Trabecular Microarchitecture of Hominoid Thoracic Vertebrae

Abstract

Spontaneous vertebral fractures are a common occurrence in modern humans, yet these fractures are not documented in other hominoids. Differences in vertebral bone strength between humans and apes associated with trabecular bone microarchitecture may contribute to differences in fracture incidence. We used microcomputed tomography to examine trabecular bone microarchitecture in the T8 vertebra of extant young adult hominoids. Scaled volumes of interest from the anterior vertebral body were analyzed at a resolution of 46 lm, and bone volume fraction, trabecular thickness, trabecular number, trabecular separation, structure model index, and degree of anisotropy were compared among species. As body mass increased, so did trabecular thickness, but bone volume fraction, structure model index, and degree of anisotropy were independent of body mass. Bone volume fraction was not significantly different between the species. Degree of anisotropy was not significantly different among the species, suggesting similarity of loading patterns in the T8 vertebra due to similar anatomical and postural relationships within each species' spine. Degree of anisotropy was negatively correlated with bone volume fraction (r 2 ¼ 0.85, P < 0.05) in humans, whereas the apes demonstrated no such relationship. This suggested that less dense human trabecular bone was more preferentially aligned to habitual loading. Furthermore, we theorize that trabeculae in ape thoracic vertebrae would not be expected to become preferentially aligned if bone volume fraction was decreased. The differing relationship between bone volume fraction and degree of anisotropy in humans and apes may cause less dense human bone to be more fragile than less dense ape bone. Anat Rec, 292:1098Rec, 292: -1106Rec, 292: , 2009. V V C 2009 Wiley-Liss, Inc.

The Effect of the Achilles Tendon on Trabecular Structure in the Primate Calcaneus

“…4). Although these data are consistent with other findings that apes tend to have thicker cortical bone than humans (Cotter et al, 2009), they are unexpected if tensile forces produced by the Achilles were influencing cortical thickness. Along these same lines, we do find one aspect of our negative results as potentially illuminating and worthy of further consideration.…”

Lumbar Vertebral Body Bone Microstructural Scaling in Small to Medium‐Sized Strepsirhines

“…To begin with, the body size range of the sample appears to impact the scaling relationship of Tb.Th when the results reported here are compared with those for hominoids and mammals. Femoral, humeral, and vertebral trabecular thicknesses consistently scale with negative allometry in broad samplings of nonvolant mammals and in hominoids (Swartz et al, 1998;Cotter et al, 2009;Doube et al, 2011). But in those studies the specimen samples included species with body masses much greater than the strepsirhine species sampled here.…”

“…At present, reconciling these strepsirhine lumbar vertebral body data with other comparative and scaling studies is challenging. Studies vary in trabecular morphometric approaches (three-dimensional direct transformation, two-dimensional plate model, and twodimensional direct measures), taxonomic samples, target bones, the size variable used to determine allometric equations (femoral head radius, estimated body mass from skeletal dimensions, and published species body mass averages) and scaling results (Mullender et al, 1996;Swartz et al, 1998;Fajardo and Mü ller, 2001;MacLatchy and Mü ller, 2002;Ryan and Ketcham, 2002;Fajardo et al, 2007b;Cotter et al, 2009;Ryan and Walker, 2010;Doube et al, 2011). The few studies that have investigated comparative strepsirhine trabecular bone architecture have not assessed the scaling relationships quantitatively.…”

“…Several studies of the primate proximal femur (MacLatchy and Mü ller, 2002;Ryan and Ketcham, 2002;Fajardo et al, 2007;Ryan and Walker, 2010), sampling from different sites therein, and with different approaches, reported invariance of Tb.Th and other parameters with body mass. Recently, Cotter et al (2009) reported trabecular bone scaling relationships for the eighth thoracic vertebra. They did not directly categorize their results as isometry, positive, or negative allometry, but based on the isometry predictions presented here, those data suggest that Tb.Th scales with negative allometry and Tb.N scales with positive allometry.…”

Gracility of the modernHomo sapiensskeleton is the result of decreased biomechanical loading

“…The etiology of this relative gracility remains uncertain, and this uncertainty hinders the development of strategies for mitigating fracture risk and morbidity. The progressive gracilization of the Homo postcranial skeleton was originally detected in cortical bone structure (1, 2), but has now been demonstrated in the trabecular bone microstructure of joints (12,14,(16)(17)(18)(19), where osteoporotic fracture risk is highest (20). Most notably, in an analysis of thoracic vertebral bodies, Cotter et al (12) found that young adult humans have significantly lower trabecular bone volume fraction (BV/TV) and thinner vertebral shells than similarly sized apes.…”