++
Foot anesthesia is readily accomplished by blocking the five peripheral
nerves that innervate the area by means of local anesthetic deposition
either slightly proximal or distal to the malleoli.1–5 This technique is easily learned and simple to perform, using
straightforward visual and palpable anatomic landmarks. It does not require
special equipment, paresthesia elicitation, nerve stimulation, special
positioning, or patient cooperation.1–5
++
Ankle block can be used for all types of foot surgery and is safe and
reliable, with success rates of 89–100%.2,3,5–9
++
Because it does not cause motor blockade of the leg, patients are able to
ambulate with crutches immediately after surgery and can be discharged home
without recovery.4 With the use of long-acting local
anesthetics such as bupivacaine or ropivacaine, prolonged postoperative
analgesia of up to 17 hours or longer may be
accomplished.6,9
+++
Indications & Contraindications
++
All types of foot surgery can be carried out with the patient under
ankle block, including hallux valgus repair, forefoot
reconstruction, arthroplasty, osteotomy, and amputation.1–10
Ankle block can also provide analgesia for fracture and soft
tissue injuries11 and gouty arthritis.12
Moreover, it can be used for diagnostic and therapeutic purposes with
spastic talipes equinovarus13 and sympathetically mediated
pain.14 Because motor block of the leg is avoided, ankle
block may be preferable to sciatic/femoral (saphenous) nerve block for
outpatient forefoot surgery.15
++
Ankle block should be avoided whenever there is infection, edema, burn,
soft tissue trauma, or distorted anatomy with scarring in the area of block
placement. Ankle block should also be avoided in a patient with vascular
compromise due to compartment syndrome. In patients with severe
coagulopathy, the risk of hematoma is increased, and if ankle block is
performed, a more distal approach such as the midtarsal approach, in which
blood vessels are more superficial and compressible, may be preferable.
++
++
The foot is supplied by five nerves (Figures 39–1 and
39–2). The medial aspect is innervated by the saphenous nerve, a terminal branch
of the femoral nerve (Figure 39–3). The rest of the foot is
innervated by branches of the sciatic nerve:
++
-
The lateral aspect is innervated by the sural nerve arising from the tibial and
communicating superficial peroneal branches (Figure 39–4).
-
The deep plantar structures, muscles and sole of the foot are innervated by
the posterior tibial nerve, arising from the tibial branch (Figure 39–5).
-
The dorsum of the foot is innervated by the superficial peroneal nerve, arising from the common
peroneal branch (Figure 39–6).
-
The deep dorsal structures and web space between the first and second toes
are innervated by the deep peroneal nerve (see Figure 39–2).16,17
++
++
++
++
++
++
++
At the level of the malleoli, the saphenous, superficial peroneal, and
sural nerves are relatively superficial and subcutaneous. The posterior
tibial and deep peroneal nerves are deep to the flexor and extensor
retinaculi, respectively, and are more difficult to locate.
++
The posterior tibial nerve passes with the artery posterior to the medial
malleolus deep to the flexor retinaculum, giving off a medial calcaneal
branch to supply the lower and posterior surface of the
heel.18 The nerve and artery then become superficial and
more accessible as they curve behind and underneath the sustentaculum tali,
a bony ridge on the calcaneus about 2 to 3 cm below the medial malleolus. The
nerve then divides into medial and lateral plantar
nerves.2
++
The deep peroneal nerve passes lateral to the anterior tibial artery,
extensor hallucis longus, and tibialis anterior tendons, and medial to the
extensor digitorum longus tendon deep to the extensor retinaculum. It
becomes more superficial to travel with the dorsalis pedis artery on the
dorsum of the foot, where it is easily accessible.
++
Sensory innervation of the foot is highly variable. For example, in a study
of 100 patients, 40% had the sural nerve extend medially to involve the
fourth toe, and 10% had the saphenous nerve extend distally to involve
the first metatarsophalangeal joint and occasionally the great
toe.18
++
Because the deep structures of the foot are supplied by the deep peroneal
and posterior tibial nerves and because cutaneous innervation is variable,
all five nerves should be blocked for any foot surgery, especially if a
tourniquet is used.19 The one exception would be purely
cutaneous surgery without tourniquet in the distribution of the sural,
saphenous, or superficial peroneal nerves.20 Selective
versus complete ankle block for forefoot surgery under ankle tourniquet
demonstrated that 43 versus 89% of patients were completely pain-free
during surgery, suggesting that complete ankle block is preferable under
these conditions.8
++
++
The landmarks for ankle block are the medial and lateral malleoli, the
Achilles tendon, extensor hallucis longus tendon (identified by having the
patient extend the great toe) (Figure 39–7), the posterior tibial
and dorsalis pedis arteries, and the sustentaculum tali (a bony medial
calcaneal ridge 2 to 3 cm below the malleolus).
++
++
For blockade at the level of the malleoli, the saphenous, sural, and
superficial peroneal nerves are blocked with a circumferential subcutaneous
injection of 10–15 mL of local anesthetic along a line just proximal to the
malleoli and anterior from the Achilles tendon medially to laterally
(Figures 39–8, 39–9, and 39–10). The deep peroneal nerve is blocked
by injection of 5–8 mL of local anesthetic just lateral to the extensor
hallucis longus tendon deep to the retinaculum along the same
circumferential line (Figure 39–11). The posterior tibial nerve is
blocked by injection of the same volume of local anesthetic just posterior
to the posterior tibial artery if palpable, or midway between the Achilles
tendon and medial malleolus deep to the retinaculum (Figure
39–12).
++
++
++
++
++
++
For block at the midtarsal level, the saphenous, sural, and superficial peroneal nerves are
blocked with a circumferential subcutaneous injection of 10–15 mL of local
anesthetic along a line distal to the malleoli from the Achilles tendon
medially to laterally. The deep peroneal nerve is blocked just lateral to
the extensor hallucis longus tendon and medial to the dorsalis pedis artery.
The posterior tibial nerve is blocked on the calcaneus on either side of the
posterior tibial artery (if palpable) or posterior and inferior to the ridge
of the sustentaculum tali.
++
No special equipment other than disinfectant, gauze, and 10-mL syringes
with 1½-in., 25-gauge needles is required for ankle block.
Although nerve stimulation is not necessary for distal approaches, it has
been described for the proximal approach to the posterior tibial
nerve.21 Although there are no data regarding the use of
ultrasound for ankle block, this modality can identify nerves, visualize
needles and the spread of local anesthetic around the nerves, and may be
useful for proximal approaches to the deep peroneal and posterior tibial
nerves.
++
If a tourniquet is required for surgery, a pneumatic ankle tourniquet
should be used rather than an Esmarch bandage, because pressures with the
latter are variable, are unknown, and may be extremely high, up to 380 mm
Hg.22,23 Tourniquet pressures just above the malleoli
between 200 and 250 mm Hg should ensure a bloodless field and maximize
safety.24,25 Ankle tourniquets are tolerated better than
those placed at the midcalf or thigh, with less pain and no increase in
neurologic complications.26–30 An audit of 1000
cases of ankle block revealed that with proper tourniquet application and
the option of sedation, only 3.1% of patients complained of tourniquet
pain. Risk factors for tourniquet pain were age over 70 and tourniquet times
greater than 30 minutes.30
++
++
Sterile disposable tourniquets are available if the surgery requires a
more proximal operative area.
+++
Alternative Techniques
++
There are several techniques for performing ankle block; they can be
classified as perimalleolar or inframalleolar (midtarsal) block. The
location of the block determines the procedures that can be done. With
midtarsal block, forefoot surgery is easily accomplished. For midfoot and
more proximal foot surgery, perimalleolar block is required. Because success
rates are higher with inframalleolar technique, in which the deep peroneal
and posterior tibial nerves are more superficial, this technique is
preferable for forefoot surgery.2,3
++
For all approaches, the patient can be supine, with a pillow under the
calf of the leg to be blocked to facilitate access. The anesthesiologist can
sit on a stool at the foot of the bed, if desired.
+++
Saphenous, Superficial Peroneal, and Sural Nerve Blocks
++
The saphenous, superficial peroneal, and sural nerves are already
subcutaneous just proximal to the malleoli, and all can be blocked by a
subcutaneous ring of local anesthetic at this location from just anterior to
the Achilles tendon medially to laterally (see Figures 39-8, 39-9, and 39-10). The advantage of blocking these nerves here is that the area under
an ankle tourniquet will be anesthetized and tourniquet pain is less likely.
By injecting slowly and continuously advancing a 1½-in., 25-gauge
needle into the previously injected area, the number of injections and
discomfort from them can be minimized. This subcutaneous ring of local
anesthetic can also be performed distal to the malleoli for a midtarsal
block.
+++
Deep Peroneal Nerve Blocks
++
For the perimalleolar approach, the patient is asked to extend the
great toe, which will tense and identify the extensor hallucis tendon (see
Figure 39–7). A 1½-in., 25-gauge needle is inserted immediately
lateral to the tendon, perpendicular to the tibia, and is advanced until it
contacts bone (see Figure 39–11). The needle is then withdrawn a few
millimeters, and after negative aspiration, 8 mL of local anesthetic are
injected. For the inframalleolar or midtarsal approach, the extensor
hallucis tendon is identified as previously mentioned above, but more
distally, and the pulse of the dorsalis pedis artery is identified on the
top of the foot as well. A 1½–in., 25-gauge needle is inserted
immediately lateral to the tendon and medial to the artery, and after
negative aspiration, 5 mL of local anesthetic are injected.
+++
Posterior Tibial Nerve Block
++
For the retrotibial approach, a 1½-in., 25-gauge needle is
inserted just posterior to the pulse of the posterior tibial artery behind
the medial malleolus, or if it cannot be palpated, midway between the
Achilles tendon and the posterior aspect of the medial malleolus (see Figure 39–12). The needle is directed toward the tibia at a 45-degree angle to
contact bone. The needle is then withdrawn a few millimeters, and after
negative aspiration, 8 mL of local anesthetic are injected.
++
For the midtarsal, there are two approaches. Either the posterior tibial
artery is identified below and distal to the medial malleolus on the
calcaneus, or the sustentaculum tali is identified. The needle is directed
toward the calcaneus, slightly under the bony shelf of the sustentaculum
tali, or on either side of the tibial artery. After contact with bone, the
needle is withdrawn 2 mm, and 8 mL of local anesthetic are injected.
++
++
Block of the saphenous, sural, and superficial peroneal nerves by
circumferential subcutaneous injection can always be performed proximal to
the malleoli even when the deep peroneal and posterior tibial nerve blocks
are done more distally. This may help with tourniquet tolerance.