Background: The definitive treatment for knee osteoarthritis is Total Knee Replacement (TKR), which results in clinically meaningful improvements in pain and physical function. However, evidence suggests that physical activity remains unchanged after TKR. This randomized clinical trial is investigating the efficacy, fidelity, and safety of a physical therapist administered physical activity intervention for people after TKR.

Methods/Design: One hundred and twenty individuals, over the age of 45, who seek outpatient Physical Therapy (PT) following a unilateral TKR will be randomized into a control and intervention group. The intervention group will receive a weekly physical activity intervention during PT, which includes a FitbitTM monitor, individualized step goals, and face-to-face feedback provided by the physical therapist. Efficacy of the intervention will be measured by minutes/week spent in Moderate-to-Vigorous Physical Activity (MPVA) using an Actigraph GT3X monitor from enrollment to discharge, 6 months and 12 months from discharge from PT. The association of self-efficacy for exercise and kinesiophobia with physical activity will also be measured at the same time points. Fidelity and safety of the intervention will be assessed during outpatient PT.

Discussion: This study is designed to fill a critical clinical need to increase physical activity after TKR. The primary objective of the study is to evaluate the efficacy of a physical therapist administered physical activity intervention for people after TKR. The secondary objectives are to evaluate the fidelity and safety of a physical therapist administered physical activity intervention for people after TKR and to investigate changes in self-reported and performance-based physical function after a physical therapist administered physical activity intervention for people after TKR. The tertiary objective is to explore the association of psychosocial factors with physical activity 6 and 12 months after discharge from a physical therapist administered physical activity intervention for people after TKR. The findings will be used to support a large multi-site clinical trial to test the effectiveness, implementation, and cost of this intervention.

Inclusion Criteria:

1. Over the age of 45
2. Seeking outpatient physical therapy for a unilateral TKR

Exclusion Criteria:

1. Not interested in increasing physical activity
2. Any other medical conditions that limit your physical activity
3. Have had or are planning on having another leg surgery within 6 months that is unrelated to your TKR surgery
4. Previously enrolled in a physical activity intervention study at this clinic

This is the analytic sample size that included

• All subjects who were randomized
• The ActiGraph monitor was worn for > 4 days of 10 hours of wear at baseline.

Adverse Events were collected from enrollment until the last follow up, i.e., at 12 months after discharge from outpatient physical therapy, up to 16 months.