Ankle Block

Regional anesthesia of the ankle presents a challenge to the provider because of the complicated nerve supply to the foot and the varied locations of the nerves around the ankle. Providing local anesthesia to the foot, particularly to the sole, presents many difficulties. First, the thick but sensitive skin must be penetrated with a needle, which often must be a larger gauge than might be used elsewhere to pass through the skin — this can be very painful. By providing a regional block, the affected anatomy can be properly cleaned, explored, and treated without causing unnecessary pain to the patient. In many settings, regional anesthetic is also preferred because it prevents the distortion of the anatomy commonly seen in local anesthesia.

Five main nerves originate from the major nerve roots of the lower extremity innervating the foot (see the image below).

1.       The dorsal aspect of the foot is innervated by 3 nerves that run on the anterior side of the lower leg and ankle, The superficial peroneal, deep peroneal, and saphenous nerves

2.       The volar aspect of the foot is innervated by the posterior tibial and

3.       Sural nerves on the posterolateral aspect of the ankle.

Complete regional anesthesia of the foot requires blocking each of the 5 nerves. ^{[2, 1]}

Commonly used short-acting subcutaneous anesthetic agent is Lidocaine, which can be given as 1% or 2% mixtures. Epinephrine 1:1000 may be added to both 1% and 2% solutions. Epinephrine is typically added to local anesthetic to cause vasoconstriction, prolonging the activity of the anesthetic and limiting bleeding.

Maximum Dosing for the Most Common Short-Acting and Long-Acting Local Anesthetic Agents :

Medication	Adult	Pediatrics
Lidocaine	300 mg	3-4 mg/kg
Lidocaine with epinephrine	500 mg	7 mg/kg
Bupivacaine	175 mg	2 mg/kg
Bupivacaine with epinephrine	225 mg	3 mg/kg

Region Nerve Block

1.       Superficial peroneal nerve block

To block this nerve, palpate the extensor hallucis longus tendon and the lateral malleolus. Insert the needle just over the lateral malleolus and tunnel the needle subcutaneously toward the extensor hallucis longus tendon. Complete anesthesia of the superficial peroneal nerve is achieved by placing 5-7 mL of anesthesia in a band-like pattern between these 2 points (see image below).^{[2, 1]}  

The superficial peroneal nerve provides sensation to most of the dorsum of the foot and the dorsal aspect of each of the toes and web spaces, with the exception of the lateral portion of the great toe and the medial side of the second toe, and corresponding web space. The nerve passes subcutaneously on the anterolateral side of the ankle.

As with the administration of any anesthetic, care must be taken to draw back on the syringe before injecting medication to prevent intravascular administration.

2.       Deep peroneal nerve block

To provide anesthesia to the “flip-flop” region, first palpate the anterior tibial tendon and the extensor hallucis longus tendon by having the patient dorsiflect the foot and great toe. Insert the needle between these 2 tendons approximately 1 cm superior to the medial malleolus. Draw back to prevent intravascular administration of medication, then deposit 1 mL of anesthetic. Once beyond the extensor hallucis longus tendon, angle the needle toward the lateral malleolus and insert until the tip of the needle rests against the anterior tibia (1-2 cm). Remove the needle 1-2 mm so the tip is not resting against the bone, draw back, and then deposit 5 mL of anesthetic to the deep peroneal nerve (see image below). ^{[2, 1]}

The deep peroneal nerve provides sensation to the lateral portion of the great toe and medial side of the second digit, as well as the web space between the 2. This distribution is commonly referred to as the “flip-flop” nerve because it innervates the area surrounding the thong of a sandal. This nerve runs deeper in the ankle than the superficial peroneal nerve, hidden behind the extensor hallucis longus tendon.

3.       Saphenous nerve block

To anesthetize the arch of the patient’s foot, palpate the anterior tibial tendon and the medial malleolus, and place 3-5 mL of anesthetic in a subcutaneous wheal between these 2 landmarks (see image below). ^{[2, 1] .} The saphenous nerve provides sensation to the skin on the medial aspect of the foot along the arch and runs alongside the saphenous vein between the medial malleolus and the anterior tibial tendon

4.       Posterior tibial nerve block

            To anesthetize the sole of a patient’s foot, palpate the posterior tibial artery between the medial malleolus and the achilles tendon. Insert the needle 1 cm superior to the medial malleolus just posterior to the artery with the needle angled toward the lateral malleolus (see image below). Pass the needle until it rests on the posterior aspect of the tibia, then withdraw 1-2 mm, aspirate the syringe to prevent intravascular administration, and place 5-7 mL of anesthetic. An alternative to passing the needle to the posterior tibia is to insert the needle 1-2 cm and wiggle the tip of the needle; paresthesia elicited by movement of the needle tip indicate contact with the posterior tibial nerve. ^{[2, 1] .} The posterior tibial nerve is the largest in the ankle and branches into the medial and lateral plantar nerves in the foot, supplying sensation to the entire volar surface, as well as providing motor innervation to the intrinsic muscles of the foot. It runs deep to the posterior tibial artery

5.       Sural nerve block

nesthesia is provided to the sural nerve by first palpating the achilles tendon and the lateral malleolus. Insert the needle 1 cm superior to the lateral malleolus and deposit 5 mL in a band-shaped pattern between the 2 landmarks (see the image below). ^{[2, 1] .} The sural nerve supplies sensation to the lateral and medial aspects of the foot. It passes between the lateral malleolus and the achilles tendon.

 

References

1.        Spektor M, Kelly J. Regional Anesthesia of the Thorax and Extremities. Roberts, Hedges. Clinical Procedures in Emergency Medicine. 5th. Philadelphia, PA: Saunders Elsevier; 2010. Volume 1: Chapter 30, 528-530.

2.        Ankle Block, Regional Anesthesia. NYSORA: New York School of Regional Anesthesia. Available at http://www.nysora.com/peripheral_nerve_blocks/classic_block_tecniques/3035-ankle_block.html. Accessed: 5/28/11.

3.        Hadzic A, Vloka JD, Kuroda MM, Koorn R, Birnbach DJ. The practice of peripheral nerve blocks in the United States: a national survey [p2e comments]. Reg Anesth Pain Med. 1998 May-June. 23(3):241-6. [Medline].

4.        McGee D. Local and Topical Anesthesia. Roberts, Hedges. Clinical Procedures in Emergency Medicine. 5th. Philadelphia, PA: Saunders Elsevier; 2010. Volume 1: Chapter 29, 481-499.

5.        Reilley TE, Gerhardt MA. Anesthesia for foot and ankle surgery. Clin Podiatr Med Surg. 2002 Jan. 19(1):125-47, vii. [Medline].

6.        Reilley TE, Terebuh VD, Gerhardt MA. Regional anesthesia techniques for the lower extremity. Foot Ankle Clin. 2004 Jun. 9(2):349-72. [Medline].

7.        http://emedicine.medscape.com/article/1999563-overview#showall