might include atypical secondary osteon morphologies (zoned, connected, drifting, elongated, multiple canal). These variants often reflect osteonal branching that enhances toughness by increasing interfacial (cement line) complexity. If these characteristics correlate with strain mode/magnitude-related parameters of habitual loading, then BMUs might produce adaptive differences in unexpected ways. Methods: We carried out examinations in bones loaded in habitual torsion (horse metacarpals) or bending: sheep, deer, elk, and horse calcanei, and horse radii. Atypical osteons were quantified in backscattered images from anterior, posterior, medial, and lateral cortices. Correlations were determined between atypical osteon densities, densities of all secondary osteons, and associations with habitual strain mode/magnitude or transcortical location. Results: Osteon variants were not consistently associated with ‘tension’, ‘compression’, or neutral axis (‘shear’) regions, even when considering densities or all secondary osteons, or only osteon variants associated with relatively increased interfacial complexity. Similarly, marrow- and strain-magnitude-related associations were not consistent. Conclusion: These data do not support the hypothesis that spatial variations in these osteon variants are useful for inferring a habitual bending or torsional load strain history.

Remodeling in bone without osteocytes: Billfish challenge bone structure–function paradigms

“…This porosity is at least twice that of mammalian compact bone, even considering the contribution of the lacunar-canalicular system (28,30). The differences in canal size and density between billfish and mammalian bone result in canal networks with fundamentally different topographies, as illustrated by volume renderings of the canal systems from microcomputed tomography scans of small cubes of billfish bone and of equine cortical bone (Fig.…”

“…Despite gross shape similarity between osteocytic and anosteocytic osteons, from a histomorphometric perspective, billfish osteons are strikingly different from those of mammals (27,28), having a spatial density that is effectively an order of magnitude higher (ranging between 150 and 250 osteons/mm 2 ) and being ∼50-90% smaller (typically less than 110 μm wide, with areas 0.004-0.021 mm 2 ) (Figs. 2, 3 A-D, and 4A).…”

Understanding Entheses: Bridging the Gap Between Clinical and Anthropological Perspectives

“…Second, dense concentrations of smaller osteons will absorb energy more efficiently than larger ones as the effects resulting from accumulated microdamage are reduced, with cement lines serving to limit crack propagation (Sobelman et al, 2004;O'Brien et al, 2005). Third, smaller osteons in regions of high strain may enhance the resistance towards osteon pullout or debonding of the osteon along the cement line surface (Skedros et al, 2007).…”

Characterization of the Spatial Arrangement of Secondary Osteons in the Diaphysis of Equine and Canine Long Bones

“…A second class of osteons is that of ''atypical'' osteons, which include osteons with a noncentrally located canal, with a strongly elongated canal or even including more than one canal. Investigations on horse radii and metacarpals amongst other bones could not demonstrate a consistent relation between the frequency of atypical osteons and the loading mode (compression, tension, shear) of the bone (Skedros et al, 2007). A promising approach to connect loading and osteon morphology is the use of circularly polarized light images, which gives information about the predominant collagen fiber orientation (Skedros et al, 2009).…”

“…The osteonal arrangement in different anatomical locations in two different types of bones in horses (radii, third metacarpals) and one type of bone in dogs (radii) were analyzed. These bones are often selected for structural analysis as they represent two different loading types: the radius is loaded habitually in bending while the third metacarpal bone of horses is loaded mostly in torsion (Skedros et al, 2006;Skedros et al, 2007). With this analysis, anatomical locations with higher/lower osteonal order within specific bones could be identified.…”