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Key Points Question Can exercise programs delivered at a later stage (>2 months) after total knee replacement improve the functional limitations that persist after surgery? Findings In this randomized clinical trial of 240 individuals at a later stage after knee replacement, all arms (physical therapy, community, and control) improved physical function. There were no differences between arms in the primary outcome of patient-reported physical function, whereas the secondary outcome of performance-based physical function demonstrated greater improvement in the physical therapy arm. Meaning While the primary outcome suggests no benefit of later-stage exercise programs, the secondary outcomes suggest beneficial effects of physical therapy but require confirmation., This randomized clinical trial compares the effectiveness of later-stage exercise programs of clinic-based physical therapy exercise or community-based group exercise vs usual care after total knee replacement and explores heterogeneity of treatment effects., Importance Several functional limitations persist after total knee replacement (TKR). Intensive exercise programs could resolve these limitations but are not well tolerated by many patients until a later stage (>2 months) after surgery. Evidence for exercise at a later stage after TKR is limited. Objectives To compare the effectiveness of later-stage exercise programs after TKR and to explore heterogeneity of treatment effects. Design, Setting, and Participants Three-arm single-blind randomized clinical trial (January 7, 2015, to November 9, 2017) using an intent-to-treat approach with follow-ups at 3 months and 6 months. The setting was Allegheny County, Pennsylvania (an outpatient physical therapy clinic and 4 community centers). Participants had primary TKR performed more than 2 months previously, were 60 years or older, experienced moderate functional limitations, and were medically cleared to exercise. Interventions Clinic-based physical therapy exercise (physical therapy arm), community-based group exercise (community arm), and usual care (control arm). The control arm continued their usual care, whereas the exercise arms participated in supervised exercise programs lasting 12 weeks. Main Outcomes and Measures The primary outcome was arm differences in the Western Ontario and McMaster Universities Osteoarthritis Index–Physical Function (WOMAC-PF) at 3 months. The secondary outcomes included performance-based tests germane to knee replacement and additional surveys of physical function. Data were analyzed by linear mixed models and responder analysis. Results A total of 240 participants (mean [SD] age, 70 [7] years; 61.7% female) were allocated to physical therapy (n = 96), community exercise (n = 96), or control (n = 48). All 3 arms demonstrated clinically important improvement. At 3 months, between-arm analyses for the WOMAC-PF demonstrated no differences between physical therapy and community (−2.2; 98.3% CI, −4.5 to 0.1), physical therapy and control (−2.1; 98.3% CI, −4.9 to 0.7), and community and control (0.1; 98.3% CI, −2.7 to 2.9). Performance-based tests demonstrated greater improvement in the physical therapy arm compared with both the community (0.1 z score units; 98.3% CI, 0.0-0.2) and control (0.3 z score units; 98.3% CI, 0.1-0.4) arms and the community arm compared with the control arm (0.2 z score units; 98.3% CI, 0.0-0.3). The physical therapy arm had more than 17.7% responders than the community arm and more than 19.0% responders than the control arm. There was no difference in responder rates between the community and control arms. Conclusions and Relevance Based on the primary outcome, participation in late-stage exercise programs after TKR offered no benefit over usual care. The benefits of physical therapy identified by the secondary outcomes and responder analysis require confirmation. Trial Registration ClinicalTrials.gov Identifier: NCT02237911