Objective: The objective of this work was to compare the measurement properties of three categorical X-ray scoring methods for hip osteoarthritis (OA).
Methods: In data obtained from trials and cohorts, radiographs were evaluated using the Kellgren and Lawrence (KL) grading system, the Osteoarthritis Research Society International (OARSI) joint space narrowing score, and quantitative measurement of joint space width (JSW), analysed as a categorical variable according to Croft and Lane's cutoffs (1.5, 2.5 and 3mm). Predictive validity was assessed through logistic regression to predict joint replacement in one database. Construct validity was assessed through logistic regression between pain and function and X-ray stages. Inter-observer and intra-observer reliability were assessed in 50 subjects by weighted kappa. Sensitivity to change was assessed in 50 patients over a 24-month interval, by standardized response mean (SRM).
Results: Radiographs were available from one trial and two cohorts (1404 X-rays). All three methods predicted joint replacement in the trial. Correlation with clinical parameters was low for the three scoring methods, except for the single community-based cohort. Interrater reliability was higher for categorical JSW (kappa, 0.71 vs 0.44 and 0.47 for KL and OARSI, respectively). Intrarater reliability was similar for the three methods (0.79 vs 0.69 and 0.81). Sensitivity to change was higher for categorical JSW than KL and OARSI (SRM, 0.77 vs 0.28 and 0.35).
Conclusion: Categorical JSW has similar validity and higher sensitivity to change than the other categorical scoring techniques in hip OA. These results indicate categorical JSW may be the preferred method to evaluate structural severity in hip OA clinical trials.