Femoral Nerve Block



The femoral nerve arises from the ventral rami of L2-L4 and is one of the larger nerves arising from the lumbar plexus. It enters the femoral triangle below the inguinal ligament.

The anterior branches supply motor innervation to sartorius and pectineus muscles and sensory innervation to the anterior and medial thigh (intermediate and medial cutaneous nerves). 

The posterior branches supply motor innervation to the quadriceps femoris muscles and terminates as the saphenous nerve supplying sensory innervation to the medial leg and foot and partial innervation of the ankle joint. The posterior branch also supplies articular branches to the hip and knee joints.


The femoral nerve block will provide sensory anesthesia.  

Figure 1 - Anatomy of the Femoral Nerve












Accessed 1/13/21. Available at: https://www.physio-pedia.com/images/c/c9/1452198295_lateral-femoral-cutaneous-nerve.jpg


Figure 2 - Expected Distribution of Femoral Nerve Block2











Distribution of FNB highlighted in red. 

Clinical Use: 


Surgery on the femur, patella, quadriceps tendon and knee joint (arthroscopy, meniscus, ACL etc). Partial analgesia for hip joint fractures/procedures.

Block Technique

At the level of the inguinal crease the pulsating femoral artery and femoral vein immediately medial to it are identified by ultrasound. The femoral nerve is always deep to the superficial-most layer of fascia iliaca on the surface of the iliopsoas muscle. 

The femoral nerve can be approached using in-plane and out-of-plane techniques. Local anesthetic is injected lateral to the femoral artery, below the superficial layer of fascia iliaca, but above the iliopsoas muscle. 

In most adults, 20-30ml of a local anesthetic solution is sufficient.

Figure 3 - Correct Spread of Local Anesthetic5








In this in-plane approach, the needle tip can clearly be visualized below the superficial layer of fascia iliaca, with hypoechoic local anesthetic seen spreading within this compartment. The femoral nerve has a slightly ill-defined appearance, which is not unusual, highlighting the importance of recognizing the relevant fascial layers prior to needle insertion.


Block Duration 

As always, block duration will depend on type as well as the volume and concentration of the local anesthetic injected. In general, a typical block can be expected to last 8-12 hours. The femoral nerve is also highly amenable to continuous nerve block techniques.

Special Considerations: 


Absolute contraindications include patient refusal or infection overlying the site of injection. Additionally, pre-existing femoral neuropathy and other systemic neuropathies will need to be carefully considered on a case-by-case basis as the risk of nerve damage (prolonged or permanent) may be unacceptably high. 

Coagulopathies and anticoagulation are relative contraindications.

Side Effects/ Complications

  • quadriceps muscle weakness
  • risk of infection, hematoma and local anesthetic systemic toxicity (LAST)

Vloka JD, Hadzic A, Gautier P. Femoral Nerve Block – Landmarks and Nerve Stimulator Technique. New York Society of Regional Anesthesia (NYSORA). Accessed 1/13/21. https://www.nysora.com/techniques/lower-extremity/femoral/femoral-nerve-block/

Atchabahian A, Leunen I, Vandepitte C, et al. Ultrasound-Guided Femoral Nerve Block. Technique. New York Society of Regional Anesthesia (NYSORA). Accessed 1/13/21.https://www.nysora.com/techniques/lower-extremity/ultrasound-guided-femoral-nerve-block/

Femoral Nerve Block. Ultrasound for Regional Anesthesia (USRA). Accessed 1/13/21. http://usra.ca/regional-anesthesia/specific-blocks/lower-limb/femoralnerveblock.php

Refai NA, Tadi P. Anatomy, Bony Pelvis and Lower Limb, Thigh Femoral Nerve. [Updated 2020 Oct 27]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Accessed 1/13/21. Available from: https://www.ncbi.nlm.nih.gov/books/NBK556065/

Sykes Z, Pak A. Femoral Nerve Block. [Updated 2020 Aug 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Accessed 1/13/21. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546704/