Tarsal Tunnel Syndrome

Tarsal tunnel syndrome (TTS) is an entrapment neuropathy of the posterior tibial nerve (or one of its branches) as it passes through the tarsal tunnel — the fibro-osseous canal on the medial side of the ankle posterior to the medial malleolus. It is the foot and ankle equivalent of carpal tunnel syndrome, though less common and more complex in its clinical presentation and management.

• Tarsal tunnel anatomy: the tarsal tunnel is formed by the medial malleolus anteriorly, the calcaneus and talus laterally, and the flexor retinaculum (laciniate ligament) medially; the contents of the tarsal tunnel from anterior to posterior are: Tom, Dick And Harry — Tibialis posterior tendon, flexor Digitorum longus tendon, posterior tibial Artery (and veins), posterior tibial Nerve, flexor Hallucis longus tendon
• The posterior tibial nerve divides within or just distal to the tarsal tunnel into the medial plantar nerve, lateral plantar nerve, and medial calcaneal nerve (calcaneal branch — usually arises proximal to the tunnel)
• Incidence: less common than carpal tunnel syndrome; no clear gender predilection; associated with hindfoot valgus deformity (the most common underlying biomechanical cause)
• Proximal tarsal tunnel syndrome (classic TTS): compression of the main posterior tibial nerve in the tarsal tunnel; produces pain, burning, and tingling radiating to the entire sole; Tinel sign positive at the tarsal tunnel
• Distal tarsal tunnel syndrome: compression of the medial or lateral plantar nerve more distally; produces more localised symptoms; first branch of lateral plantar nerve (Baxter nerve) entrapment is a specific variant producing medial heel pain

• Space-occupying lesion is the most favourable cause for surgical decompression — identifiable lesion can be excised alongside decompression; ganglion cyst is the most common; MRI essential to identify

• Classic symptoms: burning, aching, or electric pain in the medial ankle and sole of the foot; tingling and numbness in the plantar surface of the foot and toes; symptoms worse with prolonged standing and walking; may radiate proximally up the medial leg (double crush syndrome); relieved by rest; worse at night (distinguishes from plantar fasciitis)
• Distribution: medial plantar nerve involvement — medial 3.5 toes and medial plantar forefoot; lateral plantar nerve — lateral 1.5 toes and lateral plantar forefoot; combined — entire plantar surface
• Tinel sign: percussion over the tarsal tunnel posterior to the medial malleolus produces tingling in the distribution of the posterior tibial nerve (sole of foot, toes); most commonly cited clinical sign but sensitivity only 35–62%
• Tourniquet test: inflate sphygmomanometer cuff above systolic pressure on the leg and hold 60 seconds; positive if symptoms reproduced in the foot; low specificity
• Dorsiflexion-eversion test: maximum passive ankle dorsiflexion and eversion held for 5–10 seconds; positive if symptoms reproduced; increases tension and reduces space in the tarsal tunnel; sensitivity approximately 80%
• Hindfoot alignment: assess for valgus deformity — an important correctable contributing factor; standing heel alignment view on X-ray quantifies valgus
• Intrinsic muscle wasting: in advanced TTS; abductor hallucis or abductor digiti minimi wasting may be visible

• EMG and nerve conduction studies (NCS): essential investigation — confirms posterior tibial nerve dysfunction; assesses which branch is involved; prolonged distal motor latency; reduced sensory nerve action potential amplitude; slowed conduction velocity; EMG shows denervation of intrinsic foot muscles in severe cases; sensitivity approximately 50–70% — a normal EMG/NCS does NOT exclude TTS (clinical diagnosis when NCS normal but symptoms typical)
• MRI: investigation of choice for identifying a space-occupying lesion; shows nerve enlargement, perineural fibrosis, ganglion cysts, varicosities, or accessory muscles; coronal sequences best for tarsal tunnel anatomy; essential before surgery
• USS: identifies space-occupying lesions dynamically; guides aspiration of ganglion cysts; less comprehensive than MRI but useful first-line in straightforward cases
• Weight-bearing foot and ankle radiographs: assess for hindfoot valgus, calcaneal malunion, or bony spurs impinging on the tunnel
• Bloods: TSH, fasting glucose/HbA1c, TFTs — screen for systemic causes; RA serology if inflammatory arthropathy suspected

• Activity modification: reduce prolonged standing; footwear with good medial arch support
• Orthotics and bracing: medial arch support insole; ankle-foot orthosis (AFO) for valgus deformity; reduces hindfoot valgus and decreases tension on the posterior tibial nerve
• Corticosteroid injection: USS-guided injection adjacent to the posterior tibial nerve within the tarsal tunnel; useful for inflammatory TTS and as a diagnostic test; approximately 40–50% short-term improvement; long-term benefit limited; may need repeating
• Physiotherapy: calf stretching, intrinsic foot strengthening
• Management of systemic causes: optimise diabetes control; thyroid replacement; treat RA with DMARDs
• Non-operative treatment for 3–6 months before considering surgery — except in cases with an identifiable compressive lesion or progressive neurological deficit

• Surgical indications: failure of 3–6 months non-operative management; progressive neurological deficit; identifiable space-occupying lesion; significant symptom impact on quality of life
• Tarsal tunnel release procedure: curvilinear incision posterior to the medial malleolus extending to the medial plantar heel; complete division of the flexor retinaculum (laciniate ligament); decompression of the main posterior tibial nerve and all three terminal branches (medial plantar, lateral plantar, medial calcaneal); excision of any identified space-occupying lesion; internal neurolysis of the nerve if fibrosis present
• Distal tunnel extension: if lateral plantar nerve or first branch of lateral plantar nerve (Baxter nerve) is compressed, dissection extends distally between the abductor hallucis and the medial border of the quadratus plantae; Baxter nerve decompression is the key manoeuvre in this variant
• Outcomes: good to excellent results in approximately 65–85% of patients with identifiable cause; less predictable in idiopathic TTS (approximately 50–60%); worse outcomes in diabetic patients and those with longstanding symptoms; neurological recovery may take 6–12 months post-decompression
• Concurrent hindfoot valgus correction: if significant hindfoot valgus is the primary biomechanical cause, medialising calcaneal osteotomy ± tendon transfer at the same time as tarsal tunnel release addresses both the cause and the compression; better outcomes than decompression alone in this group

• Baxter nerve (first branch of lateral plantar nerve) entrapment: a specific and frequently overlooked variant of distal TTS; the Baxter nerve curves around the medial heel and may be entrapped between the deep fascia of abductor hallucis and the medial surface of quadratus plantae; presents with deep medial heel pain mimicking plantar fasciitis; abductor digiti minimi weakness and atrophy in advanced cases; EMG may confirm; often coexists with plantar fasciitis; surgical release at the level of abductor hallucis deep fascia relieves compression
• Double crush syndrome in TTS: peripheral nerve may have two sites of compression — a proximal compressive lesion (lumbar radiculopathy, piriformis syndrome) makes the nerve more susceptible to distal compression; failure to recognise a proximal lesion explains some surgical failures; perform lumbar spine assessment and EMG/NCS to evaluate for double crush before surgical decompression
• Accessory muscles causing TTS: flexor digitorum accessorius longus (FDAL) is the most common accessory muscle producing TTS — an anomalous muscle belly arising from the posterior tibial region and passing through the tarsal tunnel; becomes symptomatic with exercise (compartment-like effect); MRI identifies; surgical excision relieves compression; important not to mistake for a soft tissue tumour
• Post-traumatic TTS (calcaneal fracture): calcaneal fracture with lateral wall blowout compresses the tarsal tunnel through bony impingement and fibrosis; onset may be delayed months to years after injury; MRI and CT assess bony anatomy; tarsal tunnel release combined with correction of calcaneal malunion (subtalar arthrodesis or calcaneal osteotomy) if symptomatic malunion is present

• Tarsal tunnel contents: Tom, Dick And Harry — Tibialis posterior, Digitorum longus, posterior tibial Artery + veins, posterior tibial Nerve, Hallucis longus (anterior to posterior)
• Nerve divides into: medial plantar nerve (medial 3.5 toes), lateral plantar nerve (lateral 1.5 toes), medial calcaneal nerve (heel)
• Tinel sign: 35–62% sensitivity — positive is supportive but negative does NOT exclude TTS; dorsiflexion-eversion test more sensitive (80%)
• EMG/NCS: confirms but normal in up to 50% — clinical diagnosis when NCS normal and symptoms typical
• Ganglion cyst: most common space-occupying lesion in TTS; best surgical outcome when identifiable cause excised at decompression
• Hindfoot valgus: most common biomechanical cause; correct with calcaneal osteotomy ± tarsal tunnel release for best outcome
• Baxter nerve: first branch lateral plantar nerve; entrapped at deep abductor hallucis fascia; medial heel pain + abductor digiti minimi weakness; often with plantar fasciitis
• Surgical release: divide flexor retinaculum completely; decompress all three branches; remove space-occupying lesion; internal neurolysis if fibrosis
• Outcomes: 65–85% with identifiable cause; 50–60% idiopathic; worse in diabetes and longstanding disease; recovery 6–12 months
• Double crush: proximal nerve compression increases susceptibility distally; check lumbar spine before TTS surgery if failure risk