Primary total knee replacement leads to an increase in physical activity but no changes in overall time of sedentary behaviour: a retrospective cohort study using an accelerometer

Introduction There is no consensus between patient-reported subjective scores and objectively measured physical activity (PA) behaviour after total knee arthroplasty (TKA). The aim of this study was to understand the volume and pattern of physical activity and daily energy consumption after total knee arthroplasty for osteoarthritis. Method Physical activity patterns of 36 patients (31 female, 5 male) with an average age of 67.3 +/- 6.7 (50-81) years and end-stage gonarthrosis were investigated using an accelerometer (ActiCal) for seven consecutive days prior to and six months after total knee arthroplasty. Knee Society scores, Oxford knee scores, range of motion, and muscle strength around knee were also recorded. Results Sedentary behaviour did not change after total knee arthroplasty (p = 0.975). Increases in light physical activity time (p = 0.005) and moderate-vigorous physical activity time (p = 0.006) were found significant. In the post-operative period, light PA awake time increased 25% and moderate-vigorous PA awake time increased four times compared with the pre-operative value. In addition, a significant increase was observed in the amount of daily energy expenditure after TKA (p = 0.001). The subjective functional scores were increased in the post-operative period compared with baseline values (p < 0.001). While a significant increase in knee flexion angle was found after TKA (p = 0.01), there was no increase in muscle strength around the knee (p = 0.096). Conclusion Accumulation patterns of activity evaluated by using an accelerometer objectively can give a new insight to realize the behavioral changes after total knee arthroplasty. Daily life style changes can be encouraged by means of objective evaluations.