Scanning Technique

• Position the patient supine and bolster the foot with a pillow to expose the anterior and medial portion of the lower leg and foot.
• After skin and transducer preparation, place a 10-15 MHz transducer immediately above the medial malleolus to locate the tibial nerve in the transverse (short axis) view.
• It is also easy to visualize this nerve longitudinally (long axis).
• Optimize machine imaging capability. Select the appropriate depth of field (usually within 1-2 cm), focus range (usually within 1-2 cm) and gain.

A 12 MHz hockey stick transducer over the left medial malleolus

Anatomical Correlation

Transverse View of the Tibial Nerve at the Ankle

Arrowheads = tibial nerve	FDL = flexor digitorum longus tendon	FHL = flexor hallucis longus muscle
MM = medial malleolus	PTA = posterior tibial artery	TP = tibialis posterior tendon

Nerve Localization

Tibial Nerve

• Perform a systematic anatomical survey in the medial aspect of the ankle.
• The bony medial malleolus is easily identified (bony shadow).
• Move the transducer slightly posteriorly to identify the tibialis posterior and flexor digitorum longus tendons. Both tendons are found within the flexor retinaculum of the ankle. They display a sliding movement with ankle flexion and are often hyperechoic.
• Then identify the pulsatile posterior tibial artery (Doppler use is optional).
• The tibial nerve at the ankle is often round to oval with a honeycomb appearance. It is expected to lie posterior to the posterior tibial artery.
• Trace the tibial nerve proximally. The nerve is larger and is easier to identify more cephalad in the leg. It is also easy to image the nerve longitudinally by rotating the transducer 90 degrees.

Transverse View Arrowheads = tibial nerve PTA = posterior tibial artery

Longitudinal View Arrowheads = tibial nerve

Superficial Peroneal Nerve

• The superficial peroneal nerve, a branch of the common peroneal nerve, is located between the peroneus brevis muscle and the intermuscular septum in the distal half of the leg in the lateral compartment. It eventually pierces the crural fascia to become a superficial nerve distally. Blockade of this nerve is required to provide anesthesia to the dorsum of the foot.

	Place the operative leg on the bed with the hip and knee flexed and with the leg slightly internally rotated at the hip.
	After skin and transducer preparation, place a high frequency transducer over the distal 1/3 of the leg on the lateral side to locate the superficial peroneal nerve in the transverse view.

• First identify the fibula and its hyperechoic bony outline which shapes like an inverted V. Also identify the leg muscles in the lateral and anterior compartments.

Arrowhead = superficial peroneal nerve EDL = extensor digitorum longus muscle F = fibula P = peroneus longus and brevis muscles T = tibia TA = tibialis anterior muscle

• Overlying the fibula are the peroneus muscles (peroneus longus and brevis muscles) laterally and the extensor digitorum longus muscle anteriorly. Over the anterior corner of the fibula, the superficial peroneal nerve is expected to ascend in the intermuscular septum between the peroneus and extensor digitorum longus muscles.
• As the transducer moves distally, this small hyperechoic nerve is visualized first deep to the crural fascia and then subcutaneous after it pierces the fascia.

	Superficial peroneal nerve BELOW the crural fascia in a more PROXIMAL location in the leg Arrowhead = superficial peroneal nerve
	Superficial peroneal nerve ABOVE the crural fascia in a more DISTAL location in the leg Arrowhead = superficial peroneal nerve

Deep Peroneal Nerve

• The deep peroneal nerve is a superficial branch that is located adjacent to the dorsalis pedis artery at the ankle region.

After skin and transducer preparation, place a 10-15 MHz transducer on the dorsum of the foot along the intermalleolar line to locate the dorsalis pedis artery in the transverse (short axis) view.

• Aim to find the predominantly hypoechoic deep peroneal nerve lateral to the dorsalis pedis artery and the extensor hallucis longus tendon. This nerve is small thus visualization can be difficult.

Arrow = deep peroneal nerve DPA = dorsalis pedis artery (red arrowhead)

Sural Nerve

• The sural nerve provides sensation to the lateral aspect of the foot including the 5th toe. This pure sensory nerve runs in close proximity to the lesser saphenous vein at the ankle level and often within the same superficial fascial sheath.
• Position the patient slightly lateral decubitus to expose the lateral aspect of the leg above the lateral malleolus.

After skin and transducer preparation, place a high frequency transducer above the lateral malleolus to first locate the lesser saphenous vein. The vein is easier to visualize when distended by a tourniquet applied proximally.

• Then use a high frequency 10-12 MHz transducer to capture a transverse view of the sural nerve which is often hyperechoic, round and small. The nerve may be anterior or posterior to the vein.

SuN = sural nerve SSV = short (lesser) saphenous vein

• Move the transducer proximally and distally along the course of the lesser saphenous vein should nerve visualization be challenging.

Saphenous Nerve

• The saphenous nerve, the largest cutaneous branch of the femoral nerve, runs along the tibial surface close to the great saphenous vein below the knee. A common fascia envelops both the saphenous vein and the nerve in the distal third of the calf. In the lower third of the leg, it runs posterior to the medial aspect of the tibia.
• Blockade of this nerve provides anesthesia to the area of the medial malleolus and the medial aspect of the foot.

With the patient lying supine, the knee flexed and hip rotated externally, a high frequency transducer is placed transverse just proximal to the medial malleolus in the approximate location of the greater saphenous vein.

• A tourniquet around the calf can enhance venous filling and visibility of the compressible hypoechoic great saphenous vein. A small hyperechoic, saphenous nerve may be visualized either anterior or posterior to great saphenous vein and in the same fascial plane.

GSV = great saphenous vein SaN = saphenous nerve

Needle Insertion Approach

• Ultrasound guided ankle block is considered a BASIC skill level block because this is a superficial block.
• Both In Plane (IP) and Out of Plane (OOP) approaches can be used. The IP approach is commonly used for single shot injection.

In Plane Approach

Tibial Nerve

With the patient lying supine and the leg bolstered by a pillow, insert a 4-5 cm 22-25 G needle inline with the ultrasound transducer as seen in the picture.

• The needle is most conveniently inserted from the posterior end of the transducer because the tibia bone located anteriorly obstructs needle accessibility.
• To approach the nerve posteriorly from the side of the archilles tendon, and to create some space between the bolster and the ankle for needle access, it is best to have the leg rotated outward (laterally) or ask the patient to turn slightly on the side.
• Aim to place the needle tip on each side of the tibial nerve without puncturing the posterior tibial artery.
• Nerve stimulation is usually not necessary.

Superficial Peroneal Nerve

A 22 to 25 G needle can be inserted using an in plane approach and the superficial peroneal nerve may be targeted above (usually easier) or below the crural fascia.

Sural Nerve

A 22 to 25 G needle may be inserted using an in plane or out of plane approach.

Saphenous Nerve

The saphenous nerve can be blocked using an in-plane or out-of-plane technique.

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Out of Plane Approach

Tibial Nerve

• Patient positioning and needle insertion endpoint is similar to the in plane approach.
• The advantage of the out of plane approach is needle accessibility to the nerve and the ease of placing the needle tip on each side of the tibial nerve. The tibia bone is no longer in the way of the needle path.

Deep Peroneal Nerve

• The deep peroneal nerve is a superficial branch that is located adjacent to the dorsalis pedis artery at the ankle region.
• After skin and transducer preparation, place a 10-15 MHz transducer on the dorsum of the foot along the intermalleolar line to locate the dorsalis pedis artery in the transverse (short axis) view.
• Aim to find the predominantly hypoechoic deep peroneal nerve lateral to the dorsalis pedis artery and the extensor hallucis longus tendon. This nerve is small thus visualization can be difficult.

A 25 G 2.5 mm needle can be inserted using the out of plane approach.

Local Anesthetic Injection

Tibial Nerve

• Once satisfied with the needle position, inject 5-8 mL of local anesthetic.
• Observe local anesthetic injection in real time to judge adequacy of spread. Aim to see circumferential spread of hypoechoic local anesthetic solution around the nerve "donut sign".
• Circumferential spread usually results in a complete block.
• If local anesthetic spread is deemed suboptimal, move the needle to either side of the nerve before completing the second half of the injection.
• Scan the nerve in the transverse and longitudinal planes proximally and distally to check the extent of local anesthetic spread.

Transverse View Arrowheads = tibial nerve LA = local anesthetic

Longitudinal View Arrowheads = tibial nerve LA = local anesthetic

Superficial Peroneal Nerve

• A 5 mL local anesthetic injection around the nerve often suffices.

	Needle Injection Arrows = needle Arrowhead = superficial peroneal nerve EDL = extensor digitorum longus muscle F = fibula P = peroneus longus and brevis muscles
	Post Injection EDL = extensor digitorum longus muscle Arrowhead = superficial peroneal nerve P = peroneus longus and brevis muscles F = fibula

Deep Peroneal Nerve

• If the deep peroneal nerve is clearly visualized, inject 2-3 mL of local anesthetic on each side of the nerve.
• If the nerve is not clearly visualized, inject 2-3 mL of local anesthetic on each side of the artery in the subcutaneous plane.
• Observe local anesthetic spread around the nerve circumferentially in the subcutaneous plane above bone and at approximately the same level as the artery.

	Pre Injection Arrowhead = deep peroneal nerve DPA = dorsalis pedis artery
	Post Injection Arrowheads = deep peroneal nerve DPA = dorsalis pedis artery LA = local anesthetic

Sural Nerve

• If the nerve is not readily visible, local anesthetic injection around the lesser saphenous vein in the subcutaneous plane often suffices.

Pre Injection Arrowhead = sural nerve

Post Injection Arrowhead = sural nerve

Saphenous Nerve

• If the nerve is not visualized, it is recommended to infiltrate local anesthetic around the great saphenous vein to distend the fascial plane in which it lies. Three to five mL of local anesthetic is sufficient to block the nerve.

Saphenous Nerve (arrowhead) - Post Injection GSV = greater saphenous vein

Clinical Pearls

Tibial Nerve

• The tibial nerve may not always be posterior to the posterior tibial artery. It may be found anterior to the artery or deep to it.
• It is best to scan the leg proximally above the medial malleolus to determine the optimal site for local anesthetic injection. Most commonly, the tibial nerve is bigger and easier to visualize in the distal 1/3 of the leg.
• Tendons of the tibialis posterior and flexor digitorum longus muscles over the medial malleolus resemble nerve structures. They are located more anteriorly than the tibial nerve and posterior tibial artery. Also, when scanned more proximally, the tendons will disappear into their respective muscles.

For the in plane needle insertion approach in the posterior to anterior direction, consider putting patient's operative leg on top of the non operative leg in a frog leg position.

Superficial Peroneal Nerve

• Subcutaneous local anesthetic infiltration in the dorsal aspect of the ankle just above the level of the malleolus is a common technique to block the superficial perineal nerve. However, this technique may fail to provide effective anesthesia / analgesia in ankles that are swollen. A targeted superficial perineal nerve block in the distal leg above the fibula is a more reliable approach.

Sural and Saphenous Nerves

• Both subcutaneous nerves are small thus visualization can be challenging. This can be improved by placing a tourniquet around the leg so that the saphenous veins become distended.

Catheter Insertion

Catheter insertion is seldom indicated for this particular block.

Image Gallery

Sural Nerve

Pre Injection Arrow = lesser saphenous vein Arrowhead = sural nerve

Post Injection Arrow = lesser saphenous vein Arrowhead = sural nerve LA = local anesthetic

Video Gallery

Selected References

• Coe A, Ram S. Ultrasound-guided ankle block for forefoot surgery: is sural nerve block necessary? Reg Anesth Pain Med 2013;38:251.
• Purushothaman L, Allan AGL, Bedforth N. Ultrasound-guided ankle block. Continuing Education in Anaesthesia, Critical Care & Pain 2013;0:91-9.
• Lopez AM, Sala-Blanch X, Magaldi M, Poggio D, Asuncion J, Franco CD. Ultrasound-guided ankle block for forefoot surgery: the contribution of the saphenous nerve. Reg Anesth Pain Med 2012;37:554-7.
• Chin KJ, Wong NWY, Macfarlane AJR, Chan VWS. Ultrasound-Guided Versus Anatomic Landmark-Guided Ankle Blocks: A 6-Year Retrospective Review. Reg Anesth Pain Med 2011;36:611-8.
• Fredrickson MJ, White R, Danesh-Clough TK. Low-Volume Ultrasound-Guided Nerve Block Provides Inferior Postoperative Analgesia Compared to a Higher-Volume Landmark Technique. Reg Anesth Pain Med 2011;36:393-8.
• Antonakakis JG, Scalzo DC, Jorgenson AS, Figg KK, Ting P, Zuo Z, Sites BD. Ultrasound does not improve the success rate of a deep peroneal nerve block at the ankle. Reg Anesth Pain Med 2010;35:217-21.
• Redborg KE, Sites BD, Chinn CD, Gallagher JD, Ball PA, Antonakakis JG, Beach ML. Ultrasound improves the success rate of a sural nerve block at the ankle. Reg Anesth Pain Med 2009;34:24-8.
• Accuracy of Ultrasound Guided Injections in the Foot and Ankle. 2009;30:239-42.
• Schabort D, Boon JM, Becker PJ, Meiring JH. Easily Identifiable Bony Landmarks As an Aid in Targeted Regional Ankle Blockade. Clinical Anatomy 2005;18:518-526