Validity and reliability of three definitions of hip osteoarthritis: cross sectional and longitudinal approach

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Abstract
Objectives: To compare the reliability and validity in a large open population of three frequently used radiological definitions of hip osteoarthritis (OA): Kellgren and Lawrence grade, minimal joint space (MJS), and Croft grade; and to investigate whether the validity of the three definitions of hip OA is sex dependent. Methods: Subjects from the Rotterdam study (aged ⩾55 years, n = 3585) were evaluated. The inter-rater reliability was tested in a random set of 148 x rays. The validity was expressed as the ability to identify patients who show clinical symptoms of hip OA (construct validity) and as the ability to predict total hip replacement (THR) at follow up (predictive validity). Results: Inter-rater reliability was similar for the Kellgren and Lawrence grade and MJS (κ statistics 0.68 and 0.62, respectively) but lower for Croft’s grade (κ statistic, 0.51). The Kellgren and Lawrence grade and MJS showed the strongest associations with clinical symptoms of hip OA. Sex appeared to be an effect modifier for Kellgren and Lawrence and MJS definitions, women showing a stronger association between grading and symptoms than men. However, the sex dependency was attributed to differences in height between women and men. The Kellgren and Lawrence grade showed the highest predictive value for THR at follow up. Conclusions: Based on these findings, Kellgren and Lawrence still appears to be a useful OA definition for epidemiological studies focusing on the presence of hip OA.