Tarsal Tunnel Syndrome

Tarsal tunnel syndrome is compression neuropathy of the posterior tibial nerve or its branches (medial and lateral plantar, and medial calcaneal) beneath the flexor retinaculum behind the medial malleolus. It is uncommon and underdiagnosed, occurring in adults aged 20 to 60 years.

Causes in about 60 to 70% are identifiable:

• Space occupying lesions (ganglion, lipoma, tenosynovitis, varicosities, accessory muscle, neurilemmoma)
• Trauma and fracture (calcaneus, ankle)
• Hindfoot valgus or flatfoot
• Edema, diabetes, hypothyroidism, rheumatoid arthritis

The remainder are idiopathic. Delay causes permanent sensory loss and intrinsic muscle atrophy.

• Burning, tingling or electric pain in the sole and toes, worse after standing, at night, and with exercise, relieved by rest
• Numbness in the medial plantar region, with the heel often spared if the medial calcaneal branch arises proximal to the tunnel
• Positive Tinel sign over the nerve at the tunnel, positive dorsiflexion eversion test (holding the ankle dorsiflexed and everted with the toes dorsiflexed for 5 to 10 seconds provokes symptoms)
• Weakness of toe flexion and wasting of the abductor hallucis in late disease
• Red flags: rapid onset with a mass, bilateral disease with neuropathy, a lumbar radicular pattern, and trauma

• Clinical diagnosis from the symptom pattern and provocative tests.
• Nerve conduction studies and EMG: prolonged distal motor latency of the medial or lateral plantar nerve (over 6 ms), reduced plantar sensory conduction velocity, and denervation in the abductor hallucis. Sensitivity is about 90%, and normal studies do not exclude disease.
• MRI or ultrasound for masses, varices, tenosynovitis and an accessory muscle.
• Screen for systemic causes: HbA1c, thyroid stimulating hormone, rheumatoid factor and vitamin B12.
• Lumbar spine assessment when there is a radicular pattern.

Differentials: plantar fasciitis, L5 and S1 radiculopathy, peripheral neuropathy, Morton neuroma, Baxter nerve entrapment, tibialis posterior tendinopathy, complex regional pain syndrome.

• Treat the cause: excise a mass, correct hindfoot valgus with an orthosis, and optimize glucose and thyroid function.
• Conservative therapy for 3 months: relative rest, a medial arch support or heel wedge, a night splint, and ibuprofen 400 mg orally every 8 hours with food for up to 7 days.
• Neuropathic pain: gabapentin 300 mg orally at night, increased by 300 mg every 3 days to 900 to 1800 mg/day in 3 divided doses (reduce in renal impairment, and warn of sedation and dizziness). Alternatively amitriptyline 10 mg orally at night, increased to 50 mg (avoid in cardiac conduction disease and glaucoma).
• Injection: methylprednisolone acetate 20 mg with lidocaine 1% 2 mL into the tunnel under ultrasound guidance. Complications: nerve injury, fat atrophy, rupture of a tendon.
• Surgery (failed treatment for 3 to 6 months, space occupying lesion, progressive weakness): tarsal tunnel release with division of the flexor retinaculum and decompression of the medial and lateral plantar nerves and the abductor fascia, with neurolysis and excision of the mass. Cefazolin 2 g IV before incision.
• Surgical outcomes: improvement in about 75% (better when a cause is found). Complications: recurrence, wound complication, nerve injury, complex regional pain syndrome.

Rehabilitation with a bulky dressing for 2 weeks and weight bearing as tolerated in a boot. Follow up at 2 weeks and 6 weeks. Counsel that recovery can take 6 to 12 months.