Rotator cuff tendon tears are common conditions which can lead to significant pain and dysfunction. Tears may progress over time from isolated supraspinatus tears to complete ruptures of both the supraspinatus and infraspinatus tendons, disrupting the anterior-posterior force balance provided by the subscapularis anteriorly and infraspinatus posteriorly (commonly referred to as a “force couple”) [1]. This disruption may lead to increased joint instability and result in altered glenohumeral translations which may cause damage to joint structures, such as articular cartilage and adjacent (intact) tendons. This is a particular concern for active individuals who are likely to continue high levels of overuse activity (e.g., laborers, athletes), despite the presence of rotator cuff tears. Previous studies have shown that returning to overuse activity following an isolated supraspinatus tear alters biceps and glenoid articular cartilage properties, but does not alter shoulder function or the adjacent intact subscapularis tendon [2]. However, the consequences associated with disrupting the anterior-posterior force balance (supraspinatus and infraspinatus tears) are not understood. Therefore, the objectives of this study were 1) to investigate the effect of returning to overuse activity following tears of both the supraspinatus and infraspinatus tendons on shoulder function and the remaining intact tendon and glenoid cartilage mechanical properties and 2) to begin to define the biologic mechanisms responsible for these changes. We hypothesized that overuse activity following two-tendon rotator cuff tears would H1) alter shoulder function and H2) lead to damage (indicated by inferior mechanical properties and increased production of degenerative factors, extracellular matrix, and cartilage markers) in the remaining intact tendons (including the biceps and upper and lower subscapularis tendons) and in the anterior-superior region of the glenoid articular cartilage as a result of the excessive joint loading due to overuse following the supraspinatus-infraspinatus tear.

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