Age-dependent change and intraskeletal variability in secondary osteons of elderly Australians

Abstract

There is a need to fully understand intra-skeletal variability within different populations to develop and improve age-at-death estimation methods. This study evaluates age-related histomorphometric changes in three different bones intra-individually in a modern Australian sample. Four female and 13 male elderly Australian adult donors (67-93 years) were examined for osteon population density (OPD), osteon area (On.Ar), and Haversian canal area (H.Ar) of secondary osteons to compare between femora, ribs, and humeri and assess against age. In the pooled sex sample, no statistically significant correlations were observed between age and each histological variable. In the males, OPD of the femur increased significantly with age, as did porosity in the rib. In the male humeri, OPD increased moderately with age, while H.Ar was decreased moderately with age. Intra-bone comparisons showed that males had significantly higher osteon counts in their ribs compared to their femora, while their ribs showed statistically significantly less porosity than their humeri. When bone size was accounted for, by adjusting the femur and humerus histology data by robusticity indices, histology values were found to be similar between bones within the same individual. This is despite the upper and lower limbs receiving different ranges and types of biomechanical load. Our findings demonstrate that bone size influences histomorphometry, and this could confound age-at-death estimations that have not been adjusted for robusticity. Future studies would benefit from examining bone histomorphometry within a larger sample size and incorporating bone robusticity measures into histology analyses.

Keywords: age‐related histomorphometry; intra‐skeletal variation; osteon; remodelling; robusticity index.

FIGURE 1

Midshaft sample locations from right bone. The samples incorporated the linea aspera (a) on femora and the deltoid tuberosity of the humerus (b).

FIGURE 2

Selection of the regions of interest (ROI). Six ROIs were selected in the sub‐periosteal layer of intracortical bone for the anterior midshaft of the humerus, posterior midshaft of the femur, and rib mid‐shaft (bones not to scale and position of ROIs are approximate).

FIGURE 3

Examples of histomorphometric features recorded on each ROI in this study: (a) count of intact osteons (red dot), fragmentary osteons (green cross), resorption cavity (yellow circle); osteons cut off by the image border were not counted if it could not be determined if they were intact or fragmentary (opaque blue); (b) Haversian canal area measurements (μm²) (red circles) (black dots are artefacts of sample processing); (c) intact osteon area measurement (μm²) (red circles).

FIGURE 4

Scatter plot with line of best fit illustrating the moderate positive relationship between age and Haversian canal size of the rib within the pooled sex group.

FIGURE 5

Examples of the four best correlations with age within the male sample: statistically significant positive relationships (bold‐faced) with OPD of the femur (a) and Haversian canal area of the rib (b); moderate positive correlation with humerus OPD (c), and moderate negative correlation with humerus Haversian canal size (d).