What causes deep lateral femoral notch in the knee on a lateral radiograph?
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The deep lateral femoral notch is caused by an osteochondral impaction fracture of the lateral femoral condyle associated with anterior cruciate ligament (ACL) disruption. During the injury, anterior translation of the tibia relative to the femur results in impaction of the condyle against the posterior tibial plateau, creating a deepened sulcus visible on the lateral radiograph. This radiological finding is an indirect sign of acute or chronic ACL tears and indicates significant anterolateral rotatory instability of the knee.
Why is it called so?
It is named the “deep lateral femoral notch” because it manifests as an abnormally deepened depression (notch) seen on the lateral knee radiograph at the condylopatellar sulcus of the lateral femoral condyle. The term highlights both the location and the increased depth of the sulcus caused by the impaction injury.
Pathophysiology
Following ACL disruption, anterior translation and rotational instability of the tibia cause the lateral femoral condyle to impact against the posterior aspect of the lateral tibial plateau. This collision produces an osteochondral impaction fracture resulting in a deepened condylopatellar sulcus. The resulting bone depression is visible as a deep notch on the lateral radiograph, reflecting the traumatic mechanism and knee instability associated with the ligament tear.
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