Anterior tarsal tunnel syndrome

What is anterior tarsal tunnel syndrome?

The deep peroneal nerve travels down the front of the lower leg beside the shin bone. Just above the ankle, it passes under a band of tissue called the inferior extensor retinaculum, which holds the tendons at the front of the ankle in place. Beyond that band, the nerve divides. One branch is purely sensory and supplies the skin of the web space between the big toe and second toe. The other branch controls two small muscles on the top of the foot.^[1]

The space beneath that band is called the anterior tarsal tunnel. The name is meant to set it apart from the posterior tarsal tunnel on the inner side of the ankle, which is a different condition; see tarsal tunnel syndrome. When the deep peroneal nerve is squeezed under the band, or at two other places further along the top of the foot, the result is anterior tarsal tunnel syndrome.^[1]

Symptoms

• pain, aching or burning on the top of the foot and front of the ankle
• numbness or tingling in the web space between the big toe and second toe
• discomfort that is worse in tight shoes or laces, and better with shoes off
• in some people, weakness of the small muscles on the top of the foot, which is often hard to notice yourself^[1,2]

The syndrome is described as rare and poorly diagnosed, partly because these symptoms overlap with those of other conditions.^[2]

What causes it?

Anything that narrows the space at the front of the ankle, or stretches the nerve, can contribute:

• A tight fascial band or tight footwear. The inferior extensor retinaculum is the most common place the nerve is compressed.^[1] Tight shoes and laces add pressure from outside.
• Injury, such as an ankle sprain or fracture, and scar tissue afterward.
• Growths or swelling, such as a ganglion cyst, a bone spur on the top of the midfoot, or swollen tendon sheaths.
• Positions that hold the foot pointed for a long time. In one report of 14 people with the condition, all regularly spent long periods kneeling for prayer, which the authors suggested repeatedly stretched the nerve.^[3]
• No clear cause, in some people.

How it’s evaluated

Other problems that can mimic it include a pinched nerve in the lower back, peripheral neuropathy, arthritis on the top of the foot, and a compressed superficial peroneal nerve (see superficial peroneal nerve entrapment).

• History and examination: where the symptoms are and what provokes them, the strength of the toe-lifting muscles, sensation in the web space, tapping over the nerve at the front of the ankle, foot alignment, footwear, and a check of the back and circulation.
• Nerve studies: in the report above, nerve studies of the deep peroneal nerve showed slowed conduction, and EMG changes were confined to a small muscle on the top of the foot.^[3] These tests are performed by another specialist, and we coordinate them and go over the results with you.
• Imaging: X-rays can show a bone spur, and ultrasound or MRI can reveal a cyst or other structure pressing on the nerve.^[4] Read more in nerve testing for foot pain.

Treatment options

Non-surgical care

The first step is to reduce or remove pressure on the front of the foot and ankle.^[2]

• Footwear changes, such as different lacing, a padded tongue, or shoes that leave room over the top of the foot
• Activity changes, including a break from positions or activities that keep the foot pointed
• Physical therapy
• A corticosteroid injection, in selected cases^[2]
• Medicine for nerve pain, coordinated with your other clinicians

Surgery

If symptoms persist despite well-tried non-surgical care, surgery to release the nerve may be discussed. The nerve is freed from the tight tissue at the point of compression, either higher up at the extensor retinaculum or further along the top of the foot.^[2] See nerve decompression surgery.

Recovery and outlook

The evidence on this condition comes mainly from small reports, so it is hard to promise a particular result. In general, non-surgical care takes weeks to months to show its full effect. If surgery is needed, nerve symptoms usually improve gradually over months. Numbness may recover more slowly than pain.

When to seek care

Consider an evaluation if pain, burning or numbness on the top of your foot lasts more than a few weeks, or gets worse when you wear your usual shoes.