Is Geographic Socioeconomic Disadvantage Associated with the Rate of THA in Medicare-aged Patients?
Authors: Rahman Rafa , Canner Joseph K. , Haut Elliott R. , Humbyrd Casey J. 
Published: September 2020

Abstract

Background
Disparities in THA use may lead to inequitable care. Prior research has focused on disparities based on individual-level and isolated socioeconomic and demographic variables. To our knowledge, the role of composite, community-level geographic socioeconomic disadvantage has not been studied in the United States. As disparities persist, exploring the potential underlying drivers of these inequities may help in developing more targeted recommendations on how to achieve equitable THA use.

Questions/purposes
(1) Is geographic socioeconomic disadvantage associated with decreased THA rates in Medicare-aged patients? (2) Do these associations persist after adjusting for differences in gender, race, ethnicity, and proximity to hospitals performing THA?

Methods
In a study with a cross-sectional design, using population-based data from five-digit ZIP codes in Maryland, USA, from July 1, 2012 to March 31, 2019, we included all inpatient and outpatient primary THAs performed in individuals 65 years of age or older at acute-care hospitals in Maryland, as reported in the Health Services Cost Review Commission database. This database was selected because it provided the five-digit ZIP code data necessary to answer our study question. We excluded THAs performed for nonelective indications. We examined the annual rate of THA in our study population for each Maryland ZIP code, adjusted for differences across areas in distributions of gender, race, ethnicity, and distance to the nearest hospital performing THAs. Four hundred fourteen ZIP codes were included, with an overall mean ± SD THA rate of 371 ± 243 per 100,000 persons 65 years or older, a rate similar to that previously reported in individuals aged 65 to 84 in the United States. Statistical significance was assessed at α = 0.05.

Results
THA rates were higher in more affluent areas, with the following mean rates per 100,000 persons 65 years or older: 422 ± 259 in the least socioeconomically disadvantaged quartile, 339 ± 223 in the second-least disadvantaged, 277 ± 179 in the second-most disadvantaged, and 214 ± 179 in the most-disadvantaged quartile (p < 0.001). After adjustment for distributions in gender, race, ethnicity, and hospital proximity, we found that geographic socioeconomic disadvantage was still associated with THA rate. Compared with the least-disadvantaged quartile, the second-least disadvantaged quartile had 63 fewer THAs per 100,000 people (95% confidence interval 12 to 114), the second-most disadvantaged quartile had 136 fewer THAs (95% CI 62 to 211), and the most-disadvantaged quartile had 183 fewer THAs (95% CI 41 to 325).

Conclusion
Geographic socioeconomic disadvantage may be the underlying driver of disparities in THA use. Although our study does not determine the “correct” rate of THA, our findings support increasing access to elective orthopaedic surgery in disadvantaged geographic communities, compared with prior research and efforts that have studied and intervened on the basis of isolated factors such as race and gender. Increasing access to orthopaedic surgeons in disadvantaged neighborhoods, educating physicians about when surgical referral is appropriate, and educating patients from these geographic communities about the risks and benefits of THA may improve equitable orthopaedic care across neighborhoods. Future studies should explore disparities in rates of appropriate THA and the role of density of orthopaedic surgeons in an area.

Level of Evidence
Level III, therapeutic study.