To estimate annual incidence rates (IRs) of knee symptoms and 4 knee osteoarthritis (OA) outcomes (radiographic, symptomatic, severe radiographic, and severe symptomatic), overall and stratified by sociodemographic characteristics and knee OA risk factors.
We analyzed baseline (1991-1997) and first followup (1999-2003) data (n = 1,518) from the Johnston County Osteoarthritis Project. Participants were African American and white adults, ages ≥45 years, living in Johnston County, North Carolina, US. Knee symptoms were pain, aching, or stiffness on most days in a knee. Radiographic OA was Kellgren/Lawrence grade ≤2 (severe radiographic ≥3) in at least 1 knee. Symptomatic OA was defined as symptoms in a radiographically affected knee; severe symptomatic OA was defined as severe symptoms and severe radiographic OA.
The median followup time was 5.5 years. Average annual IRs were 6% for symptoms, 3% for radiographic OA, 2% for symptomatic OA, 2% for severe radiographic OA, and 0.8% for severe symptomatic OA. Across outcomes, IRs were highest among those with the following baseline characteristics: age ≥75 years, obese, a history of knee injury, or an annual household income ≤$15,000.
The annual onset of knee symptoms and 4 OA outcomes in Johnston County was high. This may preview the future of knee OA in the US and underscores the urgency of clinical and public health collaborations that reduce risk factors for, and manage the impact of, these outcomes. Inexpensive, convenient, and proven strategies (e.g., physical activity, self-management education courses) complement clinical care and can reduce pain and improve quality of life for people with arthritis.