Abstract
Purpose of the study: The sub-fibular bone occurs as an ossicle adjacent to the apex of the lateral malleolus. Observed in 2% of children, it is generally a fortuitous x-ray discovery considered as a normal variant. Its rather high frequency in victims of former ankle trauma suggests the hypothesis of a traumatic origin. We have observed a high frequency of subfibular bone associated with functional ankle instability after trauma in children. The purpose of this study was to evaluate the function outcome after inverted ankle trauma in children with an avulsion fracture of the distal point of the lateral malleolus or a subfibular bone. We tested the hypothesis that presence of a subfibular bone corresponds to a sequelae of a former trauma and that it could led to a high frequency of mid- and long-term ankle stability.
Material and methods: This series included 50 children with a diagnosis of subfibular bone identified after trauma with ankle inversion. At least six months after the trauma, stability measurements were made to quantify residual functional instability of the ankle. Clinical signs of subjective instability were noted. A standardized protocol for stress x-rays was performed using the trauma-free contralateral ankle as the control.
Results: In more than 50% of patients, presence of a subfibular bone was associated with clinical signs of functional instability one year after ankle trauma. The quantitative measures of joint stability confirmed the significant presence of this instability, rarely associated with residual ligament laxity.
Discussion: In our series, most of the subfibular bones were interpreted as fracture-avulsions of the point of the lateral malleolus.
Conclusion: Discovery of a subfibular bone after an ankle «sprain» in children is a significant risk factor for subjective sequelar ankle instability after orthopedic treatment with a plaster cast.
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