Safety margin for needle placement during lumbar plexus block: An anatomical study using magnetic resonance imaging

  • Seokha Yoo
  • Sheung-Nyoung Choi
  • Sun-Kyung Park
  • Won Ho Kim
  • Young-Jin Lim
  • Jin-Tae KimEmail author
Reports of Original Investigations



We aimed to provide anatomic characteristics of the lumbar plexus and a safety margin for needle placement during lumbar plexus block in adults.


Lumbar spine magnetic resonance images from 377 adults were reviewed. We determined the depth of the lumbar plexus from the needle insertion point for the modified traditional and Capdevila’s approaches at the L4 and L5 levels. The relationship of age, height, and body weight with lumbar plexus depth, and the presence of the kidney on the transverse plane at the L4 level were assessed.


The lumbar plexus was deeper at the L5 level than at the L4 level for both approaches (mean difference 3.2 mm [95% confidence interval (CI), 2.4 to 4.0] for the modified traditional approach; mean difference 4.4 mm [95% CI, 3.7 to 5.2] for Capdevila’s approach). Eighty-six (22.8%) patients had an L4 transverse process shorter than 40 mm, which implies that the needle may not contact the L4 transverse process with the modified traditional approach. The mean (standard deviation) of safety margins for needle insertion, defined as the distance from the posterior aspect of the L4 transverse process to the anterior margin of the psoas muscle, were 45 (8) and 44 (6) mm, respectively for the modified traditional and Capdevila’s approach (mean difference, 0.5 mm; 95% CI, −0.1 to 1.1]). The lumbar plexus depth for each approach at the L4 level was predicted using the following equations: Depth (mm) = 87.24 − 0.36 × height (cm) + 0.69 × weight (kg) for the modified traditional approach (r2 = 0.37) and Depth (mm) = 86.51 − 0.35 × height (cm) + 0.61 × weight (kg) for Capdevila’s approach (r2 = 0.33). The kidney was observed at the L4 level in 60 (15.9%) patients, with higher incidence in patients over 70 yr and those shorter than 150 cm.


The surface anatomic relations of the lumbar plexus found in this study may be useful for performing successful and safe lumbar plexus block.

Marge de sécurité pour le positionnement de l’aiguille au cours d’un bloc lombaire : étude anatomique avec imagerie par résonance magnétique



Nous avons cherché à fournir des données anatomiques du plexus lombaire et de la marge de sécurité pour le positionnement de l’aiguille au cours d’un bloc lombaire chez l’adulte.


Les images par résonance magnétique de la colonne vertébrale lombaire de 377 adultes ont été analysées. Nous avons déterminé la profondeur du plexus lombaire à partir du point d’insertion de l’aiguille pour les approches traditionnelle modifiée et de Capdevila aux niveaux L4 et L5. Les corrélations de l’âge, de la taille et du poids corporel avec la profondeur du plexus lombaire et la présence du rein sur le plan de l’apophyse transverse au niveau de L4 ont été évaluées.


Le plexus lombaire était plus profond à l’étage L5 qu’à l’étage L4 pour les deux approches (différence moyenne : 3,2 mm [intervalle de confiance (IC) à 95 % : 2,4 à 4,0] pour l’approche traditionnelle modifiée; différence moyenne : 4,4 mm [IC à 95 % : 3,7 à 5,2] pour l’approche de Capdevila). Quatre-vingt-six patients (22,8 %) avaient l’apophyse transverse de L4 mesurant moins de 40 mm, ce qui implique que l’aiguille pourrait ne pas faire contact avec cette apophyse avec l’approche traditionnelle modifiée. Les marges de sécurité pour l’insertion de l’aiguille, définies comme étant la distance moyenne (écart-type) entre la face postérieure de l’apophyse transverse de L4 et la marge antérieure du muscle psoas, étaient de 45 (8) mm et 44 (6) mm pour, respectivement, l’approche traditionnelle modifiée et l’approche de Capdevila (différence des moyennes, 0,5 mm; IC à 95 % : −0,1 à 1,1). La profondeur du plexus lombaire pour chaque approche au niveau L4 a été prédite à l’aide des équations suivantes : Profondeur (mm) = 87,24 − 0,36 × taille (cm) + 0,69 × poids (kg) pour l’approche traditionnelle modifiée (r2 = 0,37) et Profondeur (mm) = 86,51 − 0,35 × taille (cm) + 0,61 × poids (kg) pour l’approche de Capdevila (r2 = 0,33). Le rein a été observé au niveau L4 chez 60 patients (15,9 %) avec une plus grande incidence chez les patients âgés de plus de 70 ans et chez ceux dont la taille était inférieure à 150 cm.


Les rapports anatomiques de la surface du corps et du plexus lombaire identifiés dans cette étude peuvent contribuer à la réalisation d’un bloc lombaire efficace et sécuritaire.


Conflicts of interest

None declared.

Editorial responsibility

This submission was handled by Dr. Gregory L. Bryson, Deputy Editor-in-Chief, Canadian Journal of Anesthesia.

Author contributions

Seokha Yoo contributed substantially to the study design, data acquisition, data analysis, and writing the manuscript. Sheung-Nyoung Choi contributed substantially to data acquisition and revising the manuscript. Sun-Kyung Park contributed substantially to data acquisition and writing the manuscript. Won Ho Kim contributed substantially to the study design and data analysis. Young-Jin Lim contributed substantially to the study conception and revising the manuscript. Jin-Tae Kim contributed substantially to the study conception, study design, data analysis, and revising the manuscript.

Supplementary material

12630_2018_1280_MOESM1_ESM.pdf (508 kb)
Supplementary material 1 (PDF 507 kb)


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Copyright information

© Canadian Anesthesiologists' Society 2018

Authors and Affiliations

  1. 1.Department of Anesthesiology and Pain MedicineSeoul National University HospitalSeoulKorea

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