A twelve year follow-up study on osteoarthritis of the knee in the general population : an epidemiological study of classification criteria, risk factors and prognostic factors

Criteria to diagnose the disease or assess the outcome need to be considered in every epidemiological study . The criteria are needed to classify participants as those having the disease or outcome and those who have not. Classification criteria are not always uniformly accepted and commonly more than one combination of criteria is used. The use of different classification criteria can lead to different study results and makes the comparison of different studies more difficult. Moreover, if nondifferential misclassi:fication occurs, the strength of an association between a putative risk factor and a disease is reduced as well as the power to detect an association. This methodological issue is discussed in more detail in this thesis with the aim of highlighting the consequences of this misclassification. Qassification criteria of knee osteoarthritis used in epidemiological research have almost always been based on radiographs. The criteria described by Kellgren and Lawrence have been used most commonly and were recommended for epidemiological studies at two international conferences (1,2,3). However, it was realized that these criteria should be validated and related to physical signs and symptoms (2). In this thesis the results of a study on the relationship of findings from the medical history, physical examination and serum analysis with radiographic osteoarthritis are presented. The aim of this study was to assess whether it was necessary to take a radiograph to diagnose radiographic osteoarthritis or whether it could be predicted reliably from the medical history, physical examination and serum analysis.