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Original article
peer-reviewed

Morphometric Study of Sacral Hiatus in Dry Adult Human Sacra: Its Clinical Relevance in Caudal Epidural Block



Abstract

Introduction: Correct localization of the sacral hiatus is essential for administering a successful caudal epidural block. The present study was undertaken to find out the anatomical variations of sacral hiatus by a metrical method so that it could help anaesthesiologists in the clinical field.

Materials and methods: The study was performed on 140 (83 male and 57 female) adult human sacra. Various parameters of the sacrum studied were as follows: the shape of the hiatus, length of the sacral hiatus, transverse width at the base and anteroposterior diameter at the level of the apex. For each parameter, the mean value (calculated in mm), standard deviation, range and percentage of bones identified correctly were calculated.

Results: Various shapes of sacral hiatus were observed, including inverted “U” in 73 (52.14%), inverted “V” in 33 (23.57%), irregular in 10 (7.14%), elongated in 10 (7.14%) and dumbbell-shaped in 12 (8.57%). Absent sacral hiatus was observed in two (1.43%) specimens. The mean value for the length of sacral hiatus from the apex to the midpoint of the base was found to be 23.26 mm in males and 22.38 mm in females. However, the parameter was found to be statistically not significant. The mean value for transverse width at the base of hiatus was found to be 14.19 mm in males and 13.54 mm in females. The mean value for the anteroposterior diameter of the sacral canal at the apex was found to be 4.57 mm in males and 4.32 mm in females. Both the above parameters were found to be statistically not significant.

Summary and conclusion: The anatomical knowledge of sacral hiatus and its variations are important in caudal epidural anaesthesia, and it may improve the success rate of caudal epidural anaesthesia.

Introduction

The sacrum is a large triangular bone forming the postero-superior wall of the pelvic cavity, wedged between the two innominate bones. It is formed by the fusion of five sacral vertebrae and forms the caudal end of the vertebral column. It has a base, apex, dorsal, pelvic, and lateral surfaces, and a sacral canal. On the dorsal surface below the fourth or third tubercle, there is an arched sacral hiatus in the posterior wall of the sacral canal, which is due to the failure of the laminae of the fifth sacral vertebra to meet in the median plane exposing the dorsal surface of sacrum [1].

The “sacral hiatus” is a commonly studied parameter of the sacrum. It is of immense value to anaesthesiologists and surgeons as caudal anaesthesia is administered through this route. Knowledge of the distance between the sacral hiatus and the dural sac is of clinical importance so that inadvertent iatrogenic injury to dural sac can be prevented during the procedure of caudal epidural block [2]. The present study was undertaken to find out the anatomical variations of sacral hiatus by a metrical method so that it could help anaesthesiologists in the clinical field.

This article was previously posted to the ResearchSquare preprint server on August 4, 2022.

Materials & Methods

Morphometric Study of Sacral hiatus of Human Sacrum, an analytical type of observational study was performed in the Department of Anatomy, on 140 (83 males and 57 females) adult human sacra. All the bones were dry, free from deformity and fully ossified. Clearance from the institutional ethics committee was obtained. Various parameters of the sacrum studied were as follows.

Shape

The shape of the hiatus was observed grossly.

Dimensions

Length is measured from apex to midpoint of base (Figure 1).

Transverse width at the base is measured between inner aspects of the inferior limit of sacral cornua (Figure 2).

Anteroposterior diameter at the level of apex is recorded with a divider and steel measuring scale.

For each parameter, the mean value (calculated in mm), standard deviation, range and percentage of bones identified correctly were calculated. Statistical analysis was done by using unpaired t-test, to find out the differences, if any, in the mean values. All the calculations and statistical analyses were done using Microsoft Excel. A p-value of less than 0.05 (p < 0.05) was statistically significant, while p-value of less than 0.001 (p < 0.001) was statistically highly significant. Tables and graphs were generated using Microsoft Excel software.

Results

The most common shape observed was inverted “U” in 73 (52.14%) of specimens (Figure 3).

The second most common shape observed was inverted “V” in 33 (23.57%) of specimens (Figure 4).

Other shapes were also found during the observation. Figure 5 depicts irregularly shaped sacral hiatus.

Dumbbell-shaped sacral hiatus is shown in Figure 6.

Elongated sacral hiatus is shown in Figure 7.

Absent sacral hiatus was seen in two (1.42%) of cases (Figure 8).

Total 140 sacra were studied, and various shapes found are listed in Table 1.

Sr. no. Shape Number (140) Percentage
1. Inverted – U 73 52.14
2 Inverted – V 33 23.57
3. Irregular 10 7.14
4. Elongated 10 7.14
5. Dumbbell 12 8.57
6. Absent hiatus 2 1.43
  Total 140 100

In males, the length of sacral hiatus ranged from 6.99 mm to 51.08 mm with a mean of 23.26 ± 9.41 mm and in females it ranged from 6.58 to 41.03 mm with a mean of 22.38 ± 7.29 mm. On comparing the mean values in males and females, the measurement was found to be not significant, having a p value of 0.5546 (Table 2).

  Male Female
Number of bones 82 56
Range 6.99-51.08 6.58-41.03
Mean 23.26 22.38
Standard deviation (S.D.) 9.41 7.29
t value 0.5924
p value 0.5546*

Transverse width at the base of sacral hiatus ranged from 4.61 mm to 19.11 mm, with a mean of 14.19 ± 2.61 mm in males and 5 mm to 19 mm with a mean of 13.54 ± 2.35 mm in females. On comparing the mean values in males and females the measurement was found to be not significant having a p value of 0.1340 (Table 3).

  Male Female
Number of bones 82 56
Range 4.61-19.11 5-19
Mean 14.19 13.54
Standard deviation (S.D.) 2.61 2.35
t value 1.507
p value 0.1340*

In males, the anteroposterior diameter of the sacral canal at the level of apex ranged from 2 mm to 8 mm with a mean of 4.57 ± 1.46 mm and in females, it ranged from 1 mm to 8 mm with a mean of 4.32 ± 1.62 mm. On comparing the mean values in males and females the measurement was found to be not significant, having a p value of 0.3438 (Table 4).

  Male Female
Number of bones 82 56
Range 2- 8 1 – 8
Mean 4.57 4.32
Standard Deviation (S.D.) 1.46 1.62
t value   0.9500
p value   0.3438 *

Discussion

The caudal epidural route was used for the first time for analgesia drug delivery into the epidural space through sacral hiatus in 1900 [3]. The technique of caudal epidural injection [4] was further developed in 1901. Continuous caudal epidural anaesthesia [5] was introduced later in 1942.

Epidural space is approached through sacral hiatus for giving analgesia and anaesthesia for various surgical procedures, treatment of lumbar spinal disorders and management of chronic back pain, administration of epidural anaesthesia in obstetrics for painless deliveries, perineal surgeries, colposcopy, orthopaedic procedures like treatment of sciatica to give corticosteroids injections, to provide pre and post-operative analgesia in adults and children [6].

A needle is passed through the skin, subcutaneous tissue and sacrococcygeal ligament and finally the caudal epidural space to achieve drug delivery into the epidural space [7]. When an ultrasound-guided caudal epidural block is performed, the success rate increases up to 100%, but it is not always possible to perform the procedure under the guidance of ultrasound, mostly due to the unavailability of an instrument [8].

Thorough and detailed knowledge of anatomical variant features of sacral hiatus will improve the success rate of caudal epidural block for anaesthesia and analgesia. According to Aggarwal et al. [9] depth of sacral hiatus, less than 3 mm may be the cause of failure of needle insertion. Surrounding bony irregularities, different shapes of sacral hiatuses and defects in the dorsal wall of the sacral canal should be taken into consideration before undertaking a caudal epidural block to avoid its failure. Mustafa MS et al [10] found that needle insertion into the sacral hiatus for a caudal block should be done at its base to avoid the anatomic variations of the apex.

In the present study, various parameters of sacral hiatus were studied and compared. Various shapes of sacral hiatus found are discussed in Table 5. Kumar et al. [11] in their study found an inverted “V” in 94 of the specimens studied, making it the most common of all the shapes of sacral hiatuses. Nagar et al. [12], Patel et al. [13], and Shewale et al. [14] also found inverted “U” as the most common shape followed by inverted “V” as the second most common one.

Sr. no. Shape of sacral hiatus Kumar et al. (1992) [11] , n* = 202 Nagar (2004) [12], n =270 Patel et al. (2011) [13], n=150 Shewale et al. (2013) [14], n=204 Present study, n= 140
No. % No. % No. % No. % No. %
1. Inverted- U 60 29.70 112 41.5 74 49.3 83 40.69 73 52.14
2. Inverted- V 94 46.53 73 27 30 20 66 32.35 33 23.57
3. Irregular - - 38 14.1 - 4 19 9.31 10 7.14
4. Elongated 28 13.86 - - 41 21.1 19 9.31 10 7.14
5. Dumbbell 15 7.43 36 13.3 6 4 12 5.89 12 8.57
6. Absent hiatus 2 0.99 - 0.7 2 1 2 0.98 2 1.42

Table 6 enlists a comparison of the length of sacral hiatus from the apex to the midpoint of the base as measured by different researchers. Kumar et al. [11] in their study found the mean value for the length of sacral hiatus to be 20 mm in males and 18.9 mm in females. Similarly, Shewale et al. [14] in their study found the mean value for the length of sacral hiatus to be 23.44 mm in males and 20.44 mm in females. Trotter and Lanier [15] found the mean value for length 24.8 mm in males and 19.8 mm in females.

Sr. no. Name of the worker Length from apex to midpoint of base(mm)
    Mean Range
        Male Female Male Female
1. Trotter and Lanier (1945) [15] 24.8 19.8 - -
2. Kumar et al. (1992) [11] 20 18.9 3-37 9-36
3 Shewale et al. (2013) [14] 23.44 20.44 5-53.5 9-42
4. Present study 23.26 22.38 6.99- 51.08 6.58-41.03

The comparison of transverse width at the base of hiatus is shown in Table 7. Kumar et al. [11] in their study found the mean value of transverse width at the base of hiatus to be 13 mm in males and 12.50 mm in females. Similarly, the study conducted by Shewale et al. [14] on 204 sacra showed the mean value of transverse width at the base of hiatus to be 13.68 mm in males and 13.45 mm in females. On comparing the findings of the present study with that of other studies, it was found that the mean value of the transverse width at the base of hiatus was more in males as compared to females.

Sr. no. Name of the worker Transverse width at base of hiatus (mm)
      Mean Range
      Male Female Male Female
1. Kumar et al. (1992) [11] 13 12.50 5-20 8-18
2. Shewale et al. (2013) [14] 13.68 13.45 4.5-19 7.5-18
3. Present study 14.19 13.54 4.61-19.11 5-19

Table 8 depicts a comparison of the antero-posterior diameter of the sacral canal at the level of the apex as observed by different researchers. Kumar et al. [11] observed the mean value of anteroposterior diameter at the apex to be 4.8 mm with a range of 0 to 12 mm. Similarly, Nagar [12] found the mean value of anteroposterior diameter at the apex to be 4.88 mm with a range of 2 to 14 mm. A glimpse at the table given below will reveal that the mean value of the anteroposterior diameter at the apex of the present study correlated quite well with those of other studies. Trotter and Letterman [16] found the mean value of anteroposterior diameter at the apex to be 5.3 mm with a range of 0 to 11 mm.

Sr. no.   Name of the worker   Anteroposterior diameter at apex (mm)
      Mean Range  
1. Trotter and Letterman (1944) [16] 5.3 0-11
2. Kumar et al. (1992) [11] 4.8 0-12
3. Nagar (2004) [12] 4.88 2-14
4. Present study 4.57 2-8

The present study has some limitations as the study was done on a sample size of 140 adult sacra and did not include a sample from the pediatric population. Also, the bones studied belong to the Indian subcontinent and did not include other races. Thus, the results derived cannot be generalised for worldwide application.

Conclusions

Various shapes of sacral hiatus were observed, including inverted “U” in 73 (52.14%), inverted “V” in 33 (23.57%), irregular in 10 (7.14%), elongated in 10 (7.14%) and dumbbell-shaped in 12 (8.57%). Absent sacral hiatus was observed in two (1.43%) specimens. Thus, it concludes that variations in the shapes of sacral hiatuses should be kept in mind for successful caudal epidural anaesthesia.


References

  1. Gray's Anatomy, The Anatomical basis of Clinical Practice. 40th edition. Standring S (ed): Churchill Livingstone Elsevier, Spain; 2008.
  2. Chen CP, Tang SF, Hsu TC, et al.: Ultrasound guidance in caudal epidural needle placement. Anesthesiology. 2004, 101:181-4. 10.1097/00000542-200407000-00028
  3. Senoglu N, Senoglu M, Oksuz H, et al.: Landmarks of the sacral hiatus for caudal epidural block: an anatomical study. Br J Anaesth. 2005, 95:692-5. 10.1093/bja/aei236
  4. Collins VJ: Principles of Anaesthesiology. Lea & Febiger, Philadelphia; 1976.
  5. Edward WB. Hingson RA: Continuous caudal anesthesia in obstetrics. Am J Surg. 1942, 57:459-64. 10.1016/S0266-6138(87)80006-2
  6. Rajani S: Anatomical variations of sacral hiatus and associated clinical relevance - a review. Int J Anat Var. 2017, 10:96-8.
  7. Sekiguchi M, Yabuki S, Satoh K, Kikuchi S: An anatomic study of the sacral hiatus: a basis for successful caudal epidural block. Clin J Pain. 2004, 20:51-4. 10.1097/00002508-200401000-00010
  8. Desai RR, Jadhav SD, Doshi M, Ambali M, Desai A: Variations in anatomical features of the sacral hiatus in Indian dry sacra. Int J Med Res health Sci. 2014, 3:634-8. 10.5958/2319-5886.2014.00409.3
  9. Aggarwal A, Aggarwal A, Harjeet, Sahni D: Morphometry of sacral hiatus and its clinical relevance in caudal epidural block. Surg Radiol Anat. 2009, 31:793-800. 10.1007/s00276-009-0529-4
  10. Mustafa MS, Mahmoud OM, El Raouf HH, Atef HM: Morphometric study of sacral hiatus in adult human Egyptian sacra: their significance in caudal epidural anesthesia. Saudi J Anaesth. 2012, 6:350-7. 10.4103/1658-354X.105862
  11. Kumar V, Pandey SN, Bajpai RN, Jain PN, Longia GS: Morphometrical study of sacral hiatus. J Anat Soc India. 1992, 41:7-13.
  12. Nagar SK: A study of sacral hiatus in dry human sacra. J Anatom Soc India. 2004, 53:18-21.
  13. Patel ZK, Thummar B, Rathod SP: A multicentric study of dry human sacrum of Indian population in Gujrat region. NJIRM. 2011, 2:31-5.
  14. Shewale SN, Laeeque M, Kulkarni PR, Diwan CV: Morphological and morphometrical study of sacral hiatus. Int J Recent Trends Sci Technol. 2013, 6:48-52.
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Original article
peer-reviewed

Morphometric Study of Sacral Hiatus in Dry Adult Human Sacra: Its Clinical Relevance in Caudal Epidural Block


Author Information

Nisha Yadav Corresponding Author

Anatomy, Uttar Pradesh University of Medical Sciences, Etawah, IND

Vishal R. Jasuja

Anatomy, Uttar Pradesh University of Medical Sciences, Etawah, IND

Mamta Rani

Anatomy, Uttar Pradesh University of Medical Sciences, Etawah, IND

Monika Srivastava

Anatomy, Uttar Pradesh University of Medical Sciences, Etawah, IND

Nityanand Srivastava

Anatomy, Uttar Pradesh University of Medical Sciences, Etawah, IND

Anurag Yadav

Radiology, Uttar Pradesh University of Medical Sciences, Etawah, IND


Ethics Statement and Conflict of Interest Disclosures

Human subjects: All authors have confirmed that this study did not involve human participants or tissue. Animal subjects: All authors have confirmed that this study did not involve animal subjects or tissue. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: All authors have declared that they have no financial relationships at present or within the previous three years with any organizations that might have an interest in the submitted work. Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.



Original article
peer-reviewed

Morphometric Study of Sacral Hiatus in Dry Adult Human Sacra: Its Clinical Relevance in Caudal Epidural Block


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