The (deep) lateral femoral notch sign describes a depression on the lateral femoral condyle at the terminal sulcus, a junction between the weight-bearing tibial articular surface and the patellar articular surface of the femoral condyle. It is occasionally referred to as a deep sulcus sign, not to be confused with the deep sulcus sign in pneumothorax on supine chest radiograph.
Pathology
The likely mechanism is a hyperextension or impaction injury with a collision of the femoral condyle and the posterior tibial plateau during the rotational movement responsible for injuring the ACL, most commonly the pivot-shift.
Radiographic appearance
Lateral femoral notch sign is usually first appreciated on the lateral radiograph and is suggestive of an osteochondral fracture 1,2. The depth of the lateral femoral notch sign has been shown to correlate with anterior cruciate ligament (ACL) tear 2.
A normal sulcus is located within 10 mm of Blumensaat's line on lateral projection 3.
Plain radiograph
On a lateral projection, a line is drawn from the normal articular surface of the lateral femoral condyle. The depth of the abnormal depression/notch can then be measured. A study compared the depth of the lateral femoral notch in patients with proven ACL tear and healthy individuals. A notch depth of 1.5 mm is shown as a useful additional sign of a torn ACL 2.
Internal derangement should also be suspected if the notch is irregular.
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