Lifetime risk and age at diagnosis of symptomatic knee osteoarthritis in the US

Abstract

Objective: To estimate the incidence and lifetime risk of diagnosed symptomatic knee osteoarthritis (OA) and the age at diagnosis of knee OA based on self-reports in the US population.

Methods: We estimated the 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, 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 at diagnosis and lifetime risk.

Results: The estimated incidence of diagnosed symptomatic knee OA was highest among adults ages 55-64 years, ranging from 0.37% per year for nonobese men to 1.02% per year for obese women. The estimated median age at knee OA diagnosis was 55 years. The estimated lifetime risk was 13.83%, ranging from 9.60% for nonobese men to 23.87% in obese women. Approximately 9.29% of the US population is diagnosed with symptomatic knee OA by age 60 years.

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 health care utilization resulting from earlier diagnosis of knee OA.

Figure 1. Estimated Prevalence of Diagnosed Symptomatic Knee OA by Age in the US (Internal Validation of OAPol Model Estimates Using NHIS 2007–2008 Data)

Dashed curves represent prevalence among non-obese persons and solid curves represent prevalence among obese persons. Female prevalence is in black; male prevalence is in gray. Prevalence from NHIS is depicted by squares for obese and diamonds for non-obese persons and accompanied by 95% confidence intervals.

Figure 2. Estimated Age of Diagnosis among Persons with Symptomatic Knee OA

The black curve is the cumulative incidence using calculated and calibrated incidence estimates. The vertical dashed line denotes the median age of diagnosis (i.e. the age by which 50% of cases have been diagnosed).

Figure 3. Estimated Cumulative Incidence of Diagnosed Symptomatic Knee OA from Age 25 in the US Population, Stratified by Sex and Obesity Status

The patterned dark gray curve represents the overall cumulative incidence of diagnosed symptomatic knee OA from age 25. Dashed curves represent the cumulative incidence among non-obese persons; solid curves represent the cumulative incidence among obese persons. Female cumulative incidence is in black; male cumulative incidence is in light gray. The cumulative incidence by the end of life represents the lifetime risk for each cohort, as denoted in the right margin. The point of intersection of the thin black horizontal and vertical lines emphasizes the cumulative incidence for the general US population by age 60.