Type VII All-epiphyseal Fractures of the Lateral Malleolus and the Origin of Subfibular Ossicles.

BACKGROUND

A subfibular ossicle (SO), also known as an os subfibulare, is present in ∼1% of the general population. Two theories have been proposed to explain the origin of SOs: (1) as a failure of fusion of a secondary center of ossification; (2) as a posttraumatic sequela. This report offers prospective, longitudinal radiographic evidence for the formation of SOs as a posttraumatic sequela of type VII transepiphyseal fractures of the lateral malleolus in children.

METHODS

This Institutional Review Board-approved study was performed at a tertiary care pediatric hospital from March 2012 to April 2019. The study group included 37 children with a type VII fracture of the lateral malleolus and a minimum follow-up of 6 months.

RESULTS

Twenty-one children (57%) healed their fracture. Sixteen children (43%) went on to form SOs. The most common location for the fractures was the distal third of the epiphysis, and the most common fracture type forming SOs was a sleeve avulsion fracture. Four of the children forming SOs have had surgery to address pain and recurrent sprains.

CONCLUSIONS

Overall, 43% of children who sustained a type VII fracture of the lateral malleolus went on to form SOs, giving support to the posttraumatic theory of origin. Sleeve avulsion fractures have the greatest chance of forming SOs. So far, 4 of the 16 children forming SOs have undergone surgery for ankle pain and recurrent sprains.

LEVEL OF EVIDENCE: Level II.