Morphometric study of Sacral Hiatus for Caudal Epidural Block
Abstract
Study of variation of sacral hiatus in dry bone is important as it determines access of sacral hiatus for caudal epidural anaesthesia and analgesia. So this descriptive observational study was conducted on 80 adult sacrum bones were studied at department of Anatomy, SMS Medical College, Jaipur with the aim to examine Morphometry of Sacral hiatus including shape, length, A-P diameter at apex and transverse width at base. Most commonly found shape of sacral hiatus in this study was inverted U/V shape. Length of sacral hiatus ranged 6 to 43 mm with more than half cases having length between 10-20 mm. Most sacrum (81.25%) had anterio-posterior diameter of 4 to 8 mm. Half of the sacrum had transverse width at sacral cornua between 9-13 mm. It can be concluded that anatomical variations in sacral hiatus are cause of caudal epidural anaesthesia failure and procedure related complications. Understanding these variations may improve success of caudal epidural anaesthesia and decrease incidence of complications. So this study will be useful to increase success rate of epidural anaesthesia.
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Introduction
Study of variation of sacral hiatus in dry bone is important as it determines access of sacral hiatus for caudal epidural anaesthesia and analgesia. The incomplete fusion of the posterior elements of the 4th or 5th sacral vertebra, results in the formation of sacral hiatus (SH)1,2 . The SH is important landmark to perform caudal epidural block (CEB) for treating patient with low back pain3 . The lower sacral nerve roots, coccygeal nerve roots, filum terminale and fibro-fatty tissue forms the content of this sacral hiatus. This hiatus is covered by superficial posterior coccygeal ligament which is attached to the margins of the hiatus and the deep posterior sacro-coccygeal ligament attached to the floor of sacral hiatus4 .
Success rate of CEB is based on determination of the landmarks by clinician, even though CEB has a wide range of clinical caudal epidural space, especially in adults,5. In interest of patient care, to circumvent the failure of CEB which depend on anatomic basis1 , Previous Studies indicate that, Lots of variations are found in anatomy of sacral hiatus (SH), which lead to failure of CEB.
Approach to the epidural space through sacral hiatus is used for giving analgesia and anaesthesia for various operations, treatment of lumbar spinal disorders and for management of chronic back pain. The success of caudal epidural block depends upon accurate localization of sacral hiatus for optimal access into sacral epidural space. Hence it is necessary to have a detailed knowledge of the anatomical variations in sacral hiatus which results in discrepancies in its shape and size.6
Caudal epidural block (CEB) involves the injection of anaesthetic medications into the epidural space through the sacral hiatus to provide analgesia and anaesthesia for different clinical conditions7 . It is useful when anaesthesia of the lumbar and sacral dermatomes is needed1.
Conclusion
It can be concluded that inverted 'U' and inverted 'V' shape was most common shape of sacral bone and few cases had Dum-bell and irregular shape. Length of sacral hiatus ranged from 6.6 mm to 42.8 mm with mean height 20.6 ±8.8 mm and majority (80%) of sacral bones has 10-33 mm of length. Anterioposterior (AP) diameter had range from 2 mm to 14.4 mm with mean diameter 6.2 ±1.98 mm and majority (65 i.e. 81.25%) had anterio-posterior diameter of 4 to 8 mm. Transverse width at sacral cornua had ranged from 5.6 mm to 20.5 mm with mean width 11.8 ±3.2 mm and majority (59 i.e. 73.75%) were in between 9-17 mm.