CHAPTER 26 Femoral nerve block
Clinical anatomy
The femoral nerve arises from the ventral rami of the second, third, and fourth lumbar nerves. It descends through the substance of the psoas major, emerging from the muscle at the lower part of its lateral border, and passes down between it and the iliacus muscle, deep to the fascia iliaca (Fig. 26.1). It then passes behind the inguinal ligament to enter the thigh. The nerve lies deep to the fascia lata and fascia iliaca. The fascia iliacus separates it from the vascular bundle containing the femoral artery and vein (Fig. 26.2). It divides into two major branches (anterior and posterior) early in the proximal anterior thigh (Fig. 26.1).
Sonoanatomy
To identify the femoral nerve, the transducer is placed over the femoral vessels on the anterior thigh at 90° to the expected orientation of the nerve and vessels (Fig. 26.5). The vessels may be identified as large round hypoechoic structures, and blood flow may be demonstrated using colorflow Doppler (Fig. 26.6). The femoral nerve is then visualized a variable distance lateral to the femoral artery.