The following knee x-rays are from a 24 year old who experienced a twisting injury to the knee whilst playing footie. The x-ray looks largely normal. What sign can you see and what is its significance?
The x-ray displays the lateral femoral notch sign, a depression of the lateral femoral condyle that is associated with ACL injury. There is also a small effusion in the knee joint.
An MRI scan of the knee showed partial tear of the ACL and a bone contusion involving the lateral femoral condyle as well as the lateral tibial plateau.
Lateral femoral notch sign refers to an osteochondral fracture of the terminal sulcus of the lateral femoral condyle, secondary to an ACL tear.
The lateral notch sign is present when the depth of the sulcus is greater than 1.5 – 2 mm (it is 1.8 mm in this case)
A depth of greater than 2 mm has a positive predictive value of 100% for a complete tear of ACL.
Reference: Resnick – Internal derangement of joints
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