PROJECT SUMMARY/ABSTRACT Significance: Intra-articular, prearthritic hip disorders (PAHD) result in substantial dysfunction in young adults and are proposed precursors to hip osteoarthritis. The number of surgical procedures to treat PAHD has grown exponenitally in the past decade, despite the lack of high level evidence to guide treatment decisions. The potential exists for surgery to become standard treatment before rigorous investigation of treatment options has been completed. This trend may be partially due to a lack of evidence related to rehabilitation. Although some authors believe rehabilitation can improve function in people with PAHD, others state that rehabilitation is contra-indicated and recommend surgery as the best option. There are no published clinical trials to support or refute either opinion, therefore we know little about the comparative effectiveness of rehabilitation. Innovation: Our long term goal is to develop effective treatment strategies for people with PAHD that will improve function and prevent or delay the onset of OA. Movement pattern training is an innovative rehabilitation approach designed to reduce stresses on the hip joint by optimizing the biomechanics of functional tasks through task-specific instruction. Preliminary work suggests that abnormal movement patterns may be associated with PAHD and that movement pattern training may be an effective treatment approach, however comparison to standard rehabilitation has not been completed. Purpose: We will assess the feasibility of conducting a multicenter randomized clinical trial (RCT) to determine the efficacy of movement pattern training compared to standard rehabilitation for people with PAHD. Participants enrolled at Washington University and University of Pittsburgh will be randomized into one of two treatment groups, movement pattern training or standard rehabilitation. In addition to assessing feasibility of the trial, we will obtain preliminary estimates of effect sizes for treatment outcomes in preparation for the future definitive trial. We will compare post-treatment improvements in patient-reported function as measured by the Hip disability and Osteoarthritis Outcome Score and hip adduction motion during functional tasks, a proposed mechanistic factor associated with PAHD. Upon completion of this study, we will be positioned to implement a multicenter RCT to definitively assess the efficacy of movement pattern training. Impact: Ultimately, if movement pattern training is determined to be effective, it will provide a relatively inexpensive alternative to surgical intervention. Further, the theoretical concepts of movement pattern training could be used to possibly serve a role in injury prevention, as well as optimize post-surgical outcomes in those who do require surgery.