LOW-LEVEL INCREASES IN SERUM C-REACTIVE PROTEIN ARE PRESENT IN EARLY OSTEOARTHRITIS OF THE KNEE AND PREDICT PROGRESSIVE DISEASE

Objective. To examine the role of low-grade inflammation in the etiolo gy and progression of early osteoarthritis (OA) of the knee. Methods. We used a new, high-sensitivity, automated monoclonal antibody immunoa ssay for the classic acute-phase protein, C-reactive protein (CRP), in serum, Anteroposterior radiographs of the knee with weight bearing we re obtained on 845 women (ages 44-67) on entry into a population-based study of OA in Chingford, North London, In those defined radiological ly as ''cases,'' the knee radiographs were repeated after 4 years. Res ults. Levels of CRP were higher in 105 women with knee OA defined radi ologically as Kellgren-Lawrence grade 2+ (median 2.4 mg/liter, interqu artile range [IQR] 1.0-5.1), compared with 740 women without OA (media n 0.7 mg/liter, IQR 0.3-1.8) (P < 0.001), Median levels of CRP were hi gher in the 31 women whose disease progressed at least 1 Kellgren-Lawr ence grade (median 2.6 mg/liter, IQR 1.9-4.6), compared with the 39 wh ose disease did not (median 1.3 mg/liter, IQR 0.6-2.4) (P = 0.006), Th e significance of these differences persisted after adjustment for age , weight, height, smoking, knee pain, or injury, Classifying disease b y the presence of joint space narrowing or osteophytes alone produced similar results. Conclusion. CRP levels are modestly but significantly increased in women with early knee OA, and higher levels predict thos e whose disease will progress over 4 years, suggesting that low-grade inflammation may be a significant aspect of early OA and may be amenab le to therapeutic intervention and secondary prevention.