Novel approach to estimate osteoarthritis progression: use of the reliable change index in the evaluation of joint space loss.

peer reviewedObjective: 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. Methods: 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. Results: 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. Conclusion: 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. Significance and Innovations: The aim of this research was to assess the effectiveness of the reliable change index as a novel approach to estimating OA progression, to date no studies have been identified that apply the RC index methodology within musculoskeletal research. Interestingly, the reliable change index provides a useful method to identify change in joint space width, removing many of the apparent changes that are likely to be due to measurement error. When compared to crude differences in joint space width measurements, implementation of the reliable change index dramatically reduced the proportions of study participants that were identified as having statically reliable change. This method appears to be useful for assessing change in JSW clinical and research settings from radiographs, and may have wider applications to other imaging modalities