15 yo male twisted his knee…

October 11, 2012

Knee XR, Orthopedics, Trauma


The other day I was working in pediatrics and a 15 year-old male came in from his Friday night high-school football game with knee pain.  He is a running back; he twisted his knee when he was tackled and has diffuse knee pain with a slight effusion on exam.  Here is his lateral x-ray:

Fig. 1:  Lateral knee x-ray

Can you identify the abnormality?  This is a hard one…

The patient demonstrates a “deep lateral femoral notch sign” and a small effusion.

A what?  This was a radiology interpretation which I missed entirely (and I would guess many ED physicians would as well).  The lateral femoral notch sign is an abnormally deep depression of the lateral condylopatellar sulcus (See the arrow in Fig. 2).  On the lateral projection the lateral condylopatellar sulcus (aka the lateral femoral notch) is normally a shallow groove in the middle of the femoral condyle.  An unusually deep lateral femoral notch is an indirect sign of an ACL tear (1).

Fig. 2:  Arrow indicates the lateral condylopatellar sulcus (aka lateral femoral notch)

The most common mechanism of ACL tear is rotation and valgus stress.  This causes the posteriolateral tibial plateau to impact the anteriolateral femoral condyle and can cause a impaction at the site of the lateral femoral notch.  Thus…the “Lateral Femoral Notch Sign.”

To measure the depth of the lateral femoral notch draw a tangent line across the sulcus on the anterior surface of the lateral femoral condyle.  Measure the depth with a perpendicular line to the deepest portion.  Normal depth is around 1mm.  If the depth is >2.0mm this is highly suggestive of an ACL injury.

Luckily I had suspected an ACL tear from the beginning and treated accordingly…

References

1.  Pao DG.  The Lateral Femoral Notch Sign.  Radiology 2001; 219: 800-801.

Author:  Russell Jones, M.D.

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EMREMS: Radiology in Emergency Medicine

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