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Additional MRI showed a prominent bone contusion at the location of the radiographically visible depression in the lateral femur condyle (figure 2). Remarkably, also a bone bruise was observed at the posterolateral side of the tibial plateau (figure 3). Furthermore, an empty notch sign, full disruption of the anterior cruciate ligament (ACL), oedema around an intact medial collateral ligament and an accompanying tear of the posterior horn of the lateral meniscus were also observed on MR (figure 4). The increased depth of the femoral notch, visible on the lateral plain knee radiograph, is an infrequent but characteristic radiological image, known as ‘lateral (femoral) notch sign’.
The ‘lateral notch sign’ is an abnormally deep lateral condylopatellar sulcus due to a compression fracture of the lateral femoral condyle, which has been described as an indirect sign of ACL rupture. It is caused by impression of the lateral femoral condyle against the posterior lateral corner of the tibial plateau, during subluxation in the case of acute ACL tear, similar to a Hill-Sachs lesion of the humerus caused by anterior dislocation of the glenohumeral joint. This impaction causes a pattern of injuries well known as ‘kissing contusions’, which are usually radiographic occult injuries to the cartilage and bone. In 92–100% of patients with acute ACL rupture, …
Contributors SW wrote and revised the manuscript, THPR recognized the imaging feature and revised the manuscript, CPvdH supplied the arthroscopic imaging and revised the manuscript. All authors have read and approved the final manuscript.
Competing interests None.
Patient consent Obtained.
Provenance and peer review Not commissioned; externally peer reviewed.
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