Prevalence of directional asymmetry within the acetabulum and its implications for age estimation

Age estimation is a prerequisite for human identification. Within the skeletal framework, pelvic acetabular variables constitute a promising age marker. Previous investigations with the coxal bone have utilised either acetabulum for age estimation whilst assuming bilateral symmetry or selective side standardised practices, with two published studies reporting significant bilateral asymmetry within acetabular variables. The present study delves into this aspect of bilateral asymmetry further, and explores the prevalence, and impact of these side differences on age estimation. Data for analysis was obtained from 463 CT scans (195 females, 268 males) collected ethically from a medical institute in India previously. These scans were scored using a CT-based modification of the SanMillán-Rissech acetabular age estimation method, which utilises only the first five slightly modified variables of the original method as opposed to all seven. Collected data was then statistically analysed to illustrate the prevalence of asymmetry. The Wilcoxon test, Chi-square tests, mean % directional asymmetry values and equivalency ratios were utilised to assess population level lateralisation within the acetabulum. Furthermore, the association between asymmetry/ directionality, and biological sex and chronological age was investigated, and the impact of asymmetry on age estimation was evaluated using Bayesian regression analysis. Statistically significant bilateral differences were observed with the acetabular groove in females and the apex activity in males, and for all five variables the left acetabulum garnered older/ higher scores. Males largely demonstrated a greater degree of directionality wherein one side scored higher than the other more often, and patterns of directionality were seen to mostly increase with age in both sexes. The right, and/or younger scoring acetabulum consistently garnered most accurate age estimates, contradicting previous standardised practices of using the left acetabulum more, leading to its selective utilisation. Further, in-depth, investigation is wanting with regards to anatomical factors and lived experience of individuals capable of rationalizing these findings.