Rotator cuff tears (RCT) commonly start at the anterior insertion of the supraspinatus and have been shown to propagate posteriorly. Early detection and repair of small or medium size tears has been shown to result in better clinical outcome and structural integrity than that of large or massive tears. However, it is unknown at which stage of rotator cuff tear propagation the biomechanical environment becomes altered. Previous biomechanical studies have not considered rotator cuff propagation based on the footprint anatomy, rotational glenohumeral joint kinematics, and the influence of anatomy-based muscle loading including pectoralis major and latissmus dorsi. Therefore, the purpose of this study was to determine the relationship between progressive rotator cuff tear and glenohumeral joint biomechanics using a rotator cuff tear progression model and anatomically based muscle loading including the influence of the pectoralis major and latissmus dorsi. Our hypotheses were 1) cuff tear progression will lead to abnormal glenohumeral joint biomechanics, specifically in kinematics (rotational range of motion and the path of humeral head apex) and abduction capability and 2) the pectoralis major and latissmus dorsi muscles will act as a stabilizer of the humeral head in large or massive tear.

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