| Summary: | Osteoarthritis-related changes in joint space measurements over time are small and sensitive to measurement error. The Reliable Change (RC) index determines whether the magnitude of change observed in an individual can be attributed to true change. This study aimed to examine the RC index as a novel approach to estimating osteoarthritis progression.Data from 167 men and 392 women with knee osteoarthritis (diagnosed using the ACR criteria) randomised to the placebo arm of the 3-year Strontium Ranelate Efficacy in Knee Osteoarthritis triAl (SEKOIA) and assessed annually. The RC index was used to determine whether the magnitude of change in joint space width (JSW) on radiographs between study years was likely to be true or due to measurement error.Between consecutive years, 57 to 69% of participants had an apparent (change less than 0) decrease in JSW, while 31% to 43% of participants had annual changes indicating improvement in JSW. The RC index identified decreases in JSW in only 6.0% between baseline and year 1 and 4.5% between the remaining study years. The apparent increases in JSW were almost eliminated between baseline and year 1, and between years 1 and 2 only 1.3% had a statistically significant increase, dropping to 0.9% between years 2 and 3.The RC index provides a method to identify change in JSW, removing many apparent changes that are likely to be due to measurement error. This method appears to be useful for assessing change in JSW in clinical and research settings from radiographs. This article is protected by copyright. All rights reserved.
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