Cross-sectional Geometry Properties Research Articles

Biomechanical Evaluation on the Bilateral Asymmetry of Complete Humeral Diaphysis in Chinese Archaeological Populations

Diaphyseal cross-sectional geometry (CSG) is an effective indicator of humeral bilateral asymmetry. However, previous studies primarily focused on CSG properties from limited locations to represent the overall bilateral biomechanical performance of humeral diaphysis. In this study, the complete humeral diaphyses of 40 pairs of humeri from three Chinese archaeological populations were scanned using high-resolution micro-CT, and their biomechanical asymmetries were quantified by morphometric mapping. Patterns of humeral asymmetry were compared between sub-groups defined by sex and population, and the representativeness of torsional rigidity asymmetry at the 35% and 50% cross-sections (J35 and J50 asymmetry) was testified. Inter-group differences were observed on the mean morphometric maps, but were not statistically significant. Analogous distribution patterns of highly asymmetrical regions, which correspond to major muscle attachments, were observed across nearly all the sexes and populations. The diaphyseal regions with high variability of bilateral asymmetry tended to present a low asymmetrical level. The J35 and J50 asymmetry were related to the overall humeral asymmetry, but the correlation was moderate and they could not reflect localized asymmetrical features across the diaphysis. This study suggests that the overall asymmetry pattern of humeral diaphysis is more complicated than previously revealed by individual sections.

Ontogenetic changes in femoral cross‐sectional geometry during childhood locomotor development

The femur is a major weight-bearing bone that is variably loaded throughout growth as children transition through locomotory states prior to the attainment of a mature bipedal gait. Here, we document ontogenetic trends in femoral cross-sectional geometry (CSG) and explore how changes in loading regime may impact the structural arrangement of cortical bone along the length of the developing diaphysis. Micro-CT scans of 110 immature femora were generated from a documented archaeological sample ranging in age from birth to 8.5 years old. CSG properties indicative of relative bone strength and bending rigidity were analyzed from cross-sections extracted at 35%, 50% and 65% of total intermetaphyseal length. Infants experience a marked redistribution of cortical bone between birth and 7 months facilitating a more advantageous mechanical structure for early load bearing behaviors as bone is displaced further from the section centroid. Early walkers are characterized by a mediolaterally reinforced cross-section that becomes more circular as gait continues to develop. During ontogeny the femur undergoes distinct morphological phases, which correspond with changes in loading regime. This study illustrates the importance of loading conditions in shaping immature bone morphology. Nonmechanical factors such as changes in hormonal environmental can also impact on this dynamic.

Sampling Bias in the Trend of Post‐Pleistocene Gracilization: How Terrain Affects Lower Limb Robusticity

Many studies have documented a decrease in modern human lower limb measures of cross‐sectional geometry (CSG) throughout the Pleistocene and Holocene. These decreases are often associated with subsistence changes and technology that allowed for a more sedentary lifestyle (e.g., rise of agriculture). Italian Neolithic samples (19‐4 ka) deviate from this trend, with measures similar to earlier, highly mobile populations (Marchi, 2008; Marchi et al., 2011) despite an overall trend for reduced robusticity through Holocene Europe as a whole (Holt et al., 2018). Active populations with a lifetime of mobility on rough terrain have been shown to have higher cortical thickness and CSG properties that resist bending and torsion in the anterior‐posterior plane – which would not fit within the traditional paradigm. Here, we evaluate changes in femoral and tibial midshaft CSG measures of robusticity. These include maximum and minimum second moments of area (Imax/Imin), second moments of area in the x and y plane (Ix/Iy), polar moment of area (J), and cortical area (CA) for populations in Europe, Africa, and Asia (N = 440) throughout the past 40,000 years (Early Upper Paleolithic, Late Upper Paleolithic, Holocene) using ANOVA and linear interaction models. Generally, Early and Late Upper Paleolithic groups show no significant differences, but Early Upper Paleolithic and Holocene groups were significantly different in all femoral measures, and Late Upper Paleolithic and Holocene groups were significantly different in all measures except Ix/Iy. Linear models showed no significant effect of elevation on CSP or any interaction effects except in femoral CA (Early Upper Paleolithic, p = 0.02; Late Upper Paleolithic, p = 0.03; Holocene, p = 0.01). A paradigm of gracilization throughout time is not supported in Asian populations when they are compared within regions. Reduced robusticity in Holocene Andaman Islanders as compared to Japanese/Vietnamese samples suggest that lower limb robusticity can increase because of activities on mountainous terrain, subverting the traditional paradigm. This suggests that we cannot assume that all populations experienced a reduction in robusticity into the Holocene and we must be aware of the danger of a sampling bias in our work.Support or Funding InformationThis research was supported by Sigma Xi, NSF BCS‐0314002, and the American Museum of Natural HistoryThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Diaphyseal cross-sectional geometry of the metatarsal bones in the Jomon population.

This study aimed to investigate differences in the diaphyseal cross-sectional geometry (CSG) of the metatarsal bones (MTs) between two populations with different habitual activities: the Jomon hunter-gatherers and modern Japanese people. We evaluated the first through fifth MTs of 117 skeleton samples: 59 (33 men and 26 women) were obtained from Late and Final Jomon period archeological sites and 58 (31 men and 27 women) were from modern Japanese people. CSG properties were calculated at the mid-shaft of the MTs and the relative values of the polar section modulus (Zp ) of each second-to-fifth MTs to first MTs were calculated. These variables were compared according to population and sex. Many of the CSG properties of MTs, except first MTs, were higher in the Jomon population than in the modern Japanese population for both sexes. Additionally, the relative values of the Zp of the MTs were higher in Jomon men and women than in modern Japanese men and women. Moreover, the Jomon population had sex-based differences in the ratio of the shape of third MTs and fourth MTs and the relative MTs value. Jomon women had elliptical third MTs and fourth MTs, and the relative Zp values of the third-to-fifth MTs to first MTs were higher in Jomon women than in Jomon men. Our result suggests that the habitual activity of the Jomon population placed heavy loads on the forefoot. This finding possibly relates to mediolateral forefoot loading that appears to be related to traversing uneven terrain.

Declining tibial curvature parallels ∼6150 years of decreasing mobility in Central European agriculturalists.

Long bones respond to mechanical loading through functional adaptation in a suite of morphological characteristics that together ensure structural competence to in vivo loading. As such, adult bone structure is often used to make inferences about past behavior from archaeological remains. However, such biomechanical approaches often investigate change in just one aspect of morphology, typically cross-sectional morphology or trabecular structure. The relationship between longitudinal bone curvature and mobility patterns is less well understood, particularly in the tibia, and it is unknown how tibial curvature and diaphyseal cross-sectional geometry interact to meet the structural requirements of loading. This study examines tibial curvature and its relationship with diaphyseal cross-sectional geometry (CSG) and body size in preindustrial Central Europeans spanning ∼6150 years following the introduction of agriculture in the region. Anteroposterior centroid displacement from the proximo-distal longitudinal axis was quantified at nine diaphyseal section locations (collectively representative of diaphyseal curvature) in 216 tibial three-dimensional laser scans. Results documented significant and corresponding temporal declines in midshaft centroid displacement and CSG properties. Significant correlations were found between mid-diaphyseal centroid displacement and all mobility-related CSG properties, while the relationship weakened toward the diaphyseal ends. No significant relationship was found between centroid displacement and body size variables with the exception of the most distal section location. Results support a relationship between tibial curvature and cross-sectional geometry among prehistoric Central European agricultural populations, and suggest that changes in mechanical loading may have influenced a suite of morphological features related to bone adaptation in the lower limb.