Taking X-rays of the semi-flexed knee is the most accurate way of evaluating structural damage in patients with knee osteoarthritis according to results presented today at EULAR 2007, the Annual European Congress of Rheumatology in Barcelona, Spain.
In knee OA, there are several radiographic views from which structural damage can be identified and several tools from which damage to the knee can be assessed. Radiographic measurements and associated data were gathered from 1,759 radiographs of fully extended (EV) and semi-flexed (SF) knees and analysed using semi-quantitative scores: the Kellgren Lawrence (KL) scale, and the Osteoarthritis Research Society International (OARSI) joint space width (JSW) scale. They were also assessed using precise measurement of JSW in millimeters.
Results of this study, undertaken as part of collaboration between the Outcome Measures in Rheumatology initiative and the Osteoarthritis Research Society International (OMERACT-OARSI), were analysed with the aim of comparing different radiographic views and stratifying techniques for accuracy in indicating progress of structural damage in knee OA.
The highest inter-rater reliability (see note to Editors) was found in the precise measurement of JSW in extended knees (kappa 0.86 (0.76-0.96) compared to kappa 0.56 (0.38-0.73) in using the Kellgren Lawrence scale and 0.48 (0.32-0.64) for using the OARSI scale). Intra-rater reliability was also high for categorical JSW in extended and semi-flexed views, which means these measures are highly reproducible across readings and across readers. Sensitivity to change was highest for categorical JSW in the semi-flexed knee with a standardized response mean of 0.49, compared to 0.22 and 0.34 respectively for semi-flexed knee views. This means measurement of JSW is more able to detect change over time or after treatment than the other techniques.
Study author Dr Laure Gossec, of Cochin Hospital, Paris, commented, ?Measuring joint space width, in particular in the semi-flexed knee, has been shown to be the most reliable and responsive way to determine structural severity in knee OA trials as overall, reliability and responsiveness were higher for JSW (in particular on semi-flexed view) than for the other scoring techniques.?
Inter-observer reliability was assessed in 50 sample x-rays with the aim of assessing the degree of comparability between 2 physicians assessing the x-rays. Sensitivity to change was assessed in 50 sample x-rays with the aim of determining change over time of the diagnosed findings.
Construct validity (see note to Editors) was assessed through logistic regression and adjusted on age, race, sex and body mass index.