Analysis of histomorphometric variables: Proposal and validation of osteon definitions.

Histological analysis of bone tissue has been used to explore a variety of questions relating to age-at-death, habitual behaviors, health, and nutritional stress. Identification of intact and fragmentary osteons is of key interest to many researchers in these studies, yet the definitions of these features vary between researchers making cross-study comparisons problematic. Furthermore, histological variable definitions are often ambiguous or require subjective classifications by the observer. As a result, and as indicated by previous studies, observer error and misclassification of certain variables, namely intact and fragmentary osteons, can be significant. This study proposes new definitions for intact and fragmentary osteons that are designed to limit observer subjectivity and also explore efficacy of combining osteon types into one variable. A sample of 30 6th rib cross-sections from a modern forensic population was used to test the validity of the proposed definitions. Observations of intact osteon population density (OPD(I)) and fragmentary osteon population density (OPD(F)) were made by three observers for each cross-section. These observations were used to explore the interobserver error associated with the proposed definitions and determine if combining variables into one variable (OPD) mitigates persisting classification difficulties. Results indicate that the proposed definitions significantly reduce interobserver error and misclassification of intact and fragmentary osteons. However, the interobserver error associated with fragmentary osteons is still high. Evaluation of the variables independently indicates that combining variables has potential to reduce the predictive strength of an age estimation model and the ability to interpret age-related bone remodeling.

Cortical bone histomorphology of known-age skeletons from the Kirsten collection, Stellenbosch university, South Africa.

OBJECTIVES: Normal human bone tissue changes predictably as adults get older, but substantial variability in pattern and pace remains unexplained. Information is needed regarding the characteristics of histological variables across diverse human populations. METHODS: Undecalcified thin sections from mid-thoracic ribs of 213 skeletons (138 M, 75 F, 17-82 years, mean age 48 years), are used to explore the efficacy of an established age-at-death estimation method and methodological approach (Cho et al.: J Forensic Sci 47 (2002) 12-18) and expand on it. The ribs are an age-balanced sample taken from skeletonized cadavers collected from 1967 to 1999 in South Africa, each with recorded sex, age, cause of death and government-defined population group (129 "Colored," 49 "Black," 35 "White"). RESULTS: The Ethnicity Unknown equation performs better than those developed for European-Americans and African-Americans, in terms of accuracy and bias. A new equation based solely on the study sample does not improve accuracy. Osteon population densities (OPD) show predicted values, yet secondary osteon areas (On.Ar) are smaller than expected for non-Black subgroups. Relative cortical area (Ct.Ar/Tt.Ar) is low among non-Whites. CONCLUSIONS: Results from this highly diverse sample show that population-specific equations do not increase estimate precision. While within the published range of error for the method (±24.44 years), results demonstrate a systematic under-aging of young adults and over-aging of older adults. The regression approach is inappropriate. The field needs fresh approaches to statistical treatment and to factors behind cortical bone remodeling.

Rib histomorphometry for adult age estimation.

Estimating the age at death in the adult skeleton is problematic owing to the biological variability in morphological age indicators and the differential response to environmental factors over an individual's life. It is becoming increasingly important for anthropologists to improve age estimates through the use of multiple age indicators and various modalities of assessment (e.g., macroscopic, microscopic, and radiological). Lack of instructional texts describing how to prepare histological samples and evaluate bone under the microscope has been a restricting factor in the widespread use of current histological methods within the field of forensic anthropology. The limited use of histological methods for age estimation often lies in the misunderstanding that the preparation and evaluation of cortical bone thin sections is a highly technical and an expensive endeavor. Like any method of age estimation, the researcher/practitioner must be guided through the analytical process to ensure reliable and repeatable results. This chapter provides a step-by-step instructional guide in the preparation and evaluation of histological samples removed from the sixth rib for histological age estimation.