Mini-symposium: Foot and ankle(iii) Entrapment neuropathies of the foot and ankle
Introduction
Entrapment neuropathies are a source of significant morbidity, but they are rare. They must be differentiated from radicular back pain caused by nerve root entrapment, and peripheral neuropathies secondary to systemic disease such as diabetes mellitus.1
The nerve supply to the foot comprises five peripheral nerves. Four of these (tibial, deep peroneal (DPN), superficial peroneal (SPN) and sural) are branches of the sciatic nerve and the fifth, the saphenous, is a terminal branch of the femoral nerve. Entrapment of any of these nerves along their entire length can give symptoms in the foot and ankle, which can range from intermittent pain and paraesthesia to motor weakness and muscle wasting.
Section snippets
Tarsal tunnel syndrome
Tarsal tunnel syndrome (TTS) is caused by entrapment of the tibial nerve around the ankle. It was first described in 1932 and named by Keck and Lam in 1962.2 It is an uncommon condition predominantly of adults, with a slight female predominance.2
Aetiology: The tibial nerve is a terminal branch of the popliteal nerve that descends deep to soleus with the posterior tibial vessels. It passes behind the medial malleolus in the tarsal tunnel. In 93% of the population3 it divides into its two main
Anterior tarsal tunnel syndrome
Named anterior tarsal tunnel syndrome (ATTS) in 1968 by Marinacci20 this condition is caused by entrapment of the DPN as it crosses in front of the ankle to the foot. As common in men as women, it affects adults from adolescence into the 60's.
Aetiology: The DPN is a branch of the common peroneal nerve arising as it passes around the fibular neck. It supplies the anterior compartment of the leg. Distally it passes under the superior and inferior extensor retinacula between the tendons of the
Superficial peroneal nerve (spn) entrapment
The SPN is a branch of the CPN below the fibular neck (Figure 8). The nerve runs in and supplies the peroneus longus and brevis muscles. It pierces the deep fascia 10 cm to 15 cm above the tip of the fibula, becoming subcutaneous. Its terminal branches are the medial and intermediate, which supply sensation to the dorsum of the foot and ankle, ending over all five toes, but there is a considerable overlap with the other cutaneous nerves.
Entrapment occurs as it pierces the fascia above the ankle
Anatomy
The sural nerve arises from the tibial nerve in the popliteal fossa, and then passes between the two heads of gastrocnemius. It pierces the deep fascia in the mid third of the calf, and is then joined by the peroneal communicating branch of the lateral sural cutaneous nerve. It then runs subcutaneously approximately 1 cm lateral to the Achilles tendon, onto the lateral border of the foot. It is a purely sensory nerve and its terminal branches supply the skin of the lateral side of the heel and
Anatomy
The saphenous nerve is an entirely sensory branch of the femoral nerve. It arises within the femoral triangle, passing down the thigh with the superficial femoral artery. After exiting the adductor canal through the fascia lata it divides into an infra-patellar branch, which supplies the skin over the lower knee, and a descending branch. The descending branch continues with the long saphenous vein to the foot. Two terminal branches supply the medial ankle and medial midfoot, the latter
A general caveat – the double crush phenomenon
Whenever considering the aetiology of a distal nerve entrapment, consideration should always be given to search for a second, often primary, proximal lesion. This can be synchronous or metachronous, general (e.g. diabetes) or local (e.g. radiculopathy). The proximal nerve insult can change the physiology of the distal nerve, increasing its sensitivity to entrapment. Both sites of compression must be addressed in order to achieve a satisfactory clinical outcome.27
References (27)
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Tarsal tunnel syndrome
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