Table 4.

Multivariable-adjusted association of income with pain and activity limitation after primary total knee arthroplasty

	2 years				5 years
	Moderate to severe pain		Moderate to severe functional limitation		Moderate to severe pain		Moderate to severe functional limitation
	Odds ratio (95% CI)	P value	Odds ratio (95% CI)	P value	Odds ratio (95% CI)	P value	Odds ratio (95% CI)	P value
≤ US$35, 000	0.61 (0.40 to 0.94)	0.02	0.78 (0.60 to 1.02)	0.07	0.77 (0.50 to 1.19)	0.24	0.91 (0.68 to 1.25)	0.56
> US$35, 000 to US$45, 000	0.68 (0.49 to 0.94)	0.02	0.96 (0.78 to 1.20)	0.75	0.90 (0.60 to 1.34)	0.60	1.09 (0.83 to 1.44)	0.52
> US$45, 000 (ref)	1.00		1.00		1.00		1.00

Data were additionally adjusted for the following variables at baseline: age category, gender, body mass index (BMI) category, Deyo-Charlson index, American Society of Anesthesiologists (ASA) class, distance, operative diagnosis, implant fixation, preoperative pain (for pain models) and preoperative functional limitation (for functional limitation models). Significant variables in each model included the following: (1) 2-year pain model: age (P = 0.03) and preoperative pain (P = 0.003); (2) 2-year activity limitation model: age (P < 0.001), gender (P < 0.001), body mass index (P < 0.001), ASA class (P < 0.001) and preoperative activity limitation (P < 0.001); (3) 5-year pain model: ASA class (P < 0.001), distance from medical center (P = 0.02) and implant fixation (P = 0.01); (4) 5-year activity limitation model: age (P < 0.001), gender (P < 0.001), body mass index (P < 0.001), ASA class (P < 0.001), Deyo-Charlson index (P = 0.02) and preoperative activity limitation (P < 0.001).