Variability in the Morphometrics of the Sacral Hiatus in Cadaveric Specimens, Computed Tomography Sacral Imaging, and its Clinical Significance

Abstract Background: The sacral hiatus is the lowest unfused part of the sacral lamina of the sacrum. The external characteristics of the sacral hiatus can vary greatly, including its length, shape, anteroposterior (AP) length, transverse length, and the specific spinal level at which its apex is located. In procedures such as caudal epidural anesthesia (CEA), where a precise anatomical understanding of the sacral hiatus is crucial, this heterogeneity possesses clinical significance. The study aimed at analyzing sacral hiatus morphometry, including length, shape, AP and transverse diameters, and apex vertebral level, and to mitigate risks associated with CEA based on the current study results. Methodology: This descriptive study was conducted on 300 samples, including 100 cadaveric dry sacra (51 males and 49 females) and 200 computed tomographic sacral images (114 males and 86 females) over 24 months. The study assessed the length, transverse length, AP depth, overall morphological configuration of the sacral hiatus, and specifically, the vertebral level where its apex is located. Both physical examinations of cadaveric dry specimens and computerized tomography imaging techniques were utilized. Results: According to the current study, the most common form of the sacral hiatus was an inverted U-shape (51%–53%), followed by an inverted V-shape. The craniocaudal length of the hiatus varied from 9 mm to 103 mm, while the AP depth ranged from 3 mm to 7 mm. The apex of the hiatus was most frequently located at the S4 level (52%–54%), followed by S3, S2, and S5. Conclusion: The sacral hiatus is crucial in procedures, especially those involving surgical approaches to anesthetize the regions supplied by the sacral plexus. It serves as the primary access point for CEA and injections. The morphometric variability in the sacral hiatus and varied level of its apex, particularly high hiatus might pose a risk of injuring the meninges and it also demarcates the site at which successful Caudal epidural anesthesia can be given. Improper identification of the hiatus location or misplacement of surgical instruments may lead to inadvertent nerve injury.