202406221520

Status:

Tags: Regional

Ankle block

Benefits

• no motor block of calf muscle → no foot drop
  • ∴ can ambulate
• suitable for bilateral surgery

Limitation

• tourniquet
  • calf tourniquet → give sedation
  • thigh → need SA / GA
• shorter duration cf Popliteal sciatic nerve block

Preparation

total injectate volume 25-35ml
at least 2-3ml for each, except tibial needs 5ml

Anatomy

5 nerves ("for 5 toes")

• Femoral → saphenous
• sciatic
  • tibial
  • sural
• CPN
  • deep peroneal
  • superficial peroneal

tibial & deep peronal n. are the only 2 running in bundles & supply motor, proprioception & deep sensory innervation of foot

• also larger in size → ∴ block them first to allow time for onset

Tibial n.

larger terminal branch of sciatic n.
running in tarsal tunnel

• Landmark: posterior tibial artery
• Tendons:
  • tibialis posterior
  • flexor digitorum longus
• flexor retinaculum

Branches

• medial calcaneal n.
  • ∴ need to block above the malleolus before it branches out to ensure calcaneal coverage
• medial plantar
• lateral plantar
• inferior calcaneal n.
  • Baxter's neuropathy
• muscular branches

Nerve stimulation

• big toe flexion
• current usually >0.5mA

LA 7-8ml

Superficial peroneal n.

Anatomy

descend under cover of peroneus longus
→ then rise to surface along intermuscular septum btw peroneus brevis & extensor digitorum longus
→ pierces investing crural fascia
Landmark: fibula & investing fascia

LA 2-3ml

Deep peroneal n.

Landmark: anterior tibial / dorsalis pedis artery
LA 5ml

Sural n.

Landmark: lesser saphenous vein
LA 3-5ml

Saphenous n.

pure sensory nerve
Landmark: greater saphenous v.
LA 2-3ml

References

ULTRASOUND GUIDED ANKLE BLOCK (youtube.com)
Ultrasound Guided Ankle Block (Duke)
Ultrasound-guided Ankle Block (Ki JinnChin)