Musculoskeletal (MSK) conditions affect more than half of the U.S. population and account for 1 in 5 healthcare visits. MSK care annual costs exceed $176 billion in direct and $876 billion in indirect healthcare costs and show large increases in per capita costs. Yet, there is remarkably little Level I evidence supporting this level of healthcare utilization with little consensus on proper treatment approaches across MSK conditions. Because of difficulties with randomization and blinding, less than 10% of MSK related-studies are clinical trials, and of the trials, less than 40% meet minimal guidelines. Thus, it is not surprising that substantial geographic variation exists in the use of invasive and costly treatments for MSK conditions. Using anecdotes, the popular press suggests that early surgery for new MSK conditions is overused. Simulation studies suggest that lower utilization rates of treatments not supported by clinical evidence, like surgery for MSK conditions, can dramatically lower Medicare costs without sacrificing quality. However, beyond anecdote and simulation studies, there is no evidence supporting the notion that lower surgery rates for patients with MSK conditions will lower costs and maintain quality. Lower surgery rates may keep surgery from patients who would benefit little from surgery. Conversely, lower surgery rates may result in many patients delaying beneficial treatment causing MSK conditions to worsen and result in poorer outcomes and higher long run costs. Our approach is to use the documented geographic variation in early surgery rates as natural experiments and apply instrumental variable estimators to assess the impact of higher rates of early surgery on outcomes and costs. In addition, we will use charts abstracted for a sample of patients to measure confounders unmeasured in Medicare claims to assess the assumptions underlying our natural experiment. We will then carefully interpret our estimates considering the outcomes measured and the validity of the assumptions associated with treatment effect heterogeneity and confounding. The investigative team has substantial experience assessing treatment effectiveness using Medicare data and a strong MSK clinical and empirical background. This study builds on our shoulder-related research using Medicare data from 2011. It will identify important relationships between early surgery choice, treatment success and costs for patients with MSK conditions. AHRQ has authority to conduct and support research to reflect the needs and priorities of the Medicare program. This research will provide key evidence for policy makers to assess whether early surgery for these MSK conditions are over or underused in practice for Medicare patients. Our study goals align with AHRQ’s goal of “producing evidence that can be used to increase the affordability and efficiency of health care”. 1