Correlation between sacral hiatus morphometry and internal volumetric capacity of the sacral canal in dry Thai sacra

Understanding anatomical variation in the sacral hiatus (SH) is important for improving the safety and technical success of caudal epidural block (CEB), particularly by reducing the risk of inadvertent dural puncture. However, data linking external sacral landmarks to internal volumetric capacity remain limited, especially in Southeast Asian skeletal populations. This study evaluated the relationships between external SH-related surface parameters and internal volumetric measures, particularly half-cone and caudal space volumes, in Thai dry sacra from Northeastern Thailand.

Forty-five Thai dry sacra were analyzed using 20 parameters, including SH dimensions (SH1-SH4), external sacral surface landmarks (ES5-ES20), and volumetric measurements. Associations among SH parameters, ES parameters, and volumetric measures were assessed using Pearson correlation analysis. Intra- and inter-rater reliability were also evaluated.

The most prevalent SH morphologies were the inverted-U and irregular shapes, each accounting for 17.78% of specimens. The hiatal apex was most commonly located at the S4 vertebral level (64.44%), followed by S3 (26.67%). The mean SH length was 22.02 ± 9.59 mm. No statistically significant relationship was identified between SH morphology and either internal volumetric parameter. In contrast, several external sacral surface parameters demonstrated moderate-to-strong positive correlations with volumetric capacity.

SH morphology was not associated with internal volumetric capacity, whereas the external sacral surface framework appeared to be more informative than the hiatus aperture itself. These findings suggest that selected posterior sacral surface dimensions may provide anatomically relevant indicators of internal capacity in osteological assessment related to CEB. Further imaging-based and clinical studies are needed to validate these findings.