Indications: Distal foot and toe surgery
Transducer position: about the ankle; depends on the nerve to be blocked
Goal: local anesthetic spread surrounding each individual nerve
Local anesthetic: 3–5 mL per nerve
Transducer position and needle insertion for a block of the tibial nerve using an in-plane technique.
Using an ultrasound (US)-guided technique affords a practitioner the ability to reduce the volume of local anesthetic required for ankle blockade. Because the nerves involved are located relatively close to the surface, ankle blocks are easy to perform; however, knowledge of the anatomy of the ankle is essential to ensure success.1
Ankle block involves anesthetizing five separate nerves: two deep nerves and three superficial nerves. The two deep nerves are the tibial nerve and the deep peroneal nerve. The three superficial nerves are the superficial peroneal, sural, and saphenous nerves. All nerves, except the saphenous, are terminal branches of the sciatic nerve; the saphenous nerve is a sensory branch of the femoral nerve.
The tibial nerve is the largest of the five nerves at the ankle level and provides innervation to the heel and sole of the foot. With the linear transducer placed transversely at (or just proximal to) the level of the medial malleolus, the nerve can be seen immediately posterior to the posterior tibial artery (Figures 33H–1, 33H–2, and 33H–3). Color Doppler can be very useful in locating the posterior tibial artery when it is not readily apparent. The nerve typically appears hyperechoic with honeycomb pattern. A useful mnemonic for the relevant structures in the vicinity is Tom, Dick ANd Harry, which refers to, from anterior to posterior, the tibialis posterior tendon, flexor digitorum longus tendon, artery/nerve/vein, and flexor hallucis longus tendon. These tendons can resemble the nerve in appearance, which can be confusing. The nerve’s intimate relationship with the artery should be kept in mind to avoid misidentification. If in doubt, track the structure proximally: tendons will turn into muscle bellies, whereas the nerve will not change in appearance.
Cross-sectional anatomy of the tibial nerve at the level of the ankle. Shown are the posterior tibial artery (PTA) and vein (PTV) behind the medial malleolus, the tibialis posterior (TP) and the flexor digitorum longus (FDL). The tibial nerve (TN) is just posterior to the posterior tibial vessels and superficial to the flexor hallucis longus muscle (FHL). (Reproduced with permission from Hadzic A: Hadzic’s Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed. New York: McGraw-Hill, 2011.)