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Background: The main aim of this study was to evaluate the performance of magnetic resonance imaging (MRI) and interobserver agreement in the identification of the comma sign. The second objective was to look for a correlation between the comma sign and the detachment of the superficial fascia of the subscapularis., Materials and Methods: Two radiologists, blinded to the arthroscopic findings, retrospectively assessed the magnetic resonance images of 110 shoulders and were asked to assess the presence of the comma sign and the intact subscapularis fascia. The inter-reader agreement and the MRI performance values for detection of the comma sign were calculated. In addition, the association between the intact superficial subscapularis fascia and the comma sign was evaluated., Results: The agreement between the 2 radiologists was perfect. The following values were obtained: sensitivity, 90.9%; specificity, 98.8%; positive predictive value, 95.2%; negative predictive value, 97.7%; and accuracy, 97.2%. No association between the comma sign and subscapularis fascia lesions was found., Conclusion: MRI appears to be a reliable method for preoperative assessment of the comma sign. The comma sign appears not to be formed by the detached subscapularis fascia., (Copyright © 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)