Regional Block

Ankle Block (5-Nerve Block)

The ankle block anesthetises five terminal nerves supplying the foot, all derived from the sciatic nerve (L4–S3) except the saphenous nerve (femoral nerve, L3–L4). The five nerves are: (1) Tibial nerve — posterior to medial malleolus, adjacent to posterior tibial artery; (2) Sural nerve — posterior to lateral malleolus; (3) Saphenous nerve — anterior to medial malleolus; (4) Superficial peroneal nerve — anterior lower leg, subcutaneous; (5) Deep peroneal nerve — between extensor hallucis longus and extensor digitorum longus tendons, adjacent to dorsalis pedis artery. Each nerve supplies a distinct territory of the foot.

Onset15–30 minutes for complete block

Duration8–12 hours with bupivacaine 0.5%

CoverageTibial nerve: heel, plantar foot, toes 1–5 (sole)

Clinical Note

Key safety rule: NEVER add adrenaline to LA for ankle/foot/toe blocks. This risks digit ischaemia and gangrene — a catastrophic complication. Use only plain (non-adrenaline) local anaesthetic solutions.

Indications

Forefoot and toe surgery (bunionectomy, hammertoe correction, digit amputation)
Midfoot procedures
Debridement of foot wounds
Fracture reduction in foot (phalanges, metatarsals)
Skin grafting from foot
Removal of foreign bodies in foot
Laceration repair on foot
Ingrowing toenail surgery
Diabetic foot procedures (with caveats)

Contraindications

Infection at injection sites
Known allergy to local anaesthetics
Peripheral vascular disease (relative — assess carefully; LA with adrenaline is CONTRAINDICATED in digits/toes due to vasoconstriction risk)
Lymphoedema (relative)
Patient refusal
Neuropathic foot with absent sensation (if block is for pain management)

Technique

Patient supine; ankle in neutral position or slightly plantar flexed
Tibial nerve: probe posterior to medial malleolus; identify posterior tibial artery (Doppler); nerve lies posterior to artery; inject 5 mL around nerve
Sural nerve: probe posterior to lateral malleolus; subcutaneous injection of 5 mL in tissue posterior to lateral malleolus
Saphenous nerve: anterior to medial malleolus; subcutaneous ring of 3–5 mL from malleolus to anterior shin
Superficial peroneal nerve: subcutaneous infiltration across anterior shin 5 cm above malleoli (fan injection) 5–8 mL
Deep peroneal nerve: dorsalis pedis pulsation between EHL and EDL tendons; 3–5 mL deep to deep fascia adjacent to vessel
Total volume: approximately 20–30 mL (5 mL per nerve; subcutaneous nerves require ring infiltration)
Avoid tourniquet compression during injection

Drug Doses

Agent	Concentration	Volume	Total Dose	Notes
Bupivacaine (PLAIN — no adrenaline)	0.5%	3–5 mL per nerve (total 15–25 mL)	≤75–100 mg	NEVER use adrenaline-containing LA for ankle/foot blocks due to digital ischaemia risk. Max 2 mg/kg.
Ropivacaine (PLAIN)	0.5–0.75%	3–5 mL per nerve	≤100–125 mg	Excellent choice for ankle block. Naturally vasoconstrictive (less ischaemia risk). Max 3 mg/kg.
Levobupivacaine (PLAIN)	0.5%	3–5 mL per nerve	≤75–100 mg	Good option; less cardiotoxic than racemic bupivacaine. Max 2 mg/kg.
Lidocaine (for rapid onset)	1–2% PLAIN	3–5 mL per nerve	≤200–300 mg	Rapid onset 5–10 min. Short duration 1–2h. Use when rapid onset needed. NEVER with adrenaline for foot blocks.

Onset

15–30 minutes for complete block; tibial nerve may take longest to onset

Duration

8–12 hours with bupivacaine 0.5%; 6–8 hours with ropivacaine 0.5%

Complications

Intravascular Injection

Posterior tibial artery and dorsalis pedis artery are in close proximity to tibial and deep peroneal nerves respectively. Aspirate before each injection. Use ultrasound Doppler when available.

LAST

Less common given smaller volumes per site, but total cumulative volume must remain within safe limits. Maximum dose based on total volume across all 5 injection sites.

Ischaemia

Using adrenaline-containing solutions in digital ring blocks or ankle blocks for toe surgery is CONTRAINDICATED. Risk of digital ischaemia and gangrene. Use plain LA only for foot/toe blocks.

Nerve Injury

Uncommon. Risk increased by intraneural injection or neurotoxic additives.

Inadequate Block

Missing individual nerve distributions is common. Systematic approach (all 5 nerves) and adequate volumes reduce failure. Allow 20–30 minutes for full onset.

Landmarks

Medial malleolus and posterior tibial pulse (for tibial nerve)
Lateral malleolus and short saphenous vein (for sural nerve)
Anterior to medial malleolus (for saphenous nerve)
Subcutaneous fat dorsum of ankle/extensor retinaculum (superficial peroneal)
Dorsalis pedis pulse between EHL and EDL tendons (deep peroneal)

Sensory Coverage

Tibial nerve: heel, plantar foot, toes 1–5 (sole). Sural nerve: lateral foot and 5th toe. Saphenous nerve: medial aspect of foot. Superficial peroneal: dorsum of foot (most toes). Deep peroneal: first web space. Complete ankle block provides total foot anaesthesia.

Clinical Pearls

CRITICAL: NEVER use adrenaline in ankle block or digital ring blocks — risk of ischaemia/gangrene

Ultrasound-guided tibial nerve block improves success and reduces vascular puncture

Inject ankle block proximal to malleoli level (not in foot) to ensure adequate nerve coverage

Allow full 30 minutes before operating — tibial nerve can be slow to onset

Sural and saphenous nerves are subcutaneous and require field infiltration rather than perineural injection

Consider checking adequacy of block before tourniquet application

For purely dorsal foot procedures, superficial peroneal + deep peroneal may suffice

Background & Evidence

The ankle block provides complete anaesthesia to the foot below the malleoli. It is an essential technique for emergency medicine — foot wounds, foreign bodies, fractures, and digit procedures are common presentations. The block is technically accessible with relatively low risk, and does not carry the fall risk of proximal lower limb blocks (no motor weakness of quadriceps). The tibial nerve block is the most clinically important component for plantar foot procedures.

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