Radiograph-Negative Lateral Ankle Injuries in Children: Occult Growth Plate Fracture or Sprain?

IMPORTANCE: Lateral ankle injuries without radiographic evidence of a fracture are a common pediatric injury. These children are often presumed to have a Salter-Harris type I fracture of the distal fibula (SH1DF) and managed with immobilization and orthopedic follow-up. However, previous small studies suggest that these injuries may represent ankle sprains rather than growth plate fractures.

OBJECTIVES: To determine the frequency of SH1DF using magnetic resonance imaging (MRI) and compare the functional recovery of children with fractures identified by MRI vs those with isolated ligament injuries.

DESIGN, SETTING, AND PARTICIPANTS: A prospective cohort study was conducted between September 2012 and August 2014 at 2 tertiary care pediatric emergency departments. We screened 271 skeletally immature children aged 5 to 12 years with a clinically suspected SH1DF; 170 were eligible and 140 consented to participate.

INTERVENTIONS: Children underwent MRI of both ankles within 1 week of injury. Children were managed with a removable brace and allowed to return to activities as tolerated.

MAIN OUTCOMES AND MEASURES: The proportion with MRI-confirmed SH1DF. A secondary outcome included the Activity Scale for Kids score at 1 month.

RESULTS: Of the 135 children who underwent ankle MRI, 4 (3.0%; 95% CI, 0.1%-5.9%) demonstrated MRI-confirmed SH1DF, and 2 of these were partial growth plate injuries. Also, 108 children (80.0%) had ligament injuries and 27 (22.0%) had isolated bone contusions. Of the 108 ligament injuries, 73 (67.6%) were intermediate to high-grade injuries, 38 of which were associated with radiographically occult fibular avulsion fractures. At 1 month, the mean (SD) Activity Scale for Kids score of children with MRI-detected fibular fractures (82.0% [17.2%]) was not significantly different from those without fractures (85.8% [12.5%]) (mean difference, -3.8%; 95% CI, -1.7% to 9.2%).

CONCLUSIONS AND RELEVANCE: Salter-Harris I fractures of the distal fibula are rare in children with radiograph fracture-negative lateral ankle injuries. These children most commonly have ligament injuries (sprains), sometimes associated with radiographically occult avulsion fractures. Children with fractures detectable only by MRI had a comparable recovery with those with sprains when treated with a removable ankle brace and self-regulated return to activities. This work has the potential to simplify the care of these common injuries, safely minimizing the inconveniences and costs of overtreatment.