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Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Objective

The Health Belief Model holds promise in understanding patient-related factors that may explain disparities in the use of total joint arthroplasty (TJA). We examined whether patients' health beliefs differ between African Americans and whites.

Methods

In a primary care clinic setting, 691 African Americans and whites with at least a moderately severe degree of osteoarthritis (OA) completed the Arthritis-related Health Belief Instrument. The instrument has 4 scales: perceived benefits of TJA, perceived barriers to obtaining TJA, perceived severity of arthritis, and perceived susceptibility of arthritis to worsen.

Results

The sample (40% women) consisted of 263 (38%) African Americans and 428 (62%) whites who were similar with respect to education, amount of insurance coverage, number of comorbidities, and self-report OA severity score. The African American group was younger, had less men, had more participants who reported an annual income <$15,000, and had a higher body mass index than whites. After controlling for confounders, African Americans were almost 50% (odds ratio [OR] 0.60, 95% confidence interval [95% CI] 0.42–0.86, P = 0.005) as likely as whites to perceive that TJA is beneficial or helpful for their arthritis. Furthermore, African Americans were 70% (OR 1.7, 95% CI 1.18–2.44, P = 0.004) more likely than whites to recognize barriers (e.g., risky, etc.) to TJA. Race was not associated with either the perceived severity or the perceived susceptibility of arthritis to worsen.

Conclusion

Among patients with at least moderately severe OA, African Americans were significantly less likely than whites to perceive the benefits of TJA and more likely to recognize barriers to TJA.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Osteoarthritis (OA) of the lower extremity is a leading cause of disability in the elderly, and of increasing concern in an aging US population (1, 2). For individuals with advanced knee or hip OA in whom medical treatment has failed, total joint arthroplasty (TJA) has become the accepted treatment (3, 4). TJA is a cost-effective treatment option, with 90% of recipients experiencing relief of pain and/or functional improvement (5–11).

Despite these benefits, marked ethnic differences in the utilization of TJA are well documented. Even after controlling for health insurance status, white individuals are at least twice more likely than African Americans to undergo TJA (12–16). The observed ethnic disparities cannot be attributed to differences in the prevalence or severity of OA. The burden of OA is at least as prevalent and possibly greater in African Americans than in whites (17, 18).

Factors such as geographic location, sex, and income may explain the disparities to a certain extent, but not completely. Other factors that may contribute to these discrepancies include physician indication biases and patient-level factors. Examples of potential patient-level factors include ethnic differences in health valuation (i.e., African Americans are willing to pay a significantly lower proportion of their income to get relief of joint pain or disability than are whites) (19), preferences (i.e., African Americans are less likely than whites to express willingness to consider TJA if the procedure is needed and recommended) (20), knowledge (i.e., African Americans are less likely than whites to be familiar with TJA) (21), social interactions (i.e., African Americans are much less likely than whites to have a friend or relative who underwent TJA) (21, 22), and the use of natural remedies (i.e., African Americans are more likely to perceive prayer as helpful in the treatment of arthritis and less likely to consider TJA than whites) (23).

The Health Belief Model (HBM) holds promise in further understanding patient-related factors that may explain the observed disparity in TJA use. The HBM proposes that the likelihood that an individual will take action related to a health condition is determined by the individual's perceived threat of an illness, and the weight of the perceived benefit against the perceived barriers or cost of taking the action. The perceived threat of an illness is a subjective perception determined by both the perceived susceptibility to the disease and the perceived severity of the disease (24, 25). The basic elements of the HBM are indicated in Figure 1. Prior research supports the effectiveness and applicability of the HBM in various health-related behaviors and behavior modification programs (26–30). We believe that this model of patient-based factors influencing health care decision making provides a useful preliminary organizing framework for examining the variety of patient domains thought to affect TJA decision making.

thumbnail image

Figure 1. Elements of the Health Belief Model as applied to ethnic disparity in the use of joint arthroplasty. Other than ethnicity/race, factors associated with perceptions are other demographic characteristics (e.g., age, sex, etc.), socioeconomic status, disease severity, comorbidity, and psychological variables.

Download figure to PowerPoint

In this article, we present the initial results from the Indianapolis Osteoarthritis Cohort Study, the ultimate purpose of which was to examine whether racial differences in health beliefs are associated with racial variations in orthopedic surgery referral for consideration of knee and/or hip TJA. The goal of the current study was to examine whether patients' health beliefs vary by race among whites and African Americans who have at least moderately symptomatic OA. In the context of ethnic disparity in TJA use, we hypothesized that African Americans perceived less benefits and more barriers to TJA than whites. Additionally, African Americans perceived their arthritis to be less severe and less likely to worsen than whites.

PATIENTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Patient population.

Potential participants were identified through the electronic medical record (EMR) systems of Wishard County Hospital and the Roudebush Veteran Administration Medical Center (VAMC). As the sole county hospital, Wishard caters to a predominantly indigent population comprising 60% African Americans, 38% whites, and 2% other. The county hospital has an established primary care network consisting of its primary care centers and 6 community health centers located in the neighborhood throughout Indianapolis. Approximately 1 mile from the county hospital, the Roudebush VAMC serves veterans from Indiana and the surrounding states. In fiscal year 2000, the VAMC had 65,232 outpatient visits to primary care clinics. The patient population is approximately 17% African Americans, 82% whites, and 1% other.

From January 1, 2000 to July 31, 2005, patients seen in the primary care clinics who had International Classification of Diseases, Ninth Revision codes 719.46 (knee pain) and/or 719.45 (hip pain) and/or 719.4 (joint pain) and/or 715.90 (osteoarthrosis), and who had a radiograph report of knee and/or hip OA were identified. A master list of all the potential participants was created. From this master list, potential participants were interviewed at the time of their primary care clinic visit to determine their eligibility. During the clinic visit, patients were asked 2 questions from the National Health and Nutrition Examination Survey I: “Have you ever had pain in your knee or hip on most days for at least one month?” and “Over the past month, have you had pain in the knee or hip when walking or standing on at least half of the days?” Patients who answered yes to both of these questions were screened as positive for the presence of symptomatic OA. To be eligible, patients had to be ≥50 years of age and have had at least moderately symptomatic OA defined as a Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) summary score ≥30. The WOMAC summary score ≥30 was chosen based on a previous study that demonstrated that the mean ± SD WOMAC summary score for knee OA patients in the UK undergoing preoperative evaluation for total knee arthroplasty (TKA) was 27.6 ± 2.9 (31). Patients who already underwent knee/hip TJA or who had been referred to an orthopedic surgeon for their knee and/or hip pains were excluded.

Between March 1, 2003 and September 30, 2006, a total of 1,478 patients were approached. Of these, 748 patients met the study criteria. Fifty-seven patients (27 [8.2%] African Americans and 30 [7%] whites) declined to participate. The study was approved by the Indiana University School of Medicine Institutional Review Board (IU-IRB). To comply with the Health Insurance Portability and Accountability Act of 1996, which regulates access to patients and their medical records, we followed structured procedures approved by the IU-IRB.

Primary outcome measure.

Arthritis-related Health Belief Instrument.

The modified Arthritis-related Health Belief Instrument (AHBI), which is based on the HBM (32), is a 16-item tool with 4 characteristic themes or dimension scales (33): perceived severity of arthritis (3 items, score range 3–15), perceived susceptibility for arthritis to worsen (5 items, score range 5–25), perceived benefits of arthroplasty (3 items, score range 3–15), and perceived barriers to arthroplasty (5 items, score range 5–25). Perceived severity of arthritis refers to an individual's perception of the medical and/or social consequences of having arthritis or of not treating such a condition. Perceived susceptibility for arthritis to worsen refers to an individual's subjective perception of the risk or vulnerability for arthritis to progress. Perceived benefits of arthroplasty includes an individual's beliefs about the likelihood that receiving TJA will lead to effective treatment of arthritis. Perceived barriers to arthroplasty are the potential negative aspects of TJA. These may include cost, amount of time required, how convenient or inconvenient the course of action is, side effects of the action, and degree of unpleasantness (painful, upsetting, difficult, etc.).

The 16 health belief items were measured on a 5-point Likert scale with the following response options: 1 = strongly disagree, 2 = disagree, 3 = undecided, 4 = agree, and 5 = strongly agree. In each of the scales, a higher composite score indicates a heightened perception of the specific latent construct (i.e., severity, susceptibility, benefits, and barriers) being measured. In the modified AHBI, the perceived benefits and barriers scales were preceded with the following statement: “Assume your arthritis is severe, and your doctor recommends joint replacement surgery to treat your arthritis.”

Ang and colleagues have reported that the Cronbach's alpha reliability estimates for each dimension range from 0.7 to 0.8 (33). Factor analysis indicated that the dimensions of the HBM are sufficiently distinct to be considered different beliefs (32, 33). Establishment of factorial invariance of the AHBI lends further support for the use of the instrument in comparing mean scale scores between African Americans and whites (33). The survey items for each of the 4 health belief scales are listed in Table 1.

Table 1. Arthritis-related Health Belief Scales
Perceived benefits of arthroplasty
 1. Joint replacement surgery would get rid of my joint pain.
 2. Joint replacement surgery would allow me to do things that I like to do.
 3. Joint replacement surgery will make me feel better.
Perceived barriers of arthroplasty
 1. The joint replacement surgery I am aware of is too risky and too time consuming.
 2. I would have to change too many daily activities to undergo joint replacement surgery for my arthritis.
 3. It is too inconvenient for me to get joint replacement surgery.
 4. I would experience too much pain several weeks after joint replacement surgery.
 5. To get joint replacement surgery would cause too much inconvenience to my immediate family members.
Perceived severity of arthritis
 1. My arthritis keeps me from doing things I want to do.
 2. My arthritis limits my daily activities.
 3. My arthritis interferes with my going to work or school.
Perceived susceptibility of arthritis to get worse
 1. Due to the condition of my physical health, my arthritis is likely to get worse.
 2. My chances that my arthritis will get worse are great.
 3. Within the next year my arthritis will get worse.
 4. I worry a lot about my arthritis getting worse.
 5. It worries me to think about the effect my arthritis will have on my health.

Other study measures.

The WOMAC is a 24-item questionnaire that probes 3 dimensions: pain (score range 0–20), stiffness (score range 0–8), and physical function (score range 0–68). It has been extensively validated and shown to be a reliable and responsive instrument (34). The WOMAC summary score is generated by adding scores from all 3 dimensions, and then transposing the summary score to a 0 (asymptomatic) to 100 (very symptomatic) scale.

The Arthritis Impact Measurement Scales depression subscale (AIMS-depression) is a widely used rheumatic disease health status instrument for which reliability and validity have been well documented (35–40). The AIMS-depression scale has a score range from 0 (no depression) to 10 (worst depression).

The modified Deyo-Charlson comorbidity index was used to assess overall disease burden. The index assigned nonzero weights to 19 conditions based on their risk of mortality. The weights can take on values of 1, 2, 3, or 6 and are then summed for each patient (41–46). To compute the comorbidity index, the administrative databases (with the diagnosis codes) in both institutions were used. The modified Deyo-Charlson comorbidity index has been shown to predict mortality in a prospective cohort study of community-dwelling older adults attending a large primary care practice (47).

Baseline demographic information.

Using field-tested questionnaires, interviewers gathered demographic information, such as age, sex, education level, employment status, annual household income, and marital status. Patients were asked to self-identify their ethnicity. EMR abstractions provided information on height, weight, amount and type of insurance coverage, and comorbidity.

Statistical analysis.

Comparisons between African Americans and whites in the sample were performed using t-test for continuous, normally distributed variables and chi-square test for categorical variables. Because of the clinical orientation of this study, we categorized the health belief scales to provide odds ratios. Specifically, clinically meaningful cut points of the total scores were based on the implication of the item response categories. That is, the total score was dichotomized at the cut point where the average over items indicated either agreement or nonagreement: strongly agree (score 5) and agree (score 4) in one category, and undecided (score 3), disagree (score 2), and strongly disagree (score 1) in the other category. For example, the 5-item perceived barriers scale was categorized at ≤15 versus ≥16 because 3 times 5 equals 15; thus, a score of ≥16 indicates that on average the participant agreed or strongly agreed with the items of that scale. The chi-square test was used in bivariate analyses to compare African Americans and whites on the following binary health belief variables: perceived benefits of TJA, perceived barriers to TJA, perceived severity of arthritis, and perceived susceptibility of arthritis to worsen. To determine the independent effect of race on each of the health belief variables, 4 multivariable logistic regression analyses were performed. Rather than a statistical prediction modeling approach (e.g., stepwise regression), we took an explanatory modeling approach by including all variables in the model that were of theoretical importance. Each regression model contained the following covariates: age, sex, education, income, amount and types (Medicare, Medicaid, private insurance, and VA coverage) of insurance coverage, AIMS-depression, body mass index (BMI), number of comorbidities, WOMAC-pain, WOMAC-function, and recruitment site (Wishard County–affiliated clinics versus VAMC). Additionally, we tested the interaction of race with recruitment site in each of the 4 models.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Study population.

The 691 participants had a mean ± SD age of 64.4 ± 9.6 years, 59% were men, 64% had a high school education or less, 20% were employed (either full time or part time), and 55% reported an annual household income <$15,000. The mean ± SD WOMAC summary score was 56.4 ± 14.2, suggesting moderately severe OA. As summarized in Table 2, the sample consisted of 263 African Americans (38%) and 428 whites (62%) who were similar with respect to educational attainment, amount of insurance coverage, number of comorbidities, and WOMAC summary score. As compared with whites, the African American group was younger, had fewer male patients, had more participants who reported an annual household income <$15,000, had a higher BMI, and was more likely to have patients recruited from the Wishard County–affiliated primary care clinics.

Table 2. Baseline characteristics*
VariablesAfrican Americans (n = 263)Whites (n = 428)P
  • *

    Values are the mean ± SD unless otherwise indicated. VAMC = Veterans Administration Medical Center; AIMS = Arthritis Impact Measurement Scales; WOMAC = Western Ontario and McMaster Universities Osteoarthritis Index.

Age, years62.7 ± 8.865.5 ± 9.90.0001
Male sex, %40.670.70.0001
High school diploma or less, %63.864.70.8
<$15,000 annual household income, %65.749.30.0001
Recruitment sites, %   
 County hospital affiliated65.030.30.0001
 VAMC35.069.6 
Body mass index, kg/m234.4 ± 8.233.1 ± 8.00.03
Comorbidity score0.9 ± 1.31.1 ± 1.20.1
Amount of insurance coverage1.6 ± 0.81.5 ± 0.80.3
AIMS-depression (0–10)3.2 ± 2.03.6 ± 2.00.01
WOMAC pain (0–20)11.7 ± 3.311.4 ± 3.40.2
WOMAC function (0–68)39.9 ± 11.240.3 ± 10.30.6

Relationship between race and the health belief scales.

As compared with whites, a larger proportion of African Americans (58.1% versus 44.3%; P = 0.0001) perceived less benefit from TJA (Table 3). In addition, a greater percentage of African Americans than whites (42.4% versus 30.8%; P = 0.002) perceived more barriers to undergoing surgery. Despite such differences, there were equal proportions of African Americans and whites who perceived their arthritis to be severe, or who perceived an increased susceptibility of arthritis to worsen.

Table 3. Proportion of responses between African Americans and whites on the health beliefs scales*
Health beliefs scalesAfrican AmericansWhitesP
  • *

    Values are the percentage unless otherwise indicated. TJA = total joint arthroplasty.

  • Each item was measured on a 5-point Likert scale ranging from strongly disagree (score 1) to strongly agree (score 5). Higher score means greater perceived benefits or barriers to TJA, or greater perceived severity of arthritis, or susceptibility for arthritis to become worse.

Perceived benefits of TJA (3 items)   
 Greater perceived benefits (score ≥10)41.855.60.0001
 Lower perceived benefits (score ≤9)58.144.3 
Perceived barriers of TJA (5 items)   
 Greater perceived barriers (score ≥16)42.430.80.002
 Lower perceived barriers (score ≤15)57.669.1 
Perceived severity of arthritis (3 items)   
 Greater perceived severity (score ≥10)76.176.70.8
 Lower perceived severity (score ≤9)23.923.2 
Perceived susceptibility of arthritis to get worse (5 items)   
 Greater perceived susceptibility (score ≥16)76.773.40.3
 Lower perceived susceptibility (score ≤15)23.226.5 

In the multivariable logistic regression, African Americans were almost half as likely as whites to perceive that TJA is beneficial or helpful for their arthritis (odds ratio [OR] 0.60, 95% confidence interval [95% CI] 0.42–0.86, P = 0.005) (Table 4). In the same model, recruitment site was a significant predictor of perceived benefits of TJA. Specifically, patients recruited from the county-affiliated recruitment site were significantly less likely than those recruited from the VAMC site to perceive the benefits of TJA (OR 0.45, 95% CI 0.23–0.89, P = 0.02). As expected, patients with more severe depressive symptoms were less likely to perceive benefits.

Table 4. Multivariable associations of the health belief variables with patient-related factors*
 UnivariateMultivariate
OR (95% CI)OR (95% CI)P
  • *

    OR = odds ratio; 95% CI = 95% confidence interval; HS = high school; see Table 2 for additional definitions.

  • Each regression model contained the following variables: race, age, sex, education, income, amount and types of insurance coverage, AIMS-depression, body mass index, comorbidity score, WOMAC-pain, WOMAC-function, and recruitment sites. Only variables that reached (or were close to) statistical significance are shown in the table. Reference level for the categorical variable is included in parentheses.

Perceived benefits of arthroplasty   
 Race (whites) African Americans0.57 (0.42–0.78)0.60 (0.42–0.86)0.005
 Income1.21 (1.07–1.36)1.15 (0.99–1.33)0.051
 AIMS-depression0.95 (0.88–1.02)0.90 (0.83–0.98)0.03
 Recruitment sites (VAMC) Wishard County0.67 (0.49–0.91)0.45 (0.23–0.89)0.02
Perceived barriers of arthroplasty   
 Race (whites) African Americans1.68 (1.19–2.26)1.70 (1.18–2.44)0.004
 Education (≤HS diploma) >HS0.56 (0.40–0.80)0.83 (0.70–0.99)0.05
 AIMS-depression1.08 (1.00–1.16)1.09 (0.99–1.19)0.051
Perceived severity of arthritis   
 Race (whites) African Americans0.96 (0.67–1.38)0.97 (0.62–1.53)0.9
 Income0.72 (0.62–0.83)0.77 (0.64–0.92)0.005
 AIMS-depression1.42 (1.28–1.59)1.29 (1.14–1.45)0.0001
 WOMAC-function1.07 (1.05–1.09)1.05 (1.02–1.08)0.0001
Perceived susceptibility of arthritis to worsen   
 Race (whites) African Americans1.19 (0.83–1.70)1.30 (0.84–2.02)0.2
 Sex (female) male0.86 (0.60–1.23)2.72 (1.16–6.35)0.02
 AIMS-depression1.45 (1.30–1.61)1.36 (1.21–1.53)0.0001
 WOMAC-function1.05 (1.03–1.07)1.04 (1.01–1.06)0.002
 Comorbidity score0.83 (0.73–0.95)0.78 (0.67–0.92)0.003

In the second regression model, African Americans were 70% more likely than whites to recognize barriers (i.e., risky, time consuming, inconvenience, too much postoperative pain) to TJA (OR 1.7, 95% CI 1.18–2.44, P = 0.004). Recruitment site was not a significant predictor (OR 1.38, 95% CI 0.71–2.66, P = 0.33) of the barrier health belief.

In both the first and second models, the interaction of race and recruitment site (Wishard County–affiliated clinics versus VAMC) was not significant (P < 0.4). Additional regression models showed that race was not significantly associated with either the perceived severity of arthritis (OR 0.97, 95% CI 0.62–1.53, P = 0.9) or the perceived susceptibility of arthritis to worsen (OR 1.30, 95% CI 0.84–2.02, P = 0.2). The associations of the health belief variables and the patient-related factors that reached (or were close to reaching) statistical significance are shown in Table 4.

DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

In our sample of almost 700 primary care patients with moderately severe OA, African Americans were significantly less likely to perceive the benefits of TJA and more likely to recognize barriers to TJA than whites. In contrast, African Americans and whites did not differ in their perceptions of the severity of arthritis or in their belief that their arthritis would progress.

Behavior models, such as the HBM, have guided much of current health-promotion research and practice (25, 48–51). As indicated in Figure 1, the HBM posits that health behavior is influenced by the perception an individual has of the effectiveness of treatment when deciding whether to seek medical attention (25). Individuals with moderately severe OA who are contemplating receiving TJA must first perceive that arthroplasty is efficacious. Before making a decision to undergo TJA, the individual must believe that the benefits of TJA outweigh its costs or the negative aspects (barriers) of surgery. Because multiple interacting beliefs could influence health behavior, we postulate that beliefs (i.e., lower perceived benefits and a higher perceived barrier of TJA) held by African Americans may partly explain the potential underuse of the procedure among ethnic minorities.

Our findings confirmed 2 previous reports on the role of patient-level factors in TJA use. In a cross-sectional survey study of male veterans with moderate-to-severe symptomatic knee or hip OA, Ibrahim et al reported that African American patients were more likely than white patients to express concerns about postsurgical pain and difficulty walking (20, 21). In another study of patients with knee OA attending a single urban multiclinic institution, Suarez-Almazor and colleagues found that ethnic minorities were less inclined than whites to consider TKA, and that the ethnic variation in this preference was associated with difference in the perception of the benefits of TKA (22). Methodologically, the current study differed in 3 ways. First, participants, 40% of whom were female, were recruited from 2 different multiclinic sites, thereby increasing generalizability. Second, the health belief instrument used in the study has good psychometric properties including factorial invariance or equivalence (i.e., scale scores are comparable when administered to different groups) (33). If scales are not equivalent, then findings about group differences are potentially biased (52). Third, a sample size of almost 700, the largest to date, also adds strength to the current report.

The study has several limitations. First, we cannot be sure that ethnic differences in the arthritis-related health beliefs are the true determinants of TJA use. Because referral to an orthopedic surgeon is the only means by which TJA is made available to patients with OA, we are currently doing a followup survey to determine whether ethnic differences in health beliefs predict referral to an orthopedic surgeon. Second, because a previous joint radiograph (as requested by a patient's primary care physician) indicating OA was a requirement to enter the study, patients with definite OA but no prior radiograph may have been excluded. However, because the study goal was to elicit the health beliefs of patients with OA symptomatic enough to warrant a joint radiograph, the studied population was deemed appropriate. Last, although the proportion of African Americans and whites in the final sample does not represent the distribution of patients who attend Wishard-affiliated clinics, the ethnic distribution in the final sample is close to that of Marion County, Indiana, where both the Wishard County Hospital and VAMC are located.

To our knowledge, this is the first study to assess ethnic differences in arthritis-related health beliefs based on a specific model of health behavior. The study results are significant because modifiable factors, specifically, ethnic differences in perceived benefits and barriers of TJA, may be amenable to educational or behavioral intervention. In the clinical setting, health providers should assess the patient's perceived barriers and benefits of TJA. In the interest of informed decision making, clinicians should also make sure that beliefs are based on accurate perceptions of risk and benefits (53). Further study is needed to determine whether these differences in health beliefs would explain the disparity in TJA use in the long run.

AUTHOR CONTRIBUTIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES

Dr. Ang had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

Study design. Ang.

Acquisition of data. Ang.

Analysis and interpretation of data. Ang, Monahan, Cronan.

Manuscript preparation. Ang, Monahan, Cronan.

Statistical analysis. Ang.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. PATIENTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. AUTHOR CONTRIBUTIONS
  8. REFERENCES
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