Background/Purpose: To assess whether income is associated with patient-reported outcomes (PROs) after primary total knee arthroplasty (TKA).

Methods:   We used the prospectively collected data from the Mayo Clinic Total Joint Registry to assess the association of income with index knee functional improvement, and moderate-severe pain at 2- and 5-year follow-up after primary TKA using multivariable-adjusted logistic regression analyses.  Analyses were adjusted for various characteristics previously shown to be associated with PROs after TKA, namely demographics (age, gender, body mass index (BMI), comorbidity as measured by Deyo-Charlson index, American Society of Anesthesiologist (ASA) score as a measure of perioperative mortality, implant fixation (cemented/hybrid versus not cemented), underlying diagnosis (osteoarthritis, rheumatoid/inflammatory arthritis or other) and distance from medical center (categorized <100, 100-500 and >500 miles/overseas).  ASA score was not collinear with Deyo-Charlson index (correlation coefficient <0.40).

Results:   There were 7,139 primary TKAs at 2-years and 4,234 at 5-years. In multivariable-adjusted analyses, at 2-year follow-up, both lower income groups (<=$35K and >$35-45K) were significantly associated with lower odds ratio (OR) [95% confidence interval (CI) of moderate-severe pain, OR 0.6 [95% CI, 0.4, 0.9] (p=0.02) and 0.7 [95% CI, 0.5, 0.9] (p=0.02).  The overall improvement in knee function was rated as ‘better’ more often at 2-years by patients with income in the <=$35K compared to patients with income >$45K, with OR of 1.9 [95% CI, 1.0, 3.6] (p=0.06), respectively.  At 5-years, numerically similar but non-significant odds were noted.

Conclusion:   We found that lower income was associated with better pain outcome and more improvement in knee function postoperatively.  Insights into mediators of these relationships need to be investigated to understand how income influences outcomes after TKA.