Percent intracortical porosity as a means of estimating age of older individuals
Downs, Alyssa Marie
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Age-at-death estimation in older adults is complicated because current techniques fail to capture an older individual’s age-at-death in a narrow enough range. This study aimed to test the relationship between osteoporotic change and age-at-death in the form of intracortical porosity. It was hypothesized that as individuals age, osteoporotic processes increase resulting in a higher percentage of intracortical porosity that may correlate with particular age cohorts. Forty ribs were analyzed, ranging in age from 15 to 84. Ribs sections were digitized using a 40X objective on a Nikon E600 microscope equipped with a motorized stage and a Turboscan montaging system (Objective Imaging Inc., UK). Images were made binary using image ImageJ 2.0. Nine measurements and calculations as described by the Agnew and Stout (2012) method were used: total subperiosteal area, endosteal area, cortical area, percent cortical area (%C/T), porosity area, percent porosity area, absolute cortical area, percent absolute cortical area (%CA/T), and the difference between %C/T and %CA/T. The ranges and mean values for intracortical porosity across the sample were calculated. The effect of intracortical porosity on measures of cortical area were interpreted using a calculation of the difference between %C/T and %CA/T. A Two Sample Independent T-Test was performed to see if there was a significant difference between sexes. Regression analyses were conducted to assess correlations between the traits and age-at-death. No significant difference was found between sexes in regards to intracortical porosity or the difference between %C/T and %CA/T. The mean intracortical porosity was found to be 15.30. The mean value of the difference was found to be 6.95%. Measures of intracortical porosity varied from 0.74% - 31.67% while measures of the effect of intracortical porosity varied from 0.32% - 17.85%. No correlation was found between either trait and age-at-death. There are a number of reasons intracortical porosity might not be correlated with an individual’s age-at-death including (1) processes that influence intracortical porosity, (2) hormonal changes, (3) the current understanding of the relationship between aging and bone cell functions. One should still account for intracortical porosity when conducting histomorphometric analyses, as failure to consider it would result in miscalculations.