Abstract
Introduction: Surgical site infections (SSIs) occur in 0.69% of
total hip and knee arthroplasty (THA/TKA) patients (Berrios-Torres
et al., 2014). As the U.S. population ages, the number of
arthroplasty procedures is expected to increase as arthroplasty is
more common among individuals age 65 and older. If the infection
rate remains stable, we expect to see an increase in the infection
burden. This analysis projects the burden of SSIs in the years 2020
through 2030 to provide evidence for or against a significant
increase in the infection burden. Methods: Historical procedure
rates were estimated using the National Inpatient Sample (NIS)
dataset by averaging the years 2012 through 2014. Infection rates
obtained from the National Healthcare Safety Network (NHSN) were
averaged across the years 2006 through 2009. All rates were
stratified by age and gender. We used a Markov Chain Monte Carlo
(MCMC) decision tree to model the U.S. population in the years 2020
through 2030 and track the procedures and infections in each year.
We then used the Cox-Stuart test for trend to test for significant
increases in procedures and infections. Results: The model
projected a significant increase in infections from 2020 to 2030
for both hip and knee arthroplasty (Cox-Stuart test, p = 0.04 for
THA infections; p = 0.004 for TKA infections). The average
projected SSIs following THA increased from 3,850 in 2020 to 4,360
infections 2030 while the average projected SSIs following TKA
increased from 4,710 in 2020 to 5,060 infections in 2030. The age
65 to 84 cohort contributed the largest number of projected
procedures and infections and females contributed more procedures
and infections than males. Discussion: Given a projected increase
in infection burden, we expect that attributable patient hospital
costs and mortality will increase as well. We should consider
interventions to reduce the potential impact on the U.S. healthcare
system. Our results indicate that females age 65 to 84 are a
high-risk group that would be available to target for
interventions. Next steps in this research include adding the
infection risk of additional patient characteristics and assessing
the effect of interventions on overall SSI burden.
Table of Contents
Chapter 1. Introduction 6 Background 6 Problem Statement and
Purpose Statement 6 Significance Statement 6 Definition of Terms 8
Chapter 2. Review of the Literature 12 Chapter 3. Methodology 19
Monte Carlo Method 20 Markov Chain Process 20 Markov Chain Monte
Carlo (MCMC) Model Design 21 Model Inputs 21 Population Cohort 21
Procedure Counts 22 Table 1. Total knee arthroplasty and total hip
arthroplasty procedure and infection rates stratified by age cohort
and gender 23 Infection Rates 23 Background Mortality Rate 23
Applying Model Parameterization to MCMC 23 Figure 1. Markov Chain
Monte Carlo decision tree for hip or knee arthroplasty 25
Statistical Analysis 26 Model Outputs 26 Credible Intervals 26 Test
for Trend 27 Limitations 27 Software Packages 29 Chapter 4. Results
30 Total Hip Arthroplasty 30 Table 2. Total hip arthroplasty Monte
Carlo estimators for annual procedure and infection burden for
males stratified by age with results of the Cox-Stuart test for
trend 31 Table 3. Total hip arthroplasty Monte Carlo estimators for
annual procedure and infection burden for females stratified by age
with results of the Cox-Stuart test for trend 32 Table 4. Total hip
arthroplasty Monte Carlo estimators for annual procedure and
infection burden stratified by age with results of the Cox-Stuart
test for trend 33 Total Knee Arthroplasty 34 Table 5. Total knee
arthroplasty Monte Carlo estimators for annual procedure and
infection burden for males stratified by age with results of the
Cox-Stuart test for trend 35 Table 6. Total knee arthroplasty Monte
Carlo estimators for annual procedure and infection burden for
females stratified by age with results of the Cox-Stuart test for
trend 36 Table 7. Total knee arthroplasty Monte Carlo estimators
for annual procedure and infection burden stratified by age with
results of the Cox-Stuart test for trend 37 Comparing 2006 to 2014
estimates to model projections 38 Figure 2. Graph of estimated and
projected total hip and knee arthroplasty (THA/TKA) procedures from
2006-2030 38 Figure 3. Graph of estimated and projected surgical
site infections as a result of total hip and knee arthroplasty
(THA/TKA) from 2006-2030 40 Chapter 5. Discussion 41 Summary of
Results 41 Conclusions 41 Infection Burden 41 Impact of Age 42
Impact of Gender 42 Impact of Surgery Type 43 Limitations 43 Static
Model 43 Stable Historical Rates 43 Small Sample Size 44 Credible
Intervals 44 Table 8. Comparison of credible intervals (CR) and
Monte Carlo mean estimates for 100 samples and 1,000 samples in
male total hip arthroplasty 46 Immigration 47 Table 9. Comparison
of Monte Carlo population estimators to U.S. Census projections in
2030 47 Recommendations for Further Study 47 Poisson Regression
Validation 47 Comorbidity Rates 47 Mortality 48 Interventions 48
Public Health Implications 49 Final Summary 50 References 51
About this Master's Thesis
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