Ankle Block

Indications

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

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

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.

Requires blocking of 5 nerves: