Objective. To explore the feasibility, fidelity, safety, and preliminary outcomes of a physical therapist-administered physical activity (PA) intervention after total knee replacement (TKR).Methods. People who had undergone a unilateral TKR and were receiving outpatient physical therapy (PT) were randomized to a control or intervention group. Both groups received standard PT for TKR. The intervention included being provided with a Fitbit Zip, step goals, and 1 phone call a month for 6 months after discharge from PT. Feasibility was measured by rates of recruitment and retention, safety was measured by the frequency of adverse events, and fidelity was measured by adherence to the weekly steps/day goal created by the physical therapist and participant monitoring of steps/day. An Actigraph GT3X measured PA, which was quantified as steps/day and minutes/week of engaging in moderate-to-vigorous PA. Our preliminary outcome was the difference in PA 6 months after discharge from PT between the control and intervention groups.Results. Of the 43 individuals who were enrolled, 53.4% were women, the mean ± SD age was 67.0 ± 7.0 years, and the mean ± SD body mass index was 31.5 ± 5.9 kg/m 2 . For both the control and intervention groups, the recruitment and retention rates were 64% and 83.7%, respectively, and adherence to the intervention ranged from 45% to 60%. No study-related adverse events occurred. The patients in the intervention group accumulated a mean 1,798 more steps/day (95% confidence interval [95% CI] 240, 3,355) and spent 73.4 more minutes/week (95% CI -14.1, 160.9) engaging in moderate-to-vigorous PA at 6 months than those in the control group.Conclusion. A physical therapist-administered PA intervention is feasible and safe, demonstrates treatment fidelity, and may increase PA after TKR. Future research is needed to establish the effectiveness of the intervention.ClinicalTrials.gov identifier: NCT02724137.

Objective. Knee cartilage damage is often linked to mechanical overloading. However, cartilage requires mechanical load to remain healthy, suggesting that underloading may be detrimental. This study was undertaken to examine knee overloading and underloading by defining cumulative load as the joint effects of body mass index (BMI) and daily walking, and examine the relationship between cumulative load and worsening cartilage damage over 2 years.Methods. We used data from the Multicenter Osteoarthritis Study. Steps/day, measured by accelerometry, and BMI were calculated at the 60-month visit. Cartilage damage on magnetic resonance imaging was semiquantitatively scored using the Whole-Organ Magnetic Resonance Imaging Score (WORMS) at the 60-month and 84-month visits; worsening damage was defined as increased WORMS between visits. Risk ratios (RRs) and 95% confidence intervals (95% CIs) were calculated using binomial regression, with adjustment for potential confounders.Results. Our study included 964 participants, 62% of whom were female, with a mean ± SD age of 66.9 ± 7.5 years. Participants had a mean ± SD BMI of 29.7 ± 4.8 kg/m 2 and walked a mean ± SD of 7,153 ± 2,591 steps/day. Participants who walked a moderate number of steps/day (6,000-7,900) or a high number of steps/day (>7,900) and had a high BMI (>31 kg/m 2 ) had a greater risk of worsening medial tibiofemoral (TF) damage (RR 2.83 [95% CI 1.46-5.48] and RR 2.61 [95% CI 1.50-4.54], respectively) compared with those who walked similar steps/day and had a low BMI (18-27 kg/m 2 ). Participants with a low number of steps/day (<6,000) and a low BMI had a greater risk of worsening medial TF and lateral patellofemoral (PF) damage (RR 2.03 [95% CI 1.06-3.92] and RR 2.28 [95% CI 1.06-4.85], respectively) compared with those who walked a high number of steps/day and had a low BMI. Effect estimates for other compartments of the knee did not reach statistical significance.Conclusion. This study provides preliminary evidence that both overloading and underloading may be detrimental to medial TF cartilage, and underloading may be detrimental to lateral PF cartilage.

Objective To examine joint association of moderate-to-vigorous intensity physical activity (MVPA) and sedentary behavior with the risk of developing functional limitation 4 years later in adults with knee OA. Methods Using 48-month (baseline) accelerometry data from Osteoarthritis Initiative, , we classified participants as Active-Low Sedentary (≥1 10-minute bout/week of MVPA, lowest tertile for standardized sedentary time), Active-High Sedentary (≥1 10-minute bout/week of MVPA, top two tertiles for standardized sedentary time), Inactive-Low Sedentary (0 10-minute bout/week of MVPA, lowest tertile for standardized sedentary time) and Inactive-High Sedentary (0 10-minute bout/week of MVPA, top two tertiles for standardized sedentary time) groups. Functional limitation was defined as >12sec for five repetition sit-to-stand test (5XSST) and <1.22m/sec gait speed during 20-meter walk test. To investigate the association of exposure groups with risk of developing functional limitation 4 years later, we calculated risk ratios(aRR) adjusted for potential confounders. Results Of 1,091 and 1,133 participants without baseline functional limitation, based on 5XSST and 20-meter walk test, respectively, 15% and 21% developed functional limitation 4 years later. Active- High Sedentary group didn’t have, while Inactive-Low Sedentary, and Inactive-High Sedentary groups had increased risk of developing functional limitations compared to Active-Low Sedentary group. Inactive-Low Sedentary group had 72% (aRR[95% confidence interval]1.72[1.00, 2.94]) and 52% (1.52[1.03, 2.25]) more risk of developing functional limitation based on 5XSST and 20-meter walk test, respectively, compared to Active-Low Sedentary group. Conclusion Regardless of sedentary category, being inactive (0 10-minute bouts/week in MVPA) may increase risk of developing functional limitation in adults with knee OA.

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