The femoral nerve block is a good first block to master.  There are readily identifiable landmarks, and the potential risks are lower when compared with other blocks. It is the most common lower extremity regional anesthetic performed with ultrasound guidance for knee surgery.1  This block supplies anesthesia from the antero-lateral thigh to the medial malleolus.  It is often combined with a sciatic nerve block to provide almost complete coverage during knee arthroplasty.

Indications: used in conjunction with a sciatic block for knee arthroplasty

Patient Position: supine with slight external rotation of the extremity

Transducer: 7-12 MHz transducer

Transducer Position: perpendicular to the skin and parallel to the iliac crease

Needle: 5 cm, 22 gauge stimulating needle

Local Anesthetic: 15 to 30 ml of local anesthetic

Keys To A Successful Block: passing the needle through the fascia lata and iliaca with circumferential spread observed around the nerve

The femoral nerve arises from the ventral roots of the 2nd, 3rd, and 4th nerves of the lumbar plexus.  It courses distally within the psoas major and iliac muscles running under the inguinal ligament, superior to the iliopsoas muscle, beneath the fascia lata (FL) and iliaca (FI), and lateral to the femoral artery (FA), forming what is called the “femoral triangle”.  At this level, the femoral nerve remains consolidated and is the desired area for placing local anesthetic.  As the nerve continues distally, it divides into anterior (sensory) and posterior (motor) branches, increasing the potential for an incomplete block.

 In the ultrasound image below, the femoral triange can be seen beneath the white arrows (fascia lata), lateral to the femoral artery (FA), and superior to the psosas muscle (IPSM).

 The video below shows the femoral anatomy starting at the inguinal crease, the optimal location for performing the femoral block.  The common femoral artery and vein are  visible as are the fascia lata and iliaca.  Moving caudal, the lateral circumflex artery arises from the femoral artery, coursing laterally through the femoral triangle.  Continuing distally, the femoral artery divides into the superficial femoral and profunda femoris arteries.  The transducer is then moved cephalad to its original position.

The patient is placed in the supine position, with the operative leg in a neutral, or slightly externally rotated position.  A high frequency transducer is normally used, however a mid-range transducer may be required in patients with a large body habitus.  The transducer is placed at the inguinal crease and the major anatomical landmarks are identified.  The image is optimized so that the nerve appears in the center of the screen.  Slight rotation of the transducer will often make the fascia lata and iliaca more visible.  The needle is passed using an in-plane or out-of-plane approach through the two fascia layers, just lateral to the femoral artery.  When performing the in-plane approach, the anesthetist should note the depth of the nerve to determine the approximate angle of needle insertion.  Usually a 5cm, 22 gauge blunt-tip block needle can be used for a single injection, while an 18 gauge tuohy-style needle is used if a catheter is to be placed.  The needle is inserted from lateral to medial.  The out-of-plane approach is more difficult, as only the tip of the needle or a small portion of the needle shaft is observed at any one time.  Hydro-location can be used to help determine the location of the block needle.  The posterior division of the femoral nerve innervates the quadriceps muscles.  It is generally found on the lateral aspect of the femoral triangle and the block needle should be directed there.  For new practitioners, a peripheral nerve stimulation (PNS) can be used in conjunction with US to verify proper needle placement prior to injection of local anesthetic.  Contraction of the sartorius muscle in the medial thigh is a common initial contraction.  Redirecting the needle more laterally and deeper will cause contraction of the quadriceps muscle and elicit a “patellar snap”.  20 to 30 mls of local anesthetic is injected, with circumferential spread of local anesthetic most desired.

If the femoral artery is bifurcated (below left), it is likely that the femoral nerve has divided as well, increasing the chance of an incomplete block.  Slide the transducer proximal, or cephalad, until the common femoral artery is identified.

The video below shows an ultrasound-guided femoral block used in conjunction with nerve stimulation.  The needle is inserted in-plane from lateral to medial.  Initially, a sartorius response was elicited with nerve stimulation, so the needle is redirected to a more lateral position until a “patellar snap” was attained.  The video ends with the initial injection of local anesthetic that separates the nerve from the iliopsosas muscle and pushes it superficially.


Chan VW, Abbas S, Brull R, et al. Ultrasound imaging for regional anesthesia; a practical guide. 3rd ed. Toronto. Toronto Printing Company; 2010:115-123.

Pollard BA, Chan VW. An introductory curriculum for ultrasound-guided regional anesthesia: a learner’s guide. Toronto. University of Toronto Press Inc.; 2009:50-53.

Gray AT. Atlas of ultrasound-guided regional anesthesia. Philadelphia, PA. Saunders, Elsevier; 2010:141-152.

Bigeleisen PE, ed, Orebaugh SL, Moayeri N, et al. Ultrasound-guided regional anesthesia ad pain medicine. Baltimore, MD. Lippincott Williams & Wilkins; 2010:97-103.

Morgan GE, Mikhail MS, Murray MJ. Clinical Anesthesiology. 4th ed. New York, NY: Lange Medical Books/McGraw-Hill; 2006:342-345.

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