The objectives of this research are to conduct a proof of concept randomized controlled trial with 200 patients undergoing primary total knee replacement (TKR) at Brigham and Women's Hospital (BWH). The trial will compare levels of physical activity in subjects in the behavioral and economic interventions versus "Usual Care" post TKR.

Physical activity (PA) has been shown to improve pain and function in persons with knee osteoarthritis (OA), reduce obesity, and prevent the onset and progression of heart disease, diabetes, and chronic pulmonary disease. The US Department of Human and Health Services (DHHS) guidelines recommend that adults engage in >150 minutes of moderate physical activity per week. However, adherence to PA guidelines is poor in the general population, particularly in persons with knee OA.

Total knee replacement (TKR) is widely used in patients with symptomatic, advanced knee OA. While the vast majority of persons undergoing TKR experience considerable reduction in pain and improvement in functional capacity, far fewer take this opportunity to become more physically active. Since physical activity has a direct relationship with quality of life and with prevention and amelioration of many chronic conditions, many TKR recipients do not derive maximum benefits from the procedure.

The focus of this proposal is to conduct a proof of concept RCT to establish the efficacy of a behavioral economics-based intervention that would facilitate engagement in physical activity and improve adherence to PA guidelines in the growing population of TKR recipients. We address the innovative hypothesis that the period following TKR presents a window of opportunity to fundamentally change attitudes and beliefs regarding PA, and that tangible economic incentives will effectively induce behavior change and facilitate adherence to PA guidelines.

Inclusion Criteria:

• Scheduled to undergo primary TKA at BWH
• Osteoarthritis is the principal underlying diagnosis
• Age >=40 at the projected date of TKA
• English-speaking
• Willing and able to access the internet to complete study related questionnaires

Exclusion Criteria:

• Osteoarthritis is not the principal underlying diagnosis (e.g. inflammatory arthritis)
• Dementia (can not fill out forms)
• Psychological issues that preclude participation, as identified by participating surgeons
• Does not have access to a computer and/or the internet.
• Non-English speaker (instruments are not validated in Spanish); very few non-English speakers (<5%) are otherwise eligible
• Age <40 at the projected date of TKA (TKA is usually due to major trauma, juvenile onset or congenital disease)
• Lives in a nursing home (difficult to track costs)
• Implantation of Unicompartamental Knee Arthroscopy (different clinical features and different costs)
• Bilateral TKA in same admission (simultaneous), staged or within 6 months
• Uses a wheelchair or walker to ambulate
• Has been told by a physician that he/she has a heart condition and should only do physical activity recommended by a doctor
• Has pain in his/her chest when doing physical activity
• Loses balance because of dizziness
• Loses consciousness
• Unable/unwilling to wear Fitbit® accelerometer for 5 or more days during baseline visit