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  Table of Contents 
Year : 2022  |  Volume : 23  |  Issue : 1  |  Page : 44-48

Ultrasound versus palpation method for accurate estimation of intervertebral space: A cross-sectional observational study

Department of Anesthesia, PSG Institute of Medical Sciences and Research, Coimbatore, Tamil Nadu, India

Date of Submission11-Apr-2021
Date of Decision30-Dec-2021
Date of Acceptance10-Feb-2022
Date of Web Publication23-Mar-2022

Correspondence Address:
Dr. Silvy Anna Varughese
13/1869, Ramakrishna Nagar, Vadamadurai, Coimbatore - 641 017, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/TheIAForum.TheIAForum_56_21

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Background and Aims: Spinal cord injury resulting from the central neuraxial blockade is a rare but dreadful complication. The most likely cause is believed to be misjudged level of the intervertebral space (IVS). In our study, we assessed the accuracy of IVS marked by the anesthesiologist in 170 patients who were posted for surgery under spinal anesthesia using ultrasonography.
Methodology: This was a prospective examiner-blinded observational study in 170 patients. An anesthesiologist estimated and marked the IVS using conventional palpation method (based on intercristal line), and the level was counterchecked ultrasonically by another anesthesiologist, who was blinded to the initial marked level.
Statistical Analysis: The agreement between the palpation method and ultrasound assessment of IVS was analyzed using the Chi-square test. P < 0.05 was considered statistically significant.
Results and Conclusion: The IVS estimated by conventional palpation method correlated with ultrasound estimation in only 49.4% of patients.

Keywords: Accuracy, anesthesiologist, intercristal line, intervertebral space, palpation, ultrasonogram

How to cite this article:
Seetha A, Varughese SA. Ultrasound versus palpation method for accurate estimation of intervertebral space: A cross-sectional observational study. Indian Anaesth Forum 2022;23:44-8

How to cite this URL:
Seetha A, Varughese SA. Ultrasound versus palpation method for accurate estimation of intervertebral space: A cross-sectional observational study. Indian Anaesth Forum [serial online] 2022 [cited 2023 May 30];23:44-8. Available from: http://www.theiaforum.org/text.asp?2022/23/1/44/340485

  Introduction Top

The ideal site for spinal anesthesia is below conus medullaris to avoid trauma to the spinal cord.[1],[2] Adult conus medullaris ends at the lower border of L1 but is variable. Hence, selecting the appropriate space is crucial for safe neuraxial anesthesia. The most common method of estimating and selecting IVS for neuraxial block is by palpation based on the Tuffiers line, which has an accuracy as low as 29%.[2] The intercristal line or Tuffier's line is an imaginary line joining the two superior iliac crests and it crosses the vertebra at L4 or the L4-L5 space.

Ultrasonography (USG) is a quick, simple, noninvasive, and easy-to-learn technology, which can accurately identify the appropriate space.[3]

This study aims to compare the accuracy of intervertebral space (IVS) estimation with USG versus manual palpation. The existing studies lack data on the obese (body mass index [BMI] >30), pregnant, and elderly patients due to technical challenges in achieving a quality radiological image and patient positioning.[3] We have evaluated data from all the above subsets of populations.

  Materials and Methods Used Top

Study settings

This observational study was undertaken in a tertiary level hospital over 1 year after approval by the Hospital Ethics and Research Committee, Ref no. PSG/IHEC/2019/Appr/FB/055.

A total of 170 patients undergoing surgery under spinal anesthesia were selected. Written and informed consent was taken from all patients.

Inclusion Criteria

included adults, aged 18–80 years, who were American Society of Anesthesiologists (ASA) grade 1–3 posted for surgeries under spinal anesthesia were included in the study.

Exclusion Criteria

Patients not consenting to the study, allergy to local anesthetic, injection site infection, coagulation abnormalities, or any other contraindication to neuraxial blockade were excluded from the study.

A detailed preanesthetic checkup was carried out in all cases. The clinical (e.g., ASA grade, surgical procedure, and pregnant or not) and demographic details (e.g., age, sex, height, and weight) were noted in all patients. In the operation room (OR), the patient was positioned in a sitting or lateral position according to the preference of the patient and the anesthesiologist. The anesthesiologist then proceeded to palpate and mark the desired IVS without revealing which level has been chosen. Using USG-SonoSite S-Nerve ultrasound system curvilinear probe low frequency 13-6 MHz, parasagittal transverse process view was visualized. Using sacrum as the reference landmark, which appears as a hyperechogenic line [Figure 1], the probe was moved in a cephalad direction to reach and assess the IVS. The hyperechogenic pattern with finger-like projection represents a transverse process [Figure 2] (which appears as a trident sign) and is the area adjacent to the IVS [Figure 2]. For accurate counting of the interspace, each space corresponding to the center of the probe was marked on the skin [Figure 3]. The level marked by the first anesthesiologist will be revealed and it will be compared with level defined by the expert for corroboration.
Figure 1: Hyperechoic line of the sacrum deepens and L5 lamina appears as a sharp tooth or sail-like structure. In between is the L5 sacrum interspace

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Figure 2: Transverse process appears as a finger-like acoustic shadow (trident sign)

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Figure 3: Center of ultrasonography probe marked as intervertebral space and checked for congruence with the level marked by landmark technique

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The primary objective was to compare the estimated level by palpation and the space identified by USG. The secondary objectives were to identify factors that could affect the accuracy such as the experience of anesthesiologists marking the space, the position of the patient while marking the IVS, or patient factors such as age, BMI, or pregnancy.

Statistical analysis

The sample size for the primary objective based on previous studies was estimated to be 100 ± 10, with the power of study 80% and a margin of error of 10%. We enrolled 170 patients to allow for subgroup analysis and to account for any loss to follow-up. The demographic details of the study population were presented as percentage and mean (±standard deviation). Data were analyzed using SPSS (IBM, India) software for Windows version 25.0. P < 0.05 was considered statistically significant.

  Results Top

A total of patients of 170 were enrolled and the mean age of the patients in years was 45.218 ± 16.209. The mean height recorded was 160.574 ± 9.51 cm. The mean weight recorded was 66.99 ± 13.83 (range: 32–126) kg. The majority of the patients were ASA grade 2 (71.2%), 17.1% were ASA grade 1, and 11.8% were ASA grade 3.

The block was performed in a lateral position for 80% of patients. In terms of years of experience, 45.9% of the observed anesthesiologists had more than 5 years of experience, 40.6% had 1–5 years, and 13.5% had <1 year of experience.

The IVS palpation was in agreement with ultrasound location only in 49.4% of patients (84 out of 170). This was significant with P < 0.001.

This accuracy was not influenced by age or sex or even the BMI of the patient [Table 1]. However, in pregnant patients, only 31% had an accurately estimated level, as compared to 73% in the nonpregnant group, and this was statistically significant (P = 0.016) [Table 1]. There was no significant difference in the accuracy based on the position for the block (P 0.701), accurate in 47.1% in sitting position versus 50.7% in lateral position [Table 2].
Table 1: Demographic factors and accuracy of intervertebral space marking

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Table 2: Anesthesiologists' experience and patient position and accuracy of intervertebral space marking

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There was no significant difference in the accuracy with the total experience of the anesthesiologist in the three subgroups (<1 year, 1–5 years, and > 5 years) [Table 2].

The most common level chosen by the anesthesiologists was L3-L4 in 147 (86.5%) patients, followed by L2-L3 in 14 (8.2%), L4-L5 in 6 (3.5%), and L1-L2 in (1.8%) patients.[3] The accuracy was higher on L1-L2 (66.7%) and L3-L4 (53.1%) spaces compared to L2-L3 (21.4%) and L4-L5 (16.7%) spaces, and this was found to be statistically significant (P = 0.044).

The anesthesiologist would err to mark the space higher than intended. The error was more frequent in a cephalad direction (72 out of 170 patients) and less frequent in a caudal direction (14 out of 170 patients) [Table 3].
Table 3: Correlation between physical and USG-guided marking among noncorrelated markings

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  Discussion Top

In our study, the accuracy of the palpation method to estimate IVS was 49.4% when counterchecked by ultrasound. The accuracy of palpation methods to assess IVS from previous studies was found to be between 29% and 64%.[3],[4],[5],[6] Our findings are nearly consistent with Whitty et al. who found the accuracy of the palpation method to be 55% in postpartum patients.[5]

The intercristal line, which forms an important landmark while giving spinal anesthesia, is expected to correspond to the body of the L4 vertebra or the L4-L5 vertebral interspace. However, this landmark is shown to be affected by age, sex, height, weight, BMI, and pregnancy, as well as imaging methods used to identify the space.[7],[8],[9] The position of conus medullaris itself can also vary from upper T12 to upper L3 segments, and elderly females can have low-lying conus medullaris.

In our study, we found the accuracy of the palpation method to identify the IVS to be unaffected by age, sex, height, and patient positioning. This is similar to the finding in the study by Parate et al.[3] However, unlike the study by this author, we found the accuracy to be unaffected by anesthesiologists' experience. Again, this finding could be confounded by the fact that the study population was not randomized to whether the senior faculty was performing the blockade for anticipated difficult spinal cases or not.

In pregnant patients, medullary conus is shown to vary in mid-T12-L3 spinal segments. To compound this problem, in our study, the accuracy of the marked IVS was lower in pregnant patients compared to nonpregnant patients. This finding is similar to other studies and raises concerns of inadvertent spinal cord injury during neuraxial blockade during pregnancy.[4],[6]

In our study, the accuracy of the level marked was least in the patients with BMI >30, but there was no statistically significant correlation between BMI and accuracy. This does not correlate with a study by Broadbent et al. who had found impaired accuracy with obesity.[2] However, being an observational study, this finding could be confounded by the position chosen by the anesthesiologist, sitting or lateral.

Although neurological complications with spinal anesthesia are rare, there are instances of grievous spinal cord injury.[10] A higher L2-L3 space might be chosen by an anesthesiologist if it is easily palpable or to reduce the amount of drug. Greaves reported a case of serious spinal injury caused by misidentification of the L2-L3 IVS in a patient receiving heparin.[10]

Ultrasound can be used to visualize the relevant anatomical structures for a lumbar puncture like the depth of subarachnoid space and the needle insertion point which can increase the success of a single attempt neuraxial blockade. Further research is needed if real-time USG improves the incidence of successful single attempt puncture.

Limitations of the study

We have not evaluated in our study for lumbosacral anomalies (lumbarization of the sacrum and sacralization of lumbar vertebra). The incidence of these anomalies is around 6% and can be missed by ultrasonogram. Kim et al. have shown that despite the transitional vertebrae, there appears to be a margin of safety of two IVSs and these authors consider that counting up from the lumbosacral junction is a fairly valid approach to select the interspace for spinal anesthesia.[11]

Another drawback of using ultrasound is the inability to visualize conus medullaris. However, the gold standard techniques to assess the IVS like computerized tomography (CT), magnetic resonance imaging (MRI) and even X-ray, are limited by high cost, risk of radiation, and inability to image in a flexed position. The accuracy of ultrasonogram, when compared to other various techniques to assess IVS, has been reported as 68%–76%, but with appropriate training and experience, it can enhance up to 90%.[12],[13],[14] The ultrasound estimation usually differs from CT and MRI by one space unlike in palpation where errors can be up to four spaces.

  Conclusion Top

IVS estimation by palpation has a very low accuracy of 49.4%. The accuracy was unaffected by age, sex, BMI, and anesthesiologists' experience but was lower in pregnant patients compared to nonpregnant patients. The accuracy was best in L3-L4 space and L1-L2 space, whereas it was low in L2-L3 and L4-L5 space. There was a tendency to mark the IVS higher than intended. Hence, it will be safer to choose a lower space when the space is estimated by palpation. USG is a quick, cheap, and effective tool for correct identification of desired IVS and it is prudent to use it routinely, especially in pregnant patients.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Saifuddin A, Burnett SJ, White J. The variation of position of the conus medullaris in an adult population. A magnetic resonance imaging study. Spine (Phila Pa 1976) 1998;23:1452-6.  Back to cited text no. 1
Broadbent CR, Maxwell WB, Ferrie R, Wilson DJ, Gawne-Cain M, Russell R. Ability of anaesthetists to identify a marked lumbar interspace. Anaesthesia 2000;55:1122-6.  Back to cited text no. 2
Parate LH, Manjunath B, Tejesh CA, Pujari V. Inaccurate level of intervertebral space estimated by palpation: The ultrasonic revelation. Saudi J Anaesth 2016;10:270-5.  Back to cited text no. 3
Schlotterbeck H, Schaeffer R, Dow WA, Touret Y, Bailey S, Diemunsch P. Ultrasongraphic control of the puncture level for lumbar neuraxial block in obstetric anesthesia. Br J Anaesth 2008;100:230-4.  Back to cited text no. 4
Whitty R, Moore M, Macarthur A. Identification of the lumbar interspinous spaces: Palpation versus ultrasound. Anesth Analg 2008;106:538-40.  Back to cited text no. 5
Locks Gde F, Almeida MC, Pereira AA. Use of the ultrasound to determine the level of lumbar puncture in pregnant women. Rev Bras Anestesiol 2010;60:13-9.  Back to cited text no. 6
Margarido CB, Arzola C, Balki M, Carvalho JC. Anesthesiologists' learning curves for ultrasound assessment of the lumbar spine. Can J Anaesth 2010;57:120-6.  Back to cited text no. 7
Rahmani M, Vaziri Bozorg SM, Ghasemi Esfe AR, Morteza A, Khalilzadeh O, Pedarzadeh E, et al. Evaluating the reliability of anatomic landmarks in safe lumbar puncture using magnetic resonance imaging: Does sex matter? Int J Biomed Imaging 2011;2011:868632.  Back to cited text no. 8
Pysyk CL, Persaud D, Bryson GL, Lui A. Ultrasound assessment of the vertebral level of the palpated intercristal (Tuffier's) line. Can J Anaesth 2010;57:46-9.  Back to cited text no. 9
Greaves JD. Serios spinal cord injury due to haematomyelia caused by spinal anesthesia in a patient treated with low-dose heparin. Anaesthesia 1997;52:150-4.  Back to cited text no. 10
Kim JT, Bahk JH, Sung J. Influence of age and sex on the position of the conus medullaris and Tuffier's line in adults. Anesthesiology 2003;99:1359-63.  Back to cited text no. 11
Furness G, Reilly MP, Kuchi S. An evaluation of ultrasound imaging for identification of lumbar intervertebral level. Anaesthesia 2002;57:277-80.  Back to cited text no. 12
Halpern SH, Banerjee A, Stocche R, Glanc P. The use of ultrasound for lumbar spinous process identification: A pilot study. Can J Anaesth 2010;57:817-22.  Back to cited text no. 13
Watson MJ, Evans S, Thorp JM. Could ultrasonography be used by an anaesthetist to identify a specified lumbar interspace before spinal anaesthesia? Br J Anaesth 2003;90:509-11.  Back to cited text no. 14


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3]


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