March 21, 2012 — The incidence and progression of radiographic knee arthritis appears to be lower than previously reported, according to the findings of a new, community-based cohort study.
K. M. Leyland, from the National Institute for Health and Research Musculoskeletal Biomedical Research Unit, University of Oxford, United Kingdom, and colleagues published their findings in an article published online March 15 in Arthritis & Rheumatism.
The authors note that the economic burden of osteoarthritis is increasing, making it more important to establish its natural course. "Because of the increasing health burden due to the ageing population and a projected lifetime risk of developing symptomatic knee [osteoarthritis] of 45%, there is an urgent need to understand the natural course of knee osteoarthritis in order to target preventative therapies and reduce known risk factors for both incidence and progression," the authors write.
Among the 561 women who met the inclusion criteria, 52.2% remained free of radiographic knee osteoarthritis, as categorized by a Kellgren-Lawrence grade of 0, during the 14 years of the study, whereas 38.6% of women had confirmed knee osteoarthritis (Kellgren-Lawrence grade ≥ 2) by year 15 compared with 9.5% at baseline. Between baseline and year 15, the annual cumulative incidence (change in the Kellgren-Lawrence grade from 0 - 1 to 2 or more) of knee osteoarthritis was 2.3%, the annual cumulative progression (a 1-grade increase in the Kellgren-Lawrence grade for patients with an initial score of 2 or more) was 2.8%, and the annual cumulative worsening (any increase in the Kellgren-Lawrence grade irrespective of the initial score) was 3.0%.
The authors analyzed data from women in the Chingford Study, a prospective, population-based longitudinal study of osteoporosis and osteoarthritis. The authors included women who had complete demographic data recorded at baseline and who underwent X-ray examination at baseline and at 5, 10, and 15 years, and excluded women who had incomplete data or who had rheumatoid arthritis.
Patients younger than 50 years had a significantly lower incidence of knee osteoarthritis than those older than 60 years (26.0% vs 42.2%; P < .01). In addition, patients with a baseline Kellgren-Lawrence grade of 1 had 4.5-fold higher odds (95% confidence interval [CI], 2.7 - 7.4) of developing Kellgren-Lawrence grade 2 or higher knee osteoarthritis than those with a baseline score of 0 (P < .001).
The limitations of the study included the effect of radiographic views, the scoring method, the inclusion of only white women, and the loss of patients to follow-up. The patients lost to follow-up were typically similar to those included in the study, although patients lost to follow-up were generally older (56.0 years [95% CI, 50.0 - 61.0 years] vs 53.0 [95% CI, 48.0 - 58.0]; P < .0001), more likely to be current smokers (27.4% vs 19.3%; P = .007), and more likely to have knee pain (33.5% vs 28.5%; P = .052).
The authors note that the rates of progression and worsening they report do not align with those previously reported. "Annual rates of knee progression (2.8%) and worsening (3.0%) between baseline and year 15 were found to be slightly lower than those observed in other community-based cohorts which varied between 3.5 and 8.0% for progression and 4.4% for worsening," the authors write. "The slightly lower rates found in Chingford are likely a consequence of both the relatively young age of the cohort at the start of the study and the length of the study."
The authors have disclosed no relevant financial relationships.
Arthritis Rheum. Published online March 15, 2012. Abstract
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