Physical activity levels two years after total knee arthroplasty and preoperative patient characteristics: a secondary analysis of the MOVE randomized controlled trial.

INTRODUCTION: At one year after total knee arthroplasty (TKA), patients are less physically active than age-matched peers, but physical activity (PA) trajectories two years after TKA are unclear. This study examined PA levels from baseline to two years post-TKA, quantified return to baseline PA levels over time, and evaluated associations between baseline participant characteristics and post-TKA PA levels.

METHODS: This was an exploratory secondary analysis of a randomized controlled trial. Participants (n = 135) aged 50 to 85 years undergoing primary unilateral TKA wore accelerometers preoperatively and 10 weeks, six months, and two years post-TKA to characterize light PA, moderate-vigorous PA (MVPA), and steps/day. Descriptive statistics were used to characterize PA levels. Repeated measures models estimated PA levels over time. The percentage of participants who returned to or exceeded baseline PA levels over time was quantified. Multivariate logistic regressions modeled return to baseline PA levels over time to evaluate associations with baseline participant characteristics. All models controlled for age, sex, and treatment group.

RESULTS: There was an increase of 8% steps/day and 0.75% MVPA from baseline to two years post-TKA. At two years post-TKA, 54.2, 53.1, and 55.6% of participants returned to baseline light PA, MVPA, and steps/day levels. Higher baseline PA levels were associated with lower odds of returning to baseline levels at all timepoints for MVPA (10 weeks odds ratio (95% confidence interval): 0.62 (0.46 to 0.84); six months: 0.55 (0.40 to 0.76); two years: 0.52 (0.36 to 0.75)), as well as light PA and steps/day (all P-values < 0.05). Baseline body mass index, Western Ontario and McMaster Universities Arthritis Index scores, and Functional Comorbidity Index were associated inconsistently with PA levels.

CONCLUSION: While on average, PA levels increased from baseline to two years post-TKA, participants who have higher baseline PA levels had reduced odds of returning to the same level. These findings suggest TKA and current rehabilitation may not fully address PA, and additional support (e.g., behavioral guidance or tailored rehabilitation) may be needed.