Ankle block

The following nerves must be anaesthetised when performing regional anaesthesia of

the foot. Which nerve is readily amenable to location using the peripheral nerve

stimulator?

a) Superficial peroneal (fibular) nerve

b) Deep peroneal (fibular) nerve

c) Tibial nerve

d) Sural nerve

e) Saphenous nerve

Answer: c

Explanation

The ankle block can be performed by a surface landmark technique or be ultrasound

guided. The approach to the component nerves is different according to the technique

selected. This is because the level at which the nerves are blocked using the surface

landmark technique precludes easy ultrasonographical visualisation. The nerves are

either too indistinct there or the footprint of the probe prevents consistent skin contact.

For this reason, ultrasound-guided ankle blocks involve anaesthetising the saphenous

nerve at the medial knee, the superficial peroneal at the lateral calf, the deep peroneal

on the lower third of the shin (lateral to the anterior tibial artery) and the sural and tibial

nerves in similar locations to the landmark technique. The tibial nerve is located just

posterior to the palpable pulse of the posterior tibial artery and peripheral nerve

stimulation here will cause plantar-flexion of the toes. The saphenous and sural nerves

are purely sensory. As well as its cutaneous sensation role, the superficial peroneal

nerve gives motor supply to peroneus longus and brevis. The lateral branch of the deep

peroneal nerve innervates the extensor digitorum brevis muscle, although the deep

peroneal nerve is largely sensory, supplying skin of the first webspace and innervation

to many of the small joints of the foot. Despite their motor components, peripheral

nerve stimulation of the peroneal nerves is not described.