Abstract
BackgroundMRI is the most accurate imaging modality for diagnosing knee pathologies. However, there is uncertainty concerning factors predicting false negative MRI, such as meniscal tear patterns as well as patient factors. The aims of this study were to report 1.5-Tesla MRI accuracy of ACL, meniscus and articular cartilage damage and characterize false negative lesions.MethodsTwo hundred eighteen consecutive knee arthroscopies performed in our institution between 2013 and 2016 and their respective prospectively-collected MRI reports were reviewed. Inclusion criteria were age > 15 years-old, primary arthroscopy, 1.5-Tesla MRI performed at the same institution, and time interval MRI-surgery < 6 months. Exclusion criteria were revision arthroscopy and arthroscopic-assisted fracture fixation or multiligament surgery. Accuracy measures and Kappa coefficients were calculated comparing the MRI diagnosis to the arthroscopic findings. Moreover, the arthroscopic findings of false negative MRI were compared to the findings of true positive MRI using the Fisher-exact test. Pearson correlation was used for testing the correlation between MRI accuracy and patient age.ResultsThe highest accuracy was observed in medial meniscus and in ACL findings. For the medial meniscus sensitivity, specificity, agreement, and Kappa coefficient were 77, 92, 86%, and 0.7, and for the ACL these measures were 82, 97, 87%, and 0.73. MRI accuracy was lower in the lateral meniscus and articular cartilage with Kappa coefficient 0.42 and 0.3, respectively. More specifically, short peripheral tears in the posterior horn of the medial meniscus were characteristic of false negative findings compared to true positive findings of the MRI (p < 0.01). MRI accuracy correlated negatively compared to arthroscopic findings with patient age for the medial meniscus (r = − 0.21, p = 0.002) and for articular cartilage damage (r = − 0.45, p < 0.001).Conclusion1.5-Tesla MRI will accurately diagnose ACL and medial meniscal tears and can reliably complete the diagnostic workup following physical examination, particularly in young adults. This modality however is not reliable for diagnosing short peripheral tears at the posterior horn of the medial meniscus and partial thickness articular cartilage lesion of the femoral condyles. For these lesions, definitive diagnosis may require cartilage-specific MRI sequences or direct arthroscopic evaluation.Level of evidencePrognostic study, Level III.
Highlights
Magnetic Resonance Imaging (MRI) is the most accurate imaging modality for diagnosing knee pathologies
The purpose of the current study was to add to the body of literature on current accuracy measures specific to 1.5-Tesla MRI of the knee in the adult population relating to the anterior cruciate ligament (ACL), the menisci and to the articular cartilage and to identify characteristics of false negative lesions
The following five key findings summarize this study which investigated current accuracy measures of 1.5Tesla knee MRI: (1) ACL lesions are reliably diagnosed on 1.5-Tesla MRI with specificity reaching nearly 100% and sensitivity over 80%. (2) Medial meniscal lesions at the posterior horn have overall high MRI sensitivity and specificity as ACL lesions, with the exception of short peripheral or meniscocapsular tears as a specific tear pattern at this area which should be diagnosed definitively only by direct arthroscopic evaluation
Summary
MRI is the most accurate imaging modality for diagnosing knee pathologies. there is uncertainty concerning factors predicting false negative MRI, such as meniscal tear patterns as well as patient factors. Awareness of the aforementioned information concerning specific factors which were found to be associated with a false negative MRI could potentially assist in improving MRI interpretation, there were a few limitations of previously reported data on MRI accuracy that should be remembered These include incorporating low-magnet strength MRI which is rarely used today for the diagnosis of knee lesions (i.e. lower than 1.5-Tesla) [1], not indicating accuracy measures for specific areas in the meniscus in some studies (i.e. anterior horn, body, posterior horn) [1, 10, 11], and using multiple MRI sequencing techniques in a single series of patients [1]. It was hypothesized that specific lesion characteristics of the menisci and articular cartilage in addition to patient age would be associated with MRI accuracy
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