Perceptual variation in categorizing individual peripheral joints for the presence or absence of osteoarthritis using a standard homunculus: Observations based on an Australian twin registry study of osteoarthritis

The clinical diagnosis of osteoarthritis in the peripheral skeleton is dependent on the skilled examination of several features characteristic of the condition. However, we have previously observed that even highly experienced rheumatologists in Australia and Canada may not completely agree on the clinical examination in individuals with osteoarthritis (OA), rheumatoid arthritis, ankylosing spondylitis, fibromyalgia, scleroderma and painful shoulder. Methods: The current study was part of a multifaceted diagnostics protocol, evaluating methodologic issues, in the conduct of genetic research in OA. From a cohort of 118 twin pairs, registered with the Australian Twins Registry (ATR), standard clinical examinations were performed on 74 complete and 11 incomplete pairs of twins over the age of 50. The pairs were selected both to represent 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 two pairs (NB/AK or NB/KM) of consultant rheumatologists, blind to one another's assessments. Each rheumatologist separately assessed 68 peripheral joints for the presence or absence of OA. The observations were made without reference to any radiographic or serologic information and were recorded on a standard homunculus. Results: Inter-rarer agreement was different for different anatomic areas, and was different for the two pairs of rheumatologists. Inter-rater agreement was as follows: Actual observed agreement = 0.70 to 1.00; adjusted kappa statistic = 0.39 to 1.00. In general, adjusted kappa values were higher in non-target joints for OA because of a high negative prevalence index. Agreement was also high in principal target joints for OA: D1P, P1P, 1st CMC, Hip and Knee. Assessment of the 1st MTP joint was problematic. Conclusions: Although clinical agreement was not perfect, we conclude that for genetic epidemiology purposes, while duplicate assessments may be advantageous, it is possible for subjects to be examined accurately by a single experienced rheumatologist. However, for less experienced assessors, independent examinations should be made by at least two assessors and either a consensus reached on disparate examinations or an algorithm developed to adjudicate any discrepancies.