Functional plasticity of the human humerus: Shape, rigidity, and muscular entheses

Abstract

The relationship between the mechanical loading undergone by a bone and its form has been widely assumed as a premise in studies aiming to reconstruct behavioral patterns from skeletal remains. Nevertheless, this relationship is complex due to the existence of many factors affecting bone structure and form, and further research combining structural and shape characteristics is needed. Using two-block PLS, which is a test to analyze the covariance between two sets of variables, we aim to investigate the relationship between upper-limb entheseal changes, cross-sectional properties, and contour shape of the humeral diaphysis. Our results show that individuals with strongly marked entheseal changes have increased diaphyseal rigidities. Bending rigidities are mainly related to entheseal changes of muscles that cross the shoulder. Moreover, the entheseal changes of muscles that participate in the rotation of the arm are related to mediolaterally flatter and ventrodorsally broader humeral shapes in the mid-proximal diaphysis. In turn, this diaphyseal shape is related to diaphyseal rigidity, especially to bending loadings. The shape of the diaphysis of the rest of the humerus does not covary either with rigidity or with entheseal changes. The results indicate that large muscular scars, such as those found in the mid-proximal diaphyses, seem to be related to diaphyseal shape, whereas this relationship is not seen for areas with less direct influences of powerful muscles.

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

“…The studies of Eshed et al () and Villotte and Knüsel () are based on the interpretation of enthesial changes. The interpretation of these features is controversial (Zumwalt, ; Villotte et al, ; Milella et al, ; Niinimäki, ; Ibáñez‐Gimeno et al, ; Djukic et al, ; Tatara et al, ; Thomas, ; Milella et al ; Rabey et al ). However, as no consensus has yet been reached about the informative value of enthesial changes, we accept the interpretations of Eshed et al () and Villotte and Knüsel () as valid proxies of the major activities in Neolithic times, especially because they are also supported by the archeological record (Gerling, ), and the biomechanical evaluations of humeri of Neolithic populations (Macintosh et al, ).…”

Postcranial morphological variation between hunter‐gatherers and horticulturalists from the lower Paraná River Delta, Argentina

“…Entheseal changes were found to positively correlate with structural properties of long bones in other studies (Ibáñez‐Gimeno et al, ; Mazza, ; Michopoulou, Nikita, & Henderson, ; Niinimäki & Baiges Sotos, ; Weiss, ) and there is a global trend to observe postcranial morphological differences between societies with different subsistence practices. Therefore, statistically significant differences in humeral and femoral structural properties between hunter‐gatherers and Guaraní individuals are expected to be found upon controlling for body size.…”

Taxonomic identification of Lower Pleistocene fossil hominins based on distal humeral diaphyseal cross-sectional shape

“…Although long bone cross-sectional properties are known to be responsive to mechanical loadings during life ( Ruff, Holt & Trinkaus, 2006 ; Ruff, 2009 ), the extent to which distal humeral diaphyseal shape responds to habitual limb use (or is phylogenetically constrained) is unclear. Strongly marked entheseal changes associated with muscles that cross the shoulder have been correlated with differences in humeral diaphyseal shape (and diaphyseal rigidity) in the mid-proximal region, though a similar phenomenon has not been observed in the distal diaphysis ( Ibáñez-Gimeno et al, 2013 ). It may be the case that distal diaphyseal shape is largely unaffected by age-related or activity-related variation in cross-sectional properties.…”