The present study was carried out on 100 dry sacra to evaluate the different morphometrical variations of Sacral Hiatus according to sex among the population of west Bengal. Materials and Methods: The different parameters of 100 Sacrum (50 male, 50 female) were studied by naked eye observation and measured with the help of Martin's callipers. Observation and results: The most common shape of Sacral Hiatus was Inverted-U shaped, followed by Inverted-V shaped. The apex was most commonly present at the level of 4 th Sacral segment and the base of the Sacral Hiatus was present most commonly against the body of 5 th Sacral segment. The mean length of the Sacral Hiatus of male Sacra was 19.86mm, whereas that of female Sacra was 21.12 mm. Conclusion: No significant sexual dimorphism exists considering all the parameters of Sacral Hiatus. There are anatomical variations in the shape and level of the Sacral Hiatus which may lead to failure of caudal anaesthesia.

Background: 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. Spina bifida is a developmental defect of sacral vertebrae, where the dorsal wall of sacral canal is partially or completely absent. The present study is an attempt to verify the incidence of complete agenesis of dorsal wall of sacral canal.Methods: Eighty six dry human sacra were collected from the undergraduate students and department of anatomy of three different medical colleges of Uttar Pradesh for the study of dorsal wall of sacral canal. Results: out of eighty six bones studied, two (2.33%) of the bones showed complete absence of the dorsal wall of the sacral canal.Conclusions: Complete agenesis of dorsal wall of sacral canal may lead to partial or complete failure of caudal epidural anaesthesia. Association between dorsal sacral agenesis and some other congenital malformations have also been reported by few authors. Anatomical knowledge of these variations of dorsal wall of sacral canal is important for anaesthetists, radiologists and spine surgeons.