Objective: Little is known regarding what difference in functional performance measures is significant in individuals with chronic medical disease. Our objective was to examine the important differences in gait speed in adults with radiographic knee osteoarthritis. Methods: Functional performance was measured by gait speed using 20-meter and 400-meter walk tests performed at a self-selected usual pace among adults with radiographic knee osteoarthritis participating in the Osteoarthritis Initiative at baseline and 2 years later. Both distribution-based methods and anchor-based methods were used to calculate the important differences in gait speed. Anchor-based methods used the chair stand rate and self-reported function to estimate gait speed differences related to physical function. Results: We included 2,527 participants with radiographic knee osteoarthritis. Distribution-based important difference estimates for the 20-meter walk ranged from 4.1 to 6.4 meters/minute and 400-meter walk estimates ranged from 2.9 to 6.5 meters/minute. Prevalent (cross-sectional) anchor-based estimates for the 20-meter walk ranged from 5.4 to 6.9 meters/minute and for the 400-meter walk ranged from 3.0 to 6.9 meters/minute. Longitudinal anchor-based estimates were deemed unreliable. Combining distribution-based with prevalent anchor-based methods showed that an important gait speed difference for the 20-meter walk is between 4.1 and 6.9 meters/minute and for the 400-meter walk is between 2.9 and 6.9 meters/minute. Conclusion: Our results found that the important difference in gait speed for the 20-meter walk and the 400-meter walk is consistent with important difference estimates for older adult populations. These findings can provide benchmarks for assessing and understanding functional performance outcomes when comparing exposure groups and can be used in designing future studies targeting adults with radiographic knee osteoarthritis.
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