Lower extremity joint arthroplasty, particularly revision arthroplasty, is a costly procedure, and the number of these procedures is projected to increase substantially [23, 33]. Novel payment models such as the Comprehensive Care for Joint Replacement Model have been implemented to contain costs by incentivizing reductions in surgical complications . These models include pay-for-performance elements [7, 23], which reimburse physicians on the basis of quality criteria, and bundled payments, which reimburse a predetermined amount per episode of care. However, these models may inadvertently discourage hospitals from performing surgery for patients with preexisting risk factors. The extent to which surgeons are using body mass index (BMI), hemoglobin A1c (HbA1c) level, and smoking status to determine eligibility has not been studied formally, but preliminary work suggests that many surgeons use such inflexible eligibility criteria . Because these risk factors are more prevalent in certain subpopulations [1, 42], including groups that already face disparities in access to lower extremity arthroplasty [31, 37, 38, 45], there is concern that their use for hip and knee arthroplasty eligibility may exacerbate existing racial-ethnic, gender-based, and socioeconomic disparities pertaining to access to an operation that can improve health and quality of life .
Researchers have discussed the implications of novel payment models that incentivize treatment of lower risk patients, but to our knowledge, no study has quantified the effect of specific eligibility criteria on access to lower extremity joint arthroplasty for minority groups [3, 4, 16, 17]. Furthermore, we are aware of no research into which minority groups will be affected by specific eligibility criteria for lower extremity arthroplasty. An awareness of the implications of inflexible eligibility criteria can help policymakers and individual surgeons prevent increases in lower extremity arthroplasty disparities while pursuing cost-containment strategies such as bundled payments.
We therefore asked: Does the use of inflexible eligibility criteria related to (1) BMI; (2) HbA1c level; and (3) smoking status potentially decrease the odds of lower extremity arthroplasty eligibility for members of racial-ethnic minority groups, women, and those of lower socioeconomic status more so than for non-Hispanic whites, men, and those of higher socioeconomic status?
Patients and Methods
We pooled data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2014. Conducted by the National Center for Health Statistics, NHANES uses interviews administered in the home and standardized health examinations administered in specially equipped mobile examination centers to assess the health and nutrition status of adults in the United States . NHANES uses three mobile examination centers: two are in operation at study locations and the third is either traveling or being prepared for a new study location. Each year, 15 locations are sampled for the health examination component. Rather than a single random sample, NHANES uses a complex, multistage, national area probability design to collect data from a nationally representative sample of the resident, civilian, noninstitutionalized US population. NHANES also oversamples subpopulations of interest (including those of Hispanic descent) to produce more reliable and precise estimates. Data are collected continuously and released in 2-year cycles. NHANES received approval from the National Center for Health Statistics institutional review board.
NHANES is uniquely suited to examine our study question because it includes data from physical examinations, in which trained examiners collect height and weight data to calculate BMI rather than relying on self-reports and laboratory assessments that collect HbA1c data as well as comprehensive questionnaires, and it surveys a nationally representative, diverse population. We limited our analytic sample to adults aged ≥ 50 years. There was no upper age limit. The minimum age of 50 years was chosen because lower extremity arthroplasty prevalence begins to rise after age 50 years .
Dependent variables were binary indicators of potential eligibility criteria: (1) BMI < 35 kg/m2 (all BMI values are expressed in these units, and BMI will be presented without units from here on); (2) BMI < 40; (3) HbA1c < 8%; and (4) current nonsmoker status. The BMI criterion of 40 was chosen because studies have shown that BMI > 40 is an independent predictor of postoperative morbidity . A BMI criterion of 35 was used to examine whether a lower BMI cutoff would have similar effects on disparities. An HbA1c level of 8% was chosen because surgical complication rates increase dramatically at this level . Height and weight for BMI were obtained through measurement, HbA1c concentration through laboratory testing, and smoking status through self-report. Trained medical personnel collected height and weight data and administered laboratory tests.
Independent variables were self-reported race-ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, or other), gender (male or female), and two measures of socioeconomic status: annual household income (< USD 45,000 or ≥ USD 45,000) and education (a high school degree or less [includes individuals who received some college education but did not earn a degree] or a degree beyond a high school degree [such as an associate’s degree or a bachelor’s degree]). We chose USD 45,000 to separate the income groups because it is similar to the median US household income from 1999 to 2014 . Control variables were age (continuous) and a categorical survey year indicator to adjust for year-to-year changes.
We calculated means and proportions for each variable of interest. We ran separate multivariable logistic regression models for each outcome that included all independent (race-ethnicity, gender, socioeconomic status) and control variables (age and survey year). All analyses used survey weights provided by NHANES to account for the complex survey design (including oversampling, survey nonresponse, poststratification, and sampling error) and to produce nationally representative estimates. We considered p values < 0.05 to be significant. All analyses were conducted in Stata, Version 14.2 (StataCorp LP, College Station, TX, USA).
The mean age of adults in our data set was 66 years, and 51% were women (Table 1). When using the BMI < 35 criterion, non-Hispanic blacks, women, and individuals of lower socioeconomic status were less likely to be eligible than non-Hispanic whites, men, and individuals of higher socioeconomic status, respectively, and these odds persisted with a BMI < 40 criterion (Table 2). We found that for the BMI < 35 eligibility criterion, the odds of eligibility for non-Hispanic blacks were 38% lower (odds ratio [OR], 0.62; 95% confidence interval [CI], 0.55–0.70; p < 0.001) and 23% higher for Hispanics (OR, 1.23; 95% CI, 1.04–1.44; p = 0.014) compared with non-Hispanic whites. Odds of eligibility for women were 39% lower than for men (OR, 0.61; 95% CI, 0.55–0.69; p < 0.001). Odds of eligibility for individuals with an annual household income of < USD 45,000 were 19% lower than those with an annual income of ≥ USD 45,000 (OR, 0.81; 95% CI, 0.71–0.93; p = 0.002) and odds for those with a high school degree or less were 34% lower than those with a degree beyond a high school degree (OR, 0.66; 95% CI, 0.57–0.77; p < 0.001). For the BMI < 40 criterion, odds of lower extremity arthroplasty eligibility decreased further for non-Hispanic blacks versus non-Hispanic whites (OR, 0.59; 95% CI, 0.50–0.69; p < 0.001), women versus men (OR, 0.50; 95% CI, 0.41–0.60; p < 0.001), and those with a high school degree or less versus those with a degree beyond a high school degree (OR, 0.59; 95% CI, 0.44–0.77; p < 0.001). Odds of eligibility further increased for Hispanics versus non-Hispanic whites (OR, 1.47; 95% CI, 1.16–1.87; p = 0.002). Individuals with household income < USD 45,000 versus those with ≥ USD 45,000 maintained lower odds of eligibility (OR, 0.73; 95% CI, 0.59–0.89; p = 0.003).
For the HbA1c < 8% eligibility criterion, non-Hispanic blacks and individuals of lower socioeconomic status were less likely to be eligible than non-Hispanic whites and individuals of higher socioeconomic status, respectively (Table 2). The ORs for the HbA1c < 8% criterion were as follows: odds of eligibility for non-Hispanic blacks were 56% lower (OR, 0.44; 95% CI, 0.37–0.53; p < 0.001) and 59% lower for Hispanics (OR, 0.41; 95% CI; 0.33–0.51; p < 0.001) compared with non-Hispanic whites. Odds of eligibility for women were 51% higher than for men (OR, 1.51; 95% CI, 1.28–1.78; p < 0.001). Odds of eligibility for individuals with an annual household income < USD 45,000 were 34% lower than those with an annual income ≥ USD 45,000 (OR, 0.73; 95% CI, 0.56–0.94; p = 0.008), and odds for individuals with a high school degree or less were 42% lower than those with a degree greater than a high school degree (OR, 0.58; 95% CI, 0.44–0.77; p < 0.001).
When using the nonsmoker criterion, odds of eligibility for non-Hispanic blacks were 18% lower than for non-Hispanic whites (OR, 0.84; 95% CI, 0.73–0.97; p = 0.019). Odds of eligibility for individuals with an annual household income < USD 45,000 were 47% lower than those with income ≥ USD 45,000 (OR, 0.53; 95% CI, 0.47–0.61; p < 0.001), and odds for individuals with a high school degree or less were 71% lower than those with a degree beyond a high school degree (OR, 0.29; 95% CI, 0.24–0.35; p < 0.001). Conversely, odds of eligibility for Hispanics were 65% higher than for non-Hispanic whites (OR, 1.65; 95% CI, 1.37–1.98; p < 0.001), and odds for women were 44% higher than for men (OR, 1.44; 95% CI, 1.27–1.63; p < 0.001).
Additional analyses that do not control for additional factors (including age and socioeconomic status) but that show the proportions of each subpopulation that would be affected by inflexible eligibility criteria were run for reference (Appendix Table, Supplemental Digital Content).
More than one million hip and knee arthroplasties are performed in the United States each year, increasing function and quality of life . The number of these procedures performed annually continues to rise  as do concerns about disparities in utilization by race-ethnicity, gender, and socioeconomic status [31, 37, 38, 45]. Lower extremity arthroplasty has been a prime target for beginning to transition medical care in the United States from a fee-for-service model to bundled payments or pay-for-performance models. These payment structures encourage avoidance of higher risk patients, sometimes by using inflexible eligibility criteria. The impact of inflexible eligibility criteria on racial-ethnic, gender-based, and socioeconomic disparities in lower extremity arthroplasty has been discussed but not quantified [3, 4, 16, 17]. We found that inflexible cutoffs related to BMI, HbA1c, and smoking status would substantially restrict access to lower extremity arthroplasty for non-Hispanic blacks, Hispanics, women, and individuals of lower socioeconomic status. Theoretically, removal of disparities in BMI, HbA1c, and smoking would prevent inflexible eligibility criteria from worsening disparities in lower extremity arthroplasty. However, obesity, diabetes, and smoking are complex issues intertwined with economic, social, cultural, and personal factors, and addressing these disparities is a long-term public health goal, unlikely to be eliminated in the near future. Exclusion criteria eliminate considerations of patient choice, substituting medical risk factors (such as BMI, HbA1c, smoking) for a patient-physician conversation about risks and benefits. Inflexible eligibility criteria would affect racial minorities, women, and individuals of lower socioeconomic status more than they affect non-Hispanic whites, men, and individuals of higher socioeconomic status, and therefore they raise concerns about discrimination and justice.
The main limitation of our study is that the database is not limited to patients with indications for lower extremity arthroplasty. Our model examines how eligibility would be affected, assuming that everyone would benefit from and may consider undergoing hip or knee arthroplasty. Although actual reductions in arthroplasty eligibility as a result of these criteria may differ by subpopulation, this model highlights how inflexible eligibility criteria may be a powerful source of decreased access for racial minorities, women, and individuals of lower socioeconomic status. Additionally, our model examined individual eligibility criteria. Although patients may have more than one risk factor at a time (for example, both obesity and smoking), we analyzed individual risk factors because failure to meet only one eligibility criterion is enough to prevent eligibility. NHANES also excludes persons in supervised care or custody in institutional settings as well as active-duty military personnel. Our results are not generalizable to these populations. We were missing data on some ethnic groups such as Asians, so we were unable to estimate the effects of eligibility criteria on these groups. Data on race-ethnicity, smoking status, educational level, and income were self-reported. The issue of self-reported race-ethnicity is especially complex. Race-ethnicity is both genetic and a social construct that may be a proxy for other factors that affect health such as socioeconomic status, level of social support, and healthcare access; by contrast, the genetics of race may also influence the frequency and severity of disease in some instances. It can be very difficult to tell when race and ethnicity are proxies or confounding variables and when they actually exert a biologic influence on health . We assessed some of the relationship between socioeconomic factors and inflexible eligibility criteria through two commonly used measures: income and education, yet social support and healthcare access are complex issues, of which education and income can provide only a limited picture. Self-reported smoking status may also be particularly prone to social desirability bias . Lastly, although we examined only three characteristics (race-ethnicity, gender, socioeconomic status) as they relate to arthroplasty eligibility, other factors such as insurance status, health status, and occupation also influence arthroplasty access and indications. These factors may, in turn, shape subgroup rates of eligibility for arthroplasty.
Our BMI findings are mostly consistent with those of a substantial body of evidence documenting disparities by race-ethnicity, gender, and socioeconomic status [1, 11-13, 19-21, 27, 35, 39-41]. Non-Hispanic black adults, women, and individuals of lower socioeconomic status have higher rates of obesity than non-Hispanic whites, men, and individuals of higher socioeconomic status . Our finding of increased eligibility among Hispanics compared with non-Hispanic whites differs with documented Hispanic-white disparities in obesity . One reason for this difference may be that our analysis also adjusted for age, gender, and socioeconomic status, whereas prior studies did not account for socioeconomic status and used different age ranges [32, 34, 42]. The exact relationships among age, gender, race-ethnicity, and socioeconomic status are complex and not fully understood, but socioeconomic status and age likely are confounding factors in the relationship between Hispanic ethnicity and obesity and may explain the differences between our findings and those of previous studies [25, 32, 34]. These BMI findings have important implications. First, BMI is difficult to modify. Enrollment in preoperative weight loss programs has produced weight loss in only 51% of patients, and even then, the weight loss is slight (averaging only 0.1 lbs) . Additionally, a BMI of 36 is a far different risk factor compared with a BMI of 46. In light of this, patients require knowledge of their surgical risk as it relates to their BMI to make informed decisions. However, inflexible eligibility criteria based on BMI prevent individuals from making decisions about hip or knee arthroplasty on the basis of their value systems. Individuals may decide that the functional benefits of hip or knee arthroplasty outweigh the increased surgical risks associated with their BMI, and our ability to predict personal preferences is limited because such preferences often differ by race-ethnicity, gender, and socioeconomic status . Patients who are ineligible because of inflexible criteria based on BMI would lose the ability to exercise their decision-making capacity, and thus their autonomy would be compromised. Our study shows that non-Hispanic blacks, women, and those of lower socioeconomic status would be more likely to experience such a loss of autonomy than non-Hispanic whites, men, or those of higher socioeconomic status.
Our HbA1c findings are consistent with evidence on disparities related to diabetes. Studies have documented a higher prevalence of diabetes among non-Hispanic blacks and Hispanics versus whites, men versus women , and among individuals of lower socioeconomic status versus those of higher socioeconomic status . An HbA1c level > 8% is a critical, modifiable risk factor for surgical complications and is often associated with poor support, lack of confidence in following through with treatment plans, and greater financial barriers . All of these factors also represent potential threats to the success of hip or knee arthroplasty. However, the achievability of a goal must also be considered. It has been shown that 70% of patients can obtain an HbA1c level < 8% . Given the high surgical risks associated with an HbA1c level > 8%, we do not advocate removing this eligibility criterion, and we support physicians partnering with their patients in preoperative optimization of glycemic control. Furthermore, we believe that the principle of justice requires physicians to understand and help address, when possible, the existing disparities in diabetes care.
Our findings regarding smoking status also support recent studies showing that men are more likely to smoke than women, non-Hispanic whites are more likely to smoke than Hispanics, and individuals of lower socioeconomic status are more likely to smoke than those of higher socioeconomic status . Given that smoking cessation rates at 6 months are below 10% , inflexible eligibility criteria based on smoking status may cause permanent ineligibility for hip or knee arthroplasty. Although not definitive, current studies suggest that smoking risk for arthroplasty is dose-dependent [36, 41]. Therefore, we believe that shared decision-making regarding reduced or eliminated smoking around the time of surgery should be patient-specific rather than treated as an inflexible eligibility criterion.
In summary, novel payment structures may reduce healthcare costs, but they also encourage the use of inflexible eligibility criteria based on surgical risk factors. Surgeons should be aware that policies with inflexible eligibility criteria decrease access to lower extremity arthroplasty in vulnerable, often-discriminated-against populations such as non-Hispanic blacks, Hispanics, women, and individuals of lower socioeconomic status. Our findings emphasize that payment models should include greater stratification of risk factors such as BMI, HbA1c, and smoking pack-years. Increasing the number of stratified levels would reduce the incentive to avoid patients with higher BMI, higher HbA1c level, or current smokers without removing the benefits of a cost-conscious reimbursement system.
We thank Rachel Box, Eileen Martin, and Jenni Weems for their assistance in editing this publication.
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