UMEM Educational Pearls

Category: Orthopedics

Title: Radiology in Slipped Capital Femoral Epiphysis

Keywords: Klein's line, S sign, AVN (PubMed Search)

Posted: 12/14/2019 by Brian Corwell, MD (Updated: 4/16/2024)
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Slipped Capital Femoral Epiphysis (SCFE)

Progressive, posterior medial displacement (slipping) of the proximal femoral epiphysis
- Complicated by AVN and premature physis closure

Early Diagnosis:

Klein’s Line on AP view

A line drawn from the superior aspect of the femoral neck will not intersect the femoral head epiphysis

Another virtual line may assist in diagnosis

S-sign

The S-sign is a curvilinear line drawn on the inferior margin of the proximal femoral head neck junction along the proximal femoral physis.
Discontinuity or an abrupt sharp turn are abnormal

Klein's line and S-sign

A group of 20 orthopedic surgeons, radiologists, and pediatricians viewed 35 radiographs of SCFE using Klein's line on the AP view and the S-sign on frog-leg lateral view to make the diagnosis.

Overall diagnostic accuracy was better with the S-sign than Klein's line, 92% vs 79%.
- Sensitivity of the S-sign was 89%, specificity 95%.
- Sensitivity of Klein's line was 68%, specificity 89%.

Consider adding both of these virtual lines/signs to your review of the pediatric hip plain film

Rebich et al., 2018. The S Sign: A New Radiographic Tool to Aid in the Diagnosis of Slipped Capital Femoral Epiphysis. J Emerg Med.