= entrapment / compression neuropathy (analogous to carpal tunnel syndrome) of

1. posterior tibial nerve (most common)
2. its terminal branches (= medial and lateral plantar nn., medial calcaneal n.)

Tarsal tunnel = fibro-osseous passageway from level of medial malleolus to navicular bone distally

Medial floor: tibia, talus, sustentaculum tali, medial wall of calcaneus

Lateral roof: deep fascia of leg, flexor retinaculum = lacinate lig., abductor hallucis

Contents: medial ankle tendons (tibialis posterior, flexor hallucis longus, flexor digitorum longus) + posterior tibial nerve and artery and veins

Cause:

1. intrinsic (mass effect): ganglion cyst, neural sheath tumor, lipoma, tenosynovitis of flexor hallucis longus, marked varicosities, accessory muscle, fracture, fibrosis of chronic ankle sprain, rheumatoid arthritis, diabetes
2. extrinsic (tension): tarsal coalition, excessive pronation, valgus / varus heel, repetitive stress (jogger's foot)

• burning pain, tingling, numbness, nocturnal paresthesia along plantar surface of heel, foot and toes
• radiation of paresthesia to medial aspect of calf (Valleix phenomenon)
• positive Tinel sign = percussion of posterior tibial n. posteroinferiorly from medial malleolus causes paresthesia
• mass in tarsal tunnel (ganglion, neurilemmoma, lipoma, thickened flexor retinaculum, muscle)
• muscle edema from denervation in abductor hallucis (supplied by medial plantar nerve) / abductor digiti minimi (supplied by lateral plantar nerve)
• fracture of sustentaculum tali / medial tubercle of posterior talar process
• serpiginous varicosities

Rx: orthotics, release