Ankle Block
Indications
- Surgery or manipulation of the foot or heel.
Set-Up
- 25 or 27 gauge needles
- 15-20 ml per foot – for immediate onset of the block while providing long duration of action 2% lidocaine with 0.75% Bupivacaine (1:1)
- 2% lidocaine (3-5 hours postop analgesia)
- 1.5% mepivacaine (3-5 hours postop analgesia)
- 0.75% bupivacaine (up to 24 hours of postop analgesia)
Essential Anatomy
- Extensor digitorum and extensor hallucis longus tendons,
anterior tibial artery, posterior tabial artery.
Technique
- Place patient supine with the leg resting on a pillow
so that the foot is free to rotate internally and
externally.
- Block of the posterior tibial nerve: the leg is externally
rotated with the knee flexed.
- The posterior tibial artery is palpated at the inferior
border of the medial malleolus and 1 to 2 cm anterior
to the Achilles tendon.
- The needle is directed posterior to the artery and
advanced until the flexor retinaculum is pierced or
bone contact with the tibia is made.
- 10 ml of local anesthetic is injected after a negative
aspiration.
- Block of the deep peroneal nerve is accomplished
by asking the patient to extend the foot and first toe against resistance. This allows palpation of the extensor
digitorum and extensor hallucis longus tendons
above the ankle joint at the level of the malleoli.
The needle is directed perpendicular to the
skin, medial to the anterior tibial artery and between
the tendons until the extensor retinaculum is penetrated
or bone contact with the tibia is made. After
a negative aspiration, 2 to 4 ml of local anesthetic
solution is injected.
- The saphenous, sural, and superficial peroneal
nerves and their distal branches are blocked with a
subcutaneous ring of local anesthetic extending
across the anterior portion of the ankle from the lateral
aspect of the Achilles tendon to the medial malleolus.
This ring is located just proximal to the
malleoli. It is often necessary to rotate the foot internally
and externally to complete this ring and inject 4 to 8 ml of local anesthetic solution.
Limitations
- Long onset time for blockade when intermediate/
long acting local anesthetics are used.
- Any signs of local infection.
Complications
- Intravascular or intraneural injection
Pearls
- Infiltration of local anesthetic during an ankle block
can be uncomfortable, especially during blockade
of the superficial nerves. Therefore, it is important
to provide the patient with appropriate sedation.
- A pop is sometimes felt as the needle passes through
the flexor retinaculum (posterior tibial) or extensor
retinaculum (deep peroneal). This pop is often difficult
to appreciate; therefore, the use of bone contact is more reliable. A diffuse fullness can often be
noted on injection of local anesthetic around the deep
nerves. If a paresthesia is noted, the needle is withdrawn
and redirected slightly.
- The use of epinephrine in ankle blocks is contraindicated
because the local anesthetic is injected
perivascularly at both major arteries of the foot.
Systemic absorption of local anesthetic from an
ankle block is minimal; in addition, if a longer duration
of action is desired, the choice of local anesthetic
should be altered (i.e., bupivacaine in place
of lidocaine), or a low dose of clonidine may be
added to the block.
- A variation for blocking the deep peroneal nerve is
the mid-tarsal approach described by Sharrock etal.1
- The addition of clonidine (1 µg/ml ) to lidocaine
increases the duration and the quality of the block.
References
- Sharrock, NE, Waller, JF, fierro, LE: Midtarsal block for
surgery of the forefoot. Br. J Anaesth, 58: 37-40, 1986.
These technique descriptions are presented for educational purposes and are not intended to substitute for actual hands-on training.
