Performance of distinct knee osteoarthritis classification criteria in the ELSA-Brasil musculoskeletal study

To compare the performance of different knee osteoarthritis (OA) classification criteria in a subsample of subjects of ELSA-Brasil Musculoskeletal cohort (ELSA-Brasil MSK) in comparison with the clinical-radiographic evaluation of an experienced rheumatologist.

A cross-sectional study of the diagnostic accuracy of different knee OA classification criteria: radiographic OA, symptomatic OA, clinical and clinical-radiographic criteria of the American College of Rheumatology (ACR), and the definition proposed by the National Institute for Health and Care Excellence (NICE), UK. The study also evaluated some alternative definitions of OA including a combination of criteria. In total, 250 subjects participated. Only one knee per subject was included. When both or none of the knees were affected, one knee was randomly selected for analysis. OA prevalence, sensitivity, specificity, positive and negative predictive values, and accuracy were presented (CI 95%; α = 5%).

The mean age was 56.1 years (SD = 8.7), 48.8% female, and 39.2% presented knee OA according to the rheumatologist. The sensitivity and the specificity of radiographic OA were 51% and 96.7%, respectively, while the NICE definition showed 57.0% and 76.3%, respectively. The other OA criteria showed good levels of specificity, but the levels of sensitivity were below 30%. Considering NICE and/or X-ray result in combination, the sensitivity increased (73.4%), while the specificity reduced slightly (73.0%) in relation to the original NICE definition.

Radiographic OA showed the best performance, followed by NICE definition, especially in combination with X-ray results.