Indications
Surgery on the anterior aspect of the thigh or superficial operations on the medial lower leg (saphenous nerve), as well as post-operative pain control for femur and knee surgery (knee arthroscopy requires addition of local anesthetic to the arthroscopy site). When combined with a sciatic block, a femoral nerve block can nearly completely anesthetize the leg below the mid-thigh level.
Relevant Anatomy
Femoral nerve (posterior divisions of L2-4) is formed in the psoas major muscle, runs between psoas and iliacus muscles and enters the thigh under the inguinal ligament lateral to the femoral artery, at which point it divides into multiple terminal branches (usually classified as anterior [mostly cutaneous] and posterior [mostly motor])
Landmarks and Surrounding Structures
Important landmarks include the femoral crease, ASIS, pubic tubercle, femoral artery (palpable) and veins (not palpable), both located medially
Cutaneous Innervation
The femoral nerve blocks the anterior thigh, as well as the medial lower leg (from the saphenous nerve). Note that it misses a portion of the medial thigh innervated by the obturator nerve (which also innervates the medially-located obturator externus, adductors [brevis, longus, and magnus], and gracilis muscles)
Muscular Innervation
Major muscles supplied by the femoral nerve include the anterior compartment muscles (quadriceps femoris, sartorius, and pectineus muscles), as well as the more proximal iliacus and psoas major muscles
Distributions Missed
Medial thigh (obturator nerve)
Technique
Traditional Femoral Block
A line is drawn from the ASIS to the pubic tubercle, in order to outline the inguinal ligament. The femoral artery is marked. A 4 cm 22 ga. needle is inserted just lateral to the femoral artery. The femoral nerve is often found within a triangular hyperechoic region, lateral to the femoral artery and superficial to the iliopsoas muscle. Prior to injection, scan both cephalad and caudally, to ensure that you are looking at the femoral nerve (which is continuous) and not mistaking it for lymph nodes (which are not). This is also important because sometimes the posterior division of the femoral nerve (usually located laterally) may have branched off at this level
Fascia Iliaca Block
Enter 1 cm caudal to the line between the lateral third and medial two-thirds of the inguinal ligament. Use a non-cutting needle to feel the two pops as the fascia lata and then the fascia iliaca are entered
Supplementation
Posterior
Complications
Analysis of the Closed Claims Database suggests that nerve damage is the cause of 16% of claims, with 78% of these occurring under general anesthesia and 22% occurring after regional anesthesia. The ulnar nerve is most commonly injured (28%), followed by the brachial plexus (20%). Keep in mind, however, that Closed Claims Data lacks a denominator [Kroll DA et al. Anesthesiology 73: 202, 1990]
