Posterior Lumbar Plexus Block



Fig. 24.1
Surface anatomy and landmarks for posterior lumbar plexus block



The patient lies in the lateral decubitus position with the operative side up and both hips and knees flexed after general anesthesia has been induced. Surface landmarks include:



  • Horizontal line:



    • Intercristal line – a line connecting the upper border of the iliac crests, corresponding to the level of the L4/L5 intervertebral space


  • Vertical line:



    • A line perpendicular to the intercristal line and parallel to the spinous processes, crossing through the ipsilateral posterior superior iliac spines (PSIS)

The site of needle insertion is approximately at the intersection of the two lines described above for Winnie’s technique; however, ultrasound imaging may identify a slightly different needle insertion site.


Clinical Pearl: Chayen’s Technique





  • A more medial and caudal (L5 or below) needle puncture site may be used, following a technique modification described by Chayen and colleagues [1], which places the needle midway between the L5 spinous process and the PSIS.


  • Patients often experience bilateral blockade indicative of epidural spread. This block may be advantageous in cases where epidural anesthesia is contraindicated, such as in patients with scoliosis.


  • Redirections of the needle due to bone contact (iliac bone or vertebral body) may be necessary.


  • The plexus may be reached at a significantly greater depth than when using Winnie’s approach.


  • Motor responses to nerve stimulation may be present in both the thigh and lower leg (ankle and foot).


  • The volume of local anesthetic should likely be reduced to that recommended for epidural injections.



24.3 Nerve Stimulation Technique


The authors recommend combining nerve stimulation with ultrasound guidance for lumbar plexus blocks as the nerve roots/plexus can be difficult to visualize, especially for older children.


24.3.1 Needle Insertion


A flowchart illustrating the needle insertion site and procedures is shown in Fig. 24.2.

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Fig. 24.2
Flowchart of needle insertion and procedures for lumbar plexus blocks




  • Insert an insulated 22–25G, short-bevel needle perpendicular to the skin.


  • The needle will pass through the quadratus lumborum muscle before reaching the psoas major muscle and finally the lumbar plexus. The skin-plexus distance correlated strongly with children’s weight rather than age and height in a study of children between the ages of 3 and 12 and ranged from 1.24 to 1.74 mm/kg depending on age and the level at which the lumbar plexus was visualized with ultrasound imaging (Table 24.1) [2].


    Table 24.1
    Distance of skin-plexus at different ages at L3/L4 and L4/L5
























    Levels where lumbar plexus is delineated

    >3–5 years old

    >5–8 years old

    >8–12 years old

    L3/4

    1.68 mm/kg

    1.55 mm/kg

    1.24 mm/kg

    L4/5

    1.74 mm/kg

    1.6 mm/kg

    1.31 mm/kg


    Based on data from Ref. [2]


  • If the needle contacts the bone (transverse process) at a moderate depth, the needle should be reinserted slightly cranial or caudad. This will occur more frequently if using the needle puncture site described by Chayen et al. [1] (see Clinical Pearl above).


24.3.2 Current Application and Appropriate Responses


Figure 24.3 illustrates the procedure for employing nerve stimulation techniques for lumbar plexus block.

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Fig. 24.3
Flowchart of nerve stimulation techniques for lumbar plexus blocks




  • Initially, set the nerve stimulator to apply 1–2 mA current (2 Hz), and aim to elicit motor twitches of the quadriceps muscle at a current intensity threshold of 0.5 mA. See Table 14.​3 for expected motor responses during nerve stimulation.


24.3.3 Modifications to Inappropriate Responses (Table 24.2)





Table 24.2
Responses and recommended needle adjustments for use with nerve stimulation during lumbar plexus blocks















































Correct response from nerve stimulation

 Quadriceps muscle twitch (palpable or visual) at 0.5–1.0 mA intensity

Other common responses and needle adjustment

 Muscle twitches from electrical stimulation

  Paraspinal (local twitch from direct stimulation)

   Explanation: needle tip too superficial

   Needle adjustment: advance needle tip

  Hamstring (roots of sciatic nerve)

   Explanation: needle inserted too caudally

   Needle adjustment: withdraw completely and reinsert 3–5 cm   cranially

  Thigh flexion (quite deep; psoas major muscle stimulation)

   Explanation: needle tip too deep (close to peritoneal cavity)

   Needle adjustment: withdraw needle and follow protocol

 Bone contact

  Transverse process

   Explanation: close placement; angle slightly off

   Needle adjustment: withdraw to subcutaneous tissue and   reinsert with an angle of 5° more cranially or caudally

 No response despite deep placement

  Past transverse process and lumbar plexus

   Explanation: needle tip too deep

   Needle adjustment: withdraw completely and reinsert   according to protocol

An algorithm of modifications to inappropriate responses to nerve stimulation is shown in Fig. 24.4.

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Fig. 24.4
Flowchart of modifications to inappropriate responses to nerve stimulation during lumbar plexus blocks


24.4 Ultrasound-Guided Technique


For a summary of ultrasound guidance techniques in lumbar plexus blocks, see Fig. 24.5.

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Fig. 24.5
Flowchart of ultrasound-guided techniques in lumbar plexus blocks

Major anatomical structures in the lumbar plexus as captured by MRI and VHVS images are shown with the corresponding ultrasound image in Fig. 24.6.

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Fig. 24.6
(a) VHVS and MRI images of major anatomical structures in the lumbar plexus region. (b) Ultrasound image of major anatomical structures in the lumbar plexus region. Blue rectangle indicates position of ultrasound probe

Prepare the needle insertion site and skin surface with an antiseptic solution. Prepare the ultrasound probe surface by applying a sterile adhesive dressing to it prior to needling as discussed in Chap.​ 4.


24.4.1 Scanning Technique


Traditionally, the approach for the lumbar plexus block has been at the L4–L5 level to avoid renal hematoma or other complications at the level of the kidney (L2–L3). This low approach often results in absence of analgesia in the ilioinguinal/iliohypogastric nerves and occasionally the lateral femoral cutaneous nerve. In the future, ultrasound visualization of the kidneys and vascular structures may allow needle insertion at a more cephalad level (L1–L4) to provide more consistent blockade of these nerves. It must be noted that the lower pole of the kidney can reach down even to the L4–L5 level in young children and infants (Fig. 24.6a).

Sep 22, 2016 | Posted by in ANESTHESIA | Comments Off on Posterior Lumbar Plexus Block

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