Ankle Block Anatomical Landmarks
For an ankle block, target five sensory nerves using specific bony landmarks: the tibial nerve is blocked approximately 1-2 cm posterior to the medial malleolus at the level of the malleolar tip; the deep peroneal nerve is blocked at the level of the ankle joint between the extensor hallucis longus and tibialis anterior tendons, anterior to the medial malleolus; and the sural, superficial peroneal, and saphenous nerves are blocked via subcutaneous infiltration at defined surface landmarks.
Anatomical Approach to Ankle Block
Deep Nerve Blocks (Perineural Injection)
Tibial Nerve Block:
- Landmark: Medial malleolus
- Location: The tibial nerve lies approximately 1-2 cm posterior to the most medial aspect of the medial malleolus, at the level of the malleolar tip 1
- Technique: Direct perineural injection posterior to the medial malleolus, where the nerve runs in the neurovascular tunnel alongside the posterior tibial artery 2, 3
- Depth: This is a deep block requiring needle advancement to the neurovascular bundle
Deep Peroneal (Fibular) Nerve Block:
- Landmark: Anterior aspect of the medial malleolus and extensor tendons
- Location: The nerve runs between the tibialis anterior tendon (medially) and extensor hallucis longus tendon (laterally) 2, 4
- Technique: Block at the level of the ankle joint, anterior to the medial malleolus, in the fourth fascial compartment 3
- Important caveat: The deep peroneal nerve has variable positioning relative to the anterior tibial artery—it may lie lateral (most common), anterior, medial, or even 1 cm lateral to the artery 5. Use ultrasound guidance when available to account for this anatomical variability and reduce local anesthetic systemic toxicity risk 6
Superficial Nerve Blocks (Subcutaneous Infiltration)
Sural Nerve Block:
- Landmark: Lateral malleolus
- Location: One fingerbreadth (approximately 1 cm) distal to the tip of the lateral malleolus 3
- Technique: Subcutaneous infiltration between the lateral malleolus and Achilles tendon 2
Superficial Peroneal (Fibular) Nerve Block:
- Landmark: Anterior aspect of the medial malleolus
- Location: Subcutaneous tissue on the dorsum of the foot, anterior to the medial malleolus 1, 3
- Technique: Subcutaneous infiltration across the dorsum of the foot to capture the intermediate and medial dorsal cutaneous branches
Saphenous Nerve Block:
- Landmark: Anterior aspect of the medial malleolus
- Location: Subcutaneous tissue anterior to the medial malleolus 1
- Technique: Subcutaneous infiltration in the anteromedial ankle region
Clinical Considerations
Success Rate and Technique Optimization
The ankle block has a success rate of 88-94% when performed correctly 2. The two deep nerves (tibial and deep peroneal) require direct perineural injection, while the three superficial nerves are adequately blocked with subcutaneous infiltration 2.
Safety in Trauma Settings
When performing ankle blocks in patients with lower leg trauma or fractures at risk for acute compartment syndrome:
- Use low-concentration local anesthetics (bupivacaine or ropivacaine 0.1-0.25% for single-shot blocks) without adjuncts to preserve some sensation and allow breakthrough pain detection 7
- Avoid dense, long-duration blocks that significantly exceed surgical duration 7
- Single-shot blocks with lower concentrations are not associated with delays in compartment syndrome diagnosis when appropriate postoperative surveillance is maintained 7
Ultrasound Guidance Benefits
Ultrasound guidance is strongly recommended to:
- Reduce local anesthetic systemic toxicity risk 6
- Account for variable nerve anatomy, particularly the deep peroneal nerve 5
- Ensure accurate needle placement and minimize required local anesthetic volume
Common Pitfalls
- Inadequate identification of the extensor tendon interval for deep peroneal nerve block—palpate carefully to distinguish tibialis anterior from extensor hallucis longus
- Insufficient subcutaneous infiltration of superficial nerves—ensure complete coverage across the dorsum and lateral ankle
- Failure to account for deep peroneal nerve variability—the nerve's position relative to the anterior tibial artery is inconsistent 5
- Excessive local anesthetic concentration in trauma patients—this may mask compartment syndrome symptoms 7