Factors associated with physical activity following total knee arthroplasty for knee osteoarthritis: a longitudinal study

Background: To objectively measure physical activity by intensity before and 6 months after total knee arthroplasty (TKA) using accelerometers and to determine factors associated with physical activity levels at 6 months after TKA. Methods A total of 82 patients (mean age 74.5 ± 6.4 years) with moderate-to-severe knee osteoarthritis (OA) underwent evaluation of knee function, including knee flexion/extension range-of-motion, knee-extension muscle strength, and knee pain; the timed up-and-go test; and physical activity measurements using an accelerometer. To clarify the factors associated with physical activity at 6 months after TKA, hierarchical multiple regression analysis adjusted for age, sex, body mass index, and presence of diabetes mellitus was performed. Results A higher average daily step count at 6 months after TKA was significantly associated with greater preoperative knee-extension muscle strength on the operated side ( β  = 0.155, p = 0.028) and a higher preoperative average daily step count ( β  = 0.834, p < 0.001). Similarly, longer light-intensity physical activity (LPA) time at 6 months after TKA was significantly associated with greater preoperative knee-extension muscle strength on the operated side ( β  = 0.151, p = 0.037) and longer preoperative LPA time ( β  = 0.818, p < 0.001). Furthermore, longer moderate-to-vigorous-intensity physical activity (MVPA) time was significantly associated with longer preoperative MVPA time ( β  = 0.723, p < 0.001). Conclusion Greater preoperative knee-extension muscle strength on the operated side and a higher preoperative average daily step count were associated with a higher average daily step count at 6 months after TKA. In addition, the greater the preoperative knee-extension muscle strength on the operated side and the longer the preoperative LPA time, the longer the LPA time at 6 months after TKA. Furthermore, the longer the preoperative MVPA time, the longer the MVPA time at 6 months after TKA.