Femoral Nerve Block

CLINICAL PEARLS

 

Nerve Localization

 

1. Inguinal Lymph Nodes vs. the Femoral Nerve

 

The inguinal lymph nodes may resemble the femoral nerve in cross section with a single level scan. It is therefore important to scan proximally and distally at the inguinal region and trace the course of the femoral nerve. In contrast, the inguinal lymph nodes are discrete superficial structures.

 

Arrowheads = inguinal lymph node   FA = femoral artery

Arrowheads = inguinal lymph node   FA = femoral artery   PFA = profunda femoris artery

 

2. Aberrant Femoral Nerve Location

 

It is important to scan proximal and distal to the inguinal region. The posterior division of the femoral nerve may be found above the iliopsoas muscle far lateral to the femoral artery.

 

Arrowheads = posterior division of the femoral nerve   FA = femoral artery   IPM = iliopsoas muscle

Arrowheads = posterior division of the femoral nerve   IPM = iliopsoas muscle   LA = local anesthetic   The posterior division is located more lateral than usual (location 1).

 

Needle Insertion and Local Anesthetic Injection

 

In Plane Needle Insertion Approach

• The in plane approach is also commonly used for femoral nerve block by aligning the block needle with the ultrasound beam.
• With this approach, the needle shaft and tip can be visualized distinctly but it may take a longer time to align the needle with the beam compared to the out of plane approach.

Insertion of a block needle over the left inguinal region using the in plane approach

In plane needle approach showing needle in contact with the femoral nerve   Arrows = block needle   FA = femoral artery   FV = femoral vein

In plane needle approach showing needle in contact with the femoral nerve   Arrowhead = femoral nerve   FA = femoral artery   FV = femoral vein   LA = local anesthetic

In plane needle approach showing needle in contact with the femoral nerve   Arrows = block needle   FA = femoral artery   FV = femoral vein   LA = local anesthetic

 

CATHETER INSERTION

• A catheter is most commonly placed for continuous femoral nerve block to provide analgesia following total knee replacement and anterior crucriate ligament repair surgery.
• See Catheter Technique for the principles of catheter insertion.
• Patient position, skin preparation and sterilization, and transducer selection (10-12 MHz) are identical for both the continuous catheter and single shot injection techniques.
• With the patient lying supine, insert a 8 cm 17 G insulated needle perpendicular to the ultrasound transducer (Out of Plane Approach).

Aim to place the needle and a 20 G catheter within the femoral triangle deep to the fascia iliaca.

• Once the block needle is in contact with the femoral nerve (+/- nerve stimulation), inject 5-10 mL of local anesthetic or D5W (if nerve stimulation is desired) to distend the perineural space.
• It is important to recognize improper injection that is outside the perineural space.

The catheter is often inserted without real time ultrasound guidance unless an assistant is available to hold the ultrasound transducer in place while the principal operator uses one hand to hold the needle and the other hand to thread the catheter.

• Aim to thread the catheter 3-5 cm beyond the needle tip.
• It may be difficult to visualize local anesthetic spread at the time of injection when the catheter tip is deep within the pelvis beyond the inguinal ligament.
• Catheter advancement may not necessarily follow the course of the femoral nerve because there are several channels in the perineural compartment (1, 2, 3 and 4 as shown in the figure below).

1-4 = channels around the femoral nerve   A = femoral artery   FI = fascia iliaca   N = femoral nerve   S = sartorius muscle   (Picture taken from Reg Anesth Pain Med 2006;31:393)

• This highlights the theoretical advantages of using a stimulating catheter to ensure proper perineural catheter placement.

Observe the hyperechoic catheter tip (arrow) location and local anesthetic spread at the time of injection through the catheter. It is possible to see several hyperechoic dots in the local anesthetic collection indicating coiling of the catheter.   FA = femoral artery   LA = local anesthetic

 

IMAGE GALLERY

 

1. Out of Plane Needle Injection and Injection Technique

 

A. Pre-injection sonogram   Arrow = size of subcutaneous layer   FA = femoral artery   FV = femoral vein   N = femoral nerve

B. Sonogram demonstrating the evidence of improper local anesthetic injection (asterisk) in the subcutaneous layer (note an increase in size of the subcutaneous layer (arrow)   FA = femoral artery

C. Proper local anesthetic injection beyond the fascia iliaca (FI) showing hypoechoic collection above the femoral nerve (N)   FA = femoral artery

D. Sonogram demonstrating the needle tip (NT) next to the femoral nerve (N) in the transverse scan   FA = femoral artery

E. Sonogram demonstrating proper local anesthetic (LA) around the femoral nerve (N)   FA = femoral artery

 

2. Fascia Iliaca

 

Arrowheads indicating the hyperechoic line which is the fascia iliaca

 

3. Profunda Femoris Artery

 

Transverse scan distal to the inguinal crease showing branching of the femoral artery (A) Into the profunda femoris artery   FN = femoral nerve

 

VIDEO GALLERY

 

Femoral Nerve Block (In Plane Approach)

 

Femoral Nerve Block (Out of Plane Approach)

 

Back to Page 1

 

SELECTED REFERENCES

• Casati A, Baciarello M, Di Cianni S et al. Effects of ultrasound guidance on the minimum effective anaesthetic volume required to block the femoral nerve. Br J Anaesth 2007;98:823-827.
• Tsui B C, Dillane D, Pillay J et al. Cadaveric ultrasound imaging for training in ultrasound-guided peripheral nerve blocks: lower extremity. Can J Anaesth 2007;54:475-480.
• Oberndorfer U, Marhofer P, Bosenberg A et al. Ultrasonographic guidance for sciatic and femoral nerve blocks in children. Br J Anaesth 2007;98:797-801.
• Swenson JD, Brown NA: Evaluation of a new fenestrated needle for ultrasound-guided fascia iliaca block. J Clin Anesth 2007; 19: 175-9.
• Pham D C, Guilley J, Dernis L et al. Is there any need for expanding the perineural space before catheter placement in continuous femoral nerve blocks? Reg Anesth Pain Med 2006;31:393-400.
• O'Donnell B D, Mannion S. Ultrasound-guided femoral nerve block, the safest way to proceed? Reg Anesth Pain Med 2006;31:387-388.
• Williams R, Saha B. Best evidence topic report. Ultrasound placement of needle in three-in-one nerve block. Emerg Med J 2006;23:401-403.
• Soong J, Schafhalter-Zoppoth I, Gray AT: The importance of transducer angle to ultrasound visibility of the femoral nerve. Reg Anesth Pain Med 2005; 30: 505
• Schafhalter-Zoppoth I, Zeitz I D, Gray A T. Inadvertent femoral nerve impalement and intraneural injection visualized by ultrasound. Anesth Analg 2004;99:627-628.
• Sites BD, Beach M, Gallagher JD, Jarrett RA, Sparks MB, Lundberg CJ: A single injection ultrasound-assisted femoral nerve block provides side effect-sparing analgesia when compared with intrathecal morphine in patients undergoing total knee arthroplasty. Anesth Analg. 2004; 99: 1539-43.
• Gruber H, Peer S, Kovacs P, Marth R, Bodner G. The ultrasonographic appearance of the femoral nerve and cases of iatrogenic impairment. J Ultrasound Med 2003;22:163-172.
• Marhofer P, Schrogendorfer K, Wallner T, Koinig H, Mayer N, Kapral S. Ultrasonographic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 1998;23:584-588.
• Marhofer P, Schrogendorfer K, Koinig H, Kapral S, Weinstabl C, Mayer N. Ultrasonographic guidance improves sensory block and onset time of three-in-one blocks. Anesth Analg 1997;85:854-857.