Ankle block: anatomy
Last updated: 03/04/2015
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 If no paresthesia, 7-10 ml should be injected as the needle is slowly withdrawn back from the posterior aspect of the tibia.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.
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