Perceptual variation in categorizing individuals according to American College of Rheumatology classification criteria for hand, knee, and hip osteoarthritis (OA): observations based on an Australian Twin Registry study of OA.

OBJECTIVE The American College of Rheumatology (ACR) classification criteria for osteoarthritis (OA) permit the categorization of individuals for hand, knee, and hip OA and are of defined sensitivity and specificity. They depend on both clinical and radiographic aspects of OA. The clinical diagnosis of OA in the peripheral skeleton is dependent on the skilled examination of several clinical features characteristic of the condition, while the interpretation of radiographs is a perceptual skill based on appreciating specific structural features on plain radiographs. We investigated the interrater reliability of the ACR classification criteria for OA when applied in a community based sample. METHODS The study was part of a multifaceted diagnostics protocol, evaluating methodologic issues, in the conduct of genetic research in OA. From a cohort of 118 pairs of twins registered with the Australian Twins Registry (ATR), standard clinical examinations of hands, knees, and hips were performed on 74 complete and 11 incomplete pairs of twins over age 50 years. The pairs were selected to represent both twin pairs who had previously self-reported a diagnosis of OA, as well as those who had not. Rheumatologists who performed the assessments were blind to the original self-report. All subjects were examined independently by one of 2 pairs (NB/AK or NB/KM) of consultant rheumatologists, blind to one another's assessments. Each rheumatologist separately assessed the hands, knees, and hips, rating them clinically by ACR criteria for OA. The observations were made without reference to any radiographic or serologic information. RESULTS Interrater agreement was different for the 3 different anatomic areas and was different for the 2 pairs of rheumatologists. The actual (observed) interrater agreements based on ACR clinical criteria were as follows: hand OA NB/AK = 0.92, NB/KM = 1.00; knee OA NB/AK = 0.94, NB/KM = 0.92; hip OA NB/AK = 0.98, NB/KM = 0.97. Interrater agreement based on ACR clinical criteria, as assessed by the adjusted kappa statistic, was as follows: hand OA NB/AK = 0.84, NB/KM = 1.00; knee OA NB/AK = 0.87, NB/KM = 0.84; hip OA NB/AK = 0.95, NB/KM = 0.93. CONCLUSION Since clinical agreement was extremely high in all 3 anatomic sites, and for both pairs of assessors, we conclude that for genetic epidemiology purposes, subjects can be examined by a single experienced rheumatologist using the ACR classification criteria.