Five nerves supply the foot, four of which derive from the sciatic
nerve (the tibial, the superficial and deep peroneal, the sural nerves)
and one from the femoral nerve (the saphenous nerve).
first metatarsophalangeal joint is supplied by the saphenous nerve. The
skin of the central part of the dorsum of the foot is innervated by the
superficial peroneal nerve. The skin of the lateral border of the foot
and the small toe are supplied by the sural nerve. The deep structures
and a small area of the skin between the great and second toes are
innervated by the deep peroneal nerve. The deep structures and the skin
of the sole and of the planter surface of the toes and the dorsal
surface of the toenails are innervated by the tibial nerve. The ankle
block is obtained after blocking the tibial, the deep and superficial
peroneal, the saphenous, and the sural nerves.
Tibial nerve block.
The leg is rotated laterally, the site of puncture is located medially
to the tibial artery, behind the medial malleolus toward the Achilles
tendon. Set the nerve stimulator at a frequency of 2 Hz and a current
of 1.5 mA, then insert the needle connected to the nerve stimulator and
point it perpendicular to the skin in an anteroposterior direction
until a motor response (plantar flexion of the foot) is elicited.
Adjust the position of the needle to maintain the appropriate muscle
response with a current of 0.4 mA. Then, after negative aspiration,
slowly inject the local anesthetic solution.
Deep peroneal nerve block.
The dorsalis pedis artery is identified, at the level of the
intermalleolus circular line; the direction of the needle is lateral to
the artery, perpendicular to the skin, toward the tarsal bones. Then,
after negative aspiration, slowly inject the local anesthetic solution.
Superficial peroneal nerve block. Blocked by a subcutaneous injection toward the lateral malleolus, from the anterior midpoint of the leg.
Sural nerve block. Blocked by a subcutaneous infiltration between the lateral malleolus and the Achilles tendon.
Saphenous nerve block.
Blocked by a subcutaneous injection administered along a circular line
drawn around the ankle at approximately 2 cm above the medial malleolus.
No complications have been described with
this technique, but the nerves are vulnerable and inadequate
positioning can occur, causing damage to the nerve by compression.