Femoral Nerve Block

Indications

• Surgery of the knee or medial part of the leg or pain management after operations on the femur, patella, knee and ankle

Set-Up

• Insulated 2 inch, 22 G stimulating needle or insulated 2 inch, 18 G Tuohy needle for continuous nerve block
• 15-30 ml of anesthetic of choice Essential Anatomy
• anterior superior iliac spine
• pubic tubercle
• inguinal ligament
• lateral border of the femoral artery at the inguinal crease

Technique

• Place the patient supine.
• After marking the anatomical landmarks and initial puncture site 1 cm lateral to the border of the femoral artery at the inguinal crease, prepare the skin with Betadine solution.
• Infiltrate the skin with local anesthetic at the injection site alongside the inguinal crease and just lateral to the femoral artery (25 G 1.5 inch long needle is best for skin infiltration).
• Initially set the nerve stimulator current at 0.8 mA and 2 Hz.
• Insert the stimulating needle perpendicular or alternatively at 60 degree angle to the skin cephalad and in the saggital plane.
• Maintain the same insertion plane until the twitches of the quadriceps muscle or patellar movements (signs of the main trunk of the femoral nerve stimulation) are observed.
• Once the stimulation of the femoral nerve is obtained at 0.4 mA or less, gently aspirate the syringe to rule-out intravascular placement of the needle and inject 15-30 cc of local anesthetic of choice.
• If the twitches are not obtained, withdraw the needle to the skin and redirect 5-10 degrees laterally. Advance the block needle slowly in the same fashion as during the initial insertion.
• When the nerve is not localized on the first attempt (skin puncture), withdraw the needle and repeat the same technique of needle advancement as described above through a new skin puncture (subsequent attempts) in 5 mm increments lateral to the initial insertion site.
• The appropriate response on nerve stimulation is twitches of the quadriceps muscle (patella movements). Limitations
• Quadriceps muscle weakness may interfere with ambulation for out-patient surgery
• May be contraindicated in patients where a dense sensory block can mask the onset of lower extremity compartment syndrome.
• Avoid in patients with prosthetic femoral artery grafts.

Identified landmarks

Successful needle placement

Complications

• Hematoma formation from inadvertent femoral artery puncture.
• As in all peripheral nerve blocks, nerve injury from needle puncture, intraneural injection of local anesthetics, or local anesthetic toxicity.

Pearls

• The most common (94%) initial twitch obtained, other than from the quadriceps muscle, is that from the sartorius muscle.
• Sartorius muscle twitches are not a reliable sign of adequate localization of the main trunk of the femoral nerve. After obtaining an initial sartorius muscle twitch, the needle is simply redirected laterally 15-20 degrees
• The medial redirection of the stimulating needle should always be avoided because it carries a risk of femoral artery puncture.
• The needle should be advanced and withdrawn slowly since response to nerve stimulation is commonly seen on needle withdrawal, rather than advancement.

References

1. Chia N, Low TC, Poon KH., “Peripheral nerve blocks for lower limb surgery – a choice anaesthetic technique for patients with a recent myocardial infarction,” Singapore Med J. 43(11):583- 6 (2002).
2. Iskandar H, Benard A, Ruel-Raymond J, Cochard G, Manaud B., “Femoral block provides superior analgesia compared with intra-articular ropivacaine after anterior cruciate ligament reconstruction,” Reg. Anesth. Pain Med. 28(1):29-32 (2003).

These technique descriptions are presented for educational purposes and are not intended to substitute for actual hands-on training.