Only photos on my best side, please! Implications of bilateral asymmetry of the iliac auricular surface in non-adult individuals for sex estimation

Abstract

This study aims to address the overlooked effect of bilateral asymmetry for sex estimation in non-adult paired bone structures. Using a recently developed method, disparities between right and left iliac auricular surfaces (AuSs) were quantified, also verifying the effectiveness between sides regarding the percentages of cases correctly assigned. A sample of 418 AuSs belonging to 209 individuals aged 5 gestational months to 18 years (113 males and 96 females) from the Coimbra, Lisbon, and Granada Identified skeletal collections, were studied. They were grouped into two large age cohorts (≤12 y.o. and 12.1–18 y.o.) based on the onset of menarche. The significant and distinct hormonal fluctuations between sexes in ≤2 y.o. individuals compelled an additional separation. Locomotion issues also imposed grouping individuals for comparison in non-bipedal (≤1 y.o.) and those who were still achieving emerging gait milestones (1.1–6 y.o.). Overall agreements between sides, sexes, age cohorts, and morphometric variables were compared using Cohen's κ and intraclass correlation coefficients, while chi-square and Kolmogorov–Smirnov tests were applied for statistically significant evaluation. Asymmetry directionality was calculated through standardized directional and total asymmetry scores. Slight asymmetries between sides were identified, becoming the pre-pubertal left AuS more useful for non-adult female sexing. Metric variables work better in males, possibly due to the higher variability found in females. Both sexes display a marked age-related change in asymmetry during puberty (12.1–18 y.o.), with a predominance of the right side in females and of the left side in males. Possible explanations for the identified pubertal abrupt shifts are discussed considering the various developmental biomechanical milestones. This pioneering study reinforces the complexity of somatic growth and development that characterizes non-adult phenotype, calling for further refinement of sexing methods considering bilateral asymmetry, and for complementary studies that deepen the study of dextralization and its repercussions in adults.