The superficial peroneal nerves pierces the deep fascia in
the distal third of the lateral leg and then, in the superficial fascia,
divides into branches supplying the dorsum of the foot and the toes and nor
innervated by the sural and deep peroneal nerves.
The
saphenous nerve, the sole branch of the femoral nerve below the knee, runs
along the knee, runs along the superficial fascia in front of the medial
malleolus, accompanied by the great saphenous vein, and innervates the medial
side of the foot as far as the metatarsophalangeal joint.
The plantar
nerves are the terminations for the tibial nerve, whole the dorsal digital
nerves on the dorsum of the foot are branches of the superficial peroneal
nerve.
Ankle block
(i.e., anterior and posterior blocks) is suited for surgery on the sole or
dorsum of the foot that does not involve a tourniquet or that requires a
tourniquet for less than 30 minutes. Metatarsal block is indicated for
surgical procedures on the toes, such as surgery for ingrowing toenails, and
bunionectomy.
Position. The patient's foot rests
firmly on the bed with the knee flexed. An alternative position is to
keep the leg and foot supine.
Landmarks. The medial and lateral
malleoli, the posterior calcaneal tubercle, the tendo calcaneus, the pulsation
of the tibial artery and the extensor halluces longus tendon are landmarks
identifying the appropriate injection sites.
Procedure. For a block of the deep
peroneal nerve, a skin wheal is made on the anterior aspect of the ankle
lateral to the extensor halluces longus tendon approximately at the location of
the anterior tibial artery. A 22-G, 3.75 cm needle is inserted until it
touches the bone, and 5 ml local anesthetic solution is injected.
For a block
of the superficial peroneal nerve, a skin wheal is made on the distal third of
the leg just lateral to the anterior border of the tibia at the superior border
of the lateral malleolus. The subcutaneous tissue just superficial to the
deep fascia is infiltrated with the local anesthetic solution (5 ml). The
depth of the insertion depends on the amount of subcutaneous fat. This
block is performed as a field block extending over an area 5-6 cm wide and
lateral to the anterior border of the tibia in order to block all of the
branches of the superficial peroneal nerve as they descend to the dorsum of the
foot.
To block the
saphenous nerve, 5 ml local anesthetic solution is injected subcutaneously
around the great saphenous vein anterior to the medial malleolus.
To perform a
metatarsal block, skin wheals are raised on the dorsum of the foot between the
heads of each metatarsal bone. A 22-G, 3.75 cm needle is inserted
perpendicularly toward the sole of the foot until the point can be felt in the
plantar aspect without penetrating the skin. A dose of 5 ml local
anesthetic is deposited at each intermetatarsal space from the sole to the
dorsum of the foot. A separate injection is made on the sides of the
first and fifth metatarsal bones. A subcutaneous ring solution can be
deposited, connecting all of the skin wheals on the dorsum of the foot, to
block the crossover of innervation from the saphenous nerve, sural and
calcaneal branches.
The anterior
ankle and metatarsal blocks can cause such complications as neuritis, unduly
prolonged block, and infection and hematoma.
A
posterior ankle block anesthetizes the tibial and sural nerves. The
tibial nerve descends through the midpoint of the interval between the medial
malleolus and the calcaneus on the medial side of the ankle under the flexor
retinaculum. It lies posterior to the pulsation of the posterior tibial
artery and innervates the skin and muscles of the plantar aspect of the foot.
The sural
nerve is formed by contributions from the tibial and common peroneal
nerves. It runs along the midline of the calf muscles to the lateral
aspect of the ankle midway between the lateral malleolus and the calcaneus and
proceeds toward the lateral side of the little toe.
The
posterior ankle block is normally used in conjunction with the anterior ankle
block to anesthetize the entire ankle and foot region.
Position. The patient lies prone, with
the feet hanging over the edge of the table.
Landmarks. The injection site is
identified by the same landmarks as for the anterior ankle block.
Procedure. For a tibial nerve block, a
skin wheal is made with a 27-G needle midway between the medial malleolus and
the calcaneus posterior to the pulsation of the posterior tibial artery.
A 22-G, 3.75 cm needle is then introduced to elicit paresthesia in the foot or
twitching of the intrinsic muscles of the sole of the foot when a nerve
stimulator is used. After it has been confirmed that the needle is on the
tibial nerve, 5 ml local anesthetic solution is injected. The sural nerve
is blocked by injecting 5 ml local anesthetic into a skin wheal deep to a point
midway between the lateral malleolus and the calcaneus.
Complications
associated with the posterior ankle block are neuritis, unduly prolonged block,
infection and hematoma.