Magnetic resonance imaging of clinically suspected Salter-Harris I fracture of the distal fibula.

Objectives: In skeletally immature children, isolated lateral ankle injuries without radiograph-visible fractures are often diagnosed with Salter-Harris I fractures of the distal fibula (SH1DF). However, recent magnetic resonance imaging (MRI) evidence in children suggests that sprains may be more common than previously thought. Thus, the main objective of this study was to determine the rate of MRI-confirmed SH1DF among cases where this diagnosis was made presumptively, based on clinical findings. In ankle injuries where there is no MRI evidence of SH1DF, another aim is to detect the pathology which gives rise to this clinical scenario.

Methods: This was a prospective cohort study performed at a tertiary care paediatric centre. Eligible patients included skeletally immature children with acute ankle injuries presenting with difficulty weight bearing and maximal tenderness and swelling over the distal fibular growth plate (lateral malleolus). Enrolled patients had ankle radiographs at the Emergency Department (ED) visit, MRI within 1 week of the injury, and repeat ankle X-rays at 4 weeks. All images were reviewed by two radiologists and an orthopaedic surgeon. Discrepancies between reading physicians were resolved by consensus agreement.

Results: Eighteen patients were enrolled into the study from September 2008 to August 2009. Mean (SD) age of participants was 8.7 (2.0) years. None of the 18 patients had evidence of fibular growth plate injury on MR imaging. Patients often had more than one abnormal finding on MRI. Fourteen (78%) had evidence of ligamentous sprains, 11 (61%) had bony contusions, one patient (6%) had a subtle fibular avulsion fracture, and another was found to have a minor articular cartilage injury. At 4 weeks, only one patient's radiographs demonstrated a healing fracture, which corresponded with the avulsion fracture case. All patients had returned to full weight bearing by 4 weeks.

Conclusions: In this series, the clinical diagnosis of SH1DF was incorrect in 100% of cases. Instead, in almost 90% of these patients, MRI identified ligamentous sprains and/or bony contusions. These results may influence the way children who present with this common clinical scenario are managed since the vast majority of children in this study actually had sprain/contusion injuries and none had SH1DF.