A repeatable geometric morphometric approach to the analysis of hand entheseal three-dimensional form.

OBJECTIVES: The purpose of this study was to put forth a precise landmark-based technique for reconstructing the three-dimensional shape of human entheseal surfaces, to investigate whether the shape of human entheses is related to their size. The effects of age-at-death and bone length on entheseal shapes were also assessed. MATERIALS AND METHODS: The sample comprised high-definition three-dimensional models of three right hand entheseal surfaces, which correspond to 45 male adult individuals of known age. For each enthesis, a particular landmark configuration was introduced, whose precision was tested both within and between observers. The effect of three-dimensional size, age-at-death, and bone length on shape was investigated through shape regression. RESULTS: The method presented high intra-observer and inter-observer repeatability. All entheses showed significant allometry, with the area of opponens pollicis demonstrating the most substantial relationship. This was particularly due to variation related to its proximal elongated ridge. The effect of age-at-death and bone length on entheses was limited. DISCUSSION: The introduced methodology can set a reliable basis for further research on the factors affecting entheseal shape. Using both size and shape, variables can provide further information on entheseal variation and its biomechanical implications. The low entheseal variation by age verifies that specimens under 50 years of age are not substantially affected by age-related changes. The lack of correlation between entheseal shape and bone length or age implies that other factors may regulate entheseal surfaces. Future research should focus on multivariate shape patterns among entheses and their association with occupation.

Occupational manual activity is reflected on the patterns among hand entheses.

OBJECTIVES: In anthropological sciences, entheses are widely utilized as occupational stress markers. However, the reaction of entheseal surfaces to mechanical loading is not well understood. Furthermore, previous studies on entheses relied on the individuals' occupation-at-death. Past research by one of us has identified two patterns among hand entheses, proposing that they reflect two synergistic muscle groups. Here, we investigate the association between these patterns and habitual manual activity using an extensively documented skeletal sample and a three-dimensional system of quantification. MATERIALS AND METHODS: The hand bones utilized belong to 45 individuals from mid-19th century Basel. These were male adults (18 to 48 years old) who were not directly related, showed no manual pathological conditions, and whose occupational activities during their lifetime were clearly documented and could be evaluated according to historical sources. The patterns of entheses were explored using principal component analysis on both raw and size-adjusted variables. The influence of age-at-death, body mass, and bone length was assessed through correlation tests. RESULTS: The analysis showed that the previously proposed patterns of entheses are present in our sample. Individuals with the same or comparable occupations presented similar entheseal patterns. These results were not considerably affected by entheseal overall size, age-at-death, body mass, or bone length. DISCUSSION: Individuals involved in intense manual labor during their lifetime presented a distinctive pattern of hand entheses, consistent with the application of high grip force. By contrast, individuals with less strenuous and/or highly mechanized occupations showed an entheseal pattern related to the thumb intrinsic muscles.

Patterns of activity adaptation in humeral trabecular bone in Neolithic humans and present-day people.

OBJECTIVE: The annual turnover rate of trabecular bone by far exceeds that of cortical bone and, therefore, is very sensitive to its daily loading regime. Here we test the hypothesis that the study of the trabecular bone architecture of the human humerus is able to differentiate between different habitual manual activities. MATERIALS AND METHODS: For this purpose, we compared the trabecular architecture of the humeral head in a Neolithic population to that of a sample of contemporary Europeans using micro-computed tomography (microCT). We defined in each specimen a spherical volume of interest with a diameter of 57.5 ± 2.5% of the maximal diameter of the humeral head to metrically analyze the bulk of humeral head trabecular architecture. We subsequently quantified the trabecular architectures in the VOIs, measuring seven standard 3D-morphometric parameters, and used univariate and multivariate statistical analyses for comparisons within and between populations. RESULTS: Univariate statistical analysis showed significant differences in a combination of 3D-morphometric parameters. A principal components analysis of the 3D-morphometrics of the trabecular architectures separated the Neolithic from the contemporary samples on the basis of differences in their gross trabecular architecture, including differences in the bone volume fraction (BV/TV), the number of trabeculae per unit length (Tb N), and the distance between trabeculae (Tb Sp). DISCUSSION: We interpret the significant differences found in the humeral trabecular bone of the Neolithic and the contemporary group as likely reflecting the distinct manual working routines. The trabecular bone configuration in the Neolithic sample shows presumably functional signatures of prehistoric subsistence techniques and activity levels.

A new high-resolution computed tomography (CT) segmentation method for trabecular bone architectural analysis.

In the last decade, high-resolution computed tomography (CT) and microcomputed tomography (micro-CT) have been increasingly used in anthropological studies and as a complement to traditional histological techniques. This is due in large part to the ability of CT techniques to nondestructively extract three-dimensional representations of bone structures. Despite prior studies employing CT techniques, no completely reliable method of bone segmentation has been established. Accurate preprocessing of digital data is crucial for measurement accuracy, especially when subtle structures such as trabecular bone are investigated. The research presented here is a new, reproducible, accurate, and fully automated computerized segmentation method for high-resolution CT datasets of fossil and recent cancellous bone: the Ray Casting Algorithm (RCA). We compare this technique with commonly used methods of image thresholding (i.e., the half-maximum height protocol and the automatic, adaptive iterative thresholding procedure). While the quality of the input images is crucial for conventional image segmentation, the RCA method is robust regarding the signal to noise ratio, beam hardening, ring artifacts, and blurriness. Tests with data of extant and fossil material demonstrate the superior quality of RCA compared with conventional thresholding procedures, and emphasize the need for careful consideration of optimal CT scanning parameters.

Is Bone Elevation in Hand Muscle Attachments Associated with Biomechanical Stress? A Histological Approach to an Anthropological Question.

In anthropological sciences, muscle attachments are typically utilized for reconstructing the physical activities of past human populations. This approach relies on the concept that entheseal bone morphology is influenced by cumulative biomechanical stress. A fundamental criterion for assessing the stage of entheseal change involves the proportion of elevated bone area. However, it is not yet clear if bone elevation is associated with biomechanical forces exerted during physical activity, while the histology of the entheses of the human hand, the least-bodyweight-bearing anatomical area, is not fully investigated. Multiple previous studies on entheses have concluded that the concentration of calcified fibrocartilage reflects the level of applied forces. On this basis, if hand entheseal surface elevation was associated with the level of biomechanical stress, then a greater amount of calcified fibrocartilage would be expected in entheses' central and more projecting bone areas. More importantly, individual entheses with a greater proportion of elevated bone areas would present a higher total concentration of calcified fibrocartilage. To test these hypotheses, this pilot study conducted a histological quantitative analysis on two thumb entheses of four fully-documented body donors. Across individuals, all central entheseal regions presented greater calcified fibrocartilage, while the entheses showing additional bone elevation in their marginal areas comprised substantially higher total values. The observations of this small-scale pilot study support the concept that interindividual differences in entheseal bone morphology are related to varying levels of biomechanical loading. Furthermore, they encourage future research to compile larger sample sizes, for comparing individuals with distinct lifelong activities. Anat Rec, 302:1093-1103, 2019. © 2018 Wiley Periodicals, Inc.

Structural adaptation of trabecular bone revealed by position resolved analysis of proximal femora of different primates.

The anisotropic arrangement of trabeculae in the proximal femur of humans and primates is seen as striking evidence for the functional adaptation of trabecular bone architecture. Quantitative evidence to demonstrate this adaptation for trabecular bone is still scarce, because experimental design of controlled load change is difficult. In this work, we use the natural variation of loading caused by a different main locomotor behavior of primates. Using high-resolution computed tomography and advanced image analysis techniques, we analyze the heterogeneity of the architecture in four proximal femora of four primate species. Although the small sample number does not allow an interspecies comparison, the very differently loaded bones are well suited to search for common structural features as a result of adaptation. A cubic volume of interest of size (5 mm)(3) was moved through the proximal femur and a morphometric analysis including local anisotropy was performed on 209 positions on average. The correlation of bone volume fraction (BV/TV) with trabecular number (Tb.N) and trabecular thickness (Tb.Th) leads to the suggestion of two different mechanisms of trabecular bone adaptation. Higher values of BV/TV in highly loaded regions of the proximal femur are due to a thickening of the trabeculae, whereas Tb.N does not change. In less loaded regions, however, lower values of BV/TV are found, caused by a reduction of the number of the trabeculae, whereas Tb.Th remains constant. This reduction in Tb.N goes along with an increase in the degree of anisotropy, indicating an adaptive selection of trabeculae.

Functional Analysis of the Primate Shoulder.

Studies of the shoulder girdle are in most cases restricted to morphological comparisons and rarely aim at elucidating function in a strictly biomechanical sense. To fill this gap, we investigated the basic functional conditions that occur in the shoulder joint and shoulder girdle of primates by means of mechanics. Because most of nonhuman primate locomotion is essentially quadrupedal walking-although on very variable substrates-our analysis started with quadrupedal postures. We identified the mechanical situation at the beginning, middle, and end of the load-bearing stance phase by constructing force parallelograms in the shoulder joint and the scapulo-thoracal connection. The resulting postulates concerning muscle activities are in agreement with electromyographical data in the literature. We determined the magnitude and directions of the internal forces and explored mechanically optimal shapes of proximal humerus, scapula, and clavicula using the Finite Element Method. Next we considered mechanical functions other than quadrupedal walking, such as suspension and brachiation. Quadrupedal walking entails muscle activities and joint forces that require a long scapula, the cranial margin of which has about the same length as the axillary margin. Loading of the hand in positions above the head and suspensory behaviors lead to force flows along the axillary margin and so necessitate a scapula with an extended axillary and a shorter cranial margin. In all cases, the facies glenoidalis is nearly normal to the calculated joint forces. In anterior view, terrestrial monkeys chose a direction of the ground reaction force requiring (moderate) activity of the abductors of the shoulder joint, whereas more arboreal monkeys prefer postures that necessitate activity of the adductors of the forelimb even when walking along branches. The same adducting and retracting muscles are recruited in various forms of suspension. As a mechanical consequence, the scapula is in a more frontal, rather than parasagittal, position on the thorax. In both forms of locomotion-quadrupedal walking and suspension-the compression-resistant clavicula contributes to keeping the shoulder complex distant from the rib cage. Future studies should consider the consequences for thorax shape. The morphological specializations of all Hominoidea match the functional requirements of suspensory behavior. The knowledge of mechanical functions allows an improved interpretation of fossils beyond morphological similarity.