Pitfalls in MR imaging of acute anterior cruciate ligament injuries
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LETTER TO THE EDITOR
Pitfalls in MR imaging of acute anterior cruciate ligament injuries Pieter Van Dyck1
Received: 8 August 2017 / Accepted: 24 August 2017 © European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2017
Dear Editor, I read with great interest the article by van der List et al. [2], “Preoperative magnetic resonance imaging predicts eligibility for arthroscopic primary anterior cruciate ligament repair”, published in the July 2017 issue of Knee Surgery Sports Traumatology Arthroscopy. In this study, the authors found that tear location and tissue quality of the anterior cruciate ligament (ACL) on preoperative magnetic resonance imaging (MRI) could be used to predict the eligibility for primary ACL repair. Tear locations “in the proximal quarter” were graded on MRI as proximal avulsion (>90% distal remnant length, type I), proximal (75–90%, type II), or midsubstance (25–75%, type III). Tissue quality was subjectively graded as good, fair, or poor, depending on the signal intensity characteristics and morphology of the ACL on MR images. The authors conclude that, based upon the information provided by MRI, patients can be informed that it is likely or not that arthroscopic primary repair can be performed. This study highlights the potential role of MRI in the preoperative planning for individualized ACL surgery and I congratulate the authors for their publication. However, there are some observations I would like to make concerning the use of MRI for the assessment of acute ACL injuries. In the study by van der List et al. [2], the exact tear location was determined on MRI in 130 patients with acute complete ACL tear. In a previous study [3], the authors
* Pieter Van Dyck [email protected] 1
Department of Radiology, Antwerp University Hospital, University of Antwerp, Wilrijkstraat 10, 2650 Edegem, Antwerp, Belgium
selected, based on MRI, 353 patients with acute complete ACL injury to determine tear location. However, frank discontinuity with gap formation clearly visible on MRI as a primary sign of acute ACL tear is only present in 75% of cases [5]. In contrast, abnormal signal and morphology with replacement of the ACL by an edematous, cloudlike mass and/or diffuse nonvisualisation of its fibers due to ill-defined edema and hemorrhage is a very common presentation of acute complete or partial tear on MRI [1, 4, 5], with reported incidence as high as 88% [5]. Because the morphology of the injured ligament fibers is obscured by the initial posttrauma hemorrhage, exactly locating and grading a tear is frequently not possible on MRI [4, 6, 8]. To further illustrate this point, the MRI scan of an acute ACL injury (Fig. 1a, b, reprinted with permission from [4]) and a follow-up scan at 5 months after injury (Fig. 1c, d) are shown: Sagittal PD-weighted image shows abnormal morphology with diffuse hyperintense signal of the ACL and complete nonvisualisation of its fibers in its proximal half (arrow). Note that exact tear location is not possible on MRI (Fig. 1a). Axial fat-
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