Rotator Cuff Injury and Joint Damage
Rotator cuff tears are common, affecting millions of individuals each year in the United States. Tendon tears can dramatically alter shoulder function in a complex, multifactorial manner resulting in significant, permanent damage to the shoulder joint. This damage can manifest as articular cartilage degeneration, injury to adjacent (intact) tendons, and abnormal joint motion. Together, these changes cause pain and functional limitations, common clinical results of a rotator cuff tear. Our earlier work demonstrated that rotator cuff force balance disruption is the mechanical mechanism that causes overload on intact tendons and results in tissue damage and loss of function. Results of these studies not only furthered understanding of joint damage following rotator cuff tears, but also influenced clinical treatment by providing support for surgical techniques, such as margin convergence and partial repair, that prioritize restoration of the force balance and infraspinatus integrity. The subscapularis is the largest and most powerful of the rotator cuff muscles and serves as the anterior aspect of the rotator cuff force balance. Subscapularis tears are now identified in ~50% of patients undergoing rotator cuff repair. Thus, previously unidentified and untreated subscapularis tears could contribute to continued shoulder dysfunction, chronic pain, and rotator cuff tendon re-tear and/or tear progression. Moreover, no studies have examined the critical question of how subscapularis tendon tears affect the shoulder joint, and as a result, a clear best clinical approach has not been identified for this common and debilitating condition. Therefore, the overall objective of this work is to specifically determine the effects of rotator cuff tears involving the subscapularis on joint damage, shoulder function, and pain and to elucidate the mechanical mechanisms governing these clinically important connections to advance clinical treatment. In this study, we will define how joint overload and overuse after rotator cuff tears impact joint damage, shoulder dysfunction, and paint. Joint function is assessed longitudinally using analysis of gait kinetics and kinematics and grip strength. Post-mortem experiments to determine the mechanical properties and structure of the rotator cuff tendons and glenoid articular cartilage will rigorously evaluate the extent of damage in these tissues. Recognizing that subscapularis tears are prevalent, yet the impact of subscapularis pathology and treatment remains unknown, the results of this study will provide valuable insight into how these tears impact the aging and veteran population. Ultimately, identifying subscapularis tears at risk for causing a degenerative cascade in the shoulder will allow physicians and surgeons to conduct focused prospective clinical trials to institute targeted interventions to reduce pain, improve function, and preserve long-term shoulder joint health.