Landmarks of the sacral hiatus for caudal epidural block: an anatomical study

This study determined the landmarks for caudal epidural block (CEB) after morphometric measurements of the sacral hiatus on dry sacral bones. Anatomical features of the sacral hiatus of clinical importance during CEB, along with distances and angles of use in detecting the apex, were measured. This provides detailed knowledge of the anatomy of the sacral hiatus and practical landmarks.

Ninety-six dry sacral bones were used. Anatomical measurements were made with a Vernier caliper accurate to 0.1 mm.

Two sacral bones were excluded since they had total posterior closure defect. Agenesis of the sacral hiatus was detected in six sacral bones. As the posterior superior iliac spines impose on the superolateral sacral crests of the sacrum, the latter were accepted as forming the base of a triangle. The distance between the two superolateral sacral crests and the distances between the sacral apex and the right and left superolateral sacral crest were 66.5 (SD 53.5), 67.1 (10.0) and 67.5 (9.5) mm respectively, on average.

The triangle formed between the apex of the sacral hiatus and the superolateral sacral crests was found to have the features of an equilateral triangle. The sacrum and sacral hiatus are variable anatomical structures. However, the equilateral triangle located between the apex of the sacral hiatus and superolateral sacral crests will certainly be of use in determining the location of the sacral hiatus during CEB.