What causes pain under the medial malleolus that extends to the plantar surface of the foot, and how is it treated?

Tarsal Tunnel Syndrome: Posterior Tibial Nerve Compression

The pain pattern you describe—originating posterior to the medial malleolus and radiating into the plantar foot—is classic for tarsal tunnel syndrome (TTS), a compression neuropathy of the posterior tibial nerve as it passes through the tarsal tunnel behind the medial malleolus. 1, 2

Clinical Diagnosis

Key Examination Findings

• Tinel's sign: Tap posterior to the medial malleolus to reproduce numbness/paresthesias radiating into the plantar foot 2
• Point tenderness: Palpate directly over the tarsal tunnel, just posterior and inferior to the medial malleolus 3, 1
• Dorsiflexion-eversion test: Dorsiflex and evert the ankle while extending the toes—this increases strain on the tibial nerve (+1.1%), lateral plantar nerve (+2.2%), and medial plantar nerve (+3.3%), reproducing symptoms 4
• Assess for burning, tingling, or numbness radiating into the plantar surface, medial arch, or heel 3, 5

Critical Differential Diagnoses to Rule Out

• Plantar fasciitis: Pain localizes to the plantar heel/arch, worse with first steps in morning, improves with activity 6, 4
• Posterior tibial tendon dysfunction: Tenderness along the tendon course from medial malleolus to navicular, with weakness on resisted inversion 7
• S1 radiculopathy: Back pain, positive straight leg raise, dermatomal distribution 2
• Calcaneal stress fracture: Positive calcaneal squeeze test (medial-to-lateral compression), history of increased activity 3

Important caveat: The "Heel Pain Triad" describes the coexistence of plantar fasciitis, posterior tibial tendon dysfunction, and TTS in the same patient—failure of arch support structures causes traction injury to the posterior tibial nerve 7. Examine for all three conditions simultaneously.

Diagnostic Testing

Initial Imaging

• Radiographs are NOT indicated unless Ottawa Ankle Rules are positive (inability to bear weight immediately post-injury, point tenderness over malleoli/talus/calcaneus, or inability to walk 4 steps) 8
• For chronic pain without trauma history, skip radiographs initially and proceed with clinical diagnosis 6, 3

Advanced Testing When Diagnosis Unclear

• MRI without contrast: Excellent sensitivity (93-96%) and specificity (100%) for visualizing nerve compression, space-occupying lesions, and associated soft tissue pathology 8
• Nerve conduction studies (NCS) and EMG: Abnormally slow conduction through the posterior tibial nerve predicts failure of conservative treatment and supports surgical candidacy 2
• Ultrasound: Operator-dependent but can identify nerve compression and guide injections 8

Treatment Algorithm

First-Line Conservative Management (6-8 weeks)

• Activity modification: Reduce running, prolonged standing, and activities that reproduce symptoms 6, 1
• NSAIDs: Oral ibuprofen or naproxen for pain relief and inflammation reduction 6, 3
• Orthotic devices: Custom or over-the-counter arch supports to reduce traction on the nerve by supporting the longitudinal arch 6, 1
• Physical therapy: Stretching exercises for the plantar fascia and Achilles tendon (3-5 times daily), plus nerve gliding exercises 6, 2
• Ice therapy: Apply through a wet towel for 10-minute periods to reduce inflammation 6

Second-Line Treatment (if no improvement after 6-8 weeks)

• Corticosteroid injection into the tarsal tunnel: Reduces edema around the nerve, but avoid injections near the Achilles tendon due to rupture risk 6, 3, 2
• Immobilization: Consider a walking boot or cast to completely rest the foot 6
• Confirm diagnosis with NCS/EMG: Abnormal studies support surgical intervention 2

Surgical Referral Indications

• No improvement after 6-8 weeks of appropriate conservative treatment 6, 3
• Clear identification of compression etiology (space-occupying lesion, ganglion cyst, varicosities) 2
• Positive Tinel's sign before surgery: Strong predictor of surgical success 2
• Abnormal nerve conduction studies: Predicts conservative treatment failure 2

Surgical technique: Release the flexor retinaculum from the medial malleolus down to the sustentaculum tali, with success rates of 44-96% 2. Best results occur in young patients with clear etiology, positive Tinel's sign, short symptom duration, and no previous ankle pathology 2.

Common Pitfalls

• Misdiagnosing as plantar fasciitis alone: The windlass test (toe extension) increases strain in both the plantar fascia AND the tibial/plantar nerves, making it non-specific 4. Look for neurologic symptoms (burning, numbness, paresthesias) to differentiate 3, 5.
• Missing the "Heel Pain Triad": Always examine for concurrent posterior tibial tendon dysfunction and plantar fasciitis, as arch collapse causes nerve traction 7
• Injecting corticosteroids near the Achilles tendon: This significantly increases rupture risk 6, 3
• Delaying referral: If symptoms persist beyond 6-8 weeks despite conservative treatment, refer to a podiatric foot and ankle surgeon for advanced imaging and surgical evaluation 6, 3