Knee Arthroplasty Activity Trial (KArAT)

Total knee replacement (TKR) is a common and costly procedure widely used to relieve pain and improve function in patients with symptomatic advanced knee osteoarthritis (OA). As of 2013, the annual incidence of TKR was over 680,000 surgeries and annual costs exceeded $11 billion. Growing evidence suggests that while pain and functional status improve following TKR, physical activity (PA) typically does not surpass pre-TKR levels. Engagement in PA can meaningfully improve quality of life (QoL), pain, and function. Given the large investment in TKR, the effectiveness and cost-effectiveness of TKR could be substantially increased if TKR recipients became more physically active.

The Knee Arthroplasty Activity Trial (KArAT) is a randomized controlled trial and participants will be randomly assigned to one of three arms. Participants across all arms will receive usual post-operative care for TKR surgery. Participants in the first arm will complete basic study activities, such as responding to surveys and attending two in-person clinic visits. Participants in the second arm will do the same and also receive a wrist-based physical activity tracker intervention. Participants in the third arm will receive a telephonic active coaching (motivational interviewing) and financial incentives (for reaching physical activity goals) (TAC(MI)+FI) based intervention, as well as a wrist-based physical activity tracker intervention. The second and third arms will be eligible to receive lottery-based financial rewards for wearing a wrist-worn activity tracker for twenty-four months during the study.

Study Overview

• Status: Active, not recruiting
• Conditions: Knee Osteoarthritis; Total Knee Replacement
• Intervention / Treatment: Other: Basic Study Activities; Behavioral: Wrist based activity tracker wear; Behavioral: Telephonic Active Coaching (Motivational Interviewing) + Financial Incentives

Detailed Description

The investigators have designed the KArAT trial with two specific aims. First, to conduct a parallel three-arm RCT to establish the efficacy and sustainability of the effect of personalized intervention built on the principles of behavioral science and behavioral economics in improving PA among sedentary people who have undergone TKR. Our second aim is to establish the cost-effectiveness and budget impact of TAC(MI)+FI to improve PA in persons who have undergone TKR.

The three arms will include:

Arm 1: Usual post-TKR care

Arm 2: Usual post-TKR care + Wrist-based physical activity tracker wear

Arm 3: Usual post-TKR care + Wrist-based physical activity tracker wear + Telephonic Active Coaching (Motivational Interviewing) + Financial Incentives (TAC(MI)+FI).

• Study Type: Interventional
• Enrollment (Estimated): 600
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United States
  • Illinois
    • Chicago, Illinois, United States, 60611
      • Northwestern Memorial Hospital
  • Kansas
    • Kansas City, Kansas, United States, 66160
      • University of Kansas Medical Center
  • Massachusetts
    • Boston, Massachusetts, United States, 02115
      • Brigham and Women's Hospital
  • Nebraska
    • Omaha, Nebraska, United States, 68198
      • University of Nebraska Medical Center
  • New York
    • Buffalo, New York, United States, 14215
      • University at Buffalo

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 45 years to 80 years (Adult, Older Adult)
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Age 40-85 years
• English-speaking
• Scheduled to undergo primary, unilateral total knee replacement (TKR) at one of the 4 recruitment centers
• OA is principal underlying indication for TKR
• During an accelerometer run-in period lasting one week at baseline (prior to surgery), subjects must show that they can comply with waist-worn physical activity tracker protocols by wearing the activity tracker for ≥4/7 days of the week for ≥10 hours/day
• Regular access to a personal computer, laptop, tablet, or smartphone for wrist-worn activity tracker syncing
• Satisfying average baseline steps/day criteria (calculated from waist-worn activity tracker data from the run-in period)

Exclusion Criteria:

• Non-English speaking
• Residence in nursing home
• Diagnosis of dementia, epilepsy, Parkinson's Disease, or diabetes with peripheral neuropathy
• Inflammatory arthritis (rheumatoid arthritis, ankylosing spondylitis, psoriatic arthritis, reactive arthritis, systemic lupus erythematosus, polymyalgia)
• Psychological issues that preclude participation
• Inpatient or other musculoskeletal surgery scheduled within six months following index primary TKR
• Uses a wheelchair to ambulate (subjects who use a cane will be eligible)
• Surgeon-documented other reason for study exclusion
• Subject does not have regular access to a device capable of receiving email or text messages

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Triple

Number of Arms

3

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Other: Arm1; Participants in this arm receive usual post-operative care and complete all basic study activities, which include: attending 2 in-clinic visits at designated time-points, having regular check-in calls with study staff over the intervention period, wearing and returning waist-worn activity trackers at 5 time points over two years, and completing 6 study surveys.	Other: Basic Study Activities; Basic study activities begin two-weeks before TKR and end approximately 24-months after TKR. Basic study activities include: two in-person visits at the local clinic site (2 weeks before TKR and 32-weeks after TKR), having check-in calls with study staff weekly from weeks 1-13 after surgery and every other week for weeks 14-31, completing 6 surveys, and wearing an ActiGraph activity tracker (waist-worn) for five one-week periods throughout the study (2-weeks before-TKR, 32-weeks post-TKR, one-year post-TKR, 18-months post-TKR, two-years post-TKR). All participants will be eligible to receive up to $235 for completing these activities over the course of two years.
Experimental: Arm2; Participants in this arm receive usual post-operative care, complete all basic study activities (as described in arm 1) and receive the wrist-based activity tracker intervention.	Other: Basic Study Activities; Basic study activities begin two-weeks before TKR and end approximately 24-months after TKR. Basic study activities include: two in-person visits at the local clinic site (2 weeks before TKR and 32-weeks after TKR), having check-in calls with study staff weekly from weeks 1-13 after surgery and every other week for weeks 14-31, completing 6 surveys, and wearing an ActiGraph activity tracker (waist-worn) for five one-week periods throughout the study (2-weeks before-TKR, 32-weeks post-TKR, one-year post-TKR, 18-months post-TKR, two-years post-TKR). All participants will be eligible to receive up to $235 for completing these activities over the course of two years.; Behavioral: Wrist based activity tracker wear; Activity tracking data will be collected on a weekly basis. Participants who receive this intervention are eligible to be entered into a lottery to win one of two $25 rewards for every week they wear their wrist-based activity tracker >10 hours for >4/7 days a week, beginning 6-weeks after surgery.
Experimental: Arm3; Participants in this arm receive usual post-operative care, complete all basic study activities (as described in arm 1), receive wrist-based activity tracker intervention, and receive the TAC(MI)+FI.	Other: Basic Study Activities; Basic study activities begin two-weeks before TKR and end approximately 24-months after TKR. Basic study activities include: two in-person visits at the local clinic site (2 weeks before TKR and 32-weeks after TKR), having check-in calls with study staff weekly from weeks 1-13 after surgery and every other week for weeks 14-31, completing 6 surveys, and wearing an ActiGraph activity tracker (waist-worn) for five one-week periods throughout the study (2-weeks before-TKR, 32-weeks post-TKR, one-year post-TKR, 18-months post-TKR, two-years post-TKR). All participants will be eligible to receive up to $235 for completing these activities over the course of two years.; Behavioral: Wrist based activity tracker wear; Activity tracking data will be collected on a weekly basis. Participants who receive this intervention are eligible to be entered into a lottery to win one of two $25 rewards for every week they wear their wrist-based activity tracker >10 hours for >4/7 days a week, beginning 6-weeks after surgery.; Behavioral: Telephonic Active Coaching (Motivational Interviewing) + Financial Incentives; As part of TAC(MI)+FI, participants speak with a health coach at Brigham and Women's Hospital once a week via telephone for weeks 6-13 following surgery, and once every other week for weeks 14-31 after surgery. Participants in this arm can receive financial rewards for achieving weekly physical activity goals, as well as bonus rewards for achieving goals multiple weeks in a row. Over the course of this 6-month long TAC(MI)+FI intervention period, these participants are able to receive up to $680 for meeting physical activity goals, and up to $95 in bonus rewards.; Other Names: TAC(MI)+FI

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Proportion of Subjects Engaged in at least 150 min/week of moderate-to-vigorous physical activity (MVPA).	The primary outcome of this trial is the proportion of subjects who meet or surpass the PA threshold of 150 minutes per week of at least moderate physical activity, which is defined as 3 metabolic equivalents (METs), at 32-weeks post-TKR.	32-weeks post-TKR

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in average daily step count	Change in subjects' average daily step count from pre-TKR to 32-weeks post-TKR as measured by the ActiGraph.	2-week pre-TKR to 32-weeks post-TKR
Change in weekly minutes of moderate-to-vigorous activity (MVPA)	Change in the number of minutes per week that subjects spend engaged in MVPA from pre-TKR to 32-weeks post-TKR as measured by the ActiGraph.	2 week pre-TKR to 32-weeks post-TKR
Change in average daily sedentary time	Change in subjects' daily sedentary time from pre-TKR to 32-weeks post-TKR as measured by the ActiGraph.	2 weeks pre-TKR to 32-weeks post-TKR

Other Outcome Measures

Outcome Measure	Measure Description	Time Frame
Durability of changes in activity levels	Changes in subjects' activity levels at 12-, 18-, and 24-months post-TKR as measured by the ActiGraph.	2 weeks pre-TKR to 24 months post-TKR
Change in pain and functional status	Change in subjects' pain and functional status at 8-, 12-, 18-, and 24-months post-TKR as measured by the questionnaire.	2 weeks pre-TKR to 24 months post-TKR
Change in quality of life	Change in subjects' quality of life at 8-, 12-, 18-, and 24-months post-TKR as measured by the questionnaire.	2 weeks pre-TKR to 24 months post-TKR
Change in performance measures	Change in subjects' performance at 32 weeks post-TKR as measured by performance tests.	2 weeks pre-TKR to 6 months post-TKR
Change in cost	Change in subjects' medical costs at 8-, 12-, 18-, and 24-months post-TKR as measured by the questionnaire.	2 weeks pre-TKR to 24 months post-TKR

Collaborators and Investigators

• Sponsor: Brigham and Women's Hospital
• Collaborators: University of Kansas Medical Center; University at Buffalo; University of Nebraska; Northwestern Memorial Hospital
• Investigators: Principal Investigator: Elena Losina, Ph.D., Brigham and Women's Hospital

Publications and helpful links

General Publications

• Losina E, Collins JE, Kumara M, Ehrlich-Jones L, Opare-Addo M, Safran-Norton C, Segal NA, Mitchell LM, Kopp PT, Selzer F, Mass H, Paskewicz M, Chang RW, Dunlop D, Chen AF, Lerner S, Chin S, Pellegrini C, Katz JN. KArAT (Knee Arthroplasty Activity Trial): Rationale and design features of a multicenter randomized controlled trial. Osteoarthr Cartil Open. 2024 Aug 23;7(2):100512. doi: 10.1016/j.ocarto.2024.100512. eCollection 2025 Jun.

Study record dates

Study Major Dates

• Study Start (Actual): April 27, 2023
• Primary Completion (Estimated): June 15, 2028
• Study Completion (Estimated): June 15, 2028

Study Registration Dates

• First Submitted: September 24, 2019
• First Submitted That Met QC Criteria: September 26, 2019
• First Posted (Actual): September 27, 2019

Study Record Updates

• Last Update Posted (Actual): November 24, 2025
• Last Update Submitted That Met QC Criteria: November 19, 2025
• Last Verified: November 1, 2025

More Information

Terms related to this study

• Keywords: Physical Activity; Knee Osteoarthritis; Total Knee Replacement
• Additional Relevant MeSH Terms: Musculoskeletal Diseases; Arthritis; Joint Diseases; Rheumatic Diseases; Osteoarthritis; Behavior; Osteoarthritis, Knee; Motor Activity; Health Services; Health Care Facilities Workforce and Services; Behavioral Disciplines and Activities; Directive Counseling; Counseling; Mental Health Services; Motivational Interviewing
• Other Study ID Numbers: 2019P002700

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No