What is the recommended protocol for an ankle block?

Ankle Block Protocol

For ankle and foot surgery, perform an ultrasound-guided ankle block targeting all five sensory nerves of the foot using 0.25-0.5% bupivacaine, as this technique provides superior success rates (84% vs 66%) compared to anatomic landmark guidance and delivers prolonged analgesia averaging 17 hours with minimal systemic absorption. 1, 2

Anatomic Targets

The ankle block requires anesthetizing five distinct nerve branches that supply the foot 3, 4:

• Posterior tibial nerve: Supplies the plantar aspect of the foot 3
• Deep peroneal (fibular) nerve: Supplies the web space between the great and second toes 3
• Superficial peroneal (fibular) nerve: Two branches supplying the majority of the dorsum of the foot 3
• Saphenous nerve: Supplies the medial portion of the foot 3
• Sural nerve: Supplies the lateral aspect of the foot 3

Technical Approach

Ultrasound-Guided vs. Anatomic Landmark Technique

Use ultrasound guidance rather than anatomic landmarks, as this significantly improves clinical outcomes 1:

• Success rate: 84% (USG) vs 66% (ALG) 1
• Reduced need for supplemental local anesthesia: 5% vs 10% 1
• Reduced need for unplanned general anesthesia: 7% vs 17% 1
• Lower supplemental opioid requirements: 12% vs 21% 1
• Particularly beneficial when performed by trainees or less-experienced practitioners 1

Nerve Block Technique

Deep nerves (tibial and deep peroneal): Perform direct perineural anesthesia using either ultrasound guidance or anatomical landmarks 4

Superficial nerves (superficial peroneal, saphenous, sural): Perform subcutaneous infiltration near their branches 4

Local Anesthetic Selection and Dosing

Use 0.25-0.5% bupivacaine as the preferred agent for the following reasons 2, 5:

• Provides mean analgesia duration of 17 hours 2
• Peak blood level of only 0.5 mcg/mL, well below toxic threshold 2
• Most commonly used single long-acting local anesthetic in ankle blocks 5
• Superior safety profile for this indication 2

Volume Requirements

• Bupivacaine 0.75%: 30 mL total volume 2
• Lidocaine 2%: 13 mL total volume (if shorter duration acceptable) 2
• Distribute volume across all five nerve targets 3

Safety Considerations in Lower Extremity Trauma

Compartment Syndrome Risk

Ankle blocks can be safely used without delaying compartment syndrome diagnosis when proper protocols are followed 6:

• Avoid dense, long-duration blocks that significantly exceed surgical duration 6
• Use lower concentrations of local anesthetic without adjuncts (0.25-0.5% bupivacaine preferred over 0.75%) 6
• Implement mandatory post-procedure surveillance with staff trained in compartment syndrome recognition 6
• Use objective scoring charts for monitoring 6
• Ensure equipment for measuring intracompartmental pressure is available 6

Patient Consent and Monitoring

• Provide full explanation of analgesic technique options to patients at risk for compartment syndrome 6
• Document verbal consent 6
• Perform observations at set frequencies by trained healthcare staff 6
• The anaesthetist has final authority on analgesic technique selection, not the surgeon 6

Expected Outcomes

Success Rates

• Overall success rate: 88-94% 4
• Ultrasound-guided technique: 84% success 1
• Patient satisfaction: 66-95.8% 5

Postoperative Pain Control

• VAS scores remain significantly lower at 24 hours postoperatively 5
• Immediate postoperative pain scores are low due to continued analgesic effect 5
• Mean opioid requirement in PACU: 8.7 mg IV morphine equivalent (USG technique) 1

Complications and Management

Common Complications

• Block failure: 6-12% requiring supplemental anesthesia 1, 4
• Transient nerve injuries: Rare, self-limited 5
• Need for intraoperative supplementation: 5% with USG technique 1

Critical Pitfall to Avoid

Do not use high-concentration local anesthetics (>0.5% bupivacaine) or add adjuncts when compartment syndrome risk exists, as dense blocks of long duration may delay diagnosis despite proper surveillance 6. The evidence shows that lower concentrations (0.25-0.5%) provide adequate analgesia without masking compartment syndrome symptoms when combined with appropriate monitoring 6.

Cost-Effectiveness

The ankle block is highly cost-effective compared to general anesthesia 4:

• Decreased hospital expenses 5
• Minimal side effects allowing use in multimorbid patients 4
• Reduced need for postoperative opioids 1
• Suitable for outpatient settings 5, 2