ABSTRACT Arthroscopic partial meniscectomy (APM) is the most commonly performed ambulatory orthopaedic procedure in the United States, with almost half of these procedures performed in patients over 45 years of age, often with concomitant osteoarthritis. Prior clinical trials have found no significant benefit of APM over non-surgical treatment in older patients with meniscal tears and osteoarthritis (OA) and have been suggested these patients should first undergo a course of physical therapy before pursuing APM. Even when APM is performed after a failed course of physical therapy, however, almost 20% of these patients do not have a clinically meaningful improvement. At present, there is no preoperative tool that is available which can predict the likelihood of having a successful outcome after APM in this patient population. Preoperative magnetic resonance imaging (MRI) findings have been shown to correlate with outcomes in small studies which have been exploratory in nature with significant limitations. The value of preoperative MRI, as used in routine clinical practice, to predict outcome after APM remains unclear. We believe that preoperative MRI findings, including the severity of cartilage loss, can help differentiate responders from non-responders to surgery. Our institution's large prospective cohort of greater than 1000 patients, with baseline and 1-year patient reported outcomes measures (PROMs) and preoperative MRIs, provides a unique data set to perform a study with sufficient sample size to identify the predictors of PROMs in patients undergoing APM. The objective of this study is to identify the preoperative MRI predictors in patients 45 years old and older who will have no clinically meaningful improvement in PROMs after APM. Specifically by constructing multiple variable models, we will identify preoperative MRI findings that are associated with improvement in pain and function adjusting for all potential confounders. We will also develop prediction tools, using these MRI risk factors, to identify patients who will and will not benefit from APM that can be used to help guide clinical decision making. We believe that the use of these tools will reduce unnecessary surgeries and cost to the healthcare system which we plan to test in a future randomized control trial.