Functional capacity at rehabilitation discharge predicts physical activity characteristics twenty-four 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 following total knee arthroplasty (TKA).

Design: Secondary analysis of an RCT.

Setting: Veterans Affairs Medical Center.

Participants: 87 U.S. military Veterans (age: 67±7 years, 87% male).

Interventions: 12-week rehabilitation beginning two weeks post-TKA plus random assignment to either a telehealth-based physical activity behavior change intervention (PABC) 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 (WOMAC), Veterans Rand 12-Item Health Survey (VR12)) were assessed at rehabilitation discharge (14-weeks post-TKA). Physical activity was measured using thigh-mounted accelerometry 38 weeks post-TKA. Relationships between participant characteristics (age, sex, BMI, 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=0.002) and VR12 physical health subscore (r= 0.23, p=0.036) were correlated to average daily step count at week 38. TUG time (r= -0.31, p=0.006) was correlated to peak walking cadence. Multivariate analyses: Multiple linear regression controlling for age, sex, and BMI identified TUG (B= -301.25, p=0.039) and VR12 physical health (B= 93.1; p=0.049) as predictors of daily step count. TUG time (B= -1.5, p=0.012) and assignment to PABC intervention (B= 13.7, p<0.001) predicted peak walking cadence. No significant predictors of attaining a 7500 steps/day threshold were identified.

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