Relationship of Posterior Decentering of the Humeral Head with Tear Size and Fatty Degeneration in Rotator Cuff Tear

BACKGROUND: Posterior decentering is not an uncommon finding on rotator cuff tear patients’ shoulder magnetic resonance imaging. No previous study has reported on the relationship between posterior decentering and rotator cuff tear. METHODS: We assessed patients’ rotator cuff tear humeral head positions based on humeral–scapular alignment (HSA). Subjects were classified into centering and decentering groups based on a <2 mm or >2 mm HSA value, respectively. Differences in rotator cuff tear size, degree of tear, and fatty degeneration between the two groups were evaluated. RESULTS: One hundred seventy-five patients (80 males, 95 females; mean age: 59.7 ± 6.5 years old) were selected as subjects (case-control study; level of evidence: 3). Tear size, degree of subscapularis tendon tear, and fatty degeneration of the supraspinatus, infraspinatus, and subscapularis muscles were significantly different between the two groups (p<0.001, p<0.001, p<0.001). CONCLUSIONS: The occurrence of decentering was related to rotator cuff tear size, degree of subscapularis tendon tear, and fatty degeneration of the rotator cuff muscles.