Ankle Blocks from USRA.ca
Terminal branches of the sciatic nerve in the ankle region are:
- tibial nerve
- superficial peroneal nerve
- deep peroneal nerve
- sural nerve
The tibial nerve is most prominent branch and can be blocked easily under ultrasound at the level of the medial malleolus. This nerve is often located posterior and lateral to the posterior tibial artery and medial to the flexor hallucis longus tendon. Anterior to the posterior tibial artery lie the tibialis posterior and flexor digitorum longus tendons.
The superficial and deep peroneal nerves as well as the sural nerve are superficial in the subcutaneous tissue plane. The small deep peroneal nerve may be difficult to locate. This nerve is expected to lie adjacent to the anterior tibial vessels (above the ankle) and the dorsalis pedis artery (lower down at the ankle).
Transverse View of the Ankle
- 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
Transverse View of the Tibial Nerve at the Ankle
Arrowhead = tibial nerve
FDL = flexor digitorum longus tendon
FHL = flexor hallucis longus muscle
MM = medial malleolus
PTA = posterior tibial artery
TP = tibialis posterior tendon
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
- 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 NEEDLE INSERTION APPROACH
- 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 picture below.
- 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.
- 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
- 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.
- 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
Arrowhead = deep peroneal nerve
DPA = dorsalis pedis artery
LA = local anesthetic
Ankle Block (In Plane Approach)
Lateral Decubitus Position Ankle Block (In Plane Approach)
- Schabort D, Boon JM, Becker PJ, Meiring JH. Easily Identifiable Bony Landmarks As an Aid in Targeted Regional Ankle Blockade. Clinical Anatomy 2005;18:518526
FROM MAINE MEDICAL CENTER
= Deep Peroneal Nerve = Posterior Tibial Nerve = Superficial Peroneal Nerve = Sural Nerve = Saphenous Nerve
Regional Anesthesia – Foot
Ankle BlockGeneral: An ankle block is essentially a block of four branches of the sciatic nerve (deep and superficial peroneal, tibial and sural nerves) and one cutaneous branch of the femoral nerve (saphenous nerve). This is an excellent block to use as in combination or in part for lacerations, fracture reductions, and exploring wounds. Although there is some overlap, sensory innervation in the foot can be broken down into posterior and anterior nerves.Sole of the foot – The tibial and sural nerves provide sensory innervation to sole of the foot.Dorsum of the foot – The superficial peroneal, the deep peroneal and the saphenous nerves provide sensory innervation to the dorsum of the foot.
Deep Peroneal Nerve Posterior Tibial Nerve Superficial Peroneal Sural Nerve Saphenous Nerve
Anatomy: The deep peroneal nerve lies in the groove between the extensor hallucis longus and the tibialis anterior tendon. The hallucis longus can be located by having the patient flex and extend the big toe. The tibialis interior can be located by having the patient dorsi flex the foot and invert the ankle. The injection site should be at the level of the superior malleolus and between the two tendons. Distribution of anesthesia:The deep peroneal nerve provides sensation to the web space between the first and second toe and a small area just proximal to the first and second toe on the plantar aspect of the foot. 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 the anesthetic.
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 Nerves
General: 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.
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.
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.
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.
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