Correlation of Multiple Acromion Morphological Parameters on Radiographs in a Chinese Population

Background Previous clinical studies have reported associations between the acromion index (AI), lateral acromion angle (LAA), and critical shoulder angle (CSA) and the occurrence of rotator cuff tears. The objective of this study was to analyze the correlations of these different anatomic parameters. Materials and Methods Healthy Chinese participants ( n = 66) and Chinese patients with rotator cuff tears ( n = 70) identified between January 2014 and October 2015 were included in this study. Standardized true anteroposterior radiographs were used to measure the AI, LAA, and CSA in each study participant. Results The mean AI was significantly larger (0.71 standard deviation [SD], 0.05; range 0.58–0.89 vs. 0.64 SD, 0.06; range 0.55–0.78; P < 0.001), the mean LAA was significantly smaller (77.0° SD, 5.73; range 61.0°–94.5° vs. 82.0° SD, 7.33; range 67.6°–98.3°; P < 0.001), and the mean CSA was significantly larger (36.1° SD, 5.29; range 21.3°–42.4° vs. 31.6° SD, 5.29; range 21.4°–45.8°; P < 0.001) in patients with full-thickness rotator cuff tears compared with healthy participants. Conclusions There were a negative linear relationship between the AI and LAA (rotator cuff tears: R = −0.759, P < 0.01; healthy participants: R = −0.813, P < 0.01) and a positive linear relationship between the AI and CSA (rotator cuff tears: R = 0.854, P < 0.01; healthy participants: R = 0.912, P < 0.01) in patients with rotator cuff tear and healthy participants; we termed this phenomenon “The Acromion Rule.” The AI, LAA, and CSA are independent predictors of rotator cuff tears in a Chinese population.