What is Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)?
In 1960, Koppel and Thompson first described a condition known as anterior tarsal tunnel syndrome (ATTS), also known as deep peroneal nerve (DPN) entrapment. This medical condition is a result of pressure on the deep peroneal nerve caused primarily by a tight band of tissue in the front ankle called the inferior extensor retinaculum. There are also two other possible areas where this nerve can get trapped, under a tendon in the foot and under a muscle near the first and second joints of the foot.
The deep peroneal nerve is one of two end branches of the common peroneal nerve. This nerve splits off in the lower front section of the leg and follows a path along a dividing membrane in the leg. It then passes between two tendons near the ankle joint before separating into two final branches. These branches provide functionality and sensory input to certain muscles and regions in the foot and leg.
The anterior tarsal tunnel is a pathway along the front ankle made up of different parts of the leg and foot, such as ligaments and joints. This tunnel accommodates various anatomical elements like arteries, nerves, and tendons. The common peroneal nerve, which is involved in ATTS, is connected to nerve roots located in different sections of the spine.
Symptoms of tarsal tunnel syndrome might include loss of muscle function leading to muscle wasting, loss of pain sensation, and walking abnormalities.
What Causes Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)?
Anterior tarsal tunnel syndrome is when the deep peroneal nerve, which is in the foot, gets pressed or trapped. This typically happens under the inferior extensor retinaculum, a band of fibrous tissue, because of injury or ongoing small trauma. But, there are other possible causes also:
Objects that occupy space around the area like a ganglion cyst, intraneural ganglion (a type of cyst inside a nerve) and swollen anterior tibial veins.
Bone spurs (extra bone growth) in the metatarsals, talus, cuboid or navicular bones which are all bones in your foot.
Compression by an extra bone called ‘os intermetatarseum’.
An excessively grown extensor hallucis brevis muscle in athletes. This is a muscle on the top of your foot that helps extend your big toe.
Irritation from the tendon of the extensor hallucis brevis muscle.
Compression from tight shoes, sports equipment, or military boots.
Continuous stretching of the deep peroneal nerve or extreme bending of the foot downwards as in dancing, playing soccer, diving, Islamic Namaz praying.
Pulling injury from ankle sprains or ongoing ankle instability.
Risk Factors and Frequency for Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
Anterior tarsal tunnel syndrome (ATTS) is a fairly rare condition and thus, the exact number of cases is not known. This can be attributed to the rarity of the disease and also that it is often not diagnosed. Research suggests that it accounts for about 5% of the cases where patients report feeling numbness in their feet. Moreover, it was found that in their medical practice, the condition represents about 1% of the incidences. This condition does not seem to have a preference for a specific age or gender. However, it is often observed that athletes are more frequently affected by it.
Signs and Symptoms of Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
ATTS, or Anterior Tarsal Tunnel Syndrome, is typically diagnosed through meticulous patient history and a physical examination. This condition often manifests as sharp pain, numbness, or a tingling sensation that spans along areas of the foot served by the Deep Peroneal Nerve (DPN) or its branches. These symptoms usually occur intermittently, worsen with physical activity, and get better with rest. They are most frequently experienced in the premier pocket of skin between the toes on the top side of the foot.
Patients might remember specific events, like a sprained ankle or a sudden footstrain injury, or a series of small, repetitive injuries due to activities like running or rigorous military training. Clinicians may trigger these symptoms during the physical exam by tapping on the DPN (Tinnel sign), which can cause tingling to radiate along the nerve’s path. Swelling or other detectable physical abnormalities, like varicose veins or bone spurs, might also be found in the same area. If the foot is flexed excessively or under strain, it could replicate these sensations due to the nerve being compressed or stretched.
Additional physical features, like a high-arched foot (pes cavus foot type), could be discovered during the examination. This might be contributing to the pressure on the top of the foot and leading to issues with shoe fit.
Furthermore, a comprehensive check of the lower limbs’ muscles and nerves is necessary, which includes assessments of muscle strength, vibrations, touch sensitivity, temperature, and the ability to distinguish two close points.
In a small study of 13 patients, it was found that 100% of patients showed a positive Tinel sign, and almost 92% had a noticeable bulge in the front of the ankle or foot, typical symptoms of ATTS.
Testing for Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
Diagnosing anterior tarsal tunnel syndrome, a condition affecting the nerves in the ankle, mainly relies on a detailed personal health history and a physical examination done by a doctor. Sometimes, additional imaging techniques may be needed, depending on the doctor’s preference.
The doctor might also perform some blood tests to check for diabetes, as this is a common cause of nerve problems. It’s important to note that some men with a type of arthritis called reactive arthritis might develop this syndrome and test positive for a marker known as HLA B27. Your doctor might also want to rule out other types of arthritis by doing additional tests like ESR, antinuclear antibody, and rheumatoid factor.
Simple x-rays of the foot and ankle while bearing weight can help identify certain foot conditions (like high arches, or ‘pes cavus’) or bone spurs that might be causing nerve compression and pain.
If the diagnosis is still uncertain, your doctor might order specific nerve tests, such as nerve conduction velocity and electromyography (EMG), to confirm the condition and pinpoint the exact location of the nerve compression. Nerve conduction studies involve measuring the speed of electrical signals through a nerve, and an EMG looks for nerve damage by assessing the electrical activity within muscles.
If a physical exam shows the presence of a soft tissue mass (like a cyst or varicose veins), an MRI might be advised. MR neurography, which creates images of the nerves, has been found helpful in diagnosing nerve compression in the lower extremities. High-resolution musculoskeletal ultrasound imaging is also recommended, as it can provide images of the peripheral nerves, which can be helpful since results from nerve tests can sometimes vary.
Treatment Options for Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
If you are suffering from Anterior Tarsal Tunnel Syndrome (ATTS), your treatment will depend on what is causing your condition. This may include a non-surgical approach such as:
• Modifying your shoes and how you lace them
• Over-the-counter shoe inserts or custom-made ones, or using padding
• Anti-inflammatory creams that you apply on the skin
• Painkillers you can swallow or apply topically, or drugs designed to treat nerve pain like gabapentin
• Corticosteroid/anesthetic injections that target the nerves causing you pain
• Compression socks if you have swelling or protruding veins
• A reduction in sports activity or wearing a special boot to keep your foot still
If these methods don’t work, surgical options may be considered. The type of surgery will also depend on the cause of your condition, and could include:
• Freeing or opening up space in the extensor retinaculum, which is a band of tissue, and removing any surrounding scar tissue
• Removing things taking up too much space like a cyst or a lump in a vein
• Removing bone spurs
• Performing a procedure to improve the function of the damaged nerve, wrapping the nerve, removing the neuroma (a type of nerve tumor), or removing a part of the Deep Peroneal Nerve
Surgery usually involves making a large opening, but there are also less invasive techniques that use an endoscope. Nonetheless, the surgeon must be careful to not damage the posterior tibial nerve and make a careful release of the tissue bands.
What else can Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment) be?
When trying to figure out if someone has Anterior Tarsal Tunnel Syndrome (ATTS), doctors need to consider other conditions that could also cause a tingling sensation in the foot. These include:
- Anterior Compartment Syndrome due to over-exertion
- Trapped or ‘entrapped’ Common Peroneal Nerve
- Trapped or ‘entrapped’ Superficial Peroneal Nerve
- A condition of the foot known as 1st Inter-Space Neuromas, or Heuter’s Neuroma
- A condition where there’s pain radiating from the lower spine, known as Lumbosacral Radiculopathy
- Various inflammatory diseases
- A tumor on a nerve
- A specific condition known as Mid-Foot Retinaculum Entrapment that presents symptoms similar to ATTS
By considering these other conditions, doctors can accurately diagnose the problem.
What to expect with Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
The outcome of an anterior tarsal tunnel varies greatly, but the majority of case reports and series indicate that most patients experience good to excellent improvement with surgery.
For instance, Yassin et al. found that 12 out of 13 patients reported significant improvement following surgery. Similarly, Dellon followed the progress of 18 patients who underwent surgical decompression. Almost two years after the surgery, 60% of them had excellent results, 20% had good results, while 20% saw no improvement.
Murphy, who performed 21 surgeries on 15 runners suffering from persistent nerve injuries in their feet and ankle, noted that all of them had good to excellent results. He also mentioned all his patients, including competitive athletes, were able to return to their running activities as they did before their injuries.
Possible Complications When Diagnosed with Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
If anterior tarsal tunnel syndrome isn’t treated, it can lead to constant pain or nerve conditions in the deep peroneal nerve or its branches.
Surgery to relieve the pressure on the nerves can have complications. These might include damage to the nerve or shrinking of the extensor hallucis brevis, a muscle in the foot, especially in late-stage cases. There are also other risks after the surgery:
- Infection
- Wound coming open
- Scar tissue forming
- Pain or original symptoms not going away
- Needing more or corrective surgery
Recovery from Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
In the first few weeks following an operation, especially in the front part of the ankle, post-surgery care is centered around keeping the surgical area still and allowing the incision to heal properly. This is because the wound tends to split open again, which can cause problems.
Following this, the patient is encouraged to begin a structured program of physical therapy or a routine they can do at home. This helps improve muscle strength and flexibility while also reducing swelling, pain, scar tissue, and irritation of the nerves.
Eventually, the patient should be able to walk normally and return to their usual physical activities.
Preventing Anterior Tarsal Tunnel Syndrome (Deep Peroneal Nerve Entrapment)
Currently, there are no specific guidelines to prevent or reduce the risk of anterior tarsal tunnel syndrome, a condition that affects the foot. However, it is often suggested that avoiding shoes or sports equipment that fits too tightly might help.
Different conditions can cause foot and ankle pain. Anterior tarsal tunnel syndrome is a rare but potential cause. If anyone experiences pain in the foot or ankle, as well as symptoms like burning sensations, numbness, tingling, or muscle weakness, they should reach out to a healthcare professional for evaluation and treatment.
