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Keywords:

  • Anaesthesia;
  • spinal;
  • Anatomy;
  • lumbar vertebral level

Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

The purpose of this study was to assess whether the tenth rib line (an imaginary line that joins the lowest points of the rib cage on the flanks) could be used as a marker of the lumbar vertebral level. Simple X-rays (n = 100) were taken with radiopaque markers attached on the lowest points of the rib cage and the uppermost points of the iliac crests on both flanks. The spinous process or interspinous space that the tenth rib or Tuffier's lines crossed was identified and recorded, respectively, in the neutral and fully flexed positions. With lumbar flexion, the tenth rib line (median (25th to 75th percentiles)) moved upward (L2 (L1−2 − L2) vs. L1–2 (L1–2 – L1–2); p < 0.01), but Tuffier's line moved downward (L4−5 (L4 − L4−5) vs. L4−5 (L4 − L5); p < 0.01). Because the ease of palpating the tenth rib line and its distribution patterns are comparable to those of the Tuffier's line, the tenth rib line may be useful as a new landmark of the lumbar vertebral level as well as a safeguard to prevent spinal puncture from being mistakenly performed at a dangerously high level.

The most common method of identifying lumbar interspaces is to use Tuffier's line, which joins the two iliac crests, or half of Tuffier's line, dropping a perpendicular from the iliac crest to the lumbar spine [1]. However, when anaesthetists attempted to identify a lumbar interspace by palpation of the spinous processes and iliac crests, in 33%[2] or 68%[3] of cases the actual level was reported to be above the level at which they believed it to be [3]. When the intended level was the L3−4 interspace, one of the most frequently used interspaces in the practice of anaesthesia, one experienced anaesthestist even made the error of choosing the T11−12 interspace [3]. Because the clinical use of Tuffier's line requires palpation through a variable amount of subcutaneous fat, high placement is especially likely in the obese [4]. Term parturients with pre-eclampsia, which is often associated with generalised oedema, may cause the same error [5].

The variation in the position of the conus follows a normal distribution, with the peak incidence at the lower third of L1 and ranging from the upper or middle third of T12 to upper third of L3[6, 7]. As a result of this uncertainty, Reynolds suggested that spinal anaesthesia should not be attempted even at the L2−3 interspace [1]. Thus it is clear that a safeguard is required to prevent spinal puncture from being performed mistakenly at a dangerous high level.

The tenth rib line, which joins the two lowest points of the rib cage on the flanks, can be physically constructed in the same way as Tuffier's line. The purpose of this study was to assess the possibility that the tenth rib line could be used as a marker for counting lumbar intervertebral spaces. In addition, this study was performed to identify any potential role of the tenth rib line as a double-check for the selection of a safe intervertebral space.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

After obtaining institutional review board approval and informed consent, 100 volunteers of either sex (n = 50 each) with normal body build were enrolled. Simple X-rays were taken in three positions; supine, lateral decubitus and lateral fully flexed (forehead-to-knees). After each positioning, radiopaque markers were attached on the lowest points of the rib cage and the uppermost points of the iliac crests on both flanks in the same way as when identifying Tuffier's line during spinal block. Additionally, two metal clips were fixed with plaster on the midline of the back, respectively, at the level of the tenth rib and Tuffier's lines. For the skin surface line of the back to be seen clearly on simple X-ray films, a piece of thin wire was longitudinally and tightly fixed with plaster on the midline of the back. To compensate for any inequality of the level on both sides of the rib cages or ilium during the taking of lateral films and any rotation of the rib cage or pelvis during lumbar flexion, in the lateral neutral and flexed views, the tenth rib and Tuffier's lines were formed on the X-ray films as follows in a similar manner to our previous study [8]. A potential line that should cross the midpoint of both markers was drawn perpendicularly to the tangential line at the point where the potential line crossed the skin surface line of the back (Fig. 1). When the above-mentioned conditions were fulfilled and the vertebral levels of the imaginary tenth rib and Tuffier's lines were around the metal clips fixed on the back, the tenth rib and Tuffier's lines were finally formed.

image

Figure 1. Schematic diagram showing how the tenth rib or Tuffier's lines were formed and the vertebral levels decided. In the lateral plain films, the tenth rib and Tuffier's lines were drawn, respectively, from the midpoint of the two radiopaque markers to the back when the lines are, respectively, perpendicular to the tangential line on the skin at the intersection points. From the tangential line a, which was drawn on the film to touch the two successive spinous processes, another imaginary line b parallel to line a was drawn 1 cm toward the vertebral bodies. The spinous process or interspinous space that the tenth rib or Tuffier's lines crossed was identified on line b.

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From the tangential lines that were drawn on the film to touch the two successive spinous processes (line a; Fig. 1), another parallel imaginary line was drawn 1 cm toward the vertebral bodies (line b; Fig. 1). The spinous process or interspinous space that the tenth rib or Tuffier's lines crossed was identified on the imaginary lines and recorded in the neutral and flexed positions. The level was determined by regarding T1 as the vertebra articulated with a normal first rib [9] or T12 as the lowest vertebra that was associated with a rib and by counting down from this vertebra [10]. Formation of the tenth rib and Tuffier's lines was performed by the same assessor, who was unaware of the study design and purposes. The two imaginary lines (the tenth rib and Tuffier's lines) formed on the lateral films were used for final data analysis.

For the purpose of statistical analysis, we assigned a number to each spinous process or interspinous space, such that L5 = 1, L4−5 = 2, L4 = 3, L3−4 = 4 … L1–2 = 8 and L1 = 9. Statistical evaluation for the variability of the tenth rib and Tuffier's line depending on the position of the lumbar spine was performed by the Wilcoxon signed rank test. The statistics program SPSS software (version 9.0; SPSS Inc., Chicago, IL) was used. A p-value < 0.05 was considered statistically significant.

Supplementary measurement

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

A supplementary comparison was performed simultaneously with the main study to check the accuracy of the method for the formation of the tenth rib and Tuffier's lines in the lateral films. When the lowest points of the rib cage or the highest points of the iliac crests were not, respectively, at the same horizontal level in the antero-posterior neutral films, the tenth rib or Tuffier's lines were formed by connecting the centre of the two radiopaque markers. The segment of the vertebral body where the two lines cross the vertebral column was checked in the antero-posterior films. The segment of the vertebral body where the two lines crossed the vertebral column was checked in the lateral neutral films by drawing a perpendicular line from the midpoint of both markers to the tangential line at the intersection point with the skin of the back. The tenth rib and Tuffier's lines formed in the lateral neutral films were found to be exactly at the same segment of the vertebral body as in the antero-posterior neutral films (Fig. 2). Thus, the supplementary measurement confirmed the accuracy of the method for the formation of the two lines in the lateral films.

image

Figure 2. Schematic diagram showing how the accuracy of the method for the formation of the tenth rib and Tuffier's lines in the lateral films was tested. The segment of the vertebral body where the tenth rib or Tuffier's lines cross the vertebral column was checked in the antero-posterior and the lateral neutral films. The tenth rib and Tuffier's lines formed in lateral neutral film were found to be exactly at the same segment of the vertebral body as in the antero-posterior neutral film.

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Results

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Volunteers' age (mean (SD) [range]) was 44.7 (14.3) [20–69] years: 44.5 (14.5) [20–69] years for men and 44.9 (14.3) [20–69] years for women. Height was 161.8 (10.0) [134–182] cm: 167.9 (7.5) [158–182] cm for men and 155.8 (8.6) [134–170] cm for women. Body mass index was 23.5 (3.1) [21.1–32.9] kg.m−2: 22.8 (2.6) [18.3–27.4] kg.m−2 for men and 24.1 (3.6) [18.7–32.9 kg.m−1 for women.

Individual changes of the spinous process level with lumbar flexion, at which the tenth rib or Tuffier's lines intersect, are shown in Fig. 3. With maximum flexion of the lumbar spines, the vertebral level (median (25th to 75th percentiles)), at which the tenth rib line crosses, moved upward when compared with the neutral position (L2 (L2 – L2) vs. L1−2 (L1−2 – L1−2); p < 0.01), but Tuffier's line moved downward (L4 (L4 − L4−5) vs. L4−5 (L4 − L4−5); p < 0.01) in men. In women as well, the tenth rib line moved upward in full flexion (L2 (L1−2 − L2) vs. L1−2 (L1 − L2); p < 0.05) and Tuffier's line moved downward (L4−5 (L4 − L4−5) vs. L4−5 (L4−5 − L5); p < 0.01). Overall, the tenth rib line moved upward with full lumbar flexion compared with the neutral position (L2 (L1−2 − L2) vs. L1−2 (L1−2 − L1−2); p < 0.01), but Tuffier's line moved downward (L4−5 (L4 − L4−5) vs. L4−5 (L4 − L5); p < 0.01) (Fig. 4).

image

Figure 3. Individual change of the spinous process level, at which the tenth rib or Tuffier's lines intersect, while fully flexing the lumbar spine (p < 0.01, respectively). The numbers on both sides of the arrows denote the incidences that the Tuffier's line intersects each bony segmental level (spinous process or interspinous space), and those on the lines denote the number of persons when the bony segmental levels change in such a direction with lumbar flexion.

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image

Figure 4. Effect of full lumbar flexion on the spinous process level at which the tenth rib or Tuffier's lines intersect. The box boundaries are the 25th to 75th percentiles. A thick dotted line within the box represents the medians. Whiskers above and below the box are the 10th to 90th percentiles. Dots give the full range of data.

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Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

Tuffier's line has been the most popular landmark for rapid and easy identification of the lumbar intervertebral level during spinal block. Bony segmental levels at which Tuffier's line crosses the vertebral column are distributed in a normal fashion [7, 10, 11]. However, palpating the upper iliac crests and drawing a line to join them seems to be an unreliable guide in determining the intervertebral space, with a tendency to be one or two spaces higher than assumed [12]. Other approaches appear to be less practicable. Thavasothy [13] recommends a method of identifying the vertebra that is attached to the twelfth rib and counting down from this vertebra, but this is also likely to prove difficult, particularly in the obese [1, 3]. Counting down from the spinous process of C7 could be an alternative technique, but may be tedious and difficult, especially in obese patients, and may introduce an additional source of error [1, 3, 13]. However, the tenth rib line can be formed as easily as Tuffier's line at the bedside, and seems to be easily identifiable on the flanks even after aseptic preparations for spinal or epidural blocks.

Because the clinical use of Tuffier's line requires palpation through a variable amount of subcutaneous fat, high placement is especially likely in the obese [4] or in term parturients with oedema [5]. Palpation of the lowest points of the rib cage will have the same tendency but in the opposite, caudad, direction. In practice, the distance between the lumbar spinous processes will be increased with maximal hip and spine flexion [14]. Thus, when the intervertebral level is guided by palpating the lowest points of rib cage (the tenth rib line) and the upper iliac crest (Tuffier's line) on the flanks, they will move in a caudad and cephalad direction, respectively, and simultaneously, as demonstrated in this study. If we consider the tenth rib line at least as a double-check in combination with Tuffier's line, a more accurate intervertebral level may be sought regardless of the degree of lumbar spine flexion or obesity. Mistakes arising from misidentification of an unusually high interspace as a safe space may thus be prevented, minimising potential risks of cord damage.

During the study, patients' backs were flexed as much as possible during the position for performing spinal puncture and only volunteers of normal body build were recruited. The two lines must have been formed exactly in the same way as during lumbar puncture because radiopaque markers were used on both sides for checking the level of the two lines to prevent errors such as the ‘vertical displacement sign’[15], which occurs while converting three-dimensional structures to two-dimensional plane. During supplementary measurements, the tenth rib and Tuffier's lines in the lateral neutral films were confirmed as crossing the same segment of the vertebral body as in the antero-posterior neutral films. The two imaginary lines formed in the lateral X-ray films were used for the final data analysis because more uniform results could be obtained, regardless of body build, by excluding the subcutaneous thickness [7] and more accurate determination of the corresponding vertebral level was possible. The vertebral level of Tuffier's line in this study closely matches those of other previous reports [7, 10, 11], suggesting that this study was performed accurately. Additionally, because the tenth rib line was measured between the neutral and fully flexed lumbar positions, we think that our results would hold true for any position for spinal or epidural anaesthesia except in the unlikely position of exaggerated lumbar lordosis.

In conclusion, because of the ease of palpation of the tenth rib line at the bedside and because the distribution patterns in both the neutral and fully flexed lumbar positions are comparable to those of Tuffier's line, the tenth rib line seems to be as useful as Tuffier's line as a landmark of the lumbar vertebral level. Even if the tenth rib line may not be used for the identification of a lumbar vertebral level, it can be used at least as a safeguard to prevent a spinal puncture from being performed mistakenly at a dangerously high level, by ensuring that the spinal block is performed at some level lower than the tenth rib line.

Acknowledgements

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References

This work was performed at Seoul National University Hospital, and was supported solely from departmental sources.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Supplementary measurement
  5. Results
  6. Discussion
  7. Acknowledgements
  8. References