ACL reconstruction can reliably restore knee stability and allow competitive and recreational athletes to return to their sports quickly, during the first year after injury. However, the longer-term risk of post-traumatic arthritis is a significant concen for these patients and their physicians. Meniscus tear and cartilage injury have been associated with increased risk of osteoarthritis in ACL reconstruction patients, but previous investigations have been limited by heterogeneous patient populations, poorly validated outcome measures, and retrospective study designs. The aims of this proposal are (1) to determine whether differences in meniscus treatment and articular cartilage status at baseline predict radiographic signs of osteoarthritis two years after ACL reconstruction, (2) to evaluate the association between instrumented joint laxity and radiographic signs of OA 2 years after ACL reconstruction, and (3) to explore the relationship between arthroscopic treatment at baseline and MRI meniscus and articular cartilage status two years after ACL reconstruction. Along with achieving these aims, the trainee will pursue a training program that will include a combination of didactic activities as well as focused mentorship that complements the research project. The goals for the program will include the following: (1) learn to effectively manage personnel and resources in the conduct of clinical research, (2) improve study design and grant writing skills, (3) develop expertise in the application of statistical modeling to evaluate predictors of prognosi in orthopaedic outcome studies, in particular as it relates to imaging biomarkers, (4) learn to assess the incidence and progression of osteoarthritis using radiographic and MR imaging, (5) learn and apply the principles of responsible conduct of research, and (6) improve manuscript preparation and presentation skills. This mentored training program and research project will enable the trainee to make the transition to independent researcher.