10 Inguinal Paravascular Lumbar Plexus Anesthesia (Femoral Nerve Block)

10.1055/b-0035-124652

10 Inguinal Paravascular Lumbar Plexus Anesthesia (Femoral Nerve Block)

10.1 Anatomical Overview

The femoral nerve arises within the psoas muscle, usually from the anterior divisions of the four large roots L1–L4 but sometimes only from L2–L4, and is the largest nerve of the lumbar plexus (Fig. 10.1). It passes in the fascial space between psoas major and iliacus through the muscular lacuna to the thigh (Fig. 10.2). The iliopectineal fascia separates the muscular lacuna and thus the femoral nerve from the vascular lacuna through which the lymphatic vessels and the femoral artery and vein run. After giving off a few superficial cutaneous branches (anterior cutaneous branches), it lies under the fascia lata and the iliac fascia in the femoral trigone (Woodburne 1983, Hahn et al 1996, Platzer 2014; Fig. 10.3 and Fig. 10.4).

**Fig. 10.2** Lumbar plexus. 1 Common iliac artery 2 Obturator nerve 3 External iliac vein 4 Femoral artery 5 Femoral nerve 6 Lateral cutaneous nerve of the thigh 7 Iliacus muscle 8 Ilioinguinal nerve

**Fig. 10.3** Cranial view of the right inguinal region. Note that the fascia lata and the iliac fascia have to be penetrated to block the femoral nerve (“double-click”). 1 Femoral artery 2 Fascia lata 3 Iliac fascia with iliopectineal arc 4 Genitofemoral nerve 5 Femoral nerve 6 Psoas major A Anterior superior iliac spine B Symphysis

**Fig. 10.4** Cranial view of the right inguinal region. Note that the fascia lata and the iliac fascia have to be penetrated to block the femoral nerve (“double-click,” see also Fig. 10.3). 1 Femoral vein 2 Femoral artery 3 Femoral nerve 4 Iliac fascia 5 Fascia lata

In the region of the inguinal ligament, the femoral nerve is about 1 cm lateral to the artery, where it usually soon fans out (Fig. 10.5 and Fig. 10.6).

**Fig. 10.5** Anatomical overview of the inguinal region: note IVAN (from Inside: Vein, Artery, Nerve). 1 Lateral cutaneous nerve of the thigh 2 Femoral nerve 3 Femoral artery 4 Femoral vein 5 Obturator nerve

**Fig. 10.6** Overview of a femoral trigone: note IVAN (from Inside: Vein, Artery and Nerve). The femoral nerve soon branches out in a fanlike shape. The needle corresponds to the anterior superior iliac spine. 1 Femoral vein 2 Femoral artery 3 Femoral nerve 4 Lateral cutaneous nerve of the thigh 5 Inguinal ligament

The femoral nerve provides the sensory innervation of the anterior thigh and is involved in the innervation of the hip and knee joints and of the femur. It provides the motor supply to the knee extensors and hip flexors.

10.2 Femoral Nerve Block

The inguinal paravascular lumbar plexus block was described in 1973 by Winnie (Winnie et al 1973) as a so-called 3-in-1 block. However anesthesia of the obturator nerve was not proven and is also not likely given the anatomical situation. The technique is therefore called femoral nerve block.

10.2.1 Needle Approach

Landmarks

Anterior superior iliac spine, pubic tubercle.

The anterior superior iliac spine and the pubic tubercle are marked and joined by a line. This connecting line corresponds to the inguinal ligament. The classical puncture site described is 1 cm below the inguinal ligament and about 1.5 cm lateral to the femoral artery (note: IVAN = from Inside: Vein, Artery, Nerve; Fig. 10.5 and Fig. 10.6).

Divergence from the original technique is recommended, selecting the injection site about 1 cm below the inguinal crease, that is, markedly further distally (Fig. 10.7 and Fig. 10.8).

**Fig. 10.7** When index and middle finger are on the femoral artery, the puncture site is exactly at the level of the distal phalanx. Right thigh.

**Fig. 10.8** Recommended puncture site for femoral nerve block. 1 Puncture site 2 Sartorius muscle 3 Femoral nerve 4 Femoral artery 5 Inguinal ligament

Position

The patient lies supine and the leg is slightly abducted and externally rotated. In difficult anatomical situations, a flat pad can be placed under the patient′s buttocks in order to show the topography of the inguinal region better.

Method

The landmarks are marked and the femoral artery is palpated. If the artery cannot be palpated, a vascular Doppler probe can be used for orientation.

After skin disinfection and intracutaneous or superficial subcutaneous local anesthesia about 3 cm (Härtel 1916, Moore 1969) below the inguinal ligament (or 1 cm below the inguinal crease) and about 1.5 cm lateral to the artery, the skin is incised with a small lancet. The needle is then advanced cranially and dorsally at an angle of 30° to the skin and parallel to the artery until the tough resistance of the fascia lata is felt. If a short beveled needle is used, the bevel direction should be parallel to the artery. The resistance is overcome by slightly increasing pressure (Fig. 10.9 and Fig. 10.10).

**Fig. 10.9** Needle approach to the femoral nerve. Fascia lata and iliac fascia must be penetrated. Right inguinal region: 1 Fascia lata 2 Iliac fascia with iliopectineal arc

**Fig. 10.10** Needle approach for femoral nerve block. The needle is advanced proximally in the surrounding sheath using electrostimulation. It must not be forced against resistance. If the response is lost, it can be useful to direct the needle tip somewhat anteriorly by lowering the hub of the needle. Right thigh.

While cautiously advancing the needle further, there is often a second “loss of resistance” when the tip of the needle passes through the iliac fascia (so-called “double-click”). The end of the needle should then be lowered before advancing the needle further proximally parallel to the artery under peripheral nerve stimulation (PNS).

Practical Note

Contractions in the quadriceps femoris muscle and “dancing” of the patella indicate that the tip of the needle is in the correct position in the immediate vicinity of the femoral nerve.

Following negative aspiration, 20 to 40 mL of a medium-acting or long-acting local anesthetic is injected. Digital pressure distal to the needle can promote distribution of the local anesthetic in cranial direction (Fig. 10.11, Fig. 10.12, Fig. 10.13).

**Fig. 10.11** After aspiration, 30 to 40 mL of local anesthetic is injected slowly and with repeated aspiration. Digital compression distal to the needle can be helpful. Right inguinal region.

**Fig. 10.12** Introduction of a flexible catheter by the needle. The catheter should not be advanced more than 3 to 4 cm beyond the needle tip.

**Fig. 10.13** Spread of local anesthetic, shown radiologically using contrast medium. Note the lateral spread. Contrary to the idea of a 3-in-1 block, there is not necessarily central spread toward the lumbar plexus.

If a continuous technique is planned, a flexible 20G catheter is advanced approximately 3 to 5 cm beyond the tip of the needle after injection of the local anesthetic. Before connecting the catheter to a bacterial filter, the catheter should be aspirated again to exclude an intravascular position. Checking the position using ultrasound makes it possible to correct the position by withdrawing the catheter if spread is insufficient in the target region (Fig. 10.14).

**Fig. 10.14** Check of the position of a femoral nerve catheter using ultrasound (the local anesthetic injected through the catheter spreads around the femoral nerve).

Local Anesthetic, Dosages

Initially: 30 mL of a 1% (10 mg/mL) medium-acting local anesthetic (e.g., mepivacaine, prilocaine) or a long-acting local anesthetic (e.g., ropivacaine 0.75% [7.5 mg/mL])

Continuous block: 8 to 10 mL/h ropivacaine 0.2–0.375% (2–3.75 mg/mL)

Combination block with the sciatic nerve: see below

10.2.2 Needle Approach with Ultrasound

Linear transducer: 10 to 12 MHz

Needle: 6 cm

Nerve Localization

Finding the femoral nerve appears to be difficult for beginners. It is always located in the inguinal region close (lateral) to the femoral artery in a triangle formed by the femoral artery (medially), the iliopsoas muscle (laterally), and the iliac fascia/fascia lata (anteriorly). The femoral nerve has stronger anisotropic behavior than other nerves, making it important to have the correct angle of the transducer (Soong et al 2005). Because they have similar reflective properties, it often cannot be clearly distinguished from the surrounding fatty tissue until after the local anesthetic is injected (Fig. 10.18).

Practical Note

The femoral nerve can be best visualized somewhat proximal to the origin of the deep femoral artery from the femoral artery at the level of the inguinal ligament in the short axis.

It is usually an oval hyperechoic structure lying on the iliopsoas muscle lateral to the femoral artery (Fig. 10.15). Further distally in the region of the origin of the deep femoral artery, the nerve soon begins to divide into its branches, so that even after injection of local anesthetic, the compact structure of a single nerve is no longer seen, but individual branches (Fig. 10.16). The nerve is covered by the fascia lata and iliac fascia. Lymph nodes are visible above the fascia in some patients (Fig. 10.17).