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Objective The prevalence of symptomatic knee osteoarthritis (OA) has been increasing over the past several decades in the United States concurrent with an aging population and the growing obesity epidemic. We quantify the impact of these factors on the number of persons with symptomatic knee OA in the first decades of 21st century. Methods We calculated prevalence of clinically diagnosed symptomatic knee OA from the National Health Interview Survey 2007–08 and derived the proportion with advanced disease (Kellgren-Lawrence grades 3–4) using the Osteoarthritis Policy Model, a validated simulation model of knee OA. Incorporating contemporary obesity rates and population estimates, we calculated the number of persons living with symptomatic knee OA. Results We estimate that about fourteen million persons had symptomatic knee OA, with advanced OA comprising over half of those cases. This includes over three million African American, Hispanic, and other racial/ethnic minorities. Adults under 45 years of age represented nearly two million cases of symptomatic knee OA and individuals between 45 and 65 years of age six million more. Conclusion Over half of all persons with symptomatic knee OA are younger than 65 years of age. As many of these younger persons will live for three decades or more, there is substantially more time for greater disability to occur and policymakers should anticipate healthcare utilization for knee OA to increase further in upcoming decades. These data emphasize the need for the deployment of innovative prevention and treatment strategies for knee OA, especially among younger persons.

Objective The impact of increasing utilization of total knee arthroplasty (TKA) on lifetime costs in persons with knee OA is under-studied. Methods We used the Osteoarthritis Policy Model to estimate total lifetime costs and TKA utilization under a range of TKA eligibility criteria among US persons with symptomatic knee OA. Current TKA utilization was estimated from the Multicenter Osteoarthritis Study and calibrated to Health Care Utilization Project (HCUP) data. OA treatment efficacy and toxicity were drawn from published literature. Costs in 2013 USD were derived from Medicare reimbursement schedules and Red Book Online®. Time costs were derived from published literature and the US Bureau of Labor Statistics. Results Estimated average discounted (3%/year) lifetime costs for persons diagnosed with knee OA were $140,300. Direct medical costs were $129,600, with $12,400 (10%) attributable to knee OA over 28 years. OA patients spent, on average, 13 (SD 10) years waiting for TKA after failing non-surgical regimens. Under current TKA eligibility criteria, 54% of knee OA patients underwent TKA over their lifetimes. Estimated OA-related discounted lifetime direct medical costs ranged from $12,400 (54% TKA uptake) when TKA eligibility was limited to K-L 3 or 4 to $16,000 (70% TKA uptake) when eligibility was expanded to include symptomatic OA with a lesser degree of structural damage. Conclusion Due to low efficacy of non-surgical regimens, knee OA treatment-attributable costs are low, representing a small portion of all costs for OA patients. Expanding TKA eligibility increases OA-related costs substantially for a population, underscoring the need for more effective non-operative therapies.

Objective To estimate incidence and lifetime risk of diagnosed symptomatic knee OA and age of diagnosis of knee OA based on self-reports in the US population. Methods We estimated incidence of diagnosed symptomatic knee OA in the US by combining data on age-, sex-, and obesity-specific prevalence from the 2007–2008 National Health Interview Survey (NHIS) with disease duration estimates derived from the Osteoarthritis Policy (OAPol) Model, a validated computer simulation model of knee OA. We used the OAPol Model to estimate the mean and median ages of diagnosis and lifetime risk. Results The estimated incidence of diagnosed symptomatic knee OA was highest among adults aged 55 to 64, ranging from 0.37% per year for non-obese males to 1.02% per year for obese females. The estimated median age of knee OA diagnosis was 55 years. The estimated lifetime risk was 13.83%, ranging from 9.60% for non-obese males to 23.87% in obese females. About 9.29% of the US population is diagnosed with symptomatic knee OA by age 60. Conclusion The diagnosis of symptomatic knee OA occurs relatively early in life suggesting that prevention programs should be offered relatively early in the life course. Further research is needed to understand the future burden of healthcare utilization resulting from earlier diagnosis of knee OA.