The natural history of radiographic knee osteoarthritis: A fourteen-year population-based cohort study

Objective To establish the natural history of radiographic knee osteoarthritis (OA) over 14 years in a community-based cohort. Methods We examined women from the Chingford Women's Study, a community-based cohort followed up for more than 14 years. We selected women for whom bilateral radiographs of the knees (with the legs in full extension) were obtained at approximately 5-year intervals. Radiographs were scored for OA in a blinded manner, using Kellgren/Lawrence (K/L) grades. Descriptive statistics and odds ratios (ORs) were used to compare the incidence, worsening, and progression of radiographic knee OA. Results A complete radiography series was available for 561 of the original 1,003 subjects enrolled in the study. The median age of these subjects at baseline was 53 years (interquartile range 4858 years). At baseline, 13.7% of the subjects had radiographic knee OA (K/L grade =2) in at least one knee, and the prevalence increased to 47.8% by year 15. The annual cumulative incidence of radiographic knee OA was 2.3% between baseline and year 15. The annual rates of disease progression and worsening between baseline and year 15 were 2.8% and 3.0%, respectively. Subjects with a K/L grade of 1 at baseline were more likely to experience worsening by year 15 compared with subjects with a baseline grade of 0 (OR 4.5, 95% confidence interval 2.77.4). Conclusion This is the longest natural history study of radiographic knee OA to date. The results showed relatively low rates for the incidence and progression of radiographic knee OA; more than half of all subjects had no radiographic evidence of knee OA over a 15-year period of time. Subjects with a baseline K/L grade of 1 were more likely than subjects with other baseline K/L grades to experience worsening of knee OA.