Ultrasonography Outperforms Magnetic Resonance Imaging in Diagnosing Partial-Thickness Subscapularis Tear

To evaluate the diagnostic reliability of ultrasonography (US) and magnetic resonance imaging (MRI) for subscapularis (SSC) tears with shoulder arthroscopy as the gold standard and to investigate the diagnostic value of 2 MRI signs (lesser tuberosity cysts and subcoracoid cysts) for SSC tears. We consecutively enrolled 437 patients who were scheduled to undergo arthroscopic rotator cuff repair from January 2019 to December 2020. Patients with previous shoulder surgery or shoulder fracture, recurrent shoulder instability, and systemic inflammatory disease were excluded. Preoperative US and MRI of the shoulder were performed and interpreted with a standardized approach. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of US and MRI were calculated using arthroscopic findings as the gold standard. Of the 437 patients, 157 had SSC tears confirmed at the time of arthroscopy, 126 of whom had partial-thickness tears. US correctly diagnosed 122 of 157 patients with SSC tears, with an overall sensitivity of 77.7% (confidence interval [CI] 70.6%-83.5%), which was significantly greater than that of MRI (49.7%, CI 42.0%-57.4%, P < .001). For partial-thickness SSC tears, US correctly diagnosed 93 of 126 positive patients and 276 of 311 negative patients. This resulted in a sensitivity of 73.8% (CI 65.5%-80.7%), specificity of 88.7% (CI 84.8%-91.8%), and accuracy of 84.4% (CI 80.7%-87.5%). As with MRI, the sensitivity, specificity, and accuracy were 38.1% (CI 29.7%-47.2%), 86.5% (CI 82.3%-89.9%), and 72.5% (CI 68.2%-76.5%), respectively. Lesser tuberosity cysts and subcoracoid cysts were 2 MRI signs with high specificity (98.2% and 94.6%); however, their sensitivities were relatively low (19.8% and 33.8%). US is a reliable and accurate diagnostic method for SSC tears, especially in easily missed partial-thickness tears. Lesser tuberosity cyst and subcoracoid cyst are highly specific but insensitive MRI signs for SSC tear. Level I, diagnostic, testing of previously developed diagnostic criteria.