Project Summary Rotator cuff tears are a significant clinical problem, resulting in 30% of all visits to orthopaedic surgeons and over 150,000 surgical procedures per year. Rotator cuff tears occur frequently in the middle-to-late aged population and can cause severe pain, disability and activity limitations. Exercise therapy is typically prescribed for initial treatment of rotator cuff tears and is often effective at relieving symptoms. However, exercise therapy fails to relieve symptoms in 25-50% of cases, requiring surgical intervention. Thus, we conducted a prospective observational cohort study of 109 individuals with a symptomatic isolated supraspinatus tendon tear who underwent a personalized exercise therapy program (POETT Cohort). In addition to a much lower incidence of surgery (6.4%) at 2-year follow-up, our exercise therapy program led to significant improvements in passive glenohumeral range of motion, isometric muscle strength, patient-reported outcomes, and in-vivo arthrokinematics without increases in rotator cuff tear size. Initial computational modeling efforts using subject- specific inputs demonstrate that individuals who underwent surgery have less stable glenohumeral joints after exercise therapy. Due to the lower incidence of surgery in the POETT Cohort and the aforementioned findings, we seek to determine the mechanistic and clinical factors that could be associated with the improved outcomes. Therefore, the overall objective of our project is to determine the long-term viability of exercise therapy for treatment of individuals with rotator cuff tears using our unique POETT Cohort by assessing important biomechanical and clinical parameters. The project will address three specific aims: Aim 1) Determine durability of an exercise therapy program to provide clinicians with information related to factors associated with the success or failure of exercise therapy. Changes in PROs at 3-, 4-, and 5-years; rotator cuff tear size at 5-years; in-vivo glenohumeral kinematics at 5-years and subsequent surgery following exercise therapy will be collected; Aim 2) Assess the relative magnitude of improvements in arthrokinematics over 5- years for the POETT Cohort with respect to healthy control subjects; Aim 3) Assess restoration and maintenance of glenohumeral joint stability in subjects with a rotator cuff tear that undergo exercise therapy. Changes in the magnitude and direction of the glenohumeral joint reaction force will be determined for those that were successfully treated with exercise therapy compared to those that underwent subsequent surgery and control subjects utilizing musculoskeletal models. We hypothesize that exercise therapy maintains the health of the rotator cuff over a period of 5-years and joint function will be similar to age-, sex- and hand dominance frequency matched individuals. These analyses will allow for continued development of individualized treatment protocols through determination of the durability of ...