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Osteoarthritis (OA) is defined as boney inflammation of a joint or joints. OA is the most common form of arthritis in the United States and Europe. Given the prolonged life expectancy in the United States and the aging of the “baby boomer” cohort, the prevalence of OA is expected to increase further. Although the precise cause of OA is unknown, it is likely that multiple causes and many factors influence disease expression.

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Epidemiological and observational studies provide important clues to the mechanisms by which OA develops and progresses and, thus, identify risk factors that might comprise intervention targets for OA prevention and management.

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Age and Gender

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Advanced age is the strongest risk factor for the development of OA across all anatomical sites. Prevalence rates for both radiographic OA and, to a lesser extent, symptomatic OA (moderate or severe) increase with age, with a steep rise after the age of 50 years in men and age of 40 years in women. Radiographic OA of the hand is the most prevalent form, followed by knee, then hip. It is not unusual to find incidental radiographic OA in an otherwise asymptomatic older patient. Symptomatic OA of the knee and hip OA are the most prevalent in both sexes, with symptomatic involvement of the hands increasing in women beginning at menopause.

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Changes in the hormonal milieu are thought to contribute to OA pathogenesis and are supported by reports of reduced risk of incident hip OA in women receiving hormonal therapy. However, estrogen/progestin replacement has not been proven to reduce the chance of developing knee pain or disability in women with knee symptoms. Whether estrogen or hormonal therapy is beneficial with regard to OA thus remains controversial and further emphasizes that OA symptom and disease pathogenesis likely develop through different mechanisms.

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Joint Trauma and Nontraumatic Biomechanical Factors

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Joint trauma of a severity that causes swelling and discomfort lasting several days or longer has been shown to increase risk of knee OA. Prior surgical removal of a meniscus in the knee is also a predisposing factor to OA of the knee. Meniscectomy is associated with a sixfold increase in risk for development of radiographic OA, even if limited rather than total meniscal resection is employed. Obesity, female sex, and preexisting early-stage OA of the knee and concurrent hand OA compound the risks incurred following meniscectomy. Occupation- and sports-related repetitive injury and physical trauma contribute to the development of OA of specific joints (e.g., knees in soccer players, elbows of baseball pitchers, and upper limbs of air hammer operators) and account for occurrence at sites not usually affected by OA. Although the prevalence of knee OA is greater in adults who have engaged in occupations that require repetitive bending and strenuous activities, an association with intense exercise or recreational physical activity such as jogging has not been proven. Joint malalignment and varus–valgus laxity...

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