Os subtibiale

Last revised by Ammar Ashraf on 26 Jun 2022

An os subtibiale is a rare, genuine accessory ossicle and normal variant related to the posterior colliculus of the medial malleolus 1. It is present in ~1% of the population 5

They usually are asymptomatic although they may eventually cause painful syndromes or degenerative changes in response to overuse and trauma.

Normally, the secondary center of ossification of the distal tibia appears during the first year of life. It fuses with the shaft at ~15 years in females and ~17 years in males. The medial malleolus is generally an extension from the distal epiphysis and ossifies in the seventh year.

An accessory bone is formed when the separate epiphysis of the medial malleolus fails to fuse with the distal tibia.

  • projects posteriorly, adjacent to the posterior colliculus
  • typically measures more than 4 mm
  • well-rounded 5
  • malleolar fracture (when radiographs are taken following an injury to the ankle) 3, 4
  • ossicles related to the anterior colliculus (unfused medial malleolus ossification center)
    • present in ~2% of the population 5
    • differentiated from other ossicles in this region by its smaller size to os subtibiale, its rounded and well-defined shape, and its anterior position 1,5
  • post-traumatic ossification of the deltoid ligament complex 5

ADVERTISEMENT: Supporters see fewer/no ads

Cases and figures

  • Case 1
    Drag here to reorder.
  • Case 2
    Drag here to reorder.