Background: The associations among income, total knee arthroplasty,
and underlying rates of knee osteoarthritis are not well understood. We
studied whether high-income Medicare recipients are more likely to have a knee
arthroplasty and less likely to suffer from knee osteoarthritis.
Methods: Two data sources were used: (1) the 2000 United States
Medicare claims data measuring the incidence of total knee arthroplasty by
race, ethnicity, zip (postal) code income, and region (n = 27.5 million) and
(2) the National Health and Nutrition Examination Survey (NHANES III) for
individuals with an age of sixty years or more (n = 1926) with radiographic
and clinical evidence of osteoarthritis. Logistic regression methods were used
to adjust for covariates.
Results: At the national level, age-adjusted rates of total knee
arthroplasty in the high-income quintile were no higher than those in the
low-income group (odds ratio, 0.98; 95% confidence interval, 0.96 to 1.00).
Within regions, access to care was better for high-income groups (odds ratio,
1.19; 95% confidence interval, 1.17 to 1.22). Racial disparities in
arthroplasty were significant (p < 0.001); the odds ratio was 0.36 (95%
confidence interval, 0.34 to 0.38) for black men and 0.45 (95% confidence
interval, 0.41 to 0.49) for Asian women. There was no evidence of an income
gradient for most clinical and radiographic measures of arthritis. The
exception was a significant negative association between income and pain on
passive motion (p < 0.05).
Conclusions: High-income Medicare enrollees are no less likely to
have osteoarthritis than low-income enrollees but have somewhat better access
to care. Racial disparities are more important than those that are
attributable to socioeconomic status.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.