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The Femoral Nerve Block

T-drop1he femoral nerve block procedure was one of the very first blocks written on the Neuraxiom website so it is clearly time to re-write and update the details of the block.

The femoral nerve is commonly approached just at or below the level of the inguinal ligament. Blocking it here can provide post-operative analgesia to the entire front of the upper thigh down to and including the patella as well as the medial side of the lower leg to approximately the medial malleolus.

The femoral block is useful for procedures of the anterior thigh and knee, especially those that do involve posterior elements of the leg, such as, anterior cruciate ligament repair without an autologous graft from the posterior leg.  For patients having total knee arthroplasties the femoral nerve block alone will provide good analgesia to about half of patients, the rest will have light to fairly severe pain in the posterior leg in the sciatic distribution.

Because of this the femoral nerve is probably best performed with a proximal sciatic block for more complete coverage of operative procedures from about mid-thigh to the bottom of the foot.

The anterior approach to the sciatic is easily performed in combination with the femoral block within a single prepped field and with a single needle.

Anatomy in Brief

The femoral nerve is actually many separate nerve fibers traveling together.  They arise from the Lumbar Plexus which consists of spinal nerves from 12th thoracic through 5th lumbar levels.

The Fascia Iliaca Compartment Block  is concerned with nerves of the Lumbar Plexus as well but the aim of the fascia iliaca block is to intervene at a more proximal level.  The other major nerves of the leg arising from the lumbar plexus are the obturator and accessory obturator nerve, and the lateral femoral cutaneous nerve. These nerves diverge from the path of the femoral higher in the pelvis and are not generally included in the femoral nerve block.  By approaching the common plane of the nerves which runs beneath the anterior fascia of the iliopsoas muscle, in the fascia iliaca block, we are able to create nerve blocks which can cover the hip area and proximal thigh as well as the anterior thigh to the patellar. 

The femoral nerves exit the pelvis at the top of the thigh while still beneath the fascia of the iliopsoas muscle which wraps around the femoral head and neck.  In many patients some of the femoral nerves can still be seen beneath an anterior “cap” of fascia on the iliopsoas muscle just posterior and lateral to the femoral artery on ultrasound.  This is an important target when it exists in the ultrasound survey, but it is important to note that other components of the femoral nerve have already departed the sub-fascial bundle at this point and are traveling lateral to the femoral artery.  In fact, in many patients the sub-fascial bundle is not present at all and all of the femoral nerve components are found in loose association lateral to the femoral artery.


The Block in Brief

The Femoral Nerve Block



Patient Position



Ultrasound Probe

8 – 14 mHz Linear





Needle Approach

In-Plane or Out-of-Plane

No obvious advantage to either.

Local Solution Volume

20 – 30 ml


Key Anatomy Landmark

Femoral Artery

Femoral Nerves will be lateral to the artery


Look for the subfascial grouping of femoral nerves within the superficial iliopsoas muscle lateral and posterior to artery.

Danger of Patient Falling while block working


A Nerve Block Warning Protocol

In addition to the sensory/pain block, the femoral nerve block can also cause motor block of the quadriceps muscles in the front of the thigh.  The quadriceps group is essential for stabilizing the knee during weight-bearing so all patients who receive a femoral block should be forcefully warned of the greatly increased risk of falling if they attempt to stand or walk using the blocked leg.  This cannot be over-stressed.  Every year many patients fall because of nerve block and some of them have quite serious injuries with life-changing sequelae.

Please consider adopting or developing a formal protocol of warning patients of the dangers attendant on nerve blocks as well as an adhesive label placed directly on the effected limb warning the patient and those coming in contact with the patient that a nerve block has been performed, to take precautions to protect the limb, exercise caution to prevent falls, and the approximate date and time that the block should wear off along with instructions to remove the warning label when the block has dissipated.

This type of comprehensive Nerve Block Warning Protocol costs very little and really works to avoid many potentially serious block-related falls and accidents.

Below you will see an example of a warning label that can be inexpensively reproduced and placed on patients. At our institution we place the label directly on the outer layer of dressing on the limb with the block.  We place an arbitrary date and time of 24 hours on the presumed length of the block with instructions that it may have a longer or shorter duration.




The Femoral Nerve Block Procedure

With the patient supine, place the ultrasound probe just inferior and parallel to the inguinal ligament. Locate the femoral artery, note the position of the femoral veins.  If you are having trouble locating the vessels, turn on the color or power Doppler to hi-light the flow in the vessels.


The common femoral artery bifurcates in the upper thigh, usually a few centimeters below the inguinal ligament.  Occasionally you will find that the femoral artery will bifurcate just at or slightly below the inguinal ligament, move your probe cephalad to try to find a survey location which only shows the common femoral artery. This is possible in most cases. In the rare event where you cannot find a position above the bifurcation pleasure local anesthetic solution lateral to both the superficial and deep femoral arteries.

Once you've found a position in which to survey picture shows the single common femoral artery clearly the femoral nerve will lie lateral to the artery. As stated above many times some portion of the femoral nerves will lie below the iliopsoas fascia just lateral and inferior to the plane of the artery. The nerves will appear as bright, echodense targets. In the vast majority of cases they will be arranged in a pennant flag shape with the base touching the femoral artery and extending lateral to it.

Regardless of the needle approach used your goals should be to place the local anesthetic in three distinct areas lateral to the common femoral artery. These are shown in the flash tutorial at the bottom of this page. The areas suggested for injection are; firstly at the base of the flag area holding the nerves directly lateral to it even when the femoral artery, secondly deep to that same position, thirdly lateral to the base at the tip of the pennant flag shape.


The Femoral Nerve Block Tutorial

Below you find an animated tutorial for the femoral nerve block. It is only a few screens long and may help.  Below the tutorial you will find a link to the Target Practice Page.  I encourage you to visit the Target Practice Page and look at the series. 

Thanks for visiting Neuraxiom.




The Neuraxiom Femoral Target Practice Page.



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