Osteoarthritis (OA) is the most common joint disorder in the United States, affecting 10% of men and 13% of women aged 60 years or older. The prevalence of symptomatic knee OA is expected to rise due to aging and the obesity epidemic. OA is a multi-factorial condition influenced by age, gender, obesity, knee injury, joint use, bone density, muscle weakness, and joint laxity. Modifying these factors can reduce OA risk and prevent pain and disability. OA is associated with significant disability and is the most common reason for total hip and knee replacement. Epidemiological studies define OA pathologically, radiographically, or clinically, with radiographic grading being the standard. Radiographic OA is graded from 0 to 4, with higher grades indicating more severe disease. Prevalence of radiographic knee OA is 19.2% in the Framingham Study and 27.8% in the Johnston County Osteoarthritis Project. Radiographic hand OA is 27.2% in Framingham participants. Hip OA is less common than knee or hand OA. Symptomatic OA is defined by joint pain, and its prevalence varies by study. The cumulative incidence of OA is difficult to estimate due to competing risks. Systemic risk factors include age, gender, and hormones. Women are more likely to develop OA and experience more severe symptoms. Hormonal factors may play a role, but results from studies on estrogen are conflicting. Race/ethnicity also influences OA prevalence, with differences observed between Chinese and white populations. Genetic factors contribute to OA, with heritability estimated at 50-65%. Twin and family studies show a genetic influence on hand and hip OA. Genome-wide association studies have identified genetic variants associated with OA risk. Local risk factors include obesity, injury, and occupation. Obesity increases OA risk, especially in the knee. Knee injury is a strong risk factor, with meniscal damage and ligament injuries increasing OA risk. Occupation involving repetitive joint use is associated with higher OA risk. Dietary factors such as vitamin D and C are linked to OA risk. Low vitamin D levels are associated with increased knee OA risk, while low vitamin C intake is linked to OA progression. Selenium deficiency is associated with bone abnormalities, and low selenium levels are linked to increased knee OA risk. Mechanical factors such as knee alignment and limb length inequality also influence OA risk. Malalignment and limb length inequality are associated with increased OA risk. Laxity in the knee is another risk factor. Symptomatic OA is influenced by factors such as physical activity, knee injury, and trauma. Studies show that high physical activity levels may increase OA risk, but moderate activity does not. Symptomatic OA is more common in African Americans than in whites. In conclusion, OA is a complex condition with multiple risk factors. Understanding these factors can help in developing interventions and preventionOsteoarthritis (OA) is the most common joint disorder in the United States, affecting 10% of men and 13% of women aged 60 years or older. The prevalence of symptomatic knee OA is expected to rise due to aging and the obesity epidemic. OA is a multi-factorial condition influenced by age, gender, obesity, knee injury, joint use, bone density, muscle weakness, and joint laxity. Modifying these factors can reduce OA risk and prevent pain and disability. OA is associated with significant disability and is the most common reason for total hip and knee replacement. Epidemiological studies define OA pathologically, radiographically, or clinically, with radiographic grading being the standard. Radiographic OA is graded from 0 to 4, with higher grades indicating more severe disease. Prevalence of radiographic knee OA is 19.2% in the Framingham Study and 27.8% in the Johnston County Osteoarthritis Project. Radiographic hand OA is 27.2% in Framingham participants. Hip OA is less common than knee or hand OA. Symptomatic OA is defined by joint pain, and its prevalence varies by study. The cumulative incidence of OA is difficult to estimate due to competing risks. Systemic risk factors include age, gender, and hormones. Women are more likely to develop OA and experience more severe symptoms. Hormonal factors may play a role, but results from studies on estrogen are conflicting. Race/ethnicity also influences OA prevalence, with differences observed between Chinese and white populations. Genetic factors contribute to OA, with heritability estimated at 50-65%. Twin and family studies show a genetic influence on hand and hip OA. Genome-wide association studies have identified genetic variants associated with OA risk. Local risk factors include obesity, injury, and occupation. Obesity increases OA risk, especially in the knee. Knee injury is a strong risk factor, with meniscal damage and ligament injuries increasing OA risk. Occupation involving repetitive joint use is associated with higher OA risk. Dietary factors such as vitamin D and C are linked to OA risk. Low vitamin D levels are associated with increased knee OA risk, while low vitamin C intake is linked to OA progression. Selenium deficiency is associated with bone abnormalities, and low selenium levels are linked to increased knee OA risk. Mechanical factors such as knee alignment and limb length inequality also influence OA risk. Malalignment and limb length inequality are associated with increased OA risk. Laxity in the knee is another risk factor. Symptomatic OA is influenced by factors such as physical activity, knee injury, and trauma. Studies show that high physical activity levels may increase OA risk, but moderate activity does not. Symptomatic OA is more common in African Americans than in whites. In conclusion, OA is a complex condition with multiple risk factors. Understanding these factors can help in developing interventions and prevention