Association of daily walking with the risk of total knee replacement over 5 years: an observational study
H. Master Osteoarthritis and Cartilage VOLUME 26, SUPPLEMENT 1, S237-S238, APRIL 01, 2018
Purpose: The presence of functional limitation, such as difficulty getting up from a chair or out of bed, is a reason adults elect for a total knee replacement (TKR), the definitive treatment for end-stage knee osteoarthritis (OA). Regular participation in physical activity, such as walking ≥6000 steps/day, reduces the risk of functional limitation in people with knee OA. However, it is not known whether walking more and in particular walking ≥6000 steps/day are associated with less risk of TKR. Moreover, given that functional limitation is more common in older (≥65 years) versus younger (<65 years) adults, it is not known whether the association of daily walking with TKR may be different for older versus younger adults. Therefore, the purpose of our study was to determine the association of daily walking and risk of TKR over 5 years. We also separately investigated this association in older and younger adults with or at high risk of knee OA to identify to whom daily walking may be most important for reducing the risk of TKR.
Methods: Using data from the Osteoarthritis Initiative (OAI), we included participants who did not have TKR at or before the 48-month follow-up visit, which we considered our study baseline. Physical activity was measured with an accelerometer (Actigraph GT1M) worn during waking hours over the right hip during the baseline and quantified as steps/day. Time to TKR was quantified in months from the baseline visit date to the date of TKR through the 108-month OAI follow-up visit, i.e., 5 years later. The date for TKR was confirmed through adjudicated medical records whenever it was available during the course of OAI study. Participants without TKR at the 5-year follow-up were censored. Death and loss to follow-up in those without a TKR were considered competing events to TKR when they occurred between baseline and the 5-year follow-up. Hazard ratios (HR) with 95% confidence intervals (CI) were calculated from the Fine and Gray sub-distribution hazard model to assess the strength of the association between daily walking and risk of TKR in presence of competing events while adjusting for potential confounders (baseline age, BMI, sex, race, education, comorbidities, frequent knee pain, previous knee injuries or surgeries, and radiographic OA status). Daily walking was quantified as a continuous (i.e., per 1000 steps/day) and a categorical (< or ≥6000 steps/day) exposure measure in separate models. To examine if the association for daily walking and risk of TKR may be different by age groups, we performed subgroup analyses stratified by older (≥65 years) and younger (<65 years) adults.
Results: Of the 1816 participants without TKR at baseline and who wore the monitor for >4 days (age [mean ± sd] 65.0 ± 9.1 years, BMI [mean ± sd] 28.4 ± 4.8 kg/m2, 55% female), 108 (6%) participants had TKR over 5 years. There was no significant association between daily walking (i.e., either continuous or dichotomous measures) and risk of TKR over 5 years in the overall sample or in younger adults (table). However, older adults were 12% less likely to have TKR for each additional 1000 steps/day walked (adjusted HR 0.88, 95% CI [0.79–0.99]). Moreover, older adults who walked > 6000 steps/day were 52% less likely to have TKR (adjusted HR 0.48, 95% CI [0.26–0.89]) compared to people who walked <6000 steps/day (table).
Conclusions: Taking more steps/day and particularly walking >6000 steps/day may moderately reduce the risk for TKR in older (>65 years), but not younger (<65 years) adults. Our findings highlight the potential benefit of walking for older adults with or at risk of knee OA. A moderate reduction in risk of TKR may be an added benefit of walking more for older adults with or at risk of knee OA.
