To investigate whether knowledge of the sequence of radiographs impacts inter- and intraobserver reproducibility and sensitivity to change for measuring joint space width (JSW) in patients with knee osteoarthritis (OA).
A cohort of 70 postmenopausal women with radiologic knee OA was assessed through the measurement of knee radiographs acquired in the semiflexed posteroanterior view, using a positioning frame and fluoroscopy, at baseline and 48 months later. Paired readings of radiographs were made using landmarks at baseline by 2 independent observers unblinded to sequence and blinded to sequence. Intra- and interobserver reproducibility was assessed on JSW measurements at baseline and 4 years later and on the longitudinal difference (joint space narrowing [JSN]), using intraclass correlation coefficient (ICC) and Bland and Altman methods. The sensitivity to change was assessed through standardized response means (SRMs).
For JSW and JSN and with both methods, ICCs were high for the intra- and interobserver reproducibility (0.90-0.99 for JSW and 0.77-0.89 for JSN). For the Bland-Altman method, the mean difference was close to 0, with no bias for both observers and methods. The SRMs ranged from 0.38 to 0.48. All of the results were numerically in favor of measuring with knowledge of time sequence, but without a statistically significant difference between the methods.
Intra- and interobserver reproducibility was high with or without blinding of the radiograph sequence. Reading with knowledge of time sequence using baseline landmarks tended to improve sensitivity. Therefore, in longitudinal studies of OA radiographs can be read unblinded to sequence.