Rotator cuff tendon tears are common conditions which can alter shoulder joint function and over time, cause secondary damage to the surrounding tissues, including the cartilage and other remaining tendons. Glenohumeral joint stability is dependent on a dynamic balance between rotator cuff forces, in particular the subscapularis anteriorly and the infraspinatus posteriorly. An intact rotator cuff stabilizes the joint, allowing for concentric rotation of the humeral head on the glenoid. However, a massive rotator cuff tear involving the supraspinatus and infraspinatus may disrupt the normal balance of forces at the joint, resulting in abnormal joint loading. This is of particular concern in populations who perform activities requiring repeated overhead activity (e.g., laborers, athletes). Our lab has previously demonstrated that restoration of the subscapularis-infraspinatus anterior-posterior force balance improves shoulder function by providing a stable fulcrum for concentric rotation of the humeral head on the glenoid [1]. However, the long term consequences caused by disruption of the anterior-posterior force balance (supraspinatus and infraspinatus tear) on the glenoid cartilage and adjacent (intact) tendons, particularly in the case of an overuse population, remains unknown. Therefore, the objective of this study was to investigate the effect of disrupting the anterior-posterior force balance on joint function and joint damage using a clinically relevant overuse model system. We hypothesized that a disrupted anterior-posterior force balance (supraspinatus and infraspinatus tear) would result in H1) decreased joint function and H2) inferior adjacent tissue (glenoid cartilage, biceps and subscapularis tendon) properties compared to an intact anterior-posterior force balance (supraspinatus only tear).

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