Foot pain often presents with vague, burning sensations that can be difficult for patients to localize. For the board-certified physician, the distinction lies in the anatomical “bottleneck”—is the compression occurring at the fibro-osseous tunnel of the ankle (Tarsal Tunnel) or between the metatarsal heads (Morton’s)?

1. Tarsal Tunnel Syndrome (TTS)

TTS is the “Carpal Tunnel of the foot,” involving compression of the Posterior Tibial Nerve (or its branches) as it passes through the tarsal tunnel behind the medial malleolus.

• Anatomy: The tunnel is covered by the Flexor Retinaculum.
  • Contents (Tom, Dick, and Very Nervous Harry): Tibialis posterior, flexor Digitorum longus, posterior tibial Artery/Vein, tibial Nerve, and flexor Hallucis longus.
• Clinical Presentation:
  • Burning pain and paresthesia in the sole of the foot, often worse at night or after prolonged standing.
  • Proximal Sparing: Unlike a lumbar radiculopathy, symptoms are strictly distal to the ankle.
• Physical Exam:
  • Tinel’s Sign: Percussion behind the medial malleolus reproduces radiating pain into the sole.
  • Valleix Sign: Proximal radiation of pain (retrograde) when the nerve is compressed at the tunnel.
  • Dorsiflexion-Eversion Test: Maximize the volume of the nerve in the tunnel by passively dorsiflexing and everting the foot.

2. Morton’s Neuroma

Morton’s neuroma is not a true tumor, but rather a perineural fibrosis of the common plantar digital nerve.

• Anatomy: It most commonly occurs between the third and fourth metatarsal heads (3rd webspace). This is because the digital nerve here is often thicker (formed by a communication between the medial and lateral plantar nerves) and is compressed by the deep transverse metatarsal ligament.
• Clinical Presentation:
  • The “Stone in the Shoe” sensation: Patients feel like they are walking on a pebble or a folded-over sock.
  • Pain is worsened by wearing narrow, tight-fitting shoes (e.g., high heels) and relieved by being barefoot.
• Physical Exam:
  • Mulder’s Click: Squeezing the metatarsal heads together with one hand while applying pressure to the interspace with the other. A palpable “click” or reproduction of pain is a positive sign.
  • Webspace Tenderness: Localized pain on the plantar aspect of the affected webspace.

3. High-Yield Board Comparison

Feature	Tarsal Tunnel Syndrome	Morton’s Neuroma
Nerve Involved	Posterior Tibial Nerve	Common Plantar Digital Nerve
Location of Pain	Entire sole / Medial heel	3rd and 4th toes / Ball of foot
Primary Trigger	Standing / Night pain	Tight shoes / Walking
Key Maneuver	Tinel’s at Medial Malleolus	Mulder’s Click
EMG/NCS	Often abnormal (prolonged latency)	Usually normal (nerve is too distal)

4. Diagnostic Imaging and Electrodiagnosis

• NCS/EMG: Useful for TTS to confirm a delay in the medial or lateral plantar nerve branches. It is rarely useful for Morton’s Neuroma due to the small size of the digital nerves.
• Ultrasound: Highly effective for Morton’s Neuroma; it appears as an oval, hypoechoic mass between the metatarsal heads. For TTS, it can identify space-occupying lesions (ganglion cysts, varicosities) within the tunnel.

5. Management

• For TTS:
  • Orthotics: Correcting over-pronation (which stretches the nerve) with medial arch support.
  • Surgery: Tarsal tunnel release is indicated if a mass lesion is present or conservative care fails.
• For Morton’s:
  • Footwear Modification: Moving to a wider “toe box” and lower heels to reduce metatarsal compression.
  • Metatarsal Pads: Placed just proximal to the neuroma to “spread” the metatarsal heads.
  • Injections: Ultrasound-guided corticosteroid or alcohol sclerosing injections.

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6. High-Yield Board “Fast Facts”

• 3rd Webspace: The most common site for Morton’s Neuroma.
• Tom, Dick, and Harry: The sequence of structures in the tarsal tunnel (Ant to Post).
• Night Pain: Favors a diagnosis of Tarsal Tunnel Syndrome.
• Mulder’s Click: The pathognomonic exam finding for Morton’s.
• Pronation: A biomechanical risk factor for TTS.