Regional Anesthesia: Foot & Ankle
Miguel F. Agrait González, MD FACEP FAAEM CAQ-SM
Assistant Professor of Emergency Medicine, Ponce Health Sciences University
San Lucas Episcopal Hospital Emergency Medicine Residency
Sports Medicine Director – Pravan Health Clinic
Summary & Introduction
Posterior nerve distribution of the lower leg/foot  Credit to Orthopaedicsone, Accessed 10/31/2022. https://www.orthopaedicsone.com/display/Clerkship/Peripheral+Nerves+and+Arteries+of+the+Lower+Extremity
- Achilles rupture
- Ankle or tibia/fibula fractures
- Ankle dislocation
- Complex lower leg injury such as burn, laceration, foreign body
- Patient position:
- Prone positioning is optimal if patient can tolerate it
- If not possible, can be performed with patient supine and leg propped on pillows/blankets and knee slightly flexed
- Another option is patient in lateral decubitus with lateral aspect of affected leg positioned towards ceiling
- For either supine or lateral decubitus, it’s beneficial to have an assistant help elevate the leg for the duration of the procedure
- Prone positioning is optimal if patient can tolerate it
- Anatomic landmark: popliteal crease
- Scanning Protocol: Position ultrasound probe at popliteal crease, visualize popliteal vessels and scan cephalad
- Injection area is located 5-8cm proximal to popliteal crease
- Nerve will be superficial (closer to screen) to popliteal artery and vein
- Attempt to visualize the sciatic nerve before it bifurcates into the tibial and common peroneal nerves.
- Tibial nerve is large and can be confused for sciatic
- Target is just distal to bifurcation of nerves or just prior to bifurcation
- Has faster onset and longer duration if injected at or just distal to bifurcation rather than when combined as sciatic nerve
- Can aim for plane between the two nerves and fluid will track around them if done just at bifurcation site
- 20-30 mL of anesthetic needed
- Needle path will be lateral to medial in line with full needle visualization throughout
- Best to try to maintain horizontal needle path to keep optimal needle visualization
- Done by inserting needle at level of planned injection site rather than at an angle near probe
- Anesthetic should surround nerve(s)
- Retract needle, provide local pressure to ensure homeostasis and apply bandage
- Allow 15-20 minutes for block to take full effect
Saphenous Nerve Block (Adductor Canal Block)
- Medial lower leg injuries from knee to ankle
- Medial malleolar ankle injuries
- Medial calf abscess requiring I+D
- May need to perform for complex ankle injuries if sciatic block does not provide adequate anesthesia to medial ankle
- Patient position
- Patient supine with “frog leg” positioning of affected extremity
- Anatomic landmark
- Medial mid thigh ~10 cm cephalad to knee
- High frequency US probe in transverse orientation visualizing distal femoral artery and vein along with sartorius muscle superficial to them
- Nerve runs below sartorius immediately adjacent to vessels
- Target location is immediately below sartorius muscle and its fascia, roughly 9 o’clock position with regards to femoral artery
- Needle inserted in-plane towards sartorius and the fascial plane separating it from the vastus medialis muscle
- May feel pop when fascial plane is entered
- Key is injecting just below sartorius muscle in fascial plane
- Inject in 5 mL aliquots and aspirate to ensure no intravascular injection
- Total of 10-15mL needed for anesthesia
Posterior Tibial Nerve Block
- Calcaneal fracture
- Lisfranc injury
- Sole of foot laceration or foreign body requiring exploration or repair
- Does NOT provide anesthesia for ankle joint
- Patient position
- Hip in external rotation with slight knee flexion (medial malleolus exposed or lateral decubitus exposing affected medial ankle superiorly
- Anatomic landmark: medial malleolus and posterior tibial artery
- US probe in transverse orientation just cephalad and posterior to medial malleolus of ankle
- Identify tarsal tunnel
- Nerve and artery run together
- Slide cephalad if necessary to see nerve separate from arter
- Injection will be done in-plane posterior to anterior, inserting near Achilles (NOT through Achilles)
- Visualize needle tip throughout and avoid intraneural or intravascular injection
- Aim needle tip just inferior to nerve and inject slowly
- Can use small amount of NS or D5W to separate nerve from vascular bundle followed by anesthetic injection
- Apply pressure for hemostasis and bandage appropriately
Deep Peroneal Nerve Block
- The deep peroneal branch of the common peroneal nerve innervates the ankle extensor muscles, the ankle joint and the web space between the first and second toes.
- Clinically, for the emergency department this likely has the least utility due to the small effect size
- The nerve can be found at the level of the ankle as it crosses the anterior tibial artery from a medial to lateral position.
- A transducer placed in the transverse orientation at the level of the extensor retinaculum will show the nerve lying immediately lateral to the artery, on the surface of the tibia . In some individuals the nerve courses along the medial side of the artery. The nerve usually appears hypoechoic with a hyperechoic rim, but it is small and often difficult to distinguish from the surrounding tissue.
Superficial Peroneal Nerve Block
- The superficial peroneal nerve innervates the dorsum of the foot with the exception of the lateral edge over the 5th metatarsal and the webspace between the 1st and 2nd toe
- The superficial peroneal nerve emerges superficial to the fascia 10–20 cm above the ankle joint on the anterolateral surface of the leg and divides into two or three small branches. A transducer placed transversely on the leg, approximately 5-10 cm proximal and anterior to the lateral malleolus, will identify the hyperechoic nerve branches lying in the subcutaneous tissue immediately superficial to the fascia. To identify the nerve proximal to its division, the transducer can be traced proximally until, at the lateral aspect, the extensor digitorum longus and peroneus brevis muscle can be seen with a prominent groove between them leading to the fibula.
Sural Nerve Block
- The sural nerve innervates the lateral margin of the foot and ankle.
Proximal to the lateral malleolus, the sural nerve can be visualized as a small hyperechoic structure that is intimately associated with the small saphenous vein superficial to the deep fascia. The sural nerve, can be traced back along the posterior aspect of the leg, running in the midline superficial to the Achilles tendon and gastrocnemius muscles . A calf tourniquet can be used to increase the size of the vein and facilitate its imaging; the nerve is often found in the immediate vicinity of the vein.
Pearls & Pitfalls
- Do not delay pain management while setting up nerve block
- Block should decrease need for additional medications, but patient should not be in pain while preparing for injection
- Gentle injection is key. Consider injecting in 3-5mL aliquots and reassessing
- Allow time for blocks to work, the larger the nerve, the longer time to effect
- Although rare, always be prepared for possibility of local anesthetic systemic toxicity (LAST) which will require prompt recognition and management
- Ultimate treatment is lipid emulsion therapy if any seizures or signs of cardiovascular collapse appear
- Monitor for: perioral numbness, auditory changes, metallic taste in the mouth, anxiety, or agitation all of which can be early signs of LAST
- In the presence of a fracture which will require orthopedic evaluation and management emergently discuss block with orthopedic surgeon prior to performing
- Two person technique is optimal whenever possible with one person guiding needle and visualizing on US and another injecting medication upon instruction
- If nerve and/or needle tip cannot be visualized, pause stop the procedure, identify needle before proceeding
- Blind injections can lead to vascular and neurologic injury
- Stop procedure if significant resistance is met upon injection or there is a change in resistance while injecting as this would suggest needle migration and possible intraneural injection
- Do not advance needle, reposition needle or inject without direct US visualization
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|↑1, ↑6, ↑7, ↑8||Credit to Orthobullets, Accessed 10/31/2022. https://www.nysora.com/topics/regional-anesthesia-for-specific-surgical-procedures/lower-extremity-regional-anesthesia-for-specific-surgical-procedures/foot-and-anckle/ultrasound-guided-popliteal-sciatic-block/|
|↑2||Credit to Orthopaedicsone, Accessed 10/31/2022. https://www.orthopaedicsone.com/display/Clerkship/Peripheral+Nerves+and+Arteries+of+the+Lower+Extremity|
|↑3, ↑4, ↑5||Credit to NYSORA, Accessed 10/31/2022. https://www.nysora.com/topics/regional-anesthesia-for-specific-surgical-procedures/lower-extremity-regional-anesthesia-for-specific-surgical-procedures/foot-and-anckle/ultrasound-guided-popliteal-sciatic-block/|