PROJECT SUMMARY A critical gap in rotator cuff tear research is understanding why some individuals have a torn rotator cuff but are free of symptoms, while others experience pain and dysfunction. Dr. Pozzi’s Katz R01 (parent project, AR080058) approaches this problem by examining the neural and somatosensory aspects (neuroimaging, central sensitization, psychosocial distress) of symptoms in well-characterized cohorts of symptomatic tears, asymptomatic tears, and healthy controls (no tears, no pain). We have a unique window of opportunity to submit an ancillary project that evaluates the musculoskeletal aspects of symptoms, specifically neuromuscular control and glenohumeral joint health, in the same cohorts as the parent project. The high prevalence of individuals with asymptomatic rotator cuff tears as well as the success of some conservative exercise interventions for symptomatic tears suggests neuromuscular control strategies can mitigate symptoms. However, since the anatomical integrity of the torn tendon is not restored, to what extent previously identified changes of neuromuscular control are adaptive versus pathological remains unknown. Current investigation on the interaction between rotator cuff tears and glenohumeral joint health are limited to murine models, radiographic imaging studies, and studies characterizing end-stage disease (i.e., co-presence of massive tears and glenohumeral osteoarthritis). We will advance this prior work through three aims. In Aim 1, we will elucidate the interrelationship between neuromuscular control and symptom expression in individuals with rotator cuff tears by simultaneously measuring shoulder motion (including scapular motion) and electromyography (EMG) of shoulder muscles (including intramuscular EMG of rotator cuff muscles) during functional tasks. In Aim 2, we will elucidate the interrelationship between neuromuscular control, symptom expression, and shoulder joint health in individuals with rotator cuff tear using static (magnetic resonance imaging to characterize cartilage) and dynamic (musculoskeletal simulations to calculate glenohumeral joint forces) measures. In Aim 3, we will explore potential treatment targets by leveraging recent advances in explainable artificial intelligence to evaluate the relative contributions of various organ systems to rotator cuff symptoms. The organ systems evaluated in the parent (nervous and somatosensory systems) and ancillary (musculoskeletal system) projects will be explicitly studied. Completing this ancillary project will advance our knowledge of the musculoskeletal factors that influence patient outcomes. Integrated analyses of the musculoskeletal (ancillary), neural (parent), and somatosensory (parent) contributions to symptom expression will further elucidate the biological mechanisms driving outcomes, thereby aiding the identification of rotator cuff tear phenotypes and treatment targets.