Medial malleolus ossicle

Case contributed by Dr Henry Knipe

Presentation

Bicycle vs tree - painful and swollen right ankle

Patient Data

Age: 40 years
Gender: Male

Ankle

X-ray

Small well corticated bony fragments lies at the anterior aspect of the medial malleolus. 

Marked soft tissue swelling over the lateral malleolus with a small bony fragment and increased lucency at the tip which is suspicious for an avulsion fracture. Alignment is normal. 

Case Discussion

The differential diagnosis for this bony fragment at the medial malleolus includes:

  • fracture - unlikely as non-tender and well corticated
  • prior trauma - if prior history of trauma
  • os subtibiale - lies in association with the posterior colliculus; this ossicle lies in relation to the anterior colliculus
  • unfused malleolar accessory ossification center - smaller than os subtibiale, more rounded and lie anteriorly

Given appearances and history an unfused malleolar accessory ossification or old avulsion fracture are favored. 

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