This is a randomized clinical trial (RCT) to assess the efficacy of bariatric surgery vs medical weight loss vs. the "usual standard of care" to optimize a morbidly obese patient with end-stage osteoarthritis of the hip or knee joint for total joint arthroplasty (TJA). The study population will include patients with hip or knee joint osteoarthritis and BMI (Body Mass Index) \> 40 kg/m2 who are evaluated in the joint arthroplasty clinic at Boston Medical Center. The primary objective of the study is to determine if bariatric surgery or medical weight loss is more effective than the usual standard of care in optimizing a morbidly obese patient with osteoarthritis of the hip or knee joint for TJA. This will be determined by comparing the number of patients within each group who are able to lose weight through either bariatric surgery, medical weight loss, or the usual standard of care to achieve a BMI ≤ 40 kg/m2 to eventually undergo TJA. The secondary objectives of this study are to compare total operative time, postoperative complication rates, readmission rates, percentage of total body weight lost, revision rate, and reoperation rate. The ability of patients within each study arm to maintain a BMI ≤ 40 kg/m2 for up to 2 years after undergoing TJA will also be assessed, as well as their level of satisfaction before and after being in the study.