Background and indications: Femoral nerve block has traditionally been used in conjunction with block of the sciatic nerve for surgery of the knee, leg, or foot, as well as saphenous vein stripping. In the past, practitioners used a blind approach (fascia iliaca), which relied on palpating the iliac crest and the pubic ramus. Other practitioners used electrolocation or paresthesia, or they simply infiltrated around the femoral artery after palpating a pulse. Because of the variable distribution and location of the femoral nerve, ultrasound has made the procedure more reliable.

Anatomy: The femoral nerve is formed from roots L2, L3, and L4. These roots combine to form the femoral nerve, which travels in the space between the psoas and iliacus muscles (Fig. 23.1A). In most cases, the nerve actually travels within the subsTance of the psoas muscle (Fig. 23.1B). The nerve emerges below the inguinal ligament, lateral to the femoral artery and deep to the fascia iliaca. Many textbooks portray the nerve as a single round or oval structure. In fact, the nerve is often flat, giving rise to its many branches that subserve the thigh.

Patient position: Supine or recumbent with groin exposed.

Transducer: 8 to 12 MHz linear array or 5 to 8 MHz curved array.

Transducer position: The transducer is placed axially anywhere between the inguinal crease to the inguinal ligament (Fig. 23.2A).

Needle: 5-cm, 22G nerve block needle.

Local anesthetic: 10 (saphenous), 20 (femoral), or 20 to 40 mL (fascia iliaca).