Epidemiology

OA is the most common form of arthritis, affecting an estimated 302 million people globally, and 30.8 million adults in the US.[7][8]

OA is more common in women than in men, with incidence increasing sharply around age 50 years, and levelling off after age 70 years.[9][10][11]​​

In the US, the incidence rate of knee OA is between 164 per 100,000 patient-years and 240 per 100,000 patient-years.[12][13] The incidence of hand OA ranges from 2% to 4% per year.[1] The incidence rate of hip OA is between 47 per 100,000 patient-years and 88 per 100,000 patient-years.[12][13]

The Johnston County OA Project reported annual incidence rates as 37 per 1000 person-years for hip symptoms, 24 per 1000 person-years for radiographic hip OA, 13 per 1000 person-years for symptomatic hip OA, and 2.9 per 1000 person-years for severe radiographic hip OA in adults of 45 years and above followed for a median of 5.5 years.[14]​ 

The Framingham Osteoarthritis Study showed that the prevalence of radiographic OA increases with age from 27% in people younger than 60 years to 44% in those older than 70 years.[15] In addition, the Framingham study found that 2% of women (mean age 71 years) develop radiographic knee OA every year, and 1% of women develop symptomatic knee OA every year.[16] Rates of incident knee OA were 1.7 times higher in women than in men.[16] A subsequent Framingham Osteoarthritis Study publication reported that the prevalence of radiographic hip OA was 19.6% and that of symptomatic hip OA was 4.2% (in a population of 978 people over a 5-year period). Overall, men had significantly higher prevalence of radiographic hip OA compared with women, but no difference was seen between sexes for symptomatic hip OA.[17]

The Beijing Osteoarthritis Study reported a very low crude prevalence of radiographic hip OA in Chinese people aged 60-89 years (approximately 1% in both men and women); the prevalence of knee OA in Chinese women was higher when compared with US cohorts.[18][19]

One population study in Spain concluded that rates of knee and hip OA increased continually with age, with the highest female-to-male ratio at age 70 to 75 years. However, the risk of OA of the hand peaked at 60 to 65 years, with the highest female-to-male ratio at 50 to 55 years.[10]

There is also evidence to suggest that osteoarthritis is more prevalent in low income and lower-middle income countries, with an estimated one in six of study participants reported to have OA.[20]

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