A 30-year-old woman with acute knee injury
- 1Department of Orthopaedic Surgery, Academic Medical Centre, Amsterdam, The Netherlands
- 2Department of Radiology, Tergooi Hospitals, Hilversum, The Netherlands
- 3Department of Orthopaedic Surgery, Bergman Clinics, Naarden, The Netherlands
- Correspondence to Suzanne Witjes, Department of Orthopaedic Surgery, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands;
- Received 26 January 2012
- Accepted 2 August 2012
- Published Online First 6 December 2012
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, proved with surgery, bone contusions can be found at MRI within 5 days of injury.1 The non-contact trauma mechanism like the one described in our case more specifically can be called a ‘pivot shift injury’, which mostly occurs in skiers when a valgus load is applied to the knee in flexion combined with external rotation of the tibia or internal rotation of the femur with manoeuvres such as rapid deceleration and simultaneous direction change.2
Like the ‘Segond fracture’, the lateral notch sign is a secondary sign of ACL tears, which can be seen on the conventional knee radiography. The Segond fracture is the best-known avulsion fracture of the knee which involves a lateral cortical avulsion of the tibial insertion of the middle third of the lateral capsular ligament as a result of internal rotation of the knee and varus stress, another trauma mechanism that can cause ACL injury.3 Although the Segond fracture is significantly more infrequent, because it is caused by a less frequent trauma mechanism for ACL rupture, the ‘lateral notch sign’ is a relatively less known image among orthopaedic surgeons and surprisingly few papers have been published about this phenomenon.
Lateral femoral notch
The physiological lateral (femoral) condylopatellar sulcus normally forms a shallow groove in the middle of the lateral femoral condyle. It represents the junction zone on the lateral femoral condyle where the tibiofemoral and patellofemoral radii of curvature meet. On the lateral radiograph of the knee, it is aligned more parallel to the central ray of the x-ray beam than the anteriorly located medial condylopatellar sulcus. This results in the lateral sulcus projecting farther posteriorly and appearing more conspicuous than the medial sulcus, which facilitates distinction between the lateral femoral condyle and overlapping medial femoral condyle on the lateral projection. On a lateral radiograph with the knee fully extended, the lateral sulcus is projected just posterior to the continuation of the Blumensaat line, which is the dense line that corresponds to the roof of the intercondylar notch (figure 1B). The lateral sulcus can be measured through a line drawn from the deepest point of the sulcus perpendicular to a tangent line, lying across the sulcus on the articular surface of the lateral femoral condyle (figure 1B).4–7
In the past, it has already been suggested that a deep lateral femoral notch, with depth greater than 1.5 mm, is a useful indirect sign of an ACL tear.6–8 Jones et al claimed that a lateral femoral notch was only attributed to chronic ACL insufficiency and was not an evident sign in acute ACL tears,6 but Garth et al later on reported in his study that these radiographic changes were also present in 7.5% of acute ACL ruptures.4
Meaning and treatment
The coexistence of lateral compartment bone bruises has been reported extensively as indirect MR signs, which could be pathognomonic for complete ACL ruptures.1 ,9 Because bone bruises usually resolve within 6–8 weeks after the injury, most of these lesions cannot be seen on MR anymore by that time and they cannot be visualized at arthroscopy at all. Most impacted fractures can neither be detected by arthroscopy and only some cartilage fissures of the lateral femoral condylopatellar sulcus can be detected in patients undergoing arthroscopic assisted surgical repair of a torn ACL.8 Mostly, these arthroscopically visible osseous lesions still are minimal depressions that do not need further treatment. However, significant depression fractures can occur, resulting in joint incongruity as a possible precursor of post-traumatic degenerative changes. Garth showed that lateral meniscal tears are significantly associated with radiographic visible notches and depressions, like in our presented case. In addition, the fact that the lateral notch sign mostly occurs in young vigorously and active adolescents, who typically desire to continue high-impact athletics, raises further concern for prognosis of these chondral lesions.4
There is hardly any literature regarding the treatment of evident depression fractures of the lateral femoral notch. To our knowledge only four case reports are described concerning treatment of these injuries of the lateral femoral condyle. One reported open reduction, autologous cancellous bone grafting and secondary ACL reconstruction using bone-patellar tendon-bone graft.10 The second and third cases both described a one-stage arthroscopically assisted reduction of a large femoral notch compression fracture and primary ACL reconstruction using a hamstring tendon graft.11 ,12 In the second case, a bioabsorbable interference screw was used to fill up the intracondylar bone defect and in the third case the defect was filled up with a cancellous bone allograft. The fourth case of Sharma et al13 described a severely displaced osteochondral fracture of the lateral femur condyle associated with an ACL tibial avulsion fracture, which were both repaired by open reduction and internal fixation with Herbert screws. A pain-free knee with ligament stability and full range of motion was achieved in all four cases after a minimum follow-up of 6 months. Although long-term follow-up is needed, these four cases exemplify the importance of recognizing severe compression fractures, on the basis that open or arthroscopically assisted reduction and internal fixation may restore anatomy and improve long-term results.
In our case, ACL reconstruction using a hamstring autograft was carried out 4 months after trauma, because of persistent pain in deep flexion at the lateral side and giving way in activities of daily living, despite adequate conservative treatment. In addition to complete ACL rupture, the accompanying longitudinal tear of the posterior horn of the lateral meniscus, which was seen on MRI, was still present (figure 5A). It was treated by partial meniscectomy and not by sutures, because of an additional horizontal cleavage tear at the peripheral site of the meniscal tear. At inspection of the lateral condyle, only a small depression of the lateral femoral notch was visible, which could be left untreated (figure 5B). Seven months after ACL reconstruction and intensive rehabilitation total absence of pain and swelling, full range of motion, full quadriceps and hamstrings strength and restored ligament stability of the right knee were achieved.
With this case and radiographic image, we hope to provide an educational article that illustrates the role of imaging in supporting a clinical diagnosis. A condylopatellar sulcus of more than 1.5 mm can be a reliable indirect conventional radiographic sign of an acutely torn ACL.5 ,8 Although an accurate patient history and careful clinical examination can lead to a correct diagnosis in the majority of cases, it is important to carefully search for and recognize the infrequent lateral femoral notch sign on conventional radiography.
In addition to the diagnostic value to suggest ACL rupture, this secondary sign also provides an indication of the severity of the knee injury, because it is associated with high-impact intra-articular injury, caused by compressive forces from external rotation trauma of the flexed femur over a fixed, valgus-angulated tibia, which may need additional treatment.4 ,7 ,8 ,10–13
We would like to thank Dr D Haverkamp and Bram Daams for editing the illustrations.
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.