Prevalence of radiographic osteoarthritis--it all depends on your point of view.

OBJECTIVES Knee pain and disability in older people may occur in the apparent absence of radiographic osteoarthritis. However, the view chosen to define radiographic osteoarthritis may be critical. We have investigated the prevalence and compartmental distribution of radiographic osteoarthritis in people with knee pain using different combinations of three separate radiographic views. METHODS We performed a population-based study of 819 adults aged 50 yr and over with knee pain (part of the Clinical Assessment Study - Knee [CAS(K)]). Three radiographic views were obtained: weight-bearing posteroanterior (PA) semiflexed/metatarsophalangeal view; supine skyline; and supine lateral. RESULTS Complete data for all three views were available on 777 subjects. The distribution of compartmental radiographic osteoarthritis was 314 (40%) combined tibiofemoral/patellofemoral, 186 (24%) isolated patellofemoral, 31 (4%) isolated tibiofemoral and 246 (32%) normal. Hence, the overall prevalence of radiographic osteoarthritis was 531/777 (68.3%) in this symptomatic population. Using a PA view alone (reflecting tibiofemoral osteoarthritis only) would identify 56.7% of the 531, whilst the addition of a skyline or lateral view increased this to 87.0%. When using both skyline and lateral views in addition to the PA view, 98.7% cases of radiographic osteoarthritis were identified. In addition to prevalence, compartmental distribution altered markedly when different combinations of views were used. CONCLUSIONS Multiple views detect more radiographic osteoarthritis than single views alone. When different combinations of views are used, the prevalence and compartmental distribution of osteoarthritis changes and this may alter the accepted relationship, or lack of it, between symptoms and radiographic change.