Restoration of Anterior-Posterior Rotator Cuff Force Balance Alters Glenoid Properties in a Chronic Cuff Tear Rat Model

INTRODUCTION: Physiologic shoulder motion is dependent on a complex balance of forces. In particular, the anterior-posterior (AP) force balance in the shoulder is primarily comprised of the subscapularis and infraspinatus-teres minor complex of the rotator cuff [1]. Massive chronic rotator cuff tears, a common clinical problem, can disrupt this balance and present a management challenge. Moreover, chronic tears can lead to joint damage, presumably from altered joint mechanics leading to changes in cartilage loading [2]. A patient with only a supraspinatus tear can have good function, suggesting that an intact AP force balance can play a pivotal role in maintaining joint function. Previous rat model studies have shown that partial repair of a twotendon tear can restore joint kinetics similar to a two-tendon repair [3]. However, the effect of a partial repair on glenoid cartilage health remains unknown. Therefore, the objective of this study was to evaluate the effect of partial repair of a massive chronic tear of the rotator cuff on glenoid cartilage thickness and mechanical properties. We hypothesized that, compared to no-repair, partial repair of the rotator cuff tear would lead to H1) changes in thickness, H2) improved mechanical properties, and H3) no significant differences in cartilage between animals with a partial repair and those with a two-tendon repair in either comparison.