Lesson-Ankle

1 – Indications

The indications of an ultrasound guided ankle block is forefoot surgery as an alternative to a combined popliteal sciatic and midthigh saphenous nerve blockade

It is not indicated for surgical anaesthesia if a tourniquet is applied proximal to the ankle level

All five nerves innervating the foot have to be anaesthetized which can be painful in the awake patient

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The ultrasound guided deep peroneal blockade

2 – Anatomy: The trajectory of the sural nerve

The sural nerve is a sensory nerve made of the fusion of the medial sural cutaneous nerve from the tibial nerve and of a communicating branch from the lateral sural cutaneous nerve from the common fibular nerve

The two sural cutaneous nerves pierce the deep fascia – together with the short saphenous vein – before the fusion that makes the sural nerve

The sural nerve descends posterior to the lateral malleolus together with the short saphenous vein

The sural nerve innervates the postero-lateral part of the skin cover of the ankle and supply calcaneal branches that innervate the lateral heel and lateral dorsal cutaneous nerves that innervate the lateral margin of the foot

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Sural nerve (magenta), lateral calcaneal branches (cyan), lateral dorsal cutaneous branches (green)

3 – Anatomy: The trajectory of the superficial peroneal nerve

The superficial peroneal nerve (SPN) branches off the common peroneal nerve in the proximal lateral compartment of the leg

The SPN descends in the lateral compartment between the peroneal muscles and the fibula. It innervates the peroneal muscles

Approx. 10 cm above the lateral malleolus the SPN emerges between the lateral compartment (peroneal muscles) and the anterior compartment (the extensor muscles of the foot) and pierces the deep fascia of the leg

Above the deep fascia the SPN splits into the intermediate and medial dorsal cutaneous nerves that supply cutaneous innervation to the antero-lateral part of the distal leg, ankle and dorsum of foot – including the dorsal digital nerves that supply innervation of dorsal part of the toes and the interdigital spaces – except the first interdigital space

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Superficial peroneal nerve (magenta), medial dorsal cutaneous branch (green), intermediate dorsal cutaneous branch (cyan)