Ankle Block: Five Nerves Requiring Blockade
An ankle block requires blocking five nerves to provide complete anesthesia of the foot: the tibial nerve, deep peroneal (fibular) nerve, superficial peroneal (fibular) nerve, sural nerve, and saphenous nerve 1, 2.
The Five Nerves and Their Territories
Deep Nerves (Perineural Injection Required)
- Tibial nerve: Supplies the plantar (bottom) aspect of the foot
- Deep peroneal nerve: Innervates the web space between the great toe and second toe
Superficial Nerves (Subcutaneous Infiltration)
- Superficial peroneal nerve: Provides sensation to the majority of the dorsum (top) of the foot through two branches
- Sural nerve: Supplies the lateral (outer) aspect of the foot
- Saphenous nerve: Innervates the medial (inner) portion of the foot
Important Clinical Considerations
Saphenous Nerve Territory
The saphenous nerve's contribution is more limited than traditionally taught. Recent ultrasound-guided studies demonstrate that its sensory territory extends only approximately 57 mm distal to the medial malleolus, ending about 22 mm proximal to the first tarsometatarsal joint 3. For bunion surgery specifically, 97% of patients do not require saphenous nerve blockade since the surgical field lies distal to its innervation zone 3.
Modern Technique Evolution
Traditional ankle blocks required five separate injections, but newer ultrasound-guided approaches have simplified this. The "five-in-two" (FIT) technique achieves complete foot anesthesia with only two punctures: one mid-calf injection targeting the superficial and deep fibular nerves, and one distal transverse injection 5 cm above the medial malleolus targeting the tibial, saphenous, and sural nerves 4. This approach achieved 96% surgical anesthesia success rates with minimal patient discomfort 4.
Success Rates and Safety
Ankle blocks demonstrate success rates of 88-94% 1, with ultrasound guidance improving accuracy and reducing local anesthetic volumes. The technique is particularly valuable for multimorbid patients due to minimal systemic side effects 1. Block duration typically provides 9-10 hours of sensory anesthesia and motor blockade 4.
Common Pitfall
Do not assume all five nerves must be blocked for every foot surgery—tailor the block to the surgical site. For forefoot procedures like bunion surgery, omitting the saphenous nerve block is appropriate in most cases and reduces unnecessary needle punctures 3.