Femoral Nerve Block

Blockade provides anaesthesia to:

Indications

Surgery on:

  • Anterior thigh
  • Knee
  • Femur

Contraindications

  • General contraindications:
    • Patient refusal
    • LA allergy
    • Local infection
  • Specific contraindications
    • Previous femoral bypass

Anatomy

Innervation of the lower extremities occurs via the lumbosacral plexus, which divides into the:

  • Sciatic nerve
  • Femoral nerve

Sciatic Nerve and Branches

The sciatic nerve:

  • Arises from L4-S3
  • Directly provides:
    • Motor supply to the posterior compartment of thigh
    • Sensory supply to posterior thigh
  • Divides at a variable location (but usually close to the popliteal fossa) into the:
    • Common peroneal nerve
      Divides at the knee into two branches which provides sensation to the posterolateral leg:
      • Superficial peroneal nerve
        Provides sensation to dorsum of foot and toes.
      • Deep peroneal nerve
        Provides sensation to the web space between the great and second toe.
    • Tibial nerve
      Innervates the posterior compartment and sole of the foot. Gives off the:
      • Sural nerve
        Provides sensation to the heel, back of the ankle, and the lateral malleolus.
      • Posterior tibial nerve

Femoral Nerve and Branches

The femoral nerve:

  • Arises from L2-4
    Largest branch.
  • Directly provides:
    • Motor supply to knee extensors
    • Sensory supply to anteromedial thigh
  • Divides into the:
    • Obturator nerve
      Formed from L2-4, and enters thigh through obturator foramen. Provides:
      • Motor supply to hip adductors
      • Sensory supply to a variable aspect of the medial thigh/knee
    • Lateral femoral cutaneous nerve
      Formed from L2-3, and runs on ventral surface of iliacus, beneath fascia iliaca. Provides:
      • Sensory supply to lateral aspect of thigh and knee
    • Saphenous nerve
      • Lies in the adductor canal, close to the femoral artery and vein
        Deep to sartorius and superficial to vastus medialis.
        • Typically not visible on ultrasound
          May be seen as a small, round, hyperechoic structure medial to the artery.
        • Typically 2-3cm deep
      • Entirely sensory nerve, providing sensation to medial lower leg and ankle.

Equipment

  • Standard nerve block tray
  • High-frequency linear probe
  • 5-10cm 22G short-bevel needle
  • 20ml local anaesthetic

Technique

  • Position patient supine
  • Identify the inguinal ligament and the femoral artery by palpation or ultrasound
  • Standard prep, drape, skin anaesthesia, etc
  • Place probe in the transverse plane close to the femoral crease, over the femoral artery
  • Identify femoral artery and common femoral vein
  • Identify femoral nerve lateral to the femoral artery
    Features include:
    • Hyperechoic triangular or oval in shape
    • Lies in a sulcus in the iliopsoas muscle
    • Typically 2-4cm deep
    • More visible during dynamic cranial/caudal tilting
    • Best visualised prior to bifurcation of CFA
  • Perform block:
    • Pass needle IP, lateral to medial, through the iliopectineal fascia
    • Aim to place needle adjacent to lateral aspect of the nerve
      May be below fascia iliac, or between its two layers.
    • Inject 1-20ml of LA around nerve, ensuring it remains contained underneath the fascia
      Proper location should result in:
      • Nerve being elevated off iliopsoas
      • LA spreading into the wedge-shaped space lateral to the femoral artery

Complications

  • General complications
    • Intravascular injection
    • LAST
    • Nerve injury
    • Infection
    • Failure
    • Allergy to LA

References

  1. Chuan A, Scott DM. Regional Anaesthesia: A Pocket Guide. 1st Ed. Oxford University Press.
  2. NYSORA. Ultrasound Guided Femoral Nerve Block. Accessed September 2018.
  3. Range C, Egeler C. Fascia Iliaca Compartment Block: Landmark and Ultrasound Approach. WFOSOA. 2010.