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!
Not anymore.
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.
Results?
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?
No.
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.
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