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: 2/19/2020)
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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

http://www.raymondliumd.com/images/SCFE%20illustrated%20and%20cropped.jpg

Early Diagnosis:

  • Allows best chance for intervention and good functional outcome
  • Subtle and difficult with X-ray
  • Classic teaching is Klein’s line

Klein’s Line on AP view

  • A line drawn from the superior aspect of the femoral neck will not intersect the femoral head epiphysis
  • Modified line
    • >2mm difference in width lateral to line between each side

https://pedemmorsels.com/wp-content/uploads/2018/01/Slipped-Capital-Femoral-Epiphysis-3.png

 

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

https://images.squarespace-cdn.com/content/v1/562149a6e4b0bca6fa53cb35/1530197888065-AOF0LA079Y81Q6M89RJU/ke17ZwdGBToddI8pDm48kE2XMWnCJSZ3ROkmIxQ7DdsUqsxRUqqbr1mOJYKfIPR7LoDQ9mXPOjoJoqy81S2I8N_N4V1vUb5AoIIIbLZhVYxCRW4BPu10St3TBAUQYVKcIZH9X6Fb-UKi0lvZd9RVmtFt1P_lj4JzgsdTxe78uiejbzfgXQaCWxJNArJhpf7P/Screen+Shot+2018-06-26+at+10.09.17+AM.png?format=1500w

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%. 
  • Combined S-sign + Klein's line sensitivity was 96%, specificity 85%.

 

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

References

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