Giorgio Ivani
Valeria Mossetti
Patient Position: The patient lies supine in neutral position or slight internal and then external rotation according to the nerve to be blocked.
Indications: Anesthesia and postoperative analgesia of the foot.
Needle Size: A 23- to 25-gauge, 35-mm, insulated beveled needle and a short beveled needle for the subcutaneous infiltration.
Volume: 2 to 4 mL ropivacaine 0.2% for each nerve.
Anatomic Landmarks: 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).
The skin of the medial side of the foot as far as the 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.
Approach and Technique:
1. 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.
2. 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.
3. Superficial peroneal nerve block. Blocked by a subcutaneous injection toward the lateral malleolus, from the anterior midpoint of the leg.
4. Sural nerve block. Blocked by a subcutaneous infiltration between the lateral malleolus and the Achilles tendon.
5. 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.
Tips
1. 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.
Suggested Readings
Dalens B. Lower limb blocks. Distal conduction blocks. In: Dalens B, ed. Pediatric regional anesthesia. Boca Raton: CRC Press, 1990:333–348.
Schurman DJ. Ankle-block anesthesia for foot surgery. Anesthesiology 1976;44:348–352.