| Use of microscopic techniques to estimate adult age at death is well established within physical anthropology’s subfields of bioarchaeology and forensic anthropology. In order to become a more robust approach, however, the long-standing problems of the osteon population density (OPD) asymptote and high standard error of the estimate (SEE) must be overcome.;Review of the microscopic age at death estimation literature revealed that arbitrarily changing skeletal elements, histological variables, sample demographics, and sampling locations have not allowed for accurate age estimation of individuals over ∼50 years or reduced the standard error of age estimates. This investigation therefore began with substantiated theory. All healthy, mobile femurs have in common: genetic programming to establish initial size and shape; the developmental processes of endochondral ossification, appositional growth, and modeling; biomechanical and periosteal adaptation; cortical thinning and shape change during aging; mechanosensation and mechanotransduction; and bone remodeling.;Building from this theoretical knowledge base, it was first hypothesized that topographical variation in remodeling exists around human femoral midshaft periosteal cortices that reflects the constraints of normal anatomical development, customary biomechanical usage, and standard mechanobiological functioning. Second, it was hypothesized regions of interest (ROIs) associated with the Imin second moment of area would exhibit the lowest remodeling as a result of minimal biomechanical loading. Third, it was hypothesized remodeling at biomechanical ROIs would be histomorphometrically more consistent than at anatomical ROIs due to femoral functional constraints related to obligate striding bipedalism.;These hypotheses were tested by counting remodeling events at eight standardized periosteal ROIs [four anatomical—A (anterior), P (posterior), M (medial), L (lateral)—and four biomechanical—ImaxAnt, I maxPost, IminMed, and IminLat] of 200 adult femoral midshaft cross-sections originally harvested by M.F. Ericksen from George Washington University dissecting room cadavers.;While no evidence was found for reduced remodeling at Imin ROIs or for more consistent remodeling at biomechanical ROIs, 14 statistically significant differences were found between ROI OPD medians indicating topographical variation in remodeling exists around the femoral midshaft. Specifically, the lowest OPDs occurred at the Anterior ROI, followed by the Posterior, I minMed, ImaxPost, ImaxAnt, IminLat, Medial, and Lateral ROIs.;Additionally, although the anterior femoral cortex has traditionally been sampled for microscopic age at death estimation, here, the Anterior ROI was found to reach the OPD asymptote at approximately 50 years of age and was associated with the highest SEE. Alternatively, the Posterior ROI, the location possessing the second lowest median OPD value, was found to be associated with the lowest SEE and showed no sign of having reached the OPD asymptote. It is therefore suggested bioarchaeologists and forensic anthropologists utilize the Posterior ROI for production of the most accurate and precise microscopic age at death estimates from adult human skeletal remains. |
