| Summary: | Background: Some researchers have stated that magnetic resonance imaging (MRI) is useful for assessing the coracoacromial ligament (CAL) at the acromial undersurface. However, few studies have investigated the reliability and clinical significance of MRI findings for the CAL at the acromial undersurface. The purpose of this study was to determine the association between CAL thickness at the acromial undersurface and rotator cuff tear size. Methods: The CAL thickness at the acromial undersurface was evaluated in 182 patients with rotator cuff tears (mean age: 64.9 ± 8.4 years) using a 3.0-Tesla MRI system. The association between CAL thickness at the acromial undersurface and rotator cuff tear size determined by the DeOrio and Cofield classification (partial; small: <1 cm; medium: 1-3 cm; and large or massive: >3 cm) was analyzed statistically. The intraobserver and interobserver reliabilities for MRI measurements of CAL thickness at the acromial undersurface were determined by calculation of intraclass correlation coefficients and their 95% confidence intervals. Results: The mean CAL thickness at the acromial undersurface was 2.7 ± 1.4 mm (range: 0-6.5 mm). Increasing rotator cuff tear size was significantly associated with decreasing CAL thickness at the acromial undersurface (P = .004). The intraobserver and interobserver intraclass correlation coefficients for CAL thickness at the acromial undersurface were almost perfect (0.98 and 0.91, respectively). Conclusion: The present study clarified that (1) MRI was a reliable tool for evaluation of CAL thickness at the acromial undersurface and (2) increasing rotator cuff tear size was significantly associated with decreasing CAL thickness at the acromial undersurface. These findings may assist toward understanding the progressive pathology in rotator cuff disease.
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