Tarsal Tunnel Syndrome

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Anatomy

The tarsal tunnel is a bony canal found below the medial malleolus. The posterior tibialis, flexor hallucis longus, flexor digitorum, posterior tibial artery and vein, and tibial nerve all run through the tarsal tunnel.

Aetiology

It can occur form anything that increases pressure on the tunnel such as improper foot orthoses, pressure areas in boots, and scar tissue from previous surgery. It is also seen in runner who don't have good hip stability during midstance resulting in the opposite foot hitting the tarsal tunnel as it swings forward. Excessive pronation can also lead to tension on the tibial nerve. Injuries to the posterior tibialis or flexor hallucis tendons can also lead to increased pressure in the tarsal tunnel.

Clinical Features

Patients get neuropathic pain from the tibial nerve. The pain may be aching or burning and they may complain or numbness or tingling. The pain radiates to the plantar surface of the forefoot via the medial and lateral plantar branches or the medial calcaneus via the medial calcaneal branch. In other words it can involve the sole of the foot, distal foot, toes, and sometimes the heel. It can also radiate up the medial ankle. The pain tends to be worse at night. It can also be aggravated by standing and some patients will take their shoes off when this occurs.

Look for chronic abrasions on the posterior medial ankle and oedema inferior and posterior to the medial malleolus. The triple compression test can be used to help assess for the condition. Tinel's sign may be positive over the tibial nerve posterior to the medial malleolus. There may be reduced sensation over the plantar surface of the foot, but this shouldn't extend onto the dorsal foot.

Differential Diagnosis

Occasionally compression of the tibial nerve can occur in the popliteal fossa e.g. from a Baker's cyst. Also patients may have isolated medial and lateral plantar neuropathies of the foot from trauma, fibrosis, or entrapment.

Investigations

Rarely nerve conduction studies are required.

Treatment

First line treatments are NSAIDs, shoe modification, and orthotics.

Second line treatment is corticosteroid injection and this can also be helpful diagnostically.

In refractory cases surgical decompression can be offered, but surgery has a very high complication rate of 30%. Surgical outcomes are more favourable with shorter durations of pain, presence of a ganglion, no history of sprains, and low work demands.