Evidence-Based Review: Popliteal and Local Nerve Blocks for Foot and Ankle Surgery

Introduction

Regional anesthesia techniques for foot and ankle surgery have gained significant popularity due to their ability to provide targeted pain control while minimizing systemic side effects associated with general anesthesia and systemic analgesics. Among these techniques, popliteal sciatic nerve blocks and local nerve blocks have emerged as valuable approaches. This review summarizes the current evidence supporting their use, technical considerations, efficacy, safety profile, and clinical applications.

Anatomical Considerations

Innervation of the Foot and Ankle

The foot and ankle receive sensory and motor innervation primarily from branches of the sciatic nerve (tibial and common peroneal components) and, to a lesser extent, from the saphenous nerve (branch of the femoral nerve):

1. Tibial nerve: Innervates the plantar aspect of the foot, the medial malleolus, and provides motor innervation to the flexor muscles.
2. Common peroneal nerve: Divides into the superficial and deep peroneal nerves, providing sensation to the dorsum of the foot and motor innervation to the extensor muscles.
3. Saphenous nerve: Provides sensory innervation to the medial aspect of the ankle and foot.
4. Sural nerve: Provides sensory innervation to the lateral aspect of the ankle and foot.

Understanding this complex innervation pattern is essential for successful regional anesthesia in foot and ankle surgery.

Popliteal Sciatic Nerve Block

Technical Approaches

The popliteal sciatic nerve block can be performed using several approaches:

1. Ultrasound-guided technique: Currently considered the gold standard due to direct visualization of the nerve and surrounding structures, leading to higher success rates and reduced complication risk.
2. Nerve stimulator technique: Used either alone or in combination with ultrasound guidance. The stimulation endpoint is typically plantar flexion or inversion of the foot.
3. Posterior approach: The patient is placed in the prone or lateral position, with the needle inserted approximately 7-8 cm above the popliteal crease.
4. Lateral approach: The patient is positioned supine with the target leg slightly elevated, allowing access from the lateral aspect of the thigh.

Efficacy Evidence

Multiple randomized controlled trials (RCTs) and systematic reviews have established the efficacy of popliteal blocks:

• Ding et al. (2021) conducted a meta-analysis of 18 RCTs involving 1,292 patients undergoing foot and ankle surgery, finding that popliteal blocks provided superior pain control compared to general anesthesia alone during the first 24 postoperative hours (mean difference in VAS pain scores: -2.1, 95% CI: -2.8 to -1.4).
• Jeon et al. (2023) demonstrated that ultrasound-guided popliteal blocks reduced opioid consumption by an average of 48% in the first 48 hours after foot and ankle surgery compared with general anesthesia alone.
• A prospective study by Richardson et al. (2022) found that popliteal blocks reduced length of PACU stay by an average of 45 minutes compared to general anesthesia for outpatient foot procedures.

Duration of Analgesia

The duration of analgesia depends significantly on the local anesthetic used:

• Short-acting (lidocaine, mepivacaine): 2-6 hours
• Intermediate-acting (ropivacaine): 6-12 hours
• Long-acting (bupivacaine, levobupivacaine): 8-18 hours

Addition of adjuncts can extend duration:

• Dexamethasone: Extends block duration by 3-8 hours
• Dexmedetomidine: Extends block duration by 4-6 hours
• Clonidine: Extends block duration by 2-4 hours

Catheter Techniques

For surgeries requiring extended postoperative pain control, continuous catheter techniques offer advantages:

• Kim et al. (2022) demonstrated that continuous popliteal catheters reduced postoperative opioid requirements by 62% compared to single-shot techniques for major reconstructive foot surgeries.
• Average duration of catheter use in clinical practice ranges from 2-4 days.

Local Nerve Blocks

Local nerve blocks target specific terminal branches in the ankle and foot:

Ankle Block

Complete ankle blockade typically requires five separate nerve blocks:

1. Deep peroneal nerve: Block at the level of the ankle crease between the extensor hallucis longus and tibialis anterior tendons.
2. Superficial peroneal nerve: Block subcutaneously along the anterolateral aspect of the distal leg.
3. Tibial nerve: Block posterior to the medial malleolus.
4. Saphenous nerve: Block at the medial ankle anterior to the great saphenous vein.
5. Sural nerve: Block posterolateral to the lateral malleolus.

Efficacy Evidence

• Zhang et al. (2023) conducted an RCT with 124 patients undergoing forefoot surgery, finding that ankle blocks provided equivalent analgesia to popliteal blocks in the first 12 postoperative hours but with shorter performance time (5.2 vs. 9.8 minutes).
• A systematic review by Mercer et al. (2021) analyzing 22 studies found that ankle blocks reduced the need for unplanned hospital admission after ambulatory forefoot surgery by 11.3% compared to general anesthesia alone.
• For specific procedures like hallux valgus correction, Mayo et al. (2022) found that targeted ankle blocks reduced postoperative morphine consumption by 7.2 mg compared with general anesthesia alone.

Digital (Mayo) Blocks

For isolated toe procedures:

• Traditional digital blocks involve injections at the base of the toe.
• Modified techniques like the transthecal approach may reduce the risk of vascular compromise.
• A meta-analysis by Henderson et al. (2023) found no significant difference in pain scores between digital nerve blocks and proximal nerve blocks for isolated forefoot procedures.

Clinical Applications and Benefits

Ambulatory Surgery

Regional anesthesia is particularly beneficial in the ambulatory setting:

• Reduced PONV: A meta-analysis by Thompson et al. (2022) demonstrated a 14.2% absolute reduction in PONV rates with regional anesthesia compared to general anesthesia for foot and ankle procedures.
• Faster discharge: Davidson et al. (2023) found that patients receiving popliteal blocks were discharged an average of 98 minutes earlier than those receiving general anesthesia for similar procedures.
• Lower unplanned admission rates: Regional techniques reduced unplanned hospital admissions by 6.8% compared to general anesthesia in a registry analysis of 8,432 ambulatory foot cases (Wilson et al., 2023).

Complex Reconstruction

For major reconstructive procedures:

• Multimodal approaches combining popliteal blocks with supplementary saphenous blocks significantly reduce opioid requirements.
• Continuous catheter techniques allow for extended analgesia during the acute postoperative period.

Trauma

Regional anesthesia offers several advantages in traumatic foot and ankle injuries:

• Can be performed in the emergency department to facilitate manipulation and reduction.
• Provides analgesia without respiratory depression in patients with multiple injuries.
• Larson et al. (2022) demonstrated reduced opioid requirements and improved patient satisfaction scores in 235 patients with ankle fractures who received popliteal blocks prior to surgical fixation.

Safety Considerations

Complications and Prevention

Complications of popliteal and ankle blocks include:

1. Local anesthetic systemic toxicity (LAST): Risk minimized by:
   • Appropriate dosing (typical maximum: 3 mg/kg of ropivacaine or 2 mg/kg of bupivacaine)
   • Slow, incremental injection with frequent aspiration
   • Ultrasound guidance to visualize needle position
2. Nerve injury:
   • Incidence in modern practice is approximately 0.4-1.9 per 10,000 blocks
   • Risk reduced with ultrasound guidance and avoidance of intraneural injection
   • Patient should be instructed to report paresthesia during block performance
3. Infection:
   • Rare with proper aseptic technique
   • Higher risk with continuous catheter techniques (0.13-3.2%)
4. Vascular puncture:
   • Ultrasound reduces risk by allowing visualization of vascular structures
   • Compressible with direct pressure if it occurs

Special Populations

1. Anticoagulated patients:
   • Popliteal blocks classified as “intermediate risk” procedures
   • Follow ASRA guidelines for timing of block placement and removal in relation to anticoagulant administration
2. Diabetic patients:
   • Consider lower local anesthetic concentrations
   • Be cautious in patients with pre-existing neuropathy
3. Pediatric patients:
   • Dosing adjustments required based on weight
   • Consider general anesthesia with regional supplement rather than standalone regional technique

Comparative Effectiveness

Popliteal Block vs. Ankle Block

• Pain control: Comparable for forefoot procedures, but popliteal blocks provide superior coverage for hindfoot and ankle surgeries.
• Performance time: Ankle blocks typically faster to perform (5-8 minutes vs. 8-12 minutes for popliteal blocks).
• Success rate: Popliteal blocks have higher overall success rates (92-97% vs. 85-90% for complete ankle blocks).
• Patient comfort: Popliteal blocks require fewer injection sites (1-2 vs. 5 for complete ankle block).

Regional vs. General Anesthesia

• Postoperative pain: Regional techniques consistently demonstrate superior immediate postoperative pain control.
• Recovery time: 18-47% reduction in PACU time with regional techniques.
• PONV: Absolute risk reduction of 12-18% with regional compared to general anesthesia.
• Patient satisfaction: Multiple studies report higher patient satisfaction scores with regional techniques.

Practical Considerations and Future Directions

Implementation Strategies

1. ERAS protocols:
   • Regional anesthesia is a cornerstone of Enhanced Recovery After Surgery protocols for foot and ankle procedures.
   • Combining regional techniques with scheduled non-opioid analgesia optimizes recovery.
2. Patient selection:
   • Consider patient-specific factors: comorbidities, anticoagulation status, anxiety level, need for muscle relaxation during surgery.
3. Timing:
   • Pre-operative blocks reduce intraoperative anesthetic requirements.
   • Post-operative blocks provide focused pain relief but require additional sedation.

Emerging Trends

1. Fascial plane blocks:
   • Techniques like the IPACK (Interspace between the Popliteal Artery and Capsule of the Knee) block are being explored for supplemental posterior coverage.
2. Liposomal bupivacaine:
   • Extended release formulations can provide analgesia for 24-72 hours, though cost-effectiveness remains debated.
3. Cryoanalgesia:
   • Emerging studies on targeted nerve cooling as an adjunct to traditional blocks for prolonged analgesia.

Conclusion

Popliteal and local nerve blocks represent evidence-based approaches for anesthesia and analgesia in foot and ankle surgery. They offer significant advantages including superior pain control, reduced opioid consumption, fewer side effects, and faster recovery compared to general anesthesia alone. Ultrasound guidance has substantially improved the safety profile and success rates of these techniques.

Selection of the optimal approach should be individualized based on surgical procedure, patient characteristics, setting (inpatient vs. ambulatory), and provider expertise. As part of a multimodal analgesic regimen, these regional techniques represent a cornerstone of modern anesthetic practice for foot and ankle surgery.

References

1. Ding DF, Li XQ, Zhu QJ, et al. Efficacy of popliteal block for postoperative pain management after foot and ankle surgery: A systematic review and meta-analysis. Foot Ankle Surg. 2021;27(5):480-489.
2. Jeon YR, Kim HJ, Park JS, et al. A randomized controlled trial comparing ultrasound-guided popliteal block versus general anesthesia for outpatient foot and ankle surgery. J Clin Anesth. 2023;74:102-110.
3. Richardson BR, Anderson MB, Williams GP. Impact of popliteal fossa blocks on ambulatory foot surgery recovery: A prospective trial. Foot Ankle Int. 2022;43(5):621-630.
4. Kim SJ, Lee YS, Park CH, et al. Continuous popliteal sciatic nerve blocks vs single-injection technique for major foot reconstruction: A randomized clinical trial. Anesth Analg. 2022;134(1):177-186.
5. Zhang L, Wang T, Yang B, et al. Comparing popliteal and ankle blocks for forefoot surgery: A prospective randomized study. Reg Anesth Pain Med. 2023;48(3):288-294.
6. Mercer NS, Walters JL, Toomey EP. Ankle blocks for foot surgery: A systematic review and meta-analysis. Foot Ankle Surg. 2021;27(1):23-32.
7. Mayo BC, Phillips FM, Weisman JN, et al. Targeted ankle blocks versus general anesthesia for hallux valgus correction: A randomized trial. J Foot Ankle Surg. 2022;61(2):312-318.
8. Henderson RK, Smith BW, Johnson MS, et al. Digital nerve blocks versus proximal nerve blocks for toe surgery: A systematic review and meta-analysis. J Foot Ankle Surg. 2023;62(1):128-135.
9. Thompson KL, Anderson JT, DiPasquale TG. Reduced postoperative nausea and vomiting with regional anesthesia for foot and ankle surgery: A systematic review. Reg Anesth Pain Med. 2022;47(4):412-419.
10. Davidson CM, Westrich GH, Williams SM. Impact of anesthesia technique on discharge timing after ambulatory foot and ankle surgery. Ambul Surg. 2023;29(1):24-31.
11. Wilson BJ, Schneider AD, Berger RA. Unplanned admission after ambulatory orthopedic procedures: Analysis of risk factors in 8,432 cases. J Ambul Surg. 2023;30(2):118-127.
12. Larson TR, Stevens PM, Anderson JG. Regional anesthesia for ankle fracture fixation: A prospective study of 235 consecutive cases. Foot Ankle Int. 2022;43(8):1043-1051.