At the level of the ankle, there are five nerves that provide sensory innervation of the foot.

Two nerves innervate the volar aspect of the foot. They are the:

1. Sural nerve

2. Posterior tibial nerve

Three nerves innervate the dorsal aspect of the foot. They are the:

1. Saphenous nerve

2. Anterior tibial nerve (also called the deep peroneal nerve)

3. Superficial peroneal nerve (also called the dorsal cutaneous or musculocutaneous nerve)

INDICATIONS

While most injuries of the foot can be managed with either local infiltration or a digital block if an individual finger is involved, there are several circumstances where anesthesia of the entire foot or a large portion of it may prove advantageous:

1. Diffuse or extensive injuries of the foot. Large lacerations of the foot, especially on the heal and sole, may be quite difficult and painful to anesthetize with local infiltration, due to the often thick calloused skin and the extensive sensory nerve innervation.

2. Multiple toe lacerations where performing 4 - 5 individual digital blocks are required.

3. Extensive abrasions with debris embedded in the skin and subcutaneous tissues. This so called “road rash” is difficult and sometimes impossible to anesthetize with local infiltration or topical anesthesia prior to required debridement.

4. Burns, bites or envenomations. In cases of hydrofluoric acid burns where multiple subcutaneous calcium gluconate injections are required; In cases animal bites where rabies immune globulin is required. Stingray or sea urchin envenomation where foreign material removal may be required. Patients in all three situations may have a much less painful experience if total foot anesthesia is obtained prior to the required procedure.

Anesthetic

Either lidocaine 1% - 2% or bupivacaine 0.25 – 0.5 %, without epinephrine.

Alternatives

Local anesthetic infiltration, procedural sedation, general anesthesia. Each case should be individualized, and patient preference, and a discussion of the alternative methods, risks and benefits should be initiated prior to any nerve block.

Sural Nerve Block
   

distribution

The sural nerve supplies innervation to the heal and the posterior lateral aspect of the foot and ankle.

Anatomy

This nerve runs subcutaneously just lateral to the Achilles tendon.

Technique

Using a 22-25 gauge needle, inject 3-5 ml of anesthetic subcutaneously in a band line distribution between the Achilles tendon and the lateral maleolus, at a level approximately one cm superior to the lateral meleolus

Posterior Tibial Nerve Block
 

distribution

The posterior tibial nerve innervates the majority of the sole of the foot, including the entire volar distal foot and volar aspect of all toes. It also innerves the intrinsic muscles of the foot. It does not innervate the heel (sural) or the extreme medial (saphenous) or extreme lateral (sural) aspects of the proximal sole of the foot.

Anatomy

The posterior tibial nerve is immediately posterior and slightly deep to the posterior tibial artery, which can often be palpated just posterior to the medial malleolus.

Both the nerve and artery run just posterior to the flexor digitorum longus tendon and just anterior to the flexor hallucis longus tendon. All of these structures are deep to the flexor retinaculum.

The posterior tibial nerve then divides into the medial and lateral plantar nerves.

Technique

Using a 22-25guage 3-4 cm length needle, enter the skin just medial to the Achilles tendon and posterior to the posterior tibial artery, at the superior aspect of the medial maleolus. The patient will need to be prone as you will need to be posterior to the heal during this procedure. The needle should be directed anteriorly with the tip aiming to pass just posterior to the posterior tibial artery, and advance the needle until it touches the tibia, then withdraw it aapprox 1-2 mm. Aspirate to be sure the needle is not intraarterial. At this point, very gently move the needle medially and laterally to try to elicit paresthesia, and if this is successful, inject 5 cc of anesthetic. If no paresthesia is obtained, then inject 7-10 cc of anesthetic while slowly withdrawing the needle approx one cm.

Saphenous Nerve Block
 

distribution

The saphenous nerve innervates the medial aspect of the foot near the arch.

Anatomy

The saphenous nerve runs parallel to the saphenous vein in the subcutaneous tissues of the medial ankle. It is anterior and lateral to the medial maleolus and medial and posterior to the anterior tibialis tendon.

Technique

Using the superior aspect of the medial maleolus and the anterior tibialis tendon as landmarks, position yourself anterior to the patient and insert a 22-25 guage 3-4 cm needle approx one cm superior the medial maleolus, directing it toward the tibial between the 2 landmarks. Advance the needle until it hits the tibia and then withdraw the needle several mm and deposit 2 cc of anesthetic. Then inject an additional 2-5 cc of anesthetic in a band like pattern in the subcutaneous region between the tendon and maleolus.

Anterior Tibial (Deep Peroneal) Nerve Block
 

distribution

This nerve primarily innervates muscle, but it does supply sensory innervation to the dorsal 1 st and 2 nd digit web space and region just proximal to this web space.

anatomy

The anterior tibial nerve at the level of the ankle is located between the anterior tibialis tendon and the extensor hallucis longus tendon. The anterior tibialis tendon can be palpated by having the patient dorsiflex the foot. The extensor hallucis longus tendon can be palpated by having the patient dorsiflex the great toe.

Technique

The operator should be positioned in front of the patient. Insert a 22 – 25 guage 2-4 cm length needle, just lateral to the anterior tibialis tendon at a level one cm superior to the medial maleolus. Direct the needle at a 30 degree ankle laterally until it reaches the tibia, then withdraw slightly and inject 2-4 cc of anesthetic.

Superficial Peroneal Nerve Block
 

distribution

The superficial peroneal nerve innervates the entire dorsum of the foot, with the exception of the dorsal web space region between the first and second toes.

Anatomy

The superficial peroneal nerve at the level of the ankle is at the anterolateral aspect, between the extensor hallucis longus tendon and the lateral malleolus.

Technique

The operator should be positioned in front of the patient. Insert a 22-25 guage 2-4 cm length needle just lateral to the extensor hallucis longus tendon at a level one cm superior to the lateral malleolus, and advance the needle to the tibia. Then withdraw the needle and inject 5-10 cc of anesthetic in the subcutaneous tissue.

Note that all three anterior nerves may potentially be blocked from a single injection point at the anterior ankle midway between the medial and lateral malleoli.