The incidence and natural history of knee osteoarthritis in the elderly. The Framingham Osteoarthritis Study.

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To determine the incidence of radiographic knee osteoarthritis (OA) and symptomatic OA (symptoms plus radiographic OA), as well as the rate of progression of preexisting radiographic OA in a population-based sample of elderly persons. Framingham Osteoarthritis Study subjects who had knee radiographs and had answered questions about knee symptoms in 1983-1985 were reexamined in 1992-1993 (mean 8.1-year interval) using the same protocol. Subjects were defined as having new (incident) radiographic OA if they developed grade > or = 2 OA (at least definite osteophytes or definite joint space narrowing). New symptomatic OA was present if subjects developed a combination of knee symptoms and grade > or = 2 OA. Progressive OA was diagnosed when radiographs showing grade 2 disease at baseline showed grade > or = 3 disease on followup. Of 1,438 participants in the original study, 387 (26.9%) died prior to followup. Of the 1,051 surviving subjects, 869 (82.7%) participated in the followup study (mean +/- SD age 70.8 +/- 5.0 at baseline). Rates of incident disease were 1.7 times higher in women than in men (95% confidence interval [CI] 1.0-2.7), and progressive disease occurred slightly more often in women (relative risk = 1.4; 95% CI 0.8-2.5) but rates did not vary by age in this sample. Among women, approximately 2% per year developed incident radiographic disease, 1% per year developed symptomatic knee OA, and about 4% per year experienced progressive knee OA. In elderly persons, the new onset of knee OA is frequent and is more common in women than men. However, among the elderly, age may not affect new disease occurrence or progression.