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  • Indications: surgery of the anterior thigh and knee surgery
  • Landmarks: femoral (inguinal) crease, femoral artery pulse
  • Nerve stimulation: twitch of the patella (quadriceps) at 0.2–0.5 mA
  • Local anesthetic volume: 15–20 mL

Figure 21-1.

Needle insertion for femoral nerve block.

A femoral nerve block is a quintessential nerve block technique that is easy to master, carries a low risk of complications, and has significant clinical application for surgical anesthesia and postoperative pain management. The femoral block is well-suited for surgery on the anterior thigh and knee, quadriceps tendon repair, and postoperative pain management after femur and knee surgery. When combined with a block of the sciatic nerve, anesthesia of almost the entire lower extremity from the midthigh level can be achieved.

The femoral nerve is the largest branch of the lumbar plexus, arising from the second, third, and fourth lumbar nerves. The nerve descends through the psoas muscle, emerging from the psoas at the lower part of its lateral border, and it runs downward between the psoas and the iliacus. The femoral nerve eventually passes underneath the inguinal ligament into the thigh, where it assumes a more flattened shape (Figure 21-2). The inguinal ligament is a convergent point of the transversalis fascia (fascial sac lining the deep surface of the anterior abdominal wall) and iliac fascia (fascia covering the posterior abdominal wall). As it passes beneath the inguinal ligament, the nerve is positioned lateral and slightly deeper than the femoral artery between the psoas and iliacus muscles. At the femoral crease, the nerve is on the surface of the iliacus muscle and covered by the fascia iliaca or sandwiched between two layers of fascia iliaca. In contrast, vascular fascia of the femoral artery and vein, a funnel-shaped extension of the transversalis fascia, forms a distinctly different compartment from that of the femoral nerve but often contains the femoral branch of the genitofemoral nerve lateral to the vessels (Figure 21-3). The physical separation of the femoral nerve from the vascular fascia explains the lack of spread of a "blind paravascular" injection of local anesthetic toward the femoral nerve.

Figure 21-2.

Anatomy of the femoral triangle.

image femoral artery.
image femoral nerve.
image femoral vein.
image anterior superior iliac spine.
image inguinal ligament.
image sartorius.

Figure 21-3.

Arrangement of the fascial sheaths at the femoral triangle. Femoral nerve is enveloped by two layers of fascia iliaca, whereas femoral vessels are contained in the vascular (femoral) sheath made up of fascia lata.

The branches to the sartorius muscle depart from the anteromedial aspect of the femoral nerve toward the sartorius muscle. Because sartorius muscle twitch may be the result of the stimulation of this specific branch and not the femoral nerve, the sartorius motor response ...

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