European Journal of Cardiovascular Medicine

Sacrum is a large triangular fusion of five progressively smaller sacral vertebrae and their costal elements, maintaining the integrity of the spinal column [1]. It contributes to the stability of the pelvic ring by its situation, being wedged between the two hip bones and also endures weight transmission [2]. Sacrum is the target of lumbo-sacral fusion and instrumentation that are commonly done for metastatic, infectious, traumatic and degenerative diseases. Sacral screw insertion is commonly done at the S1 sacral wing (antero-laterally) or into the S1 promontory (antero-medially) [3].

S2 screw applications are usually chosen for sacral block fixations but rigid posterior S1 pedicle screw fixation enhanced by placement of S2 screws is becoming a common technique in lumbosacral fusion procedures [4,5]. Percutaneous fixation with ilio-sacral screws is a technically demanding technique and failure of sacral screw fixation may occur due to various factors, such as sacral anatomic variations and dysmorphism, insufficient sacral bone acquisition, inapt course of the screw or depth of the screw insertion and osteoporosis of the sacrum [3,4].

With the advance of minimally invasive surgical techniques, it is essential that the available implants are precontoured to the exact anatomical location which necessitates the comprehensive knowledge of morphometry of sacrum [6]. Differences exist in the morphometric values of sacrum across different study populations. So far, out of the studies available, few determine the morphometry of sacrum, especially in the Indian population. [7] The present study was an attempt to quantify morphometric characteristics of the Indian sacra for safe screw placement during surgical instrumentation which is crucial for constructing a strategy to treat sacrum related diseases in Indian population.

The study was conducted on 50 dry adult human sacra in the Department of Anatomy, Guntur Medical College, Guntur, Andhra Pradesh for a period of 2 years (From April 2022 to March 2024). Ethical committee clearance obtained for this study. Sacra with damages or bony outgrowth which may alter the measurements were excluded from the study. The measurements were taken with the digital verniercalipers which was accurate up to 0.01 mm

Linear parameters [Fig-1-4]

First Anterior Sacral Foramina (ASF):

• Height of first ASF: Maximum vertical distance between the superior and inferior border of first anterior sacral foramen.
• Width of first ASF: Maximum transverse distance between the medial and lateral border of first anterior sacral foramen. Furthermore, the height and width of the first ASF were also analogous on both the sides.
• Transverse distance between the first ASF:Measured as the transverse distance between the two points on the medial border of first anterior sacral foramina at the level of first transverse fusion line between the first anterior sacral foramina.

Second Anterior Sacral Foramina (ASF):

• Height of second ASF: Maximum vertical distance between the superior and inferior border of second anterior sacral foramen.
• Width of second ASF: Maximum transverse distance between the medial and lateral border of second anterior sacral foramen.
• Transverse distance between the second ASF: Measured as the transverse distance between two points on the medial border of second anterior sacral foramina at the level of second transverse fusion line between the second anterior sacral foramina.
• Distance between the inferior border of the first ASF and the superior border of the second ASF: The vertical distance between the inferior border of first anterior sacral foramen and the superior border of the second anterior sacral foramen.
• Height of S1 vertebral body: The vertical distance between the middle of promontory and the middle of first transverse fusion line between the first anterior sacral foramina.
• Height of S2 vertebral body: The vertical distance between the middle of first transverse fusion line between the first anterior sacral foramina and middle of second transverse fusion line between the second anterior sacral foramina.
• Anterior pedicle height: The vertical distance between the superior border of first anterior sacral foramen and the superior border of the sacrum.

First Posterior Sacral Foramina (PSF):

• Height of first Posterior Sacral Foramina (PSF): Maximum vertical distance between the superior and inferior border of first posterior sacral foramen.
• Width of first PSF: Maximum transverse distance between the medial and lateral border of first posterior sacral foramen.
• Transverse distance between the first PSF: Measured as the transverse distance between the two points marked on the medial border of first posterior sacral foramina at the level of first articular tubercle.

Second Posterior Sacral Foramina (PSF):

• Height of second PSF: Maximum vertical distance between the superior and inferior border of second posterior sacral foramen.
• Width of second PSF: Maximum transverse distance between the medial and lateral border of second posterior sacral foramen.
• Transverse distance between the second PSF: Measured as the transverse distance between two points marked on the medial border of second posterior sacral foramina at the level of second articular tubercle.
• Posterior pedicle height: Measured as the vertical distance between the superior border of first posterior sacral foramen and the superior border of the sacrum.
• Distance between the inferior border of the first PSF and the superior border of the second PSF: Measured as the vertical distance between the inferior border of first posterior sacral foramen and the superior border of the second posterior sacral foramen.
• Antero-medial Screw Trajectory distance (STD): The distance between the infero-lateral aspect of S1 facet joint and the antero-medial point of S1 vertebra (middle of the promontory).
• Antero-lateral Screw Trajectory distance (STD): The distance between the infero-lateral aspect of S1 facet joint and the junction of anterior and lateral border of the ala of sacrum.
• S1 pedicle depth: Measured as the minimal distance between the anterior and posterior borders of the pedicle.
• Sacral wing depth: Measured as the maximum antero-posterior distance between the most posterior point of the ala of sacrum and a point on the anterior surface of the ala.
• Height of S1 facet joint: The maximum vertical distance between the superior and inferior border of S1 facet.
• Width of S1 facet joint: Measured as the maximum transverse distance between the medial and lateral borders of S1 facet.
• Distance between the S1 facet joints: The maximum transverse distance between the medial borders of S1 facets.
• S1 vertebral body Antero-Posterior diameter (APD): Measured as the midline antero-posterior distance between the anterior and posterior borders of S1 vertebral body.
• S1 vertebral body Transverse diameter (TD): Measured as the maximum transverse distance of S1 vertebral body.
• Height of S1 body
• Height of S2body
• Sagittal diameter of the spinal canal: Measured as the midline antero-posterior distance between the anterior and posterior borders of superior aperture of sacral canal.
• Transverse diameter of the spinal canal: Measured as the maximum transverse distance of the superior aperture of sacral canal.
• Sacrum length
• Sacrum width

Statistical Analysis

Results were expressed as Mean±SD (standard deviation). The comparison of morphometric dimensions of the right and left sides was performed using Student’s t-test and p-value was calculated.

Linear Parameters:

The mean height and width of first ASF as well as height of the first PSF were comparable on both the sides but the width of the first PSF was found to be significantly greater on the left side. Furthermore, the height and width of the second ASF and second PSF were also analogous on both the sides. The height and width of the ASF were observed to be greater than the corresponding dimensions of the PSF. Although the transverse distances between the ASF were found to be lesser than the transverse distances between PSF [Table-1]. Mean anterior pedicle height of the sacrum was measured which was significantly greater on the left side. Mean posterior pedicle height was also observed to be slightly more on the left side. Distance between the first ASF and second ASF as well as the distance between the first PSF and second PSF were comparable on both the sides. Antero-medial STD was slightly larger on the right side whereas antero-lateral STD was almost similar on both the sides. Likewise, S1 pedicle depth and S1 wing depth were also observed to be comparable on both the sides. Width of S1 facet joint was more on the right side, though the height of the S1 facet joint was analogous on both the sides [Table - 1]

Table -1:

                 Table -2:

The morphometric analysis of the sacrum conducted in this study highlights the anatomical and clinical relevance of the various measurements of the anterior and posterior sacral foramina, vertebral bodies, pedicles, and other sacral structures. The results provide insights into the bilateral symmetry and variations of the sacral morphology.

Anterior and Posterior Sacral Foramina:

The dimensions of the anterior sacral foramina (ASF) were observed to be larger than those of the posterior sacral foramina (PSF), which aligns with the sacrum’s functional anatomy, accommodating larger neurovascular structures anteriorly.^[8]The measurements of first and second ASF and PSF are smaller compared to study done by Arman C et al., ^[9] in Turkish population and comparable to study done in Indian population by Sandeep Saluja et al., ^[10] The transverse distances between the ASF were found to be smaller compared to those between the PSF, reflecting the differences in spatial alignment on the anterior and posterior surfaces.^[11]These dimensions are crucial for the sacral fixation and as well as nerve stimulation procedures.

In Indian studies the mean anterior pedicle height is more comparable to the Turkish, Greek, Chinese and Egyptian studies. ^[10] In addition the distance between first and second ASF was more comparable to the Middle East and western population, emphasizing the use of posterior screw fixation with relative safe. The mean antero-lateral STD is less compared with Turkish population, hence utmost caution advised while employing screws for lumbo-sacral fixation as it may damage neurovascular structures. ^[9]

The mean height and width of S1 facet joint and also distance between the S1 facet joints in this study were comparable with studies done by Sandeep Saluja et al., and Arman C et al., The dimensions of S1 vertebra in this study are less compared to Arman C et al., study and are comparable with Sandeep Saluja et al., study. This finding signifies the need for Indian study for measurements of S1 which are crucial during posterior and anterior lumbar body fusion procedures.

The sagittal and transverse diameter of sacral spinal canal at superior aperture was comparable with other studies in the literature. These diameters play crucial role in lumbosacral procedures like thecaloscopy. Most parameters showed no statistically significant difference between the right and left sides, indicating a high degree of bilateral symmetry in sacral morphology.^[10]Exceptions were noted for the width of the first PSF, which was significantly greater on the right side, and the anterior pedicle height, which was slightly larger on the left side. These variations, though minor, may have implications in surgical procedures like screw fixation.^[12]

The dimensions of the sacral foramina, pedicles, and vertebral bodies are critical for procedures such as sacroiliac screw placement, pedicle screw fixation, and epidural anesthesia.^[13]The mean antero-medial and antero-lateral screw trajectory distances provide useful guidance for safe and effective screw placement in the S1 vertebra.^[14]The sagittal and transverse diameters of the spinal canal are crucial for assessing the feasibility of sacral canal-related interventions and avoiding neural complications.^[15]

The observed greater height and width of ASF compared to PSF highlight the functional demands of the anterior aspect of the sacrum.^[16]The comparable S1 pedicle depth and sacral wing depth on both sides indicate uniformity, which is advantageous for bilateral surgical approaches.^[17]The larger dimensions of the S1 vertebral body compared to S2 emphasize its load-bearing role and clinical importance in interventions involving the lumbosacral junction.^[18]

The study excluded sacra with damages or bony outgrowths, which might have provided additional insights into pathological variations.Future studies could include a larger sample size, incorporate 3D imaging techniques, and correlate findings with clinical outcomes to enhance the applicability of these morphometric data.

The morphometric data obtained from this study offer valuable insights into sacral anatomy, contributing to safer and more effective clinical and surgical interventions. The high degree of bilateral symmetry observed underscores the reliability of using sacral measurements for procedural planning. However, attention to minor side-specific variations is essential to optimize surgical outcomes.

1.       Rajani S: Anatomical variations of sacral hiatus and associated clinical relevance - a review . Int J Anat Var. 2017, 10:96-8.

2.       JyothinathKothapalli, SubhadradeviVelichety, Varalakshmi Desai, RoshanZameer. Morphometric study of sexual dimorphism in adult sacra of SouthIndian population. Int J Biol Med Res. 2012; 3(3): 2076–81.

3.       Sibani Mazumdar. Sexual Dimorphism and Regional Difference in Size of Sacrum: A Study in Eastern India. Al Ameen J Med Sci. 2012; 5(3):298-307.

4.       Kataria Sushma K, PraveshKulhari, Kaushal Raj Kataria, Pushpa Potaliya. A study of the sacral index in western Rajasthan population in comparison with other races. Int J Anat Res. 2014;2(2):383-85.

5.       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

6.       Shewale SN, Laeeque M, Kulkarni PR, Diwan CV: Morphological andmorphometrical study of sacral hiatus. Int J Recent Trends Sci Technol. 2013, 6:48-52.

7.       Lakshmi AT, Azra J. Surgically Relevant Morphometry of Sacral Hiatus. Anatomica Karnataka 2013;7(1):52-6. 14. Nadeem G. Knowing the level of sacral hiatus for caudal epidural anesthesia. J. Morphol. Sci., 2014;31(1):9-13

8.       Seema, Singh M, Mahajan A. An Anatomical Study of Variations of Sacral Hiatus in Sacra of North Indian Origin and Its Clinical Significance. Int. J. Morphol.2013;31(1):110-4

9.       Candan Arman 1, Sait Naderi, Amaç Kiray, Funda Taştekin Aksu, et al.,The human sacrum and safe approaches for screw placement.Journal of clinical Neuroscience. 2009 Aug;16(8):1046-9.

10.    Sandeep Saluja, Sneha Agarwal, Anitha Tuli, et al. Morphometric analysis of the sacrum and its surgical implications. Journal of clinical and diagnostic research. 2018 June; Vol – 12 (6): 01-06.

11.    Qudusia S, Shariff MH, Jacob M, Rao CP, Avadhani R. A Morphological study of sacral hiatus with its clinical implications. Indian Journal of Applied Research 2014;4(2):34-7.

12.    Liu W, Du XR, Yang LH, Wang R, Zhang JZ, Kong XC, et al. The treatmentof lumbosacral transitional vertebra using sacroiliac screws: clinical anatomicsurvey. Chinese Journal of Clinical Anatomy. 2011;29(5):520-23.

13.    Padmavathi Devi SV, Rajini T, Mokhasi V. Morphometry of the first sacral pediclein South Indian population. International Journal of Current Research and Review.2014;6(13):38-44.

14.    Sinha MB, Mrithunjay R, Soumitra T, Siddiqui AU. Morphometry of first pedicleof sacrum and its clinical relevance. International J of Healthcare & BiomedicalResearch. 2013;1(4):234-40.

15.    Murugesan ND, Dharmalingam M. First sacral pedicle–a morphometric analysis.Indian Journal of Clinical Anatomy and Physiology. 2016;3(1):30-33.

16.    Kumar, B., Kumar, S., Sinha, R. R., Akhtar, M. J., & Kumar, A. (2021). Morphometric study of sacrum and its clinical implications in population in Bihar. Indian Journal of Clinical Anatomy and Physiology, 8(4), 301-304.

17.    Tripathy, P. R., & Sinha, M. B. (2022). Comparative morphometry of the sacrum and its clinical implications: A retrospective study of osteometry in dry bones and CT scan images in patients presenting with lumbosacral pathologies. Cureus, 14(2), e22306

18.    Agarwal, S., Saluja, S., Tuli, A., Raheja, S., Tigga, S. R., & Paul, S. (2018). Morphometric analysis of the sacrum and its surgical implications. Journal of Clinical and Diagnostic Research, 12(6), AC01-AC06.

19.    Bagheri, H., &Govsa, F. (2017). Anatomy of the sacral hiatus and its clinical relevance in caudal epidural block. Surgical and Radiologic Anatomy, 39(9), 943-951.