Femoral Nerve Block
The femoral nerve is the largest terminal branch of the lumbar plexus. It originates from the ventral rami of the L2-L4 nerve roots then exits the pelvis under the inguinal ligament on top of the iliacus muscle. The femoral nerve lies laterally to femoral vessels on the anterior aspect of the tigh. From medial to lateral, the order of the structures is femoral vein, femoral artery and femoral nerve. The femoral nerve lies under two fascial planes, namely the fascia lata and the fascia iliaca. It is usually located 1 to 2 cm lateral to the artery, although there is some variability that can be appreciated under ultrasound.
Ultrasound Femoral Nerve
Colour Doppler- Femoral Vessels
Provide anaesthesia and analgesia to the anterior thigh, hip, femur, knee and medial lower leg and foot.
–Probe: High-frequency linear probe (15-10Hz)
–Needle: 80 to 100 mm short-bevel nerve block needle
–Drug choice: for long-lasting nerve blocks, use bupivacaine O.25% to 0.5%. For short-duration blocks, lidocaine 1 to 2% may be employed.
–Patient position: supine with the legs extended
–Scanning technique: place the US probe transversally on the operative leg in the inguinal crease. Locate the femoral vessels. Color Doppler imaging and occlusion of the vein by application of additional pressure with the probe can help in identifying the vessels. Scan proximally and distally to identify the division of the common femoral artery into superficial and profunda femoral artery. The femoral nerve is identified as a hyperechoic structure on top of the iliacus muscle, lateral to the femoral artery. It is best visualized proximally to the arterial division.
- In-plane approach, lateral to medial
- Out-of-plane approach, distal to proximal
Inplane Femoral Nerve Block
Out of Plane Femoral Nerve Block
Tips for Block success:
-Target: Initial injection just deep and lateral to the nerve, to ensure that the tip of the needle is located below the facia iliaca.
Testing block success
-Block success can be confirmed by an anaesthesia in the territory of the saphenous nerve (medial aspect of the leg) and by a weakness during leg extension (rectus femoris muscle)
Pearls and pitfalls
-Optimize positioning to ensure adequate exposure of the inguinal crease, especially in the obese patient.
-Remember to perform the block as proximal as possible in the inguinal crease to block all the divisions of the nerve.
-Use Doppler imaging to visualize and avoid the lateral femoral circumflex artery which can be located between the divisions of the nerve.
-Ensure the spread of local anaesthetic below the fascia iliaca.
-Electrical stimulation of the posterior branch of the femoral nerve (supplying quadriceps muscle) typically results in patellar twitch. Local anaesthetic may be injected at this point.
-Local anaesthetic systemic toxicity
-Risk of falling
Video Femoral Nerve Block
Continuous catheter technique
A continuous femoral nerve catheter may be placed to provide extended postoperative analgesia after surgeries such as total knee arthroplasty or anterior cruciate ligament repair. Femoral catheters have resulted in improved and prolonged analgesia, decreased opioid requirements, reduced incidence of opioid side effects, decreased hospital stay, improved postoperative rehabilitation and joint mobilization.
Postoperative continuous infusion regime: bupivacaine 0.125% or ropivacaine 0.2% at 5-10 ml/h.
- Kayser Enneking, F, Vincent Chan V, Greger J et al. Lower-Extremity Peripheral Nerve Blockade: Essentials of Our Current Understanding. Reg Anesth Pain Med 2005 30(1): 4–35
- Paul JE, Arya A, Hurlburt L, Ji Cheng J, Thabane L, Tidy A, Murthy Y. Femoral Nerve Block Improves Analgesia Outcomes after Total Knee Arthroplasty. A Meta-analysis of Randomized Controlled Trials. Anesthesiology 2010; 113:1144–62