The tibial nerve is the largest branch of the sciatic nerve and the largest nerve for the ankle block. It provides sensory innervation to the heel and to the sole of the foot. The tibial nerve divides into the medial calcaneal, medial plantar, and lateral plantar branches near the ankle.¹ In some subjects the takeoff of the medial calcaneal branch from the tibial nerve can be imaged above the ankle joint.

The order of anatomic structures from anterior to posterior at the medial malleolus is as follows: Tom, Dick, AVN, Harry (tibialis posterior tendon, flexor digitorum longus tendon, posterior tibial artery and veins, tibial nerve, flexor hallucis longus tendon). Therefore, the tibial nerve lies on the heel side of the posterior tibial artery. The posterior tibial artery is often accompanied by two flanking veins. This neurovascular bundle, consisting of one artery and two veins, can have a Mickey Mouse ears appearance if light touch with the transducer is applied (similar to the appearance of the brachial artery and veins near the elbow).

Edema or infection often makes routine ankle block ineffective or contraindicated.² However, tibial nerve imaging can be difficult in some surgical patients with peripheral vascular disease because vascular landmarks for the nerve are not present. Tibial nerve block in the leg avoids the footdrop that occurs with more proximal popliteal block of the sciatic nerve. This can be an advantage for ambulatory surgery patients.

Suggested Technique

The tibial nerve can be approached in-plane from the posterior (Achilles) or anterior (tibial) side in supine position with the leg externally rotated using a short-axis view of the neurovascular bundle. The best point of tibial nerve imaging in the leg is usually halfway between the medial malleolus and the bulk of the gastrocnemius-soleus muscle complex in the calf. Place the block needle tip between the posterior tibial artery and the tibial nerve so as to enter the neurovascular compartment. With the posterior approach the Achilles tendon can lie close to the point of needle entry. With the anterior approach the saphenous vein can be close to the needle path near the skin surface.

Key Points

Tibial Nerve Block	The Essentials
Anatomy	Two veins usually flank either side of the PTA.
	The TN is about 4 mm in diameter.
Image orientation	The TN lies on the heel side of the PTA in the leg.
Positioning	Externally rotate and support the leg.
	The heel points toward the operator.
Operator	Standing on the contralateral side of the table
Display	Across the table, on the ipsilateral side
Transducer	High-frequency linear, 23- to 25-mm footprint
Initial depth setting	25 mm
Needle	25 gauge, 38 mm in length
Anatomic location	Begin by scanning the medial aspect of mid-leg.
	Optimal imaging of TN usually halfway between the gastrocnemius and malleoli.
Approach	SAX view of TN, in-plane from the Achilles side
	Place the needle tip between the TN and PTA.
Sonographic assessment	Injection should track distally along the TN to MCB (SAX slide).
Anatomic variation	Some anatomic variation of the TN position with respect to the PTA.

MCB, Medial calcaneal branch of the tibial nerve; PTA, posterior tibial artery; SAX, short axis; TN, tibial nerve.

Clinical Pearls

• The ideal needle path is between the posterior tibial artery and the tibial nerve, so that the injection separates the two structures.

• Tibial nerve block with ultrasound can be used for outpatient heel surgery to avoid footdrop that occurs with more proximal popliteal block of the sciatic nerve.

• The medial calcaneal branch of the tibial nerve can sometimes be imaged, particularly after tibial nerve block in the leg.

• Be careful with long-axis assessments of local anesthetic distribution along peripheral nerves that lie close to arteries (e.g., the tibial nerve). Partial line-ups on the adjacent artery can appear similar to distributed fluid.

• The central aponeurosis of the tibialis posterior muscle lies deep to the tibial nerve in the leg. These two structures can have similar ultrasound appearance.

• When tibial nerve block is approached from the Achilles tendon side, position the patient with the leg elevated and slightly flexed.

FIGURE 50-1 External photograph showing posterior-to-anterior in-plane approach to tibial nerve block in the distal leg. This location is proximal to where the tibial nerve divides into its medial plantar, lateral plantar, and medial calcaneal branches.

FIGURE 50-2 Short-axis view of the tibial nerve in the distal leg. With a broad and deep view, both the tibia and fibula can be imaged deep to the nerve.

FIGURE 50-3 Tibial nerve block in the distal leg showing the in-plane approach from posterior to anterior. Image sequence is shown before (A), during (B), and after (C) injection. Local anesthetic surrounds the tibial nerve and separates it from the posterior tibial artery.

FIGURE 50-4 After injection, local anesthetic is distributed around the tibial nerve (A) and tracks along the nerve (B).

FIGURE 50-5 The flexor digitorum longus (FDL) tendon and tibial nerve can have similar ultrasound appearances. The FDL tendon is smaller than the tibial nerve and lies closer to the tibia. This sonogram was obtained after ankle block performed using surface landmarks (not ultrasound guidance). Local anesthetic is seen to surround both the tibial nerve and the FDL tendon.