Overview of Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
When dealing with muscle and nerve related disorders, it can be tough to identify the problem just through a patient’s medical history and a physical examination. Plus, a lot of these types of conditions don’t show up on commonly used imaging tests like an MRI or CT scan. Luckily, there are alternative tools doctors can use, and this is where electodiagnostic tests, specifically Electroneurography (ENG) and electromyography (EMG), come into play.
These tests are very helpful in identifying conditions that affect nerves in the peripheral regions (or external parts) of the body, such as when a nerve called the tibial nerve gets compressed. This can cause an uncommon condition that results in pain, tingling, and potentially weakness in your foot and ankle. This specific nerve condition affecting the foot is often called tarsal tunnel syndrome.
Tarsal tunnel syndrome can be caused by external pressure, like when your shoes don’t fit correctly or if you have a tight cast. It can also happen following an accident (like sprains or fractures), or due to fibrosis that develops after an injury. Other possible causes include lipomas (fatty lumps under the skin), cysts, tumors, soft tissue infections, and inflammatory joint diseases. An actual entrapment due to a thickened tissue called flexor retinaculum is quite rare.
An important function of the electromyography can identify which specific muscles are being affected by the nerve problem. If the nerve issue is found in the tarsal tunnel, your doctor needs to figure out what is causing the compression and discomfort.
Anatomy and Physiology of Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
The tibial nerve is simply an extension of a larger nerve called the medial trunk of the sciatic nerve. This nerve travels down to the ankle, and they go behind and below a bony bump on the inside of your ankle (this is called the medial malleolus). They then pass through a pathway (tunnel) made by a band of connective tissue called the flexor retinaculum.
When the tibial nerve gets past this tunnel, it splits into different branches. There are two sensory branches that go to the heel of your foot. Sensory nerves are the nerves in your body that let you feel things. Then there are two more mixed nerves, called plantar nerves, which contain both sensory and motor fibers. Motor fibers are responsible for making muscles move.
These nerves do different things. They help you to feel sensations on two-thirds of the bottom of your foot, and they also control the movements of specific muscles in your foot. For example, the lateral plantar nerve is in charge of making a particular muscle (abductor digiti quinti pedis) move and for feeling sensations on the outer side of the foot, along with the outer 1.5 toes. The medial plantar nerve controls movements in other specific foot muscles like the abductor halluces brevis, the flexor halluces brevis, and the flexor digitorum brevis. It is also responsible for the sensation on the inner side of the foot and in the first three toes.
If the tibial nerve gets compressed at the tarsal tunnel (a spot at the level of your ankle), it can cause problems with both sensations and movements in parts of the foot that those nerve branches serve.
Why do People Need Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
The patient is experiencing pain on one side of the foot and ankle, along with a lack of feeling on the bottom of their foot. Also, damage inside or near the ‘tarsal tunnel’ (a narrow passageway inside your ankle that nerves pass through), is causing a loss of sensation in the heel. When the doctor examines the patient, they may find that lightly tapping (‘Tinel’s sign’) over a particular nerve on the inside part of the ankle causes a tingling sensation. The patient might also have changes in sensation along the bottom of the foot.
The fact that the patient’s calf muscle is of normal strength and they have a normal ankle reflex, but weakness in the small muscles of the foot, helps pinpoint the location of the issue.
When a Person Should Avoid Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
There are certain risks associated with an EMG test, which is used to check the health of your muscles and nerves. These risks include:
Infections in the skin or soft tissues at the location where the test is conducted. This happens when bacteria get into the body through the insertion of the needle electrodes.
Complications can also arise if you have a cardiac pacemaker. The electrical signals used during the test might interfere with the device.
Another risk factor is coagulopathies, which is a medical condition that affects your blood’s ability to clot. In such cases, the needle pricks from the test might trigger excessive bleeding.
If you have lymphedema, a condition which causes swelling in your arms and legs from a blockage in the lymphatic system, an EMG test can potentially make your condition worse.
Lastly, some people might have a low tolerance to this test. This means they might find the procedure uncomfortable or experience significant pain when the needle electrodes are inserted.
Equipment used for Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
The tools used for diagnosing tarsal tunnel neuropathy, a condition involving nerve damage in the foot, include:
- An ENG/EMG machine, which records the electrical activity in your muscles and nerves
- Surface electrodes for the ENG part of the test – these are small devices that stick to your skin to pick up electrical signals
- A one-time use needle called a concentric EMG needle that’s used to send and measure electrical signals in your muscle
- A needle cable which is a wire connecting the concentric EMG needle to the EMG machine
- A ground electrode which is used to make the electrical readings more accurate.
Who is needed to perform Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy?
Doctors who have specific training and certification in studying the brain and nervous system are the ones who need to perform these special tests, known as electrophysiological studies. This kind of study helps them understand how your nerves and brain are working.
Preparing for Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
Before setting a date for the heart test, or electrophysiological test, the doctor will explain what the patient should expect during the procedure, including what it might feel like and how long it will take. The doctor will also inform the patient about the very low chances of infection and bleeding, since a needle will be used to pierce the skin. For this reason, the patient should avoid applying any skin cream before the test.
The doctor will also make sure the patient understands where on their body the test will be performed and how they should move their muscles during the test. It’s also important for the room where the test will be conducted to be at a comfortable temperature. Just before the test begins, the doctor or a nurse will clean the patient’s skin with an alcohol swab and allow it to air dry. This is an important step in ensuring the test area is clean to prevent any potential infections.
How is Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy performed
For a certain nerve and muscle test, you will need to lie flat on your back (supine) with your legs comfortably resting on the examination table. This test, known as an electromyography (EMG), studies the muscles within your foot. It measures your nerve signals to determine if they are working properly.
Your doctor will check the strength of the signal from a nerve in your lower leg, the tibial nerve, by applying a stimulus at your ankle and recording the response from two muscles in your foot – the abductor hallucis which moves your big toe away from your foot’s midline, and the abductor digiti minimi which moves your little toe away from the midline. They’ll also carry out studies on sensory and mixed-conduction nerves (which play a role in feeling and movement). The doctor uses a special averaging technique to get accurate results.
Since there is a wide range of what is considered normal in these tests, if your other foot is not affected by any conditions, your doctor can compare the results to help determine if any issues exist.
Following this, the doctor will use a needle probe to study the health of specific muscles in your foot. These muscles, which are controlled by the medial and lateral plantar nerves, include those that help move your toes and support the arch of your foot. As with the earlier tests, it’s useful to compare these findings with the unaffected foot, if applicable.
To complete the study, your doctor will also examine the muscles in your calf. The health of these muscles, which are controlled by the tibial nerve (in your leg) and the peroneal nerve (on the outside of your calf), must be normal. This comprehensive examination ensures a thorough understanding of how well your nerves and muscles are functioning.
Possible Complications of Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy
An electromyogram (EMG), a test that checks the health of the muscles and the nerves controlling the muscles, does come with some risks. These include bleeding, infection, and damage to the nerves.
There can also be technical difficulties during the test. For instance, it can be challenging for the medical professionals to tell the difference between normal and abnormal activity in the small muscles within the foot.
What Else Should I Know About Electrodiagnostic Evaluation of Tarsal Tunnel Neuropathy?
Tarsal tunnel syndrome is a condition that affects your foot and ankle. It’s important to catch it early so you can start treatment right away. Depending on the reason behind your tarsal tunnel syndrome, non-surgical treatments may be all you need. For instance, if you’re experiencing this syndrome because of tight shoes, simply switching to more comfortable footwear could solve the problem.
If your tarsal tunnel syndrome keeps getting worse, you might need surgery. The operation involves a detailed look at the nerves in an area of your foot known as the tarsal tunnel. By conducting two specific tests called electromyography (EMG) and nerve conduction study (ENG), doctors can diagnose tarsal tunnel syndrome in its early stages, which is the ideal time for treatments to work effectively.
