This is a basic article for medical students and other non-radiologists
Perthes disease is the name given to idiopathic osteonecrosis of the femoral epiphysis in children. It most often occurs in children around the age of 5-6 years and is one of the common considerations when children present with an atraumatic limp or hip pain.
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Reference article
This is a summary article. For more information, you can read a more in-depth reference article: Perthes disease.
Summary
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epidemiology
5-15/100,000
5 times more boys than girls
peak presentation at 5-6 years (CI 2-14 years)
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presentation
atraumatic hip pain or limp
may be coincidental history of trauma (precipitates presentation)
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pathology
lack of blood supply to the femoral head
fragmentation and bone loss
15% of cases are bilateral
cause of osteonecrosis in Perthes disease is unclear
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radiology
pelvic radiograph for assessment and diagnosis
MRI for persistent pain in children with normal radiographs
US may detect an effusion, but is not sensitive for osteonecrosis
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treatment
symptom control in the early phase
degeneration as the disease progresses may require operative management
Radiographic features
Plain radiograph
The radiographic changes to the femoral epiphyses depend on the severity of osteonecrosis and the amount of time that there has been alteration of blood supply:
early: there may be no appreciable change
established: reduction in epiphysis size, lucency
late: fragmentation, destruction
As changes progress, the width of the femoral neck increases (coxa magna) in order to increase weight-bearing support.
MRI
On MRI, there is typically bone edema and evidence of an effusion. Bone edema will be bright on fluid-weighted sequences, e.g. T2/STIR.