Atypical Morphological Variations of the Sacrum in the Korean Population: A PMCT-Based 3D Reconstruction Study

Background and Objectives: The sacrum is formed by five fused vertebrae and connects the lumbar spine to the coccyx. It has four pairs of foramina for sacral nerves and shows important anatomical variations. This study aims to analyze the frequency of atypical sacral morphology in the Korean population using 3D reconstruction of postmortem computed tomography (PMCT) images, and to provide a systematic classification and morphological characterization. Materials and Methods: A total of 29 PMCT datasets (10 males, 19 females) from the National Forensic Service were used to generate 3D sacral models with Mimics software for the analysis of atypical sacral morphology. Key morphometric parameters, including sacral width (SW), sacral length (SL), sacral foramina distances (SFD1, SFD2), sacral vertebral heights (SH1, SH2), sacral curvature (SC), and sacral index (SI), were measured. Sacral foramina were categorized into three groups based on completeness, and auricular surfaces were classified into three types according to their vertical position. Results: Median values for sacral dimensions were as follows: SW 95.3 mm, SL 118.6 mm, SFD1 36.1 mm, SFD2 28.8 mm, SH1 28.0 mm, SH2 29.7 mm, SC 0.92, and SI 0.78. Sacral foramina variations were identified in 12 of 29 cases (41.4%) as incomplete, including one case with an incomplete upper opening. No significant sex-based differences were found in foramen or auricular surface types, although females showed higher values for SW and SI (SW: 97.2 mm, SI: 0.86). Correlation analysis revealed positive associations between SL and both stature (r = 0.635) and weight (r = 0.645), and negative correlations between SI and stature (r = -0.663), SL (r = -0.921), and SC (r = -0.845). Two cases (6.8%) exhibited sacralization, while the remaining 25 cases had the configuration of five lumbar vertebrae and six sacral segments. Conclusions: Our findings support the notion that atypical segmentation patterns are more prevalent than sacralization. Atypical sacral morphology was observed in 29 cases (19.8%), most commonly involving a normal lumbar spine with six sacral segments. These findings highlight the relevance of sacral variation in clinical and anatomical contexts.