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>Histomorphometry of humeral primary bone: Evaluating the endosteal lamellar pocket as an indicator of modeling drift in archaeological and modern skeletal samples.
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Histomorphometry of humeral primary bone: Evaluating the endosteal lamellar pocket as an indicator of modeling drift in archaeological and modern skeletal samples.
During skeletal growth, long bones must change in size, shape, and relative position. This is accomplished diametrically by a process called bone modeling, which has been evidenced microscopically by patterned remnants of periosteal and endosteal bone distributions. It is the asymmetry of these distributions, or modeling drift, that accomplishes morphological change in the diaphysis. Until now, human modeling drift histomorphometry has received little attention. Previous research demonstrated a collection of specific histomorphological features could be used as a meta-feature, indicating the microscopic remnants of drift. This meta-feature, the endosteal lamellar pocket (ELP), is characterized by hemicircumferential lamellar orientation, primary Volkmann’s canals, and a relative decrease in the number of osteons compared to surrounding internal tissues. The current study provides a novel tissue level perspective, assessing human skeletal variation via quantification of ELP presence, position, and morphology in the humerus in order to discuss drift among individuals. Two distinct skeletal populations are compared: one archaeological, and the other, a modern control sample with known age and sex. Mid-diaphyseal, thin ground cross-sections are analyzed using custom point-count and hand-drawn techniques. Results provide: 1) an evaluation of the use of endosteal tissue, specifically the ELP, as a summary of drift; 2) an comparative assessment of the two methods used in the analysis; 3) a comparison between the position of Imax, as an indicator of adaptation to mechanical loading, with the drift direction suggested by the position of the ELP; and 4) a baseline for variance in ELP characteristics against the background of periosteal and secondary bone distributions by region across subgroups generated by sex, age category, and population sample. Results indicate the ELP is a viable means of measuring and comparing modeling drift among subgroups. Both techniques work well under differing circumstances due to their individual strengths and weaknesses. The point-count technique, accomplished in a starburst pattern, is greatly aided by the use of a custom data-entry program for tracking multiple variables and becomes competitive with hand-drawn line assessments of ELP position when combined with frequency weighted vector analysis. However, for more simple studies interested in only primary ELP position and ara data, hand-drawn techniques are much more rapid. Important variance was found in the tissue distributions among subcroups, including females having significantly more primary tissue overall even when their lower Haversian area is taken into account. Modern individuals displayed more sexual dimorphism in drift than did individuals from an archaeological context. Finally, drift in the humerus was dependably posterio-medial in direction and significantly more laterally oriented than Imax. These data have far reaching implications. Completely new variables have been generated for the structured analysis of important variation in skeletal population samples, but also the importance of taking relative tissue-age-at-formation into account becomes clear in this study. Efforts to account for drift in other applications such as those measuring, targeted remodeling, osteon type distributions, age-estimation, or stable isotopes could benefit significantly by comparing only tissues of equal ages or by applying an accurate correction factor for the given element’s local tissue-age variability.
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