[Coalition 40] Tarsal Coalition as a Cause of Tarsal Tunnel Syndrome

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Tarsal coalitions, especially talocalcaneal types, can produce mass effect in the tarsal tunnel, leading to nerve and tendon pathology.

Mechanism

• Bony overgrowth from fibrous/cartilaginous coalitions (often EA-PM or middle facet) protrudes into the tunnel.
  
  
• Ganglion cysts may arise from the coalition or tendon sheath and decompress into the tunnel, worsening compression.
  
  
• Tendons (FHL, FDL, PT) can be entrapped or attenuated by sharp excrescences of the coalition.
  
  

Nerve Involvement

• The medial plantar nerve (MPN) is most frequently affected due to its close course along the medial talus/calcaneus.
  
  
• MRI findings of neuritis:
  • Focal T2 hyperintensity (equal to or > blood vessels)
  • Caliber enlargement
  • Direct abutment/displacement by coalition or cyst
  • Secondary denervation edema in the abductor hallucis
  
  

MRI & Clinical Clues

• MRI is the gold standard: defines coalition type, space-occupying lesion, nerve signal changes, tendon pathology.
  
  
• FHL is the tendon most often involved: entrapment, thinning, split tears, tenosynovitis.
  
  
• Patients may present with pain, paresthesia, numbness in MPN/LPN distribution and a positive Tinel’s sign.
  
  

Surgical Significance

• Simple coalition resection is often insufficient if associated nerve or tendon pathology is not addressed.
  
  
• Pre-surgical recognition of neuritis or tendon disease is critical to prevent persistent pain and poor outcomes.
  
  

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#Radiology #MSKMRI #FootMRI #TalocalcanealCoalition #TarsalTunnelSyndrome #MedialPlantarNerve #FHL #OrthopedicImaging #MRIteaching #RadiologistLife #MedicalEducation

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