Morphometric study of sacral hiatus and its significance in caudal epidural anesthesia

Context: Sacral hiatus is used for administration of caudal epidural block. A frequent problem in this is needle placement as it is difficult to determine the location of sacral hiatus. The knowledge of anatomy of sacral hiatus plays a major role in the success of needle placement. Aim: To study the anatomy of sacral hiatus from point of view of caudal epidural anesthesia. Materials and Methods: The sacral hiatus of 300 sacra was studied. Parameters of sacral hiatus such as shape, level of apex and base, length, anteroposterior (AP) diameter at apex, and intercornual distance along with distance between superolateral sacral crests and their distance from apex of sacral hiatus were studied. Results: Inverted "U" shape (46.33%) was most commonly encountered. Apex and base of the hiatus were most commonly seen at the level of S4 and S5 respectively. Length of sacral hiatus ranged between 8.8 mm and 45.7 mm. AP diameter at apex of sacra and intercornual distance were seen most commonly in the range 4–6 mm and 11–15 mm respectively. Conclusion: The study of these sacra indicated the type of variations in shape and size of sacral hiatus in population of state of Maharashtra in India. While absent sacral hiatus leads to poor outcome of the caudal epidural anesthesia, dorsal agenesis of the sacrum would lead to only partial anesthesia. The formation of equilateral triangle by joining superolateral sacral crests and apex of sacral hiatus forms a practical guide in locating sacral hiatus for caudal epidural anesthesia.