Ambient Air Pollution Exposure and Acute Osteoarthritis Exacerbations: A National Case-Crossover Analysis of 8 Million Outpatient Visits in China

While the inflammatory properties of ambient air pollution may exacerbate osteoarthritis (OA), evidence on the population-level impact of multi-pollutant mixtures remains limited. This study quantifies the acute effects of short-term exposure to a complex mixture of six-criteria air pollutants on OA outpatient visits. In total, 8,146,141 OA visits from two national health insurance databases across 192 Chinese cities (2013-2017) were analyzed using a two-stage, time-stratified case-crossover design, combining conditional logistic regression with random-effects meta-analysis. The results showed that an interquartile range increase in the concentrations of PM_2.5, PM₁₀, NO₂, SO₂, O₃, and CO was associated with significant increases in OA visits of 1.75%, 2.26%, 4.01%, 3.42%, 1.98%, and 1.87%, respectively. NO₂ and SO₂ demonstrated the strongest associations across OA subtypes. Multi-pollutant models confirmed that the risk of OA visits increased significantly under combined pollutant exposure. Population attributable fractions ranged from 2.15% for PM_2.5 to 6.41% for NO₂. This large-scale analysis provides novel evidence that transient exposure to complex pollution mixtures, rather than to individual pollutants, drives OA-related healthcare demand, with gaseous pollutants (NO₂/SO₂) being critical components. Our findings advocate for integrative air quality management strategies targeting co-emitted pollutants to mitigate OA exacerbations.