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Chapter 32A. Ultrasound-Guided Femoral Nerve Block

Topographically, what is the position of the femoral nerve regarding the fascia iliaca?

A. The femoral nerve lies above the fascia iliaca.

B. The femoral nerve lies underneath the fascia iliaca.

C. The femoral nerve lies between two layers of the fascia iliaca.

D. The femoral nerve lies between the fascia lata and the fascia iliaca.

C is correct. This is mostly the position to find the femoral nerve, in between two layers of the fascia iliaca. In some patients, however, the femoral nerve lies completely underneath the fascia iliaca (Figure 32A–3).

Figure 32A–3

Arrangement of the fascial sheaths at the inguinal crease. 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.

Which is the best location/level to perform a femoral nerve block?

A. At the level of the femoral artery

B. At the level of the bifurcation of the femoral artery and the deep artery of the thigh

C. Underneath the bifurcation of the deep femoral artery and the deep artery of the thigh

D. The femoral artery is not visible when performing a femoral nerve block.

A is correct. Approaching the femoral nerve lower than the bifurcation can lead to an incomplete block due to proximal branches that already separate from the femoral nerve.

A 67-year-old woman is scheduled for a total knee replacement. She receives a femoral nerve block and multimodal analgesia is prescribed. When the patient arrives on the ward, nurses are anxiously calling because of weakness in the operated leg. What kind of weakness do you expect, so you can reassure the nurse and patient?

A. Not able to lift toes (dropfoot)

B. Not able to extend knee (quadriceps weakness)

C. Not able to flex knee (hamstring weakness)

D. Full motor block of the leg

B is correct. The femoral nerve originates from L2-3-4 and has motor branches that supply innervation of the rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius. All these muscles form the quadriceps. The quadriceps is the only extensor of the knee. So, motor weakness after ...

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