Fatty degeneration is an important clinical factor in patients with rotator cuff tears. Goutallier grade, occupation ratio, and tangent sign help identify fatty degeneration; however, little is known about how closely these measurement techniques correlate with actual muscle strength deficits. The authors evaluated each method's ability to determine the correlation between fatty degeneration and muscle strength deficits. The authors included 203 patients who underwent full-thickness rotator cuff repair (mean age, 61.29±7.92 years). All patients were evaluated with preoperative magnetic resonance imaging to identify fatty degeneration and with an isokinetic test to determine actual shoulder strength. Fatty degeneration was evaluated using Goutallier grade, occupation ratio, and tangent sign. The actual shoulder strength deficit was evaluated by abduction, whereas external and internal rotation were tested using the isokinetic test. More severe fatty degeneration was correlated with lower degrees of abduction, external rotation, and internal rotation. The occupation ratio was more closely correlated with actual muscle strength deficits. However, in patients with massive tears, the correlation between fatty degeneration and muscle strength was less pronounced. Tangent sign (+) findings had a significantly lower strength of external rotation and abduction. The fatty degeneration of the rotator cuff muscle measured by each method was correlated with actual shoulder strength deficits in patients with rotator cuff tears. However, the correlations were less clear in patients with massive rotator cuff tears. Therefore, in cases of massive rotator cuff tears, fatty degeneration was correlated with muscle strength deficits but was not directly proportional to their extent. [Orthopedics. 2018; 41(1):e15-e21.].
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