Total knee arthroplasty (TKA) is a successful operation that results in substantial improvement in quality of life for most patients1. Although TKA utilization in the United States has increased exponentially over the last 2 decades2,3, there are persistent disparities in utilization between blacks and whites4. Blacks are less willing to undergo joint replacement5,6 in part because of a perception of increased surgical risk7. Unfortunately, this perception has a basis in reality since blacks do in fact experience short-term complications of TKA more frequently than whites4,8-11. However, whether long-term outcomes of TKA are worse for United States blacks than whites is less clear.
The need for revision is the most definitive marker of long-term TKA failure; 2% to 5.7% of patients require revision TKA within 5 years12-17, most commonly for aseptic loosening or instability13,18. The risk of revision TKA is higher in patients who undergo surgery at a low-volume hospital19-21. Patient-related factors associated with an increased revision risk include being younger16,22-24 and having medical comorbidities16,20,25, but whether race and/or socioeconomic status contribute to revision risk is not clear. We performed a systematic review and meta-analysis to determine whether blacks in the United States are at greater risk of revision TKA than whites.
Materials and Methods
This systematic review was designed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines26.
We reviewed English-language articles published in peer-reviewed journals since January 1, 2000, to determine whether there was an association between black race and the risk of revision following TKA. We limited our search to studies published during or after 2000 to minimize bias related to temporal changes in TKA outcomes27. We restricted our review to articles published in peer-reviewed journals to ensure methodological oversight. We specifically avoided the use of “race” and similar terms in our search to minimize the effect of publication bias. That is, we surmised that authors might only use the term “race” in their title or abstract if race was found to be associated with revision risk, but not if an association was not found.
Study inclusion criteria were (1) performance of the study in the United States, (2) TKA as the primary procedure studied, (3) a follow-up period of at least 2 years, (4) reporting of revision rates, and (5) analysis of patient race as an independent predictor of revision.
Information Sources and Search Strategy
A medical librarian searched the MEDLINE database in PubMed, the Embase database, and the Cochrane Library (including the Cochrane Central Register of Controlled Trials, Health Technology Assessment Database, and NHS United Kingdom National Health Service] Economic Evaluation Database) using the following search strategy:
“Arthroplasty, Replacement, Knee*”[MeSH Major Topic] OR (total[Title/Abstract] AND knee[Title/Abstract] AND (arthroplasty[Title/Abstract] OR replacement[Title/Abstract]))
(((“risk”[MeSH Terms] OR “risk”[All Fields] OR “risk of”[All Fields]) AND failure[All Fields]) OR ((“risk”[MeSH Terms] OR “risk”[All Fields] OR “risk of”[All Fields]) AND revision[All Fields]) OR (rate[All Fields] AND failure[All Fields]) OR (rate[All Fields] AND revision[All Fields]) OR (revision[All Fields] AND (“risk”[MeSH Terms] OR “risk”[All Fields])) OR (“mortality”[Subheading] OR “mortality”[All Fields] OR “survival”[All Fields] OR “survival”[MeSH Terms])).
All searches were performed on March 31, 2015. The search returned 4,286 results.
Two reviewers (A.R.B, S.M.G) screened all titles, the abstracts of selected articles, and the full text of chosen abstracts (Fig. 1). We excluded studies with the following attributes: (1) study not performed in the United States, (2) procedure other than TKA (for example, unicompartmental knee arthroplasty [UKA] or total hip arthroplasty), (3) no reporting of revision rates, (4) study of TKA utilization or epidemiology, (5) study assessing outcomes of revision TKA, (6) literature review or expert opinion article, (7) wrong surgical outcome (such as short-term complications, mortality, or cost), (8) race not included in population demographics, or (9) race not analyzed as an independent variable.
We contacted the authors of papers in which revision was a primary outcome and the racial characteristics of the study population were provided, but in which the impact of race on revision rates was not published. In these cases we requested additional unpublished data from the authors. If they were unable to provide either hazard ratios (HRs) plus confidence intervals (CIs) for the risk of revision based on race, or raw data adequate for us to analyze, then the article was excluded. Data were extracted from the selected manuscripts by 1 of the authors using a standardized approach.
All included studies were graded 2b according to the Oxford Centre for Evidence-based Medicine levels of evidence28. The risk of bias within studies was low.
From each eligible study, we extracted a TKA revision HR estimate and corresponding 95% CI for blacks compared with whites from the multivariable Cox proportional hazards model with the most complete adjustment for potential confounders. Given an expected regional variation in effect size, a random-effects model was used to estimate a pooled TKA revision HR estimate with a 95% CI. We used the inverse variance method for pooling and the DerSimonian-Laird method29 to estimate between-study variance. A p value of <0.05 was considered significant for the test of overall effect. We assessed between-study heterogeneity using the Cochran Q test, with p < 0.10 considered significant, and calculated I2 to quantify the proportion of the total variation in effect estimates that can be attributed to heterogeneity as opposed to chance30. Potential publication bias was assessed by visual examination of a funnel plot, the Egger linear regression test31, and the Begg rank correlation test32, with p < 0.10 considered significant. Results of the funnel plot asymmetry tests were interpreted in the context of their noted lack of power when <10 studies are included in the analysis33,34.
Analyses were performed using the meta package implemented in R software (version 3.1.0; R Foundation for Statistical Computing).
All 4,286 identified studies were screened by title; 106, by abstract; and 24, by full text (Fig. 1). We contacted the authors of 3 studies that documented race but did not analyze it as an independent variable15,17,35 and were able to obtain additional data from 1 of them that we included in our analysis17. In the case of 2 additional publications in which race was documented but not analyzed25,36, the authors used the same data set to analyze the impact of race on revision rates in separate publications that were included in the meta-analysis13,37.
Six studies were selected for review (Table I)12-14,16,17,37. Three of the studies analyzed a nationally representative sample of Medicare beneficiaries from the Centers for Medicare & Medicaid Services (“national Medicare 5% sample”) and included overlapping populations12,17,37. Only 1 of these studies was included in the meta-analysis17. It was chosen because it encompassed the greatest time span and controlled for the most variables. Although all 4 studies suggested an increased risk of revision in blacks, we performed a meta-analysis to estimate the average magnitude of this risk.
Meta-Analysis and Study Characteristics
The meta-analysis represented 451,960 patients who underwent TKA, of whom 28,772 (6.4%) were black. Of the total patient population, 31,568 (7.0%) underwent revision surgery. The random-effects model suggested that blacks had a greater risk of revision compared with whites (pooled HR, 1.38; 95% CI, 1.20 to 1.58; p < 0.001) (Fig. 2). There was evidence of moderate heterogeneity among studies (p = 0.087; I2 = 54.4%). Neither the Egger linear regression test nor the Begg rank correlation test indicated publication bias (p = 0.996 and 0.497, respectively).
Four studies were included in the meta-analysis13,14,16,17. The study by Blum et al. used administrative data to assess racial differences in surgical complications, mortality, and revision after TKA using 2001-2007 Pennsylvania Health Care Cost Containment Council data14. They fitted a Cox proportional hazards model incorporating 5 years of follow-up, and censored patients at death or at the end of follow-up. Although they found no difference in 30-day or 1-year surgical complications or mortality for blacks compared with whites, the 5-year revision risk was 39% higher for blacks (p = 0.01).
Bolognesi et al. compared the risk of surgical complications and revision in patients undergoing UKA and TKA using data from the 1999-2009 national Medicare 5% sample17. The association of race with revision risk was not published, but at our request the authors provided results of a multivariable Cox proportional hazards model demonstrating a nonsignificant 13% increase in 5-year TKA revision risk in blacks compared with whites. Patients undergoing UKA compared with TKA had a comparable 1-year risk of infection, venous thromboembolism, or death, but more than double the risk of revision at 5 years (HR, 2.4; 95% CI, 2.03 to 2.83).
Dy et al. used the New York State Department of Health Statewide Planning and Research Cooperative System hospital discharge database as well as the California Office of Statewide Health Planning and Development hospital discharge database to analyze patient, hospital, and community-specific variables associated with TKA revision risk16. A Cox proportional hazards model was used to evaluate the time to revision TKA in the overall cohort, 5 and 9 years after index surgery. The revision risk was 39% higher in blacks (p < 0.001), and higher in patients who were of younger age, male, or underwent surgery at a low-hospital volume.
Namba et al. utilized 2001-2010 data from the Kaiser Permanente National Total Joint Replacement Registry to assess risk factors for aseptic TKA revision13. This registry includes Kaiser-insured patients from Southern and Northern California, Colorado, Georgia, Hawaii, the Northwest, and Mid-Atlantic states. Median follow-up was 2.9 years (interquartile range, 1.2 to 4.9 years). A Cox proportional hazards model revealed a 73% greater risk of TKA revision in blacks compared with whites. Revision risk was also associated with younger age, lower body mass index, diabetes, unilateral compared with bilateral TKA, and high-flexion implants.
All 4 studies controlled for age, sex, comorbidities, and hospital surgical volume (Table I). Three controlled for insurance status (Medicare compared with Medicaid)14,16,17 and the fourth study included only Kaiser Permanente-insured individuals13. Two studies controlled for geographic region (United States region and also urban compared with rural)16,17, and 1 cohort was geographically localized14. Hospital teaching status was controlled for in 3 studies14,16,17 and length of stay, in 2 of them14,17.
Three studies analyzed the national Medicare 5% sample from overlapping time periods from 1997 to 200912,17,37, of which only 1 was included in the meta-analysis17. These 3 studies all controlled for age, sex, and comorbidities. Only 1 of these 3 studies found a significant increase in revision risk for blacks37. This study differed from the other 2 in that it did not control for insurance or socioeconomic status (either Medicaid eligibility17 or eligibility for state subsidies for Medicare12) (Fig. 3). Hospital volume was controlled for only in the study by Bolognesi et al.17 but the HR for revision risk among blacks in that study was similar to the HR found in the study by Curtin et al.12 (HR, 1.13 compared with 1.19, respectively), suggesting that hospital volume was not a significant confounder in the national Medicare 5% sample.
Our meta-analysis demonstrates that blacks are at significantly higher risk of TKA revision than whites in the United States (pooled HR, 1.38; 95% CI, 1.20 to 1.58; p < 0.001) and that insurance/socioeconomic status is an important confounder in analyses of race. Specifically, in 3 published analyses of the national Medicare 5% sample12,17,37 race was a significant risk factor for TKA revision only in the study not controlling for insurance (Medicaid eligibility or eligibility for state subsidies for Medicaid), a surrogate marker for socioeconomic status. All studies that were included in the meta-analysis either controlled for insurance status14,16,17 or included patients insured by a single payer13. There was moderate heterogeneity among studies (p = 0.087; I2 = 54.4%) that could reflect regional differences among the study populations. In addition, 1 of the studies13 only analyzed the risk of aseptic revision, whereas the others included both septic and aseptic revisions. Neither the Egger linear regression test nor the Begg rank correlation test indicated publication bias; however, funnel plot asymmetry tests have low power when <10 studies are included in the analysis. Our meta-analysis was limited by the fact that many studies do not analyze race as a predictor of revision risk, even when the demographic data are available. We contacted the authors of 3 such studies15,17,35 but were only able to obtain adequate data from 1 of them17. Nonetheless, our findings are in keeping with other studies that show worse TKA outcomes in blacks 2 to 5 years after surgery, including greater pain38, poorer function39,40, and less overall patient satisfaction41.
Two-thirds of patients who undergo revision arthroplasty do so for aseptic failure (including loosening, instability, periprosthetic fracture, and arthrofibrosis) and one-third, for infection16. Blacks are more likely to have diabetes42, a risk factor for wound infection43 that is, in turn, a risk factor for septic prosthetic failure44. Blacks are at higher risk of postoperative arthrofibrosis45, and manipulation under anesthesia is a risk factor for aseptic revision46. Although blacks are more likely to live near high-volume hospitals, they are less likely than whites to use high-quality hospitals47. Even when blacks have surgery in high-volume hospitals they more commonly undergo surgery performed by residents48, and senior surgical residents have higher rates of complications than attending surgeons48. The risk of revision arthroplasty increases when the procedure lasts >120 minutes49, which is more likely with inexperienced surgeons.
The higher prevalence of poverty among blacks in the United States can make it difficult to interpret the association of race with surgical outcomes; 16% of blacks have incomes below the poverty level compared with 12% of whites, and being poor is associated with poor health50. Although most administrative databases lack data on patient socioeconomic status, insurance status can serve as a crude surrogate for income. Thirty-two percent of blacks compared with 15% of whites are insured by Medicaid51, and 21% to 26% of blacks compared with 13% to 16% of whites are uninsured50,51. Browne et al. demonstrated that Medicaid payer status is associated with a higher risk of postoperative in-hospital complications following joint arthroplasty after controlling for race52. In contrast, studies performed in countries with publicly funded universal health-care systems, such as the United Kingdom and Finland, found no significant relationship between socioeconomic status and short-term complications of joint replacement surgery53 or the risk of revision arthroplasty54. This suggests that societal factors can mitigate the impact of poverty on health-care outcomes.
Eliminating health disparities is a priority of both the United States Surgeon General55 and the United States Department of Health and Human Services56 in part because of their cost to society. It has been estimated that eliminating such disparities for minorities during the years from 2003 to 2006 would have reduced direct medical care expenditures by approximately $230 billion and indirect costs associated with illness and premature death by more than $1 trillion (in 2008 inflation-adjusted dollars)57. With regard to TKA revision specifically, hospital-level interventions should be undertaken to reduce the disparity in the risk among blacks and other disadvantaged groups. For example, preoperative education has been shown to reduce the risk of postoperative arthrofibrosis58, and preoperative diabetes and obesity management could help to reduce the risk of septic prosthetic failure. Future studies should address whether disparities in arthroplasty revision exist for both aseptic and septic revisions, since this will help to guide targeted interventions.
Investigation performed at the Hospital for Special Surgery, New York, NY
Disclosure: There was no external funding for this study. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work.
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