Arthritis is a leading cause of permanent incapacity, resulting in extensive use of health care resources and significant economic burden (1–5). As for other chronic disabling conditions, studies have documented a relationship between worse self-reported symptoms of arthritis/disability and lower socioeconomic status (SES), using a variety of accepted measures, including level of education, household income, and wealth (6–10). Observed SES differences in disease severity persist after adjustment for the prevalence of disease risk factors (7, 8). Thus, differential access to and/or use of arthritis health care services has been proposed as the most likely explanation for these observations (11–13).
Total joint arthroplasty is a well-recognized, efficacious, and cost-effective treatment for advanced hip or knee arthritis (14–20). The majority (>80%) of hip and knee replacements are performed for osteoarthritis (21). In the US, lower rates of joint arthroplasty have been reported in persons with low income versus those with high income (22). The Canadian health care system is characterized by universal access to care according to need. Nonetheless, even in Canada, SES gradients in medical care have been observed (23, 24). Studies have suggested that individuals with lower SES are less able to negotiate the health care system, which thereby impacts their access to care (25, 26). The main limitation of these prior studies is their failure to consider individuals' willingness or desire to receive treatment. The objective of this study was to assess the effect of education and income on potential need for, and willingness to consider hip and knee arthroplasty as a treatment option.
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- PATIENTS AND METHODS
Previous studies have documented lower rates of joint arthroplasty among individuals with lower SES, but to date, none have considered an important potential explanation for this finding, that is, differences in individuals' desire for care or treatment preferences. Herein we estimated both the potential need for and willingness to consider undergoing hip and knee arthroplasty in a population-based Canadian cohort, to determine whether differences existed on the basis of 2 accepted measures of SES, level of education and annual household income. As others have reported, we found that even in a setting of universal access to health care, less education and lower income were independent correlates of worse arthritis symptoms and disability, thus creating greater potential need for hip and knee arthroplasty. More importantly, for the first time, we have shown that among the individuals with potential need for this procedure, willingness to undergo joint arthroplasty did not differ by SES, and therefore did not explain the observed differences in rates of use.
Chaturvedi and Ben-Shlomo (13) documented lower rates of hip arthroplasty among individuals with lower SES, compared with individuals with higher SES, who had consulted a general practitioner in the UK for osteoarthritis. This was despite the fact that the overall rates of consultation for osteoarthritis were greater for those with lower SES. In our study, adjustment for whether or not the individual was under the care of a physician for their arthritis did not eliminate the observed SES differences in potential arthroplasty need. However, we did not quantify the frequency of visits to, or treatment prescribed by these health care practitioners, nor did we assess individuals' adherence to physicians' recommendations. Therefore, we cannot be certain that clinical practice patterns or patient compliance did not differ according to the level of education or income of the patient, as others have suggested. Neuberger et al found that individuals with fewer years of formal education had less perception of the benefits from exercise compared with those who had attained more education, potentially reducing their motivation to adhere to exercise recommendations (12). Similarly, Dexter and Brandt found that the instruction in, and monitoring of therapeutic joint exercises was conducted in a more comprehensive manner in individuals with greater education than in those without (11).
It has been suggested that arthritis severity, and thus the potential need for arthroplasty, may be greater among those with less education or lower income due to a higher prevalence of exposure to risk factors for osteoarthritis. Identified risk factors for hip and knee osteoarthritis include older age, female sex, and obesity (39, 40). In our cohort, individuals with low education and/or low income were significantly more likely to be female, and were older and heavier. However, adjustment for these potential confounders in our analyses did not eliminate the observed education/income gradients. Specific occupational exposures have also been associated with incidence of osteoarthritis, in particular, occupations requiring repetitive knee bending (41). Because most of the subjects in our cohort were retired, we did not collect information on prior occupations. Therefore, we could not examine the effect of occupational exposures on arthritis prevalence or severity.
Neither the level of education nor income was an independent correlate of individuals' willingness to undergo joint arthroplasty, after taking into consideration whether or not the individual had ever discussed this procedure with a physician. However, since relatively few individuals in our cohort had discussed arthroplasty with a physician, we could not explore, with confidence, whether or not education or income predicted physicians' recommendations regarding surgery.
Women, compared with men, have disproportionately greater potential unmet need for hip/knee arthroplasty after taking into consideration age, disease severity, and willingness to consider arthroplasty (28). In examining the interaction between sex and SES, we found that among men and women with low SES, no sex differences in potential need for arthroplasty existed. However, among those with higher SES, women were more likely than men to have need for this procedure, even after adjusting for important confounders such as age and BMI. We have previously proposed that one explanation for this difference is that barriers (actual and/or perceived) exist at the level of the interaction between the primary care provider and the hip/knee arthritis patient in referral to orthopedic surgery (28). The findings in the present study suggest that these barriers are similar for men and women with low SES, but systematically greater for women compared with men at higher levels of SES.
In addition to sex, racial background has also been associated with access to care. In particular, studies in the US have documented lower rates of joint arthroplasty among nonwhites (22, 42). In our study, there was too little racial disparity to examine, with confidence, the interactions among SES, sex, and racial background with respect to their impact on potential unmet need for joint arthroplasty. Further study is warranted to investigate the mechanisms whereby these factors interact to influence referral for, and performance of hip and knee arthroplasty.
There are several potential limitations to this study, in addition to those already noted. First, in an effort to factor in the important influence of patients' preferences on our estimates of need for arthroplasty, we adjusted our estimates of potential need by the patient's degree of willingness to have arthroplasty. The latter was evaluated by means of a standardized interview, rather than through conversations with an orthopedic surgeon. We used this approach to provide a standard and comprehensive list of the potential risks and benefits associated with arthroplasty, which we developed in light of our prior research that documented substantial variation among orthopedic surgeons in their opinions regarding the indications for, and outcomes of arthroplasty (33). We believe that because we listed all possible risks associated with arthroplasty, we obtained conservative estimates of the willingness to undergo arthroplasty. Furthermore, our approach is unlikely to have had systematically different effects depending on the participant's level of education or income.
Second, because there are no standardized guidelines regarding when and in whom arthroplasty should be performed, our criteria for potential need were based on self-reported symptoms and disability, obtained with use of a reliable and valid instrument (the WOMAC) that is widely used in North America to evaluate the outcomes of arthroplasty. Since studies indicate that the primary reasons reported by patients for undergoing arthroplasty are joint pain and functional limitation (16), these criteria seem reasonable. Furthermore, the estimates of need were adjusted for the likelihood that persons with high scores had both clinical and radiographic evidence of arthritis, and for contraindications to surgery.
Third, we estimated potential need for, and willingness to have, arthroplasty in only 2 areas of Ontario. The province of Ontario comprises approximately half the total population of Canada, and we compared the characteristics of our phase I respondents with both Ontario and Canadian census data. Nevertheless, although these respondents appeared to be representative of the underlying population, we cannot assume that similar results would be found in areas not studied.
Fourth, self-reported level of education and annual household income were used as our measures of “socioeconomic status.” Although the nonresponse rate for education was only 4% of participants, 18% did not specify their annual household income. Those who did not report their income were significantly more likely than those who did report income to have received less education, and to be nonwhite and non–English speaking. For this reason, we also ran our models including “nonresponse to income” as a covariate. As noted above, inclusion of this variable did not affect the reported relationships between income, education, and arthroplasty need or willingness. Of note, we did not collect information regarding the number of persons in the household. Thus, we could not adjust for this in examining the effect of income on arthroplasty need or willingness.
Finally, because the proportion of individuals with potential need for arthroplasty who reported definite willingness to consider having the procedure was low, we may have had insufficient power to detect significant differences in willingness by level of education or income. Among individuals with potential arthroplasty need who had low income, the likelihood of having indicated definite willingness to consider arthroplasty was much less, although not statistically so, than among those having a higher income. A larger study is needed to confirm our reported lack of an association between “willingness” and income.
In conclusion, we have documented greater potential need for hip/knee arthroplasty among individuals with less education and, in particular, low income. Among those with potential need, the proportion reporting definite willingness to consider joint arthroplasty was similar, regardless of level of education or income. As a result, there was an overall greater proportion of individuals who met our criteria for unmet arthroplasty need among those of low SES versus those of high SES. These results suggest that the previously reported lower rates of hip/knee arthroplasties performed in those with low SES (versus high SES) cannot be explained by either a lower prevalence of disabling hip/knee arthritis (i.e., demonstrable need for the procedure) or a greater unwillingness to consider arthroplasty as a treatment option in those with low SES. Instead, disparity in arthroplasty rates may be related to differences in physician management of hip/knee arthritis, and in particular, their opinions regarding when, and if, to refer for, or perform joint arthroplasty, according to the patients' level of education or income.