Functional Capacity at Rehabilitation Discharge Predicts Physical Activity Characteristics 24 Weeks Later for People With Total Knee Arthroplasty: A Secondary Analysis of a Randomized Controlled Trial.

Objective: To determine the association between performance-based and patient-reported functional capacity at the conclusion of 12-week rehabilitation with average daily step counts and peak walking cadence 38 weeks after total knee arthroplasty (TKA).

Design: Secondary analysis of a randomized controlled trial.

Setting: Veterans Affairs Medical Center.

Participants: A total of 87 US military Veterans (age: 67±7y, 87% male).

Interventions: Twelve-week rehabilitation beginning 2 weeks post-TKA plus random assignment to either a telehealth-based physical activity behavior change intervention or control group.

Main outcome measures: Performance-based (timed Up-and-Go [TUG], 30-second sit-to-stand) and patient-reported measures (Western Ontario and McMaster Universities Osteoarthritis Index, Veterans RAND 12-Item Health Survey [VR-12]) were assessed at rehabilitation discharge (14wk post-TKA). Physical activity was measured using thigh-mounted accelerometry 38 weeks post-TKA. Relationships between participant characteristics (age, sex, body mass index, group assignment), functional capacity at discharge, and long-term physical activity outcomes (average daily step count and peak walking cadence) were evaluated using single- and multiple-variable linear and logistic regressions.

Results: Univariate analyses: TUG time (r=-0.33, P=.002) and VR-12 physical health subscore (r=0.23, P=.036) were correlated with average daily step count at week 38. TUG time (r=-0.31, P=.006) was correlated with peak walking cadence. Multivariate analyses: multiple linear regression controlling for age, sex, and body mass index identified TUG (B=-301.25, P=.039) and VR-12 physical health (B=93.1, P=.049) as predictors of daily step count. TUG time (B=-1.5, P=.012) and assignment to physical activity behavior change intervention (B=13.7, P<.001) predicted peak walking cadence. No significant predictors of attaining a 7500 steps per day threshold were identified.

Conclusions: Functional capacity at discharge is related to physical activity characteristics 38 weeks post-TKA. Although behavior change interventions are needed to address physical activity deficits postoperatively, the link between functional capacity and activity suggests additional need to address functional capacity limitations during TKA rehabilitation.