Morphometrical study of sacral hiatus in dry human sacra

Rajapur Parashuram


Background: The sacral hiatus is the site for caudal epidural anaesthesia during perineal surgery and also for a painless delivery. It is also used for three dimensional colour visualization of lumbosacral epidural space in orthopaedic practice for diagnosis and treatment. Sacrum is one of the bones which exhibit variations. Therefore the importance of the normal sacral hiatus and its variations is of great clinical significance. The reliability of caudal epidural anaesthesia is 70% - 80% in the literatures. The objective of the study was to examine, measure and record the morphometry of sacral hiatus under the following headings in order to study the anatomical variations which would be useful for caudal epidural anaesthesia and improve the reliability of the same. a) Shape of sacral hiatus, b) level of apex, c) level of base, d) length of the sacral hiatus, e) transverse width at the base, and f) anteroposterior depth at the apex.

Methods: A total of 200 dry, complete, undamaged human sacra of unknown sex were used in this study. Measurements were taken using vernier calipers. In this study six parameters were taken. All the readings were tabulated and subjected to analysis.

Results: Various shapes of sacral hiatus were observed which included Inverted-U (50%), Inverted-V (27.5%), Irregular (15.5%), Dumb bell (2%), and Bifid (2%). The mean anteroposterior depth of sacral canal at the level of apex of sacral hiatus was 4.25mm. The mean length of sacral hiatus was 19.63 mm and the mean transverse width of sacral hiatus at the level of base was 11.42 mm. There was complete spina bifida in 4 (2%) and absence of sacral hiatus in 2 (1%) cases.

Conclusion: The sacral hiatus has anatomical variations. Understanding of these variations may improve the reliability of caudal epidural anaesthesia.



Sacrum; Sacral canal; Sacral hiatus; Sacral apex; Caudal Epidural Anaesthesia

Full Text:



Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 40th Ed, Elsevier Churchill Livingstone, London, 2008:724-725.

Standring S. Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 39th Ed, Elsevier Churchill Livingstone, London, 2005: 731.

Chen PC, Tang STF, Hsu, et al. Ultrasound guidance in caudal epidural needle placement. Anaesthesiol. 2004;101:181–4.

Saberski L, Kitahata L. Direct visualization of lumbosacral epidural space through the sacral hiatus. Anaesth Analg. 1995;80:839–40.

Brailsford JF. Deformities of lumbosacral region of spine. British Journal of Surg. 1929;16:562–70.

Trotter M. Variations of the sacral canal: Their significance in the administration of caudal analgesia. Anesth Analg. 1947;26(5):192–202.

Edwards WB, Hingson RA. Continuous caudal anaesthesia in obstetrics. American journal of surgery. 1942;57:459-64.

Sekiguchi M, Yabuki S, Satoh K, Kikuchi S. An Anatomical Study of the Sacral Hiatus: A Basis for Successful Caudal Epidural Block. Clinical Journal of Pain. 2004;20(1):51–4.

Nagar SK. A study of sacral hiatus in dry human sacra. J Anatomical Soc India. 2004;53(2):18-21.

Kumar V, et al. Morphometrical study of sacral hiatus. J Anatomical Soc India. 1992;41(1):7–13.

Trotter M. and Letterman GS. Variations of the female sacrum: Their significance in continuous caudal anaesthesia. Surg Gynecol Obstet. 1944;78(4):419-24.

Lanier VS, Mcknight HE, Trotter M. Caudal analgesia: An experimental and anatomical study. American J Obstet Gynaecol. 1944;47(5):633–41.

Trotter M, Lanier PF. Hiatus canalis sacralis in American whites and Negros. Human Biology. 1945;17:368-81.

Bernard Rosner. Fundamentals of Biostatistics, 5th Ed, Duxbury, 2000.

Venkataswamy Reddy. Statistics fir mental health care research, NIMHANS Publication, India, 2002.