Age estimation in a sub-adult Western Australian population based on the analysis of the pelvic girdle and proximal femur

The anthropological assessment of unidentified individual involves the creation of a biological profile. Age estimation is an essential component of the biological profile, thus is required to be accurate and precise. Skeletal age estimations should be based on the application of standards (statistical data), the recommended practice of the Scientific Working Group for Forensic Anthropology (SWGANTH).

The primary research aim is to develop age estimation models for a contemporary sub-adult Western Australian population based on the fusion of the os coxa, sacrum and proximal femur. The other research aims were to evaluate the reliability and accuracy of selected existing age estimation methods in a Western Australian sub-adult population and use novel statistical analyses of the timing of growth and development in a Western Australian sub-adult population.

The study sample comprised 562 MDCT scans (292 male, 270 female) of individuals between 0 and 25 years of age. The scans were assessed at nine morphological developmental attributes using a three stage scoring system. The iliac crest was also assessed using the Risser scoring systems (French and American).

Prior to the data collection, the intra-observer error was quantified using a precision test. The mean level of intra-observer agreement based on analysis of the total sample was: ϰ = 0.79. Bilateral asymmetry of the data was evaluated using a paired t-test. There was no significant difference (p = <0.01) between the stages assigned to the left and right sides; all attributes examined had an almost perfect correlation (r = ≥0.99). An independent t-test was used to quantify the degree of sexual variation in the timing of fusion. Statistically significant sex differences were observed in the assignment of non-fusion in the proximal femur and os coxa. The mean age of commencement of fusion is significantly earlier (2-4 years) in females and there were no sex differences in the timing of fusion in the iliac crest. The inconsistent sexual variation of fusion timing supports the use of pooled sex standards for sub-adult age estimation.

Descriptive statistics showed the fusion of the os coxa and proximal femur occurs around the 14th and 15th year of age. Polynomial regression analysis was used to formulate the predictive age estimation models. The standard error of the estimate of the models ranged from ±3.59 to ±4.58 years. Transition analysis calculates the mean and standard error of the age of transition between defined stages. Transition analysis shows timing of fusion of iliac crest is delayed in comparison to other attributes of os coxa and proximal femur. Further investigation into the timing of fusion in the sacrum is required due to variable results.

The results have shown the three stage scoring system is preferential to the Risser scoring methods when assessing the iliac crest. Transition analysis provides anthropologists with an alternative approach to traditional statistical analysis. The study addressed the lack of Australian standards, the results of the present study demonstrate that the pelvic girdle and proximal femur can be used to accurately estimate chronological age.