Ultrasound-Guided Femoral Nerve Block
Indications: femur, patella, quadriceps tendon, and knee sugery; analgesia for hip fracture (Figure 33A–1)
Transducer position: transverse, femoral crease
Goal: local anesthetic spread adjacent to the femoral nerve
Local anesthetic: 10–15 mL
Expected distribution of femorar nerve blockade. Left - Osteotomal distribution, Right - Dermatomal distribution.
The ultrasound (US)-guided technique of femoral nerve blockade allows the practitioner to monitor the spread of local anesthetic and needle placement and make appropriate adjustments to accomplish the desirable disposition of the local anesthetic. US also may reduce the risk of femoral artery puncture. Although nerve stimulation is not required for success, motor response observed during nerve stimulation often provides contributory safety information should the needle–nerve relationship be missed by US alone.
Orientation begins with the identification of the femoral artery at the level of the femoral crease. Commonly, the femoral artery and the deep artery of the thigh are both seen. In this case, the transducer should be moved proximal until only the femoral artery is seen (Figure 33A–2a, b). The femoral nerve is lateral to the vessel and covered by the fascia iliaca; it is typically hyperechoic and roughly triangular or oval in shape (Figure 33A–3a, b). The nerve is enveloped within two layers of the fascia iliaca. The femoral nerve typically is visualized at a depth of 2–4 cm.
Femoral nerve (FN) as seen distally (A) and at the femoral crease (B). Note that FN is better visualized at B, before the take off the deep artery of the thigh (DAT). Femoral vein (FV) is medial to the artery.
(A) Cross-sectional anatomy of the femoral nerve (FN) at the level of the femoral crease. The FN is seen on the surface of the iliopsoas muscle covered by fascia iliaca (white arrows). The femoral artery (FA) and femoral vein (FV) are seen enveloped within their own vascular fascial sheath created by one of the layers of fascia lata. (B) Sonoanatomy of the FN at the femoral triangle. (Reproduced with permission from Hadzic A: Hadzic’s Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed. New York: McGraw-Hill, Inc.; 2011.)