deep lateral femoral notch sign deep lateral femoral notch sign in radiology, the deep lateral femoral notch sign is a finding on a lateral radiograph that is considered an indirect sign of a torn anterior cruciate ligament (acl). it is an abnormal deepening of the lateral condylopatellar sulcus from an osteochondral impaction fracture. a depth greater than 1.5 mm is a reliable sign of a torn acl. deep lateral femoral notch sign measurement technique to determine the depth of the femoral notch on lateral x-rays