The Variations in the dimensions of the sacrum and its implications for Forensic Anthropology

With rising numbers of unidentified bodies in South Africa, the South African Police Service (SAPS) requires effective skeletal identification techniques. While the skull and pelvis are highly dimorphic, taphonomic fragmentation often renders them unavailable at forensic scenes. The sacrum is frequently well-preserved and exhibits population specific sexual dimorphism. This study aimed to evaluate the dimensions and three-dimensional (3D) shape of the ventral sacrum in a contemporary South African sample. Retrospective Computer Tomography (CT) scans of 51 black South African adults (26 females, 25 males) were obtained from Steve Biko Academic hospital. Utilising MeVisLab © (v.3.0.2), the sacra were isolated via threshold-based segmentation, and 3D landmarks were placed on the ventral sacral surface. Linear dimensions were calculated and evaluated using descriptive statistics and discriminant function analysis (DFA), while shape variations were assessed using a multivariate analysis and a two-group permutation test. Black South African males exhibited a significantly greater sacral height than females (p=0.004). The permutation test confirmed significant sex-based variation in overall ventral sacral shape (p= 0.005). DFA models predicted sex with a moderate 72.55% accuracy based on linear dimensions, but achieved an exceptional 94.12% accuracy utilising 3D shape coordinates. ROC analysis substantiated the predictive value of the ventral linear metrics (AUC = 0.73; 95% CI: 0.60 – 0.85; p = 0.004) for sacral height, yielding an optimal cut-off value of 103.41 mm (Sensitivity: 76 %, Specificity: 65.38 %). Sexual dimorphism significantly influences both the metrics and morphology of the ventral sacrum of black South Africans. Due to these distinct variations, the ventral sacral surface, particularly its 3D shape, provides a highly reliable alternative for accurate forensic sex estimation.