Os subfibulare

Last revised by David Luong on 12 Jun 2021

Os subfibulare is an accessory ossicle that lies at the tip of the lateral malleolus of the ankle and is rarely reported 1.

Os subfibulare are usually asymptomatic although they may eventually cause painful syndromes or degenerative change in response to overuse and trauma. The ossicle itself may fracture.

There are two theories regarding the origin of os subfibulare 2:

  1. An avulsion fracture attributable to pull of the anterior talofibular ligament.
  2. An unfused accessory ossification center. Typically, the secondary center of ossification of the lateral malleolus appears during the first year of life and fuses with the shaft at 15 years.

The majority are thought to be post-traumatic rather than congenital in etiology 5.

  • avulsion fracture of the lateral malleolus

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