How to diagnose tarsal tunnel syndrome?

Evaluation of Tarsal Tunnel Syndrome

The diagnosis of tarsal tunnel syndrome requires a combination of specific clinical tests, neurological examination, and electrodiagnostic studies, with MRI or ultrasound serving as adjunctive imaging modalities when clinical findings are equivocal.

Clinical Presentation and History

• Pain characteristics: Burning pain, numbness, tingling along the tibial nerve distribution (sole of foot, heel, toes)
• Timing: Often worse at night or with prolonged standing/walking
• Exacerbating factors: Trauma, ankle sprains, foot deformities, space-occupying lesions
• Duration: Symptoms may develop insidiously over months to years or have traumatic onset 1

Physical Examination

Key Diagnostic Tests

1. Dorsiflexion-Eversion Test (highest sensitivity):

   • Position: Maximally evert and dorsiflex the ankle while simultaneously dorsiflexing all metatarsophalangeal joints
   • Hold: 5-10 seconds
   • Positive result: Reproduction or intensification of symptoms 2

2. Tinel's Sign:

   • Technique: Percuss along the tibial nerve behind the medial malleolus
   • Positive result: Radiating paresthesia into the foot

3. Sensory Testing:

   • Assess for decreased sensation in the plantar aspect of the foot
   • Test both medial and lateral plantar nerve distributions separately

4. Motor Testing:

   • Assess for weakness of intrinsic foot muscles
   • Look for atrophy of the abductor hallucis muscle in chronic cases

Electrodiagnostic Studies

• Nerve Conduction Studies:

  • Measure distal motor latencies of both medial and lateral plantar nerves
  • Compare with contralateral side
  • Orthodromic compound nerve action potential latency technique is essential for confirmation 3

• Electromyography (EMG):

  • Assess for denervation in intrinsic foot muscles
  • May show fibrillation potentials in chronic cases

Imaging Studies

• MRI:

  • Highest sensitivity (95%) and specificity (95%) for detecting tendon and soft tissue changes 4
  • Can identify space-occupying lesions, varicosities, or anatomical variants

• Ultrasound:

  • More accessible and less expensive than MRI
  • Use high-frequency transducer (10 MHz or higher) as recommended by American College of Rheumatology 4
  • Can visualize the tibial nerve and identify potential causes of compression

Differential Diagnosis

• Plantar fasciitis
• Peripheral neuropathy (especially diabetic)
• S1 radiculopathy
• Calcaneal stress fracture
• Posterior tibial tendinopathy

Diagnostic Algorithm

1. Initial Evaluation:

   • Perform dorsiflexion-eversion test and Tinel's sign
   • Complete sensory and motor examination of foot

2. If Clinical Suspicion Exists:

   • Proceed to electrodiagnostic studies to confirm diagnosis
   • Both medial and lateral plantar nerve latencies must be determined 3

3. If Electrodiagnostic Studies Inconclusive:

   • Obtain imaging (ultrasound first due to accessibility, then MRI if needed)

4. If Cause Unclear:

   • Consider MRI to identify space-occupying lesions or anatomical variants

Common Pitfalls in Diagnosis

• Focusing only on the medial plantar nerve and missing lateral plantar nerve involvement
• Failing to perform the dorsiflexion-eversion test, which has high sensitivity
• Misdiagnosing as plantar fasciitis or peripheral neuropathy
• Relying solely on imaging without electrodiagnostic confirmation
• Not considering systemic conditions that may cause or exacerbate symptoms (diabetes, rheumatoid arthritis)

Early diagnosis and intervention are critical to prevent permanent nerve damage and maximize treatment outcomes, whether conservative or surgical 1.