Lumbar plexus block

Inguinal perivascular block (three-in-one block)


The inguinal perivascular block is based on the concept of injecting local anesthetic near the femoral nerve in an amount sufficient to track proximally along fascial planes to anesthetize the lumbar plexus. The three principal nerves of the lumbar plexus pass from the pelvis anteriorly: the lateral femoral cutaneous, the femoral, and the obturator nerves. As illustrated in Fig. 13.1 , the theory behind this block presumes that the local anesthetic will track in the fascial plane between the iliacus and the psoas muscles to reach the region of the lumbar plexus roots.

Fig. 13.1

Lumbar plexus anatomy: proposed mechanism of proximal local anesthetic spread.

Patient Selection. As outlined, lower extremity block is often most effectively and efficiently performed with neuraxial blocks. Nevertheless, in some patients avoidance of bilateral block or sympathectomy may make an alternative approach necessary.

Pharmacologic Choice. Local anesthetics should be selected by deciding whether a primarily sensory or a sensory and motor block is needed. Any of the amino amides can be used. It has been suggested that the volume of local anesthetic needed for adequate lumbar plexus block from this approach can be estimated by dividing the patient’s height, in inches, by three. That number is the volume of local anesthetic in milliliters that theoretically will provide lumbar plexus block.


Anatomy. The concept behind this block is that the only anatomy one needs to visualize is the extension of sheath-like fascial planes that surround the femoral nerve.

Position. The patient should be placed supine on the operating table with the anesthesiologist standing at the patient’s side in position to palpate the ipsilateral femoral artery.

Needle Puncture. A short-beveled, 22-gauge, 5-cm needle is inserted immediately lateral to the femoral artery, caudal to the inguinal ligament in the lower extremity to be blocked. It is advanced with cephalad angulation until femoral paresthesia occurs; alternatively, nerve stimulation or ultrasonographic guidance is used to identify the correct perineural location of the needle tip. At this point, the needle is firmly fixed, and while the distal femoral sheath is digitally compressed, the entire volume of local anesthetic is injected.

Potential problems

Our clinical experience suggests that the principal problem with this technique is a lack of predictability. In addition, whenever a large volume of local anesthetic is injected through a fixed “immobile” needle, the risk of systemic toxicity is increased. If the technique is used, incremental injection of local anesthetic, accompanied by frequent aspiration for blood, should be carried out.


This block should be used when the goal is lower extremity analgesia, not anesthesia during an operation. We do not believe one needs to master this technique to provide comprehensive regional anesthesia care.

Psoas compartment block


In theory, the psoas compartment block produces block of all lumbar and some sacral nerves, thus providing anesthesia of the anterior thigh. Based on the anatomical site and the expected end result of this block, it is sometimes described as a lumbar paravertebral block .

Lumbar plexus block

Relevant anatomy of the lumbar plexus

The lumbar plexus is formed by the ventral rami of the first three lumbar nerves and the greater part of the ventral ramus of the fourth nerve. The first lumbar nerve, frequently supplemented by the 12th thoracic nerve, splits into an upper branch that divides into the iliohypogastric and ilioinguinal nerves. The lower branch unites with a branch from the second lumbar to form the genitofemoral nerve.

From the remains of the second lumbar nerve, the third and fourth nerves divide into ventral and dorsal divisions. The anterior divisions unite to form the obturator nerves, and the dorsal divisions form the lateral femoral cutaneous nerve and the larger femoral nerve.

The lumbar plexus and its branches are formed within the psoas major muscle in front of the transverse processes of the lumbar vertebrae. The anterior two-thirds of the psoas muscle originate from the anterolateral aspect of the vertebral body, and the posterior one-third of the muscle originates from the anterior aspect of the transverse processes, creating a fascial plane between both compartments of the muscle that hosts the lumbar plexus.

It is important to appreciate that the lumbar plexus is located anterior to the transverse processes of the lumbar vertebrae and posterior (embedded in the post wall) of the psoas muscle. The erector spinae muscle covers the lumbar spine posteriorly medially and the quadratus lumborum muscle laterally.

Appreciation of the relations between the different muscles and spine anatomy, as well as the sonographic characteristics of these structures, is crucial to perform the block.


The lumbar plexus block is a deep block that requires a lower-frequency (2-5 MHz), curvilinear ultrasound probe. A 4- to 6-inch needle is used, depending on the body habitus. Two techniques are described to perform the block.

Paramedian longitudinal scanning technique

With the patient in the prone position (this can also be performed in the lateral position with the side blocked upwards), the ultrasound probe is placed parallel to the long axis of the sacrum to identify its flat surface. The probe is moved cephalad to identify the intervertebral space between L5 and S1 as an interruption of the sacral line continuity. The probe is moved 3-4 cm laterally (keeping the same orientation) to identify the transverse process of L5. The transverse processes of the other lumbar vertebrae are identified by cephalad scan in ascending order. The acoustic shadow of the transverse processes has a characteristic appearance often referred to as a trident sign .

The psoas muscle is imaged through the acoustic windows between the hyperechoic shadows of the transverse processes. The lumbar plexus can be identified as hyperechoic striations in the posterior wall of the psoas muscle. However, appropriate identification of the plexus is confirmed by inducing quadriceps contraction or adduction when applying nerve stimulation to the insulated needle. The needle can be introduced using both the in-plane and out-of-plane techniques in the middle of the probe or using the in-plane technique from the lower edge of the probe ( Fig. 13.2 A-D).

Jun 15, 2021 | Posted by in ANESTHESIA | Comments Off on Lumbar plexus block
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