Tarsal Tunnel Syndrome
When the tibial nerve comes under pressure near the inner ankle
Tingling, burning, or numbness in the sole of the foot can have many different causes. One possible explanation is Tarsal Tunnel Syndrome (TTS) – a compression of the tibial nerve near the inner ankle. In most cases, this refers to the so-called posterior tarsal tunnel syndrome, where the nerve is compressed beneath the flexor retinaculum just behind the medial malleolus. The symptoms can be bothersome and typically occur during standing, walking, or certain movements.
This article does not address anterior tarsal tunnel syndrome, a much rarer condition involving the deep fibular (peroneal) nerve on the top of the foot.
What is Tarsal Tunnel Syndrome?
The tarsal tunnel is a narrow anatomical passage located just behind the medial malleolus (the inner ankle bone). This tunnel contains the tibial nerve, blood vessels, and tendons, all running beneath a firm band of connective tissue called the flexor retinaculum. If the tibial nerve becomes compressed in this confined space, irritation or functional disturbance may occur – a condition referred to as Tarsal Tunnel Syndrome.
What does the tibial nerve do?
The tibial nerve is a branch of the sciatic nerve. It provides:
- Sensory supply to the sole of the foot
- Motor innervation to muscles involved in foot flexion
- Innervation to the calf muscles
As it passes through the tarsal tunnel, the tibial nerve typically branches into:
- Medial and lateral plantar nerves (for the sole of the foot)
- Medial calcaneal nerve (for the heel)
The branching pattern may vary between individuals.
Symptoms: What patients may experience
Common symptoms of Tarsal Tunnel Syndrome include:
- Tingling, burning, or numbness in the sole of the foot
- Pain near the inner ankle or heel
- Symptoms worsening with walking or prolonged standing
- Nocturnal discomfort in some cases
- Rarely, weakness of the small foot muscles (e.g., toe flexors)
Symptoms are usually unilateral, but can occur on both sides and may fluctuate in intensity.
Possible causes and risk factors
TTS can have multiple underlying causes, including:
- Space-occupying lesions: ganglions, cysts, lipomas, varicose veins
- Foot deformities: flatfoot, valgus positioning
- Scar tissue from previous injuries or surgery
- Chronic overload or inflammation
- Ankle trauma (e.g., fractures, sprains)
- Diabetes mellitus as a contributing factor
- Sometimes, no clear trigger is identified
Differential diagnoses
Because the symptoms of TTS are not specific, a careful differential diagnosis is essential. Other potential causes of similar complaints include:
- Plantar fasciitis
- Peripheral neuropathy (e.g., diabetic)
- Lumbar disc herniation
- Heel spurs
- Entrapments of other nerves, such as the sural or peroneal nerves
In practice, TTS is occasionally used as a diagnosis of exclusion, especially when other explanations are lacking – highlighting the need for detailed clinical evaluation.
How is Tarsal Tunnel Syndrome diagnosed?
1. Clinical examination
- Testing for pressure sensitivity (Tinel’s sign)
- Assessing foot sole sensation
- Checking muscle strength and reflexes
These findings may suggest the diagnosis but are not always conclusive.
2. Electrodiagnostic testing (NCS, EMG)
- Nerve conduction studies (NCS) assess signal transmission along the nerve
- Electromyography (EMG) measures muscle response to nerve input
These tests provide valuable information but can be limited in sensitivity, especially when:
- Only short nerve segments or partial branches are affected
- Sensory fibers are impaired without motor involvement
3. Imaging techniques
Structural imaging helps identify physical causes of nerve compression. Common modalities include:
- MRI: useful for detecting cysts, scar tissue, or deformities
- High-resolution ultrasound: allows dynamic visualization of the nerve and surrounding structures in real time
Ultrasound may also permit dynamic maneuvers (e.g., movement or light pressure) to correlate symptoms with nerve changes – a technique known as sonopalpation.
The choice of method depends on the clinical setting and availability.
What can imaging reveal?
Imaging may help visualize:
- Swelling or changes in nerve size
- Compression by surrounding tissue (e.g., tendons, blood vessels, cysts)
- Limited nerve mobility or altered elasticity
- Chronic irritation with subtle soft tissue changes
These findings support a more accurate diagnosis and guide further management.
Neurophysiology and Imaging: Complementary Diagnostic Tools
Electrophysiological tests such as NCS and EMG assess nerve function. They can confirm whether signal transmission is slowed or altered – often a sign of chronic nerve stress or damage.
However, these techniques do not visualize structural changes or the exact site of compression. Therefore, combining them with imaging can significantly improve diagnostic clarity.
Especially in Tarsal Tunnel Syndrome, ultrasound or MRI may reveal:
- Nerve thickening or entrapment
- Dynamic restriction during movement
- Associated soft tissue changes or underlying deformities
This integrated approach allows a more precise differential diagnosis and helps avoid unnecessary or misdirected treatments.
Summary
Tarsal Tunnel Syndrome is one possible cause of pain, tingling, or numbness on the sole of the foot – especially when symptoms worsen with activity.
A combination of clinical evaluation, nerve testing, and structural imaging is often required for a reliable diagnosis.
In uncertain cases, high-resolution imaging can help clarify the cause, visualize the nerve, and support safe, targeted further care.
Disclaimer: The information provided on this page is for general informational purposes only and does not constitute medical advice. It is not a substitute for personal consultation, examination, or treatment by a physician or other qualified healthcare professional. No guarantees of healing or cure are made. While we strive for accuracy and completeness, we cannot guarantee that all content is up to date or free from errors, and we accept no liability for any inaccuracies.