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Korean J Anesthesiol > Volume 76(3); 2023 > Article
Jung, Lee, Jeong, and Ryu: Response to "Comment on Comparison between the coronal diameters of the cervical spinal canal and spinal cord measured using computed tomography and magnetic resonance imaging in Korean patients"
We would like to thank you for your interest and appreciate your evaluation of our study [1]. The purpose of this study was to attempt to predict the location of the cervical cord on C-arm anteroposterior (AP) images since this critical structure cannot be visualized.
We agree that the AP view is used in C-arm images and acknowledge the error you have detected in our explanation.
Although it is true that the posterior epidural space is triangular and punctures near the midline can prevent cord injury, this is possible only in people with normal anatomy that do not have, for example, a ligamentum flavum defect. As described in previous studies, the rate of fusion defects of the ligamentum flavum in the cervical spine range from 51% to 74% [2]. Therefore, moving the puncture point from midline to the far lateral position could reduce the risk of cord injury. While performing a cervical epidural block from the far lateral position of the interlaminar foramen, the operator must proceed with caution if any loss of resistance is felt, just as with the midline approach. However, as the puncture point is made laterally, the thickness of the ligamentum flavum is thinner and thus even more careful attention is needed in the event of any loss of resistance. Even when using the loss-of-resistance technique, it is considered safer to carefully check the loss of resistance while advancing the needle gradually rather than continuously. The needle tip position is then confirmed in the contralateral oblique view rather than in the lateral view [3].
In our study, the spinal canal diameter, also referred to as the epidural space diameter, was defined as the distance between the innermost border of the left and right pedicle. We agree that the thickness of the ligamentum flavum is included in the diameter of the epidural space. However, considering the anatomy of the cervical spine [4], the ligamentum flavum at this point is extremely thin and is more likely to affect the AP diameter than the transverse diameter of the epidural space.
Furthermore, as mentioned in the limitations of our study, while the computer tomography and magnetic resonance imaging axial images may not exactly match, we have determined this difference to be insignificant as the images were taken at 1-mm intervals.
Finally, we wholeheartedly agree that we must keep in mind that cervical interlaminar blocks progress in the AP direction; however, as previously mentioned, the perspectives presented in this study are clearly valuable.
Thanks again for your thoughtful recommendations.


Funding: None.

Conflicts of Interest: No potential conflict of interest relevant to this article was reported.

Author Contributions: Jin Yong Jung (Conceptualization; Data curation; Writing – original draft; Writing – review & editing); So Young Lee (Investigation; Writing – original draft); Kyung Wook Jeong (Data curation; Formal analysis; Investigation; Methodology; Visualization); Taeha Ryu (Data curation; Project administration; Software)


1. Lee SY, Kim IY, Jeong KW, Ryu T, Kwak SK, Jung JY. Comparison between the coronal diameters of the cervical spinal canal and spinal cord measured using computed tomography and magnetic resonance imaging in Korean patients. Korean J Anesthesiol 2022; 75: 323-30.
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2. Lirk P, Kolbitsch C, Putz G, Colvin J, Colvin HP, Lorenz I, et al. Cervical and high thoracic ligamentum flavum frequently fails to fuse in the midline. Anesthesiology 2003; 99: 1387-90.
crossref pmid pdf
3. Gill JS, Aner M, Nagda JV, Keel JC, Simopoulos TT. Contralateral oblique view is superior to lateral view for interlaminar cervical and cervicothoracic epidural access. Pain Med 2015; 16: 68-80.
crossref pmid
4. Rahmani MS, Terai H, Akhgar J, Suzuki A, Toyoda H, Hoshino M, et al. Anatomical analysis of human ligamentum flavum in the cervical spine: special consideration to the attachments, coverage, and lateral extent. J Orthop Sci 2017; 22: 994-1000.
crossref pmid


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