Age estimation on two Mediterranean samples using rib histomorphometry

Abstract

Estimation of age is a crucial step for the identification of unknown individuals. Age is commonly assessed through macroscopic analytical methods based on the gross-examination of age degenerative changes in the skeleton. The choice of the methods relies on the taphonomic condition of the human remains and/or the skeletal element that is available. In cases of very fragmented bones, microscopic techniques remain one of the few approaches to estimate age. Thus, many histological age estimation methods have been developed for different bones and on different samples in the last forty years. Numerous intrinsic and extrinsic factors influence bone remodelling rates and have shown to affect the accuracy of histological aging methods. The present study investigates rib thin-sections from two Mediterranean samples, aiming to explore the applicability and reliability of histological methods in estimating age within these samples. Standard ribs were obtained from males and females (N = 88, Mean age = 60, SD = 17.90) from two samples, Cretans (Greece) and Greek- Cypriots (Republic of Cyprus). The costal elements were processed histologically according to standard protocols and thirteen raw and composite histomorphometric parameters (frequency number of intact and fragmentary osteons, total osteons, osteon population densities – including OPD(I) and OPD(F) – cortical area, total area, endosteal area, relative cortical area, osteon area, osteon perimeter and osteon circularity) were assessed. Intra- and inter-observer errors were examined. Due to the fragmented nature of the costal elements, sampling error was calculated as a means to explore whether the histological variables vary among six different topographical locations along the rib length. A validation study was carried out by applying four existing histological age prediction equations on the entire dataset and on the sub-datasets (sex and samples separately) in order to verify whether population-specific formulae are required for the Mediterranean samples. The relationship between the histological variables and age, as well as sex and samples, was determined through several statistical tests. Lastly, simple and multiple regression analyses were performed testing all possible combinations of variables. The best models ii were finally selected according to prediction power and goodness of fit indicators. The results from intra- and inter-observer errors indicated that most of the histological parameters achieved high levels of repeatability. The preliminary outcome from the sampling error pilot study suggested low variability among the six thin-sections from each rib. According to the validation study, three of the four age prediction equations resulted in high underestimation of age, indicating that population-specific formulae are needed to provide more accurate age estimates. Most of the histological variables showed a statistically significant correlation with age with some differences observed by sex and by sample. Forty-one models were generated concluding that osteon densities along with rib and osteon measurements formulae produced the most accurate results. The best model generated from the entire dataset included OPD and osteon circularity with a standard error of the estimate of 10.45 years. When sex and samples were separated, the best model selected included OPD and osteon perimeter producing a standard error of the estimate of 8 years for Cypriots. This research demonstrates that quantitative bone histology is a feasible method to estimate age on the Mediterranean samples obtaining errors rates that are in accordance with macroscopic ageing techniques. Inter-population variation in remodeling rates is suggested; however, the inclusion of other bones presenting different remodelling dynamics (such as femora) is recommended to further explore this hypothesis. This study contributes to the creation of population-specific standards for Cretans and Cypriots.