Method: We used the OAPol Model, a validated computer simulation model of the natural history of knee OA, to estimate the age-stratified 10-year incidence of symptomatic physician-diagnosed knee OA during two distinct time periods (the 1990s vs. the 2010s). Symptomatic knee OA incidence data for the 1990s were derived from published literature. Data for the 2010s were derived from the National Health Interview Survey 2007-08. We followed a simulated cohort from age 25 to death to track the onset of symptomatic knee OA. We coupled model output and CDC population estimates from each time period to project the number of incident cases of knee OA in the US population over each 10-year period. We compared ages of OA onset and 10-year cumulative incidence of knee OA for the two time periods.
Result: The mean age of physician-diagnosed knee OA onset fell from 72 ± 12 years (mean ± standard deviation) in the 1990s to 56 ± 18 years in the 2010s. Americans ages 35-84 in the early 2010s were expected to incur 6,475,642 incident cases of symptomatic knee OA over the next decade, with those ages 45-64 accounting for 59% of these cases (Figure). Among Americans who were ages 45-54 at the beginning of the 1990s, an estimated 412,214 incident cases of knee OA were expected over the subsequent 10 years, resulting in a 10-year cumulative incidence of 1.5%. Among people in the same baseline age group in the 2010s, 2,108,881 incident cases of symptomatic knee OA are expected over the next 10 years, a cumulative incidence of 4.8%. The projected number of 10-year incident cases among those ages 65-74 at baseline decreased slightly between the 1990s (1,169,615 cases) and the 2010s (882,997 cases).
Conclusion: Since the early 1990s, the age of onset of physician-diagnosed symptomatic knee OA has shifted dramatically, occurring on average 16 years earlier in life. This trend may reflect temporal changes in the prevalence of OA risk factors, as well as thresholds for patient care-seeking and physician diagnosis of OA. If the current OA incidence trend continues, nearly 6.5 million Americans between the ages of 35 and 84 will be diagnosed with symptomatic knee OA in the next 10 years, with those ages 45-64 accounting for more than half of these incident cases. A resulting spike in the utilization of healthcare, specifically total knee replacements, could have a dramatic economic impact and place additional burden on the healthcare system.
Disclosure: S. A. Burbine, None; A. M. Weinstein, None; W. M. Reichmann, None; B. N. Rome, None; J. E. Collins, None; J. N. Katz, None; E. Losina, None.