A child has sprained their ankle. X-rays are negative but they have tenderness over the growth plate.
This is an occult Salter-Harris I injury and they must be treated as a fracture!
These authors out of Canada sought to determine the frequency of these occult injuries by performing ankle MRI’s in 135 children between the ages of 5 to 12 who had negative plain radiography.
Only 4 out of 135 (3%; 95%CI 0.1-5.9%) had occult Salter-Harris injuries! Turns out they are pretty unusual.
But there was an even more interesting finding in this study. The MRI discovered all kinds of unanticipated injuries despite negative x-rays:
80% with ligamentous injury (ok... no surprise here as they were sprains)
80% with “bone contusions” (goodness this sounds bad)
34% or one third had distal fibular avulsion fractures! (This sounds worse!)
Did patients with these occult injuries fare worse?
They had the same recovery time as those without these injuries. (But I must clarify that all kids in this study were treated with a “removable air-stirrup brace” as this was in keeping with current practice at participating institutions. Sounds like voodoo medicine to me.)
This goes to prove that the great microscope of the MRI will demonstrate a multitude of findings that probably have no clinical importance. This is better known as overdiagnosis. The major problem with overdiagnosis is clinicians may feel compelled to act (i.e. “overact”) on these findings.
What should we take home from this study?
Occult growth plate injuries after a simple sprain in children is pretty rare. You can probably treat them as a sprain.
MRI’s find all sorts of things that we probably don’t want to know about. Even worse, they may cause harm from overdiagnosis.