Take Note:

• The superficial peroneal, sural, and saphenous nerves are located in the subcutaneous tissue encircling the ankle. These nerves branch out and anastomose extensively; therefore they do not have a single point that can be consistently anesthesitized. A field block in the subcutaneous tissue is used to anesthetize these nerves.

Deep Peroneal Nerve Block

Technique:

• The surgical field should be prepared across the anterior surface of the ankle between the superior aspect of the medial and lateral malleoli. Raise a wheal of anesthesia in the subcutaneous space and direct the needle between the tendons of the hallucis longus and the tibialis anterior at the level of the superior malleoli. Insert the needle until it is deep to the tendons or bone is struck. Inject approximately 5 milliliters of anesthetic. Withdraw the needle and redirect thirty degrees laterally and then thirty degrees medially and provide an additional 3 to 5 ml of anesthetic. If anesthesia in the saphenous distribution is also desired, bring the needle back to the level of the subcutaneous tissue and redirect it medially towards the medial malleolus. Inject an additional 5 ml in the subcutaneous space. This will block the saphenous nerve.

Pitfalls:

• Avoid inadvertent saphenous vein puncture                                                              
• Intraneural injection will cause significant pain, therefore withdraw the needle a few millimeters and continue injecting anesthetic

Posterior Tibial Nerve Block

Anatomy:

• The posterior tibial nerve runs just behind the medial malleolus, and just posterior to the posterior tibial artery. Like the deep peroneal, the posterior tibial nerve is deep to the fascia. The posterior tibial nerve can be located just posterior to the medial malleolus just superficial to the artery.

Distribution of anesthesia:

• The posterior tibial nerve provides the majority of the sensation to the plantar aspect of the foot with minor contributions from the deep peroneal and sural nerve. The posterior tibial nerve also provides sensation to the heel of the foot. Technique: The surgical field should be prepared posterior to the medial malleolus. Identify the posterior tibial artery by palpating the artery posterior to the medial malleolus. Insert the needle just posterior to the artery until it penetrates the deep fascia. If the pop of the deep fascia cannot be felt, continue inserting the needle until it contacts bone. Withdraw the needle 2 to 5 millimeters and inject 3-5 5 milliliters of anesthesia. To increase the odds of a successful block, place an additional 3 to 5 milliliters lateral and medial to the original injection site.

Pitfalls:

• Intraneural injection will cause excruciating pain with injection, therefore withdraw the needle a few millimeters and continue injecting the anesthetic.

Superficial Peroneal Nerve block

Anatomy:

• The superficial peroneal nerve is superficial and runs along the anterior lateral portion of the ankle. It can be blocked by subcutaneous injection between the lateral malleolus and the tibialis anterior tendon.

Distribution of anesthesia:

• This nerve provides sensation to the dorsal lateral aspect of the foot. Technique: Identify the tibialis anterior tendon by having the patient dorsiflex the foot and inverts the ankle. The most prominent tendon should be the tibialis anterior. The surgical field should be prepared between the tibialis anterior tendon and the lateral malleolus at the level of the superior malleoli. Inject anesthesia in the subcutaneous space from the tibialis anterior tendon to the superior portion of the lateral malleolus.

Pitfalls:

• Intraneural injection will cause significant pain, therefore withdraw the needle a few millimeters and continue injecting the anesthetic.

Sural Nerve

Anatomy:

• The sural nerve is quite superficial and can be blocked by anesthetizing the subcutaneous tissue from the superior portion of the lateral malleolus to the Achilles tendon.

Distribution of anesthesia:

• The sural nerve provides sensation to the lateral aspect of the ankle and a small area on the plantar lateral aspect of the foot.

Technique:

• The surgical field should be prepared between the Achilles tendon and the lateral malleolus at the level of the superior malleoli. Inject anesthesia in the subcutaneous space from the superior portion of the lateral malleolus to the Achilles tendon.

Pitfalls:

• Intraneural injection will cause significant pain, therefore withdraw the needle a few millimeters and continue injecting the anesthetic.

Saphenous Nerve

Anatomy:

• The saphenous nerve is a subcutaneous nerve that can be blocked by injecting anesthesia from the superior medial malleolus to the tibialis anterior tendon. Use caution around the saphenous vein.

Distribution of anesthesia:

• This nerve provides sensation to the medial aspect of the ankle.

Technique:

• Identify the tibialis anterior tendon and the superior portion of the medial malleolus. The surgical field should be prepared between the tibialis anterior tendon and the medial malleolus at the level of the superior malleoli. Inject anesthesia in the subcutaneous space from the tibialis anterior tendon to the superior portion of the medial malleolus.

Pitfalls:

• Puncture of the saphenous vein.

• Intraneural injection will cause significant pain, therefore withdraw the needle a few millimeters and continue injecting the anesthetic.

Written by Douglas Dillon, MD

Edited and Posted by Jeffrey A Holmes, MD