Anatomical Study of Variations of Sacral Hiatus and its Clinical Relevance in Caudal Epidural Block

Introduction: The human sacrum is a large, triangular shield-shaped bone formed by the fusion of five separate vertebrae along with the inter-vertebral discs. Gross morphology of sacrum shows a concave ventral surface, a convex dorsal surface and a triangular sacral canal. The sacral canal consists of an anterior wall formed by the fusion of the posterior aspect of the bodies of sacral vertebrae and the dorsal wall is formed by the fused laminae, spines and ossified ligamentum flava. Sacral hiatus is the opening present at the caudal end of sacral canal. Non fusion of laminae of 4th or 5th sacral vertebrae results in its formation. Clinically sacral hiatus is used for epidural injections.Aim of the study: Present study is aimed at determining the anatomy of sacral hiatus with the help of morphometric measurements and to identify significant anatomical variations to locate it for caudal epidural block.Material and Method: Total 96 dry human sacra from Department of Anatomy & Forensic medicine, SRMS-IMS, Bareilly, were studied.A Vernier caliper was used for anatomical measurements. Study period was from July 2016 to December 2016.Result: The average height of sacral hiatus was 34.13±11.82 mm. Different shapes of sacral hiatus were observed, inverted U shaped hiatus were most common. The apex of the sacral hiatus was most commonly found at the level of 4th sacral vertebrae.Right and left superolateral crests of the sacrum were taken as two points on dorsal surface of sacrum (forming the base of a triangle) because posterior superior iliac spines,impose on superolateral sacral crests. The distance between the two superolateral crests, the distance between the right and left superolateral sacral crest and the sacral apex were on average 60.61±6.71, 61.95±11.71 and 61.40±11.98 mm respectively. Conclusion: An equilateral triangle formed between the apex of sacral hiatus and right and left superolateral sacral crests. This equilateral triangle will help in determining the location of the sacral hiatus during caudal epidural block. Also the length of sacral hiatus should be kept in mind