THE SACRAL HIATUS: AN ANATOMIC STUDY ON BOTH CADAVERIC AND DRY BONES

Abstract

The sacral hiatus is the gap on the lower part of dorsal surface of sacrum.  It is formed due to the failure of fusion of the laminae of the 5^th sacral segment.  The sacral hiatus provides the main route of the caudal epidural nerve block.  The success rate of the caudal nerve block showed an important correlation to the variations of the sacral hiatus dimensions.  150 dry Egyptian sacra and five cadavers were used in the present study.  Different anatomical measurements were made with a Vernier caliper accurate to 0.1 mm to know the anatomical variations of the sacral hiatus.  Complete agenesis of the sacral hiatus was seen in four (2.66%) sacra.  The mean length of sacral hiatus was 27.16 mm and it showed a wide range (7-110 mm).  The mean transverse diameter (width) of sacral hiatus was 11.5 mm.  The mean anteroposterior diameter of the sacral canal at the apex of sacral hiatus was 4.78 mm.  Narrowing of the sacral canal at the apex of sacral hiatus, diameter less than 3 mm was seen in 10 (6.66%) sacra.   The apex of sacral hiatus was commonly found at the level of the 4^th sacral vertebra in 54%.  Various shapes of sacral hiatus were observed which included inverted V (38.66%), inverted U (31.33%), irregular (15.33%), dumbbell (12%) and bifid (2.66%). The base of sacral hiatus was seen at the level of S5 vertebra in 70%.  The fusion between coccyx and sacrum was observed in 18% of sacra while the sacralisation of the 5^th lumber vertebra was noticed in 14 (9.33%) sacra.  The knowledge of the anatomical variations of sacral hiatus is important during administration of the caudal epidural anaesthesia.  Moreover, it may help in improving the success rate of the caudal anaesthesia.