Ankle block: anatomy

The nerve supply of the foot is primarily from the sciatic nerve:

1) The superficial peroneal nerve (L4-S1) is located lateral to the extensor digitorum longus

• Sensory: dorsum of foot and toes except b/w the great and second toes (deep peroneal n.)
• Technique: see below, blocked with deep peroneal n. and saphenous n.

2) The deep peroneal nerve (L4-L5) is located lateral to the extensor hallicus longus

• Sensory: between the great and second toes
• Motor: extends the toes
• Technique: see below, blocked with superficial peroneal n. and saphenous n.

3) The sural nerve (S1-S2) is located superficially between the lateral malleolus and the Achilles tendon

• Sensory: posterolateral leg, lateral foot, 5th toe
• Technique: Needle is inserted lateral to the tendon and is directed toward the malleolus as 5-10 ml of local anesthetic is injected subcutaneously.

4) The tibial nerve is posterior to the medial malleolus

• Sensory: plantar surface of the foot
• Motor: flexes the toes
• Technique: the posterior tibial artery is palpated and a needle is inserted posterolateral to the artery at the level of the medial malleolus. A paresthesia is often elicited at which time 2-5 mL of local should be injected. If no paresthesia, 7-10 ml should be injected as the needle is slowly withdrawn back from the posterior aspect of the tibia.

The femoral nerve contributes one nerve to the ankle:

5) The saphenous nerve (L3-L4) is just anterior to the medial malleolus

• Sensory: anteromedial side of the leg, medial side of foot
• Technique: see below, blocked with deep peroneal n. and superficial peroneal n.

The deep peroneal, superficial, peroneal, and saphenous nerves can be blocked through a single needle entry site. A line is drawn across the dorsum of the foot connecting the malleoli and local anesthetic is infiltrated along this line across the anterior aspect of the foot.

Note: The three nerves that start with the letter S (superficial peroneal, sural, saphenous) are all Sensory only. The other 2 nerves, deep peroneal and tibial, are motor + sensory.