The tarsal tunnel is the fibro-osseous tunnel on the medial ankle, bounded by the medial malleolus anteriorly, the talus and calcaneus laterally, and the flexor retinaculum (laciniate ligament) medially. The tunnel transmits (from anterior to posterior, mnemonic Tom Dick AND Harry): tibialis posterior, flexor digitorum longus, posterior tibial artery and nerve (and two veins), and flexor hallucis longus. The tibial nerve divides within the tunnel into the medial plantar, lateral plantar, and medial calcaneal nerves.
Tarsal tunnel syndrome is compression of the tibial nerve within the tarsal tunnel producing burning pain, paresthesiae, and numbness in the plantar foot in the tibial nerve distribution. Causes include space-occupying lesions (ganglia, lipoma, accessory muscles), bony anomalies, post-traumatic fibrosis, and idiopathic (often associated with planovalgus deformity). Tinel sign at the tarsal tunnel, electrodiagnostic studies, and MRI guide diagnosis. Surgical decompression divides the flexor retinaculum along the entire tarsal tunnel length, often including distal neurolysis of the medial and lateral plantar nerves.
Tibial nerve compression within the tarsal tunnel from post-traumatic oedema, ganglion cyst, or flexor retinaculum fibrosis produces burning plantar foot pain and paresthesiae in the medial and lateral plantar distributions; flexor retinaculum release through a medial ankle incision decompresses the nerve and its plantar divisions.
