Tarsal Tunnel Syndrome
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Direct answer
Tarsal tunnel syndrome is compression of the posterior tibial nerve as it passes beneath the flexor retinaculum behind the medial malleolus, causing burning pain, numbness and tingling in the sole. A positive Tinel sign over the tunnel and abnormal nerve conduction studies with prolonged distal motor latency support the diagnosis. Release of the flexor retinaculum is the surgical treatment when conservative measures fail.
What you must remember
- Anatomy: the tunnel lies behind the medial malleolus, bounded by the flexor retinaculum, and contains the posterior tibial nerve, artery and vein along with the tendons of tibialis posterior, flexor digitorum longus and flexor hallucis longus.
- Branches: the nerve divides into the medial and lateral plantar nerves and the medial calcaneal branch, and compression can affect any of them.
- Symptoms: burning pain, numbness and tingling on the plantar aspect of the foot, often worse on standing and at night.
- Tinel sign: tapping over the tunnel behind the medial malleolus reproduces tingling in the sole, and a positive result supports the diagnosis.
- Causes: a ganglion, varicosity, mass, fracture or swelling around the medial malleolus, and flat foot with overpronation.
- Electrodiagnosis: nerve conduction studies show prolonged distal motor latency in the plantar nerves, and ultrasound or MRI looks for a space-occupying lesion.
- Treatment: rest, orthoses and injections first, with release of the flexor retinaculum, and removal of any mass, when conservative care fails.
Where the exam tries to catch you
Tarsal tunnel questions reward the distinction between a nerve entrapment and a problem of the heel or the spine.
- Trap: diagnosing plantar fasciitis when the pain spreads to the toes with numbness. Correct: numbness and burning in the sole suggest nerve compression, which points to tarsal tunnel syndrome.
- Trap: releasing the tunnel without looking for a space-occupying lesion. Correct: a ganglion or other mass in the tunnel must be found and removed, otherwise the release fails.
- Trap: attributing the symptoms to S1 radiculopathy alone. Correct: a spinal cause must be considered, but tarsal tunnel syndrome is a peripheral entrapment confirmed by the Tinel sign and nerve conduction studies.
Frequently asked questions
Which nerve is compressed in tarsal tunnel syndrome?
The posterior tibial nerve is compressed in tarsal tunnel syndrome as it runs behind the medial malleolus beneath the flexor retinaculum. Compression produces pain and numbness in the sole of the foot. The nerve's medial and lateral plantar branches are usually the ones affected.
What is the Tinel sign in tarsal tunnel syndrome?
The Tinel sign in tarsal tunnel syndrome is tingling or shooting pain that is reproduced by tapping over the posterior tibial nerve behind the medial malleolus. A positive sign indicates irritation or regeneration of the compressed nerve. It supports the clinical diagnosis but does not confirm it alone.
Which investigation confirms tarsal tunnel syndrome?
Nerve conduction studies confirm tarsal tunnel syndrome by showing prolonged distal motor latency in the plantar nerves. Ultrasound or MRI is used to look for a ganglion, varicosity or other mass in the tunnel. The combination of clinical and electrodiagnostic findings gives the diagnosis.
What is the surgical treatment of tarsal tunnel syndrome?
The surgical treatment of tarsal tunnel syndrome is release of the flexor retinaculum, with exploration of the posterior tibial nerve and removal of any mass. It is performed when conservative treatment with rest, orthoses and injections has failed. The outcome depends on the cause and the duration of symptoms.