Imaging description

In the setting of knee pain following trauma, an effusion raises concern for an internal joint derangement. Close inspection of the radiographs may reveal subtle clues to the presence of acute or chronic anterior cruciate ligament (ACL) tear, such as a deep lateral condylar notch [1]. To assess the lateral condylar notch sign, draw a line tangential to the lower articular surface of the lateral femoral condyle. Measure the depth of the notch perpendicular to this line [2]. If the sulcus measures greater than 1.5 mm in depth, an ACL injury should be suspected (Figure 87.1) [3]. Additionally abnormal angularity of the notch should also raise concern for ACL injury. A sulcus shallower than 1.5 mm does not assure integrity of the ACL (Figure 87.2) [3, 4].

Pathologically, the deep lateral femoral sulcus reflects the presence of a transchondral fracture, presumed to result from impaction on the lateral or posterolateral tibia during the twisting injury that simultaneously tore the ACL. If the impaction injury results in only a bone bruise or isolated chondral injury, it will be occult on radiograph but not on MRI.