Os subtibiale

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

Clinical presentation

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

Pathology

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.

Radiographic features

Plain radiograph

• projects posteriorly, adjacent to the posterior colliculus
• typically measures more than 4 mm
• well-rounded

Differential diagnosis

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

Siehe auch:

• akzessorische Knochen Fuß
• Os subfibulare

und weiter:

• sekundäre Ossifikationszentren
• Ossifikationszentren
• primäre Ossifikationszentren