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Abstract ObjectivesVariation in trabecular and cortical bone properties is often used to infer habitual behavior in the past. However, the structures of both types of bone are rarely considered together and may even contradict each other in functional interpretations. We examine trabecular and cortical bone properties in various athletes and sedentary controls to clarify the associations between combinations of cortical and trabecular bone properties and various loading modalities. Materials and methodsWe compare trabecular and cortical bone properties using peripheral quantitative computed tomography scans of the tibia between groups of 83 male athletes (running, hockey, swimming, cricket) and sedentary controls using Bayesian multilevel models. We quantify midshaft cortical bone rigidity and area (J, CA), midshaft shape index (Imax/Imin), and mean trabecular bone mineral density (BMD) in the distal tibia. ResultsAll groups show unique combinations of biomechanical properties. Cortical bone rigidity is high in sports that involve impact loading (cricket, running, hockey) and low in nonimpact loaded swimmers and controls. Runners have more anteroposteriorly elliptical midshafts compared to other groups. Interestingly, all athletes have greater trabecular BMD compared to controls, but do not differ credibly among each other. DiscussionResults suggest that cortical midshaft hypertrophy is associated with impact loading while trabecular BMD is positively associated with both impact and nonimpact loading. Midshaft shape is associated with directionality of loading. Individuals from the different categories overlap substantially, but group means differ credibly, suggesting that nuanced group‐level inferences of habitual behavior are possible when combinations of trabecular and cortical bone are analyzed. 

Abstract ObjectivesVariation in human trabecular bone morphology can be linked to habitual behavior, but it is difficult to investigate in vivo due to the radiation required at high resolution. Consequently, functional interpretations of trabecular morphology remain inferential. Here we introduce a method to link low‐ and high‐resolution CT data from dry and fresh bone, enabling bone functional adaptation to be studied in vivo and results compared to the fossil and archaeological record. Materials and methodsWe examine 51 human dry bone distal tibiae from Nile Valley and UK and two pig tibiae containing soft tissues. We compare low‐resolution peripheral quantitative computed tomography (pQCT) parameters and high‐resolution micro CT (μCT) in homologous single slices at 4% bone length and compare results to our novel Bone Ratio Predictor (BRP) method. ResultsRegression slopes between linear attenuation coefficients of low‐resolution pQCT images and bone area/total area (BA/TA) of high‐resolution μCT scans differ substantially between geographical subsamples, presumably due to diagenesis. BRP accurately predicts BA/TA (R²= .97) and eliminates the geographic clustering. BRP accurately estimates BA/TA in pigs containing soft tissues (R²= 0.98) without requiring knowledge of true density or phantom calibration of the scans. DiscussionBRP allows automated comparison of image data from different image modalities (pQCT, μCT) using different energy settings, in archeological bone and wet specimens. The method enables low‐resolution data generated in vivo to be compared with the fossil and archaeological record. Such experimental approaches would substantially improve behavioral inferences based on trabecular bone microstructure. 

Abstract ObjectiveThis project investigates trabecular bone structural variation in the proximal humerus and femur of hunter‐gatherer, mixed‐strategy agricultural, medieval, and human groups to address three questions: (a) What is the extent of trabecular bone structural variation in the humerus and femur between populations with different inferred activity levels? (b) How does variation in the proximal humerus relate to variation in the proximal femur? (c) Are trabecular bone microstructural variables sexually dimorphic? MethodsThe proximal humerus and femur of 73 adults from five human groups with distinct subsistence strategies were scanned using a micro‐computed tomography system. Centralized volumes of interest within the humeral and femoral heads were extracted and analyzed to quantify bone volume fraction, trabecular thickness, trabecular separation, connectivity density, degree of anisotropy, and bone surface density. ResultsIn the humerus and femur, groups with the highest inferred activity levels have higher bone volume fraction and trabecular thickness, and lower bone surface density than those with lower inferred activity levels. However, the humeral pattern does not exactly mirror that of the femur, which demonstrates a steeper gradient of difference between subsistence groups. No significant differences were identified in trabecular separation. No consistent patterns of sexual dimorphism were present in the humerus or femur. ConclusionsReduced skeletal robusticity of proximal humeral and femoral trabecular bone corresponds with reduced activity level inferred from subsistence strategy. However, human trabecular bone structural variation is complex and future work should explore how other factors (diet, climate, genetics, disease load, etc.), in addition to activity, influence bone structural variation.