Ankle block

Surgical approach (typical foot/ankle procedures where an ankle block is used)

• Often used for forefoot/midfoot surgery: hallux valgus (bunion) correction, toe arthrodesis/osteotomy, Morton’s neuroma excision, metatarsal surgery, wound debridement, skin grafts, foreign body removal
• Can be used for some hindfoot procedures (variable): Achilles/heel soft-tissue procedures, calcaneal wound care (may need additional proximal blocks depending on incision/traction)
• Tourniquet: many cases use an ankle/calf tourniquet; calf tourniquet pain may not be covered by ankle block (consider additional block/GA/sedation strategy)
  • Ankle tourniquet generally tolerated better with ankle block than calf/thigh tourniquet

Anaesthetic management (typical)

• Type of anaesthesia: regional (ankle block) often as sole technique; can be combined with sedation or GA for patient/surgical factors
  • If GA: usually SGA appropriate for short day-case foot surgery; ETT if aspiration risk, long case, prone, significant comorbidity, or surgeon preference
• Duration: block performance ~10–20 min; onset 10–30 min depending on LA; surgery commonly 30–120 min
• How painful: forefoot surgery can be moderate–severe post-op pain; ankle block provides excellent analgesia and reduces opioid requirement
• Monitoring/setting: standard monitoring; resus drugs and intralipid available; ultrasound optional (many do landmark technique)

Definition and aims

• Peripheral nerve block at the level of the ankle to anaesthetise the foot by blocking 5 terminal nerves: tibial, deep peroneal, superficial peroneal, sural, saphenous
• Aims: surgical anaesthesia for foot procedures; post-operative analgesia; opioid-sparing; facilitate day-case surgery

Indications

• Sole anaesthetic for forefoot/midfoot surgery (bunion, toe surgery, metatarsal procedures, soft-tissue surgery)
• Analgesia adjunct to GA/spinal for more extensive surgery or when tourniquet pain anticipated
• Emergency department/ward: painful foot wounds, fracture manipulation (selected), debridement/dressing changes

Contraindications

• Absolute: patient refusal; allergy to local anaesthetic; infection at injection sites; inability to cooperate/position safely
• Relative: severe peripheral vascular disease/critical limb ischaemia (risk–benefit; avoid compromising perfusion with vasoconstrictors); significant peripheral neuropathy (diabetes, Charcot) and medico-legal considerations; anticoagulation (generally low-risk superficial block but consider bleeding risk and compressibility); compartment syndrome risk (analgesia may mask pain—use caution in high-risk trauma)
  • ASRA/RA-UK principles: superficial, compressible sites are lower risk; still document neuro status and anticoagulant timing

Relevant anatomy (what you must be able to draw/describe)

• Cutaneous innervation of the foot (key exam map)
  • Tibial nerve → medial & lateral plantar nerves: plantar surface of foot; heel via calcaneal branches
  • Deep peroneal (fibular) nerve → first dorsal web space (between hallux and 2nd toe) + adjacent dorsum
  • Superficial peroneal nerve → most of dorsum of foot (except 1st web space and lateral border)
  • Sural nerve → lateral border of foot and lateral little toe
  • Saphenous nerve (femoral) → medial ankle/medial foot to 1st MTP region (variable)
• Ankle landmarks
  • Medial malleolus, lateral malleolus, Achilles tendon, tibialis anterior tendon, dorsalis pedis artery, posterior tibial artery

Technique overview (5-nerve ankle block)

• General principles
  • Asepsis; incremental injection with aspiration; avoid intraneural injection (high pressure/pain/paraesthesia); document pre-existing neuropathy
  • Typically 5 separate injections (some use field blocks for superficial peroneal and saphenous)
• Local anaesthetic choice/volume (typical adult ranges; tailor to patient and toxicity limits)
  • Common: ropivacaine 0.2–0.5% or levobupivacaine 0.25–0.5% for prolonged analgesia; lidocaine 1–2% for faster onset
  • Volume: often 20–30 mL total (e.g., 4–6 mL per nerve; tibial often 6–10 mL). Use the minimum effective volume
  • Adrenaline: may prolong and reduce systemic absorption but consider end-artery concerns are largely historical; still avoid in severe PVD/critical ischaemia and if using tight tourniquet with compromised perfusion
• Tibial nerve block (posterior tibial)
  • Landmark: posterior to medial malleolus, near posterior tibial artery (PTA) in tarsal tunnel
  • Technique: palpate PTA; insert needle just posterior to artery; advance carefully; inject after negative aspiration (US: identify nerve adjacent to PTA)
• Deep peroneal nerve block
  • Landmark: dorsum of ankle between tibialis anterior and extensor hallucis longus tendons; nerve lies near dorsalis pedis artery
  • Technique: insert just lateral to dorsalis pedis artery; small volume (often 2–5 mL) due to tight fascial compartment
• Superficial peroneal nerve block
  • Landmark: subcutaneous over anterolateral ankle; often blocked by a subcutaneous ring/field block across the dorsum from lateral malleolus towards medial malleolus (excluding saphenous territory if desired)
• Sural nerve block
  • Landmark: posterior to lateral malleolus, superficial alongside small saphenous vein
  • Technique: subcutaneous infiltration in a line posterior/inferior to lateral malleolus towards Achilles tendon
• Saphenous nerve block
  • Landmark: anterior to medial malleolus (subcutaneous); can be blocked with a subcutaneous wheal/line from tibialis anterior tendon to posterior border of medial malleolus
  • Alternative: more proximal saphenous block at knee (adductor canal) if medial coverage inadequate or for tourniquet pain (but that becomes a different block)

Assessment of block

• Test sensory territories before incision
  • Deep peroneal: pinprick/cold in 1st dorsal web space
  • Tibial: plantar surface/heel
  • Superficial peroneal: dorsum of foot
  • Sural: lateral border of foot
  • Saphenous: medial foot/ankle
• If incomplete: top-up the specific nerve territory; consider local infiltration by surgeon; convert to GA if necessary

Complications and their management

• Local anaesthetic systemic toxicity (LAST): rare but possible (multiple injections; vascular areas near PTA/dorsalis pedis)
  • Prevention: dose calculation, incremental injection, aspiration, consider US, avoid heavy sedation masking symptoms
  • Management: stop injection; call for help; airway/oxygen/ventilation; treat seizures (benzodiazepine); lipid emulsion therapy per AAGBI/RA-UK guidance; manage arrhythmias (avoid large doses of propofol in unstable patient; avoid vasopressin; use adrenaline in small increments)
• Nerve injury: intraneural injection, high pressure, needle trauma, ischaemia; higher risk with pre-existing neuropathy
  • Avoid: paraesthesia-seeking; stop if pain on injection; use low opening injection pressure; document neuro exam
• Vascular puncture/haematoma (PTA/dorsalis pedis/small saphenous vein): compress, reassess anticoagulation risk, document
• Infection: asepsis; avoid through cellulitis
• Block failure/incomplete block: anatomical variation; inadequate volume; wrong plane; tourniquet pain not covered
• Masking of compartment syndrome: consider in high-energy foot trauma; maintain vigilance; analgesia should not replace repeated clinical assessment

Perioperative considerations

• Sedation: minimal/light sedation preferred so patient can report paraesthesia or toxicity symptoms; avoid deep sedation without secured airway
• Positioning: supine; leg supported; ensure access to medial and lateral ankle; keep patient warm
• Analgesic plan: paracetamol + NSAID (if appropriate) + rescue opioid; consider dexamethasone (systemic) for PONV/analgesia; counsel on rebound pain as block wears off
• Discharge advice: protect insensate foot; mobilise with aids; avoid heat sources; driving restrictions; when to seek help (persistent numbness, weakness, severe pain, swelling)