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Inpatient Mortality After Primary Total Hip Arthroplasty: Analysis from the National Inpatient Sample Database
The Journal of Arthroplasty 30 (2015) 369–373
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Inpatient Mortality After Primary Total Hip Arthroplasty: Analysis from the National Inpatient Sample Database Kenneth D. Illingworth, MD a, Youssef F. El Bitar, MD a, Devraj Banerjee, MD a, Steven L. Scaife, MS b, Khaled J. Saleh, MD, MSc, FRCS(C) a a b
Division of Orthopaedics and Rehabilitation, Department of Surgery, Southern Illinois University School of Medicine, Springfield, IL Center for Clinical Research, Southern Illinois University School of Medicine, Springfield, IL
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Article history: Received 16 January 2014 Accepted 4 August 2014 Keywords: total hip arthroplasty mortality inpatient complications age payer status
a b s t r a c t Although inpatient mortality rates following total hip arthroplasty are low, understanding factors that influence inpatient mortality rates is important. Discharge data from the 2007–2008 HCUP Nationwide Inpatient Sample database were used in this study. Patients were identified based on whether they were admitted for a primary total hip arthroplasty and grouped based on their mortality status. All hip and acetabular fracture patients were excluded. Discharge data revealed 508,150 primary total hip arthroplasties with an inpatient mortality rate of 0.13%. The most significant pre-operative predictors of inpatient mortality were increasing age, weekend admission, increased Charlson co-mobidity score, Medicare payer status, race and a Southern hospital region. The two most significant complications post-operatively leading to increased mortality were pulmonary and cardiovascular complications. Published by Elsevier Inc.
Degenerative joint disease affects approximately 43 million Americans, often resulting in debilitating pain and decreasing functional capacity. The economic impact of degenerative joint disease is estimated to be $60 billion per year [1]. As the numbers of total joint arthroplasties (TJA) have increased, there has been little debate as to the clinical merits of these procedures. Few orthopedic surgical procedures can claim to treat adult end-stage disease with quite the same degree of consistent clinical success. With 572,000 primary total hip arthroplasties (THA) projected annually by 2030, the societal impact of THA is undeniable [2]. As technology, education, pre-operative management, and surgical techniques have improved over the last few decades, the mortality rates after THA have decreased [3–5]. However, along with such advancements, and an ever-increasing age of the general population, older and more medically-complicated patients are undergoing joint arthroplasty [5–8]. Additionally, with the improvement of implant technology and increased survivorship of modern joint arthroplasty, younger and more active patients are seeking earlier intervention for debilitating joint pain and therefore expanding the demographics of utilization of THA [8–10]. Although considered to be a safe and effective procedure, complications following THA exist and include infection, dislocation, and
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.08.002. Reprint requests: Khaled J. Saleh, MD, MSc, FRCS(C), MHCM, Division of Orthopedics and Rehabilitation, Chairman, Director of Clinical and Translational Research, Southern Illinois University School of Medicine, P.O. Box 19679, Springfield, IL 62794-9679. http://dx.doi.org/10.1016/j.arth.2014.08.002 0883-5403/Published by Elsevier Inc.
pulmonary embolism [11]. Complication rates following THA have been reported to be up to 3.9% of patients [12,13] with the most concerning of these complications being mortality [4,6,7,14–19]. Inpatient mortality rates after THA in the literature have been reported to range from 0.1 to 0.8% over the last couple of decades [4–6,8,20], lower than the older reported rates in the 1970s of 1 to 2% [3]. Technological advances, better pre-operative care and patient optimization have all impacted the decrease in inpatient mortality rates. With an increasing number of THA being performed in all age groups, identification of factors that may influence mortality would be important both for individual patient care and societal health care cost burden, and therefore it is more important than ever to identify risk factors associated with increased inpatient mortality following THA [2,6,7]. The purpose of this study was to use a large national database in order to determine what variables affect inpatient mortality rates following primary TJA. Specifically the relationships between mortality, patient demographics, hospital demographics, inpatient complications, co-morbidities and weekend admissions were assessed. We hypothesized that the most significant factors in inpatient mortality following THA will be an increasing patient age and inpatient complications. Materials and Methods A large national database was used to identify patients who had inpatient hospital stays after a primary THA. Patients were grouped by inpatient mortality and statistical analysis was done to determine the association between mortality, patient demographics, hospital demographics, inpatient complications, co-morbidities and weekend admission.
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Investigational review board approval was obtained by the Committee for Research Involving Human Subjects for this study. Discharge data from the 2007 and 2008 Nationwide Inpatient Sample (NIS), were used in this study. Data were accessed in July of 2011 [21,22]. The 2007 and 2008 NIS databases utilize longitudinal hospital inpatient information from over 40 states, and contains information on approximately 16 million inpatient stays in 1000 hospitals, reflecting 20% of U.S. hospitals. The information in the NIS database includes sources and types of admissions, diagnoses and procedures, discharge statuses, and patient demographics [21]. At the time of analysis the 2008 NIS database was the most current database available. The outcome of interest was THA and their respective inpatient mortality rates. Inclusion criteria for this study were inpatient stay for primary THA using the International Classification of Diseases, Ninth Edition (ICD-9) code 81.51. Exclusion criteria were admission for femoral neck fracture (ICD-9 codes 820.00, 820.01, 820.02, 820.03 and 820.09) and or/acetabular fracture (ICD-9 code 808.00). All identifying patient information was removed prior to analysis. The variables of interest are listed in Table 1 and included age, gender, ethnicity, primary payer type, hospital location, hospital length of stay (LOS), mean income quartile, co-morbidities, Charlson co-morbidity index, weekend admission, hospital region and hospital teaching status, patient location and inpatient complications. Mean income quartile and patient location were based off the patients' 6 digit zip code. Obesity was defined as a body mass index above 30. The presence of diabetes was determined based on subjective patient disclosure at admission. The Charlson co-morbidity index score predicts the 10-year mortality for a patient who may have a range of co-morbid conditions such as heart disease, AIDS, or cancer (a total of 22 conditions). Each condition is assigned with a score of 1, 2, 3 or 6
Table 1 Independent Variables for Inpatients Undergoing Primary THA. Age b64 65–79 N80
Location Urban Rural b
Gender Male Female Race White Black Hispanic Other Primary Payer Type Medicare Medicaid Private All othersd
c
Median household income 38,999 or less 39,000 to 47,999 48,000 to 62,999 63,000 or more Inpatient complications Cardiovascular Cerebrovascular Pulmonary Mechanical wound Infection Systemic
b
Patient location Urban Rural
depending on the risk of dying associated with this condition. Scores were divided into one of three groups for analysis; 0, 1 or 2 and greater than 3 [23]. The Charlson score was directly provided by the NIS database and was not individually calculated. Patient location was designated as rural or urban based on the National Council for Health Statistics (NCHS) 2006 rural urban classification scheme for counties [19]. This 6 level classification is scaled from most urban category with large metropolitan central counties, to the most rural with nonmetropolitan noncore counties. Micropolitan and non core areas were considered rural for the purpose of this study. Inpatient complications were categorized into 6 groups based on ICD-9 codes. The cardiovascular group included ICD-9 codes for acute myocardial infarctions; Cerebrovascular group included ICD-9 codes for cerebral infarction; pulmonary group included ICD-9 codes for pneumonia and pulmonary embolus; Mechanical wound group included ICD-9 codes for surgical wound dehiscence and hematoma; infection group included ICD-9 codes for post-operative infection; and systemic group included ICD-9 codes for systemic shock. The specific ICD-9 codes for each group are listed below Table 1. Statistical Analysis The data were weighted using the discharge weights included in the NIS. The discharge weights were calculated to permit extrapolation of the NIS sample discharges to provide national estimates. Each weighted value was rounded to the nearest whole number for statistical analysis. Univariate analyses, specifically chi-square tests, were conducted to determine significant differences between groups. The primary analysis focused on pre-operative predictors of inpatient mortality using a logistic regression analysis with odds ratios and 95% confidence intervals. The secondary analysis focused on mortality as it related to inpatient complications using a logistic regression analysis with odds ratios and 95% confidence intervals. All analysis was done on SAS version 9.2.
Co-morbidities Diabetes Obesity a Charlson Index Score 0 1 or 2 N3
Source of Funding
Weekend admission
There were 508,150 primary THAs performed from 2007 to 2008 with an overall inpatient mortality rate of 0.13%. The mortality rate after inpatient THA for the pre-operative variables is listed in Table 2. Weekend admission was associated with the highest rate of mortality, 0.86%. Patients greater than 80 years of age had a mortality rate of 0.42%. A primary payer of Medicare was associated with a mortality rate of 0.20%; while a private (including HMO) primary payer had a mortality rate of 0.05%. Patient co-morbidities and inpatient mortality rates are listed in Table 3. A Charlson co-morbidity score of N3 was associated with a mortality rate of 0.30%. Mortality rates for inpatient complications are listed in Table 4. Pulmonary and cardiovascular inpatient complications were associated with the highest mortality rates of the inpatient complications, 4.79 and 3.40%, respectively. The hospital length of stay for all inpatient THA mortality patients is presented in Fig. 1. Three hundred forty four patients died with the first 4 days after surgery, 147 died from 5 to 9 days and 169 died in the hospital greater than or equal to 10 days. Odds ratios and 95% confidence intervals for the pre-operative variables are listed in Table 5. The most significant pre-operative variables related with an increase in inpatient mortality were age N 80, weekend admission, Medicare payer type, a Charlson co-morbidity score greater than 3 and operation at a hospital in the southern region. Odds ratios and 95% confidence intervals for inpatient complications are listed in Table 6. The two most significant inpatient complications resulting in increased
Hospital length of stay Hospital region Northeast Midwest South West Hospital type Rural Urban non-teaching Urban Teaching
Cerebrovascular included occlusion and stenosis of precerebral arteries (ICD-9 codes 433.00–433.91). Pulmonary included pneumonia (ICD-9 Codes 480.00–486.00, 997.31–997.39), acute respiratory failure following trauma or surgery (ICD-9 codes 518.51–518.53) and pulmonary embolus (ICD-9 codes 415.11–415.19). Mechanical wound included hematoma complicating a procedure and disruption of operation wound (ICD-9 codes 998.12–998.13, 998.30–998.33). Infection included postoperative infection (ICD-9 codes 998.51–998.59, 999.31–999.39, 996.66). Systemic included septic shock and hemorrhage (ICD-9 codes 998.00–998.09, 998.11). a Co-morbidity was quantified using the nine disease conditions used in Charlson comorbidity index [23]. b Determined by patient zip code. c Cardiovascular included acute myocardial infarctions (ICD-9 codes 410.00–410.92). d Self pay, no charge and others were combined in a single category.
No external source of funding was necessary for completion of this study. Results
K.D. Illingworth et al. / The Journal of Arthroplasty 30 (2015) 369–373 Table 2 Pre-Operative Variables for Inpatients Undergoing Primary THA. Pre-Operative Variables
Table 4 Inpatient Complications for Patients Undergoing Primary THA.
Mortality (no) Mortality (yes) % Mortality n = 507,490 n = 660 0.13%
Age b64 235,869 65–79 206,494 N80 64,517 Gender Male 223,158 Female 282,435 Ethnicity White 322,186 Black 25,043 Hispanic 10,684 Other 12,383 Primary payer Medicare 261,834 Medicaid 15,714 Private (and HMO) 210,524 Other 18,530 Location Urban 395,381 Rural 97,696 Median household income per zip code b38,999 93,688 39,000–47,999 128,520 48,000–62,999 129,681 N63,000 145,872 Weekend admission No 504,590 Yes 2,900 Elective No 30,650 Yes 474,663 Hospital region Northeast 102,022 Midwest 139,077 South 156,124 West 110,267 Teaching status Rural 51,834 Urban non-teaching 221,393 Urban teaching 233,769
371
99 288 273
0.04 0.14 0.42
388 322
0.17 0.11
410 48 18 34
0.13 0.19 0.17 0.28
518 14 113 15
0.20 0.09 0.05 0.08
495 144
0.13 0.15
160 166 182 133
0.17 0.13 0.14 0.09
636 25
0.13 0.86
111 544
0.36 0.12
105 168 298 89
0.10 0.12 0.19 0.08
84 268 308
0.16 0.12 0.13
inpatient mortality after primary THA were pulmonary and cardiovascular complications. Discussion
Inpatient Complication Cardiovascular No Yes Cerebrovascular No Yes Pulmonary No Yes Mechanical wound problem No Yes Infection No Yes Systemic No Yes
Mortality (no)
Mortality (yes)
% Mortality
500,581 6,909
417 243
0.08 3.40
505,206 2,285
633 27
0.13 1.17
502,215 5,276
395 265
0.08 4.79
505,277 2,213
626 35
0.12 1.55
506,364 1,126
641 20
0.13 1.74
502,695 4,795
588 73
0.12 1.49
one of the most successful surgeries in terms of cost-effectiveness, decreasing pain, and improving quality of life [7,14,17,24]. Inpatient mortality after primary THA is low, however the ever-increasing number of patients needing THA in the near future makes understanding these factors that contribute to inpatient mortality rates a must for both surgeons and patients. The most significant predictor of increased inpatient mortality after primary THA was a patient age greater than 80 years. Patients over 80 years of age had a significant increase in mortality over patients less than 64 years of age (OR 10.07, CI [8.00–12.68]). Patients 65–79 years of age also had a significant increase in mortality over patients less than 64 years of age (OR 3.32, CI [2.64–4.17]), however not to the extent of the patients over 80 years of age. The findings of increased age and increased risk of mortality are consistent with the literature, with literature findings indicating that the older the patient, the higher the risk of mortality [5,6,24]. Healy et al found that in the United States, the rate of acute mortality after inpatient orthopedic surgical procedures is approximately 1% for all patients, 3.1% for patients with a hip fracture, and 0.5% for patients without a hip fracture [5]. A study by Blom et al stratified the risk of mortality in relation to age in patients undergoing THA and found that the 90-day mortality rate increased with increasing age of the patient, reaching 2.5% for patients older than 80 years [19].
The most important finding of this study is that multiple preoperative variables and post-operative inpatient complications were identified that contributed to a statistically significant increase in inpatient mortality rates after primary THA. The variables that were highly associated with an increase in inpatient mortality after primary THA were presence of inpatient complications, weekend admission, an increasing patient age and Medicare payer status. THA remains
Table 3 Co-Morbidities for Inpatients Undergoing Primary THA. Co-Morbidities
Mortality (no)
Mortality (yes)
% Mortality
No Yes
437,955 69,535
590 71
0.13 0.10
No Yes Charlson score 0 1 or 2 N3
449,651 57,930
630 30
0.14 0.05
311,856 152,451 43,183
267 263 131
0.09 0.17 0.30
Diabetes
Obesity
Fig. 1. Hospital length of stay for all inpatient mortalities occurring after primary total hip arthroplasty.
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Table 5 Odds ratios and 95% Confidence Intervals for the Pre-Operative Variables in Patients Undergoing THA. Odds Ratio Race (compared to white) Black Hispanic Other Payer status (compared to private/HMO) Medicaid Medicare Other Income quartile (compared to N$63,000) b$38,999 $39,000–$47,999 $48,000–$62,999 Charlson score (compared to score of 0) 1 or 2 3 or more Hospital region (compared to West) Midwest Northeast South Hospital type (compared to urban teaching) Urban non-teaching Rural Age (compared to b65) 65–79 N79 Female (compared to male) Rural patient location (compared to urban) Diabetes Obesity Weekend admission Non-elective
95% CI
1.52 1.35 2.18
(0.79–2.93) (0.85–2.16) (1.54–3.09)
1.65 3.68 1.52
(0.94–2.87) (3.00–4.51) (0.89–2.60)
1.87 1.41 1.54
(1.49–2.36) (1.12–1.77) (1.23–1.92)
2.02 3.54
(1.70–2.39) (2.87–4.36)
1.49 1.27 2.36
(1.15–1.93) (0.96–1.69) (1.86–2.99)
1.24 0.92
(0.97–1.57) (0.78–1.08)
3.32 10.07 0.75 1.17 0.76 0.37 6.76 3.18
(2.64–4.17) (8.00–12.68) (0.65–0.88) (0.97–1.41) (0.59–0.97) (0.25–0.53) (4.52–10.13) (2.60–3.90)
Weekend admission was associated with a significant increase in morality when compared with weekday admissions (OR 6.76 CI [4.52– 10.13]). THA performed for hip or acetabular fractures were excluded from this study, therefore, theoretically the mortality associated with hip or acetabular fractures for non-elective procedures was not a confounding factor. The database only reports on the admission day, and does not clarify if the surgery was actually done on a weekend or a weekday. Patients can be admitted on a weekend, but have their surgery done on a weekday following a few days of stay in the hospital. Elective admission of a patient for a THA is usually done on a weekday, and usually the surgery is performed the same day. Some patients with more health-related risk factors might be admitted to the hospital for medical optimization on a weekend prior to surgery in order to undergo surgery during the early weekdays. Some patients are admitted for anticoagulation bridges during the weekend in preparation for surgery at the beginning of the week. These patients necessarily have cardiovascular comorbidities that increase their mortality risk. This might be one explanation as to why mortality in these patients was higher than patients who were admitted on weekdays. Another reason as to why patients might be admitted on a weekend is the tight operating room (OR) schedule in the hospitals. In order to maximize the use of the OR, some surgeons elect to perform their elective operations on a weekend where they have more available surgical time. During the weekends, the operating room staff is at a minimum with staff from different specialties Table 6 Odds ratios and 95% Confidence Intervals for Inpatient Complications in Patients Undergoing Primary THA. Inpatient Complication Cardiovascular Cerebrovascular Pulmonary Mechanical wound Infection Systemic
Odds Ratio
95% CI
42.24 9.48 63.90 12.74 13.99 12.95
(35.99–49.56) (6.44–13.95) (54.56–74.83) (9.04–17.96) (8.93–21.94) (10.13–16.55)
covering all the cases of that same day. Although the exact reason that weekend admission increases the risk of inpatient mortality after primary THA cannot be deduced from this study, it is reasonable to assume that some of these factors play a role. There were 30,650 cases of non-elective THA reported in the NIS database. Non-elective primary THA are usually THA performed for fractures in the hip of acetabulum. However, fractures were excluded in this study, and despite that, there were still non-elective primary THAs performed. One explanation might be that surgeons label the primary THA as “non-elective” just to be able to add the case to the surgery schedule on a weekend or during a day where there is not much operating room time available except in the room dedicated to emergency cases. Another explanation might be inaccuracies in coding the procedure type as being elective or not. The literature has shown that a high Charlson co-morbidity index reflects on the overall health of patients and gives an estimate of their 10year mortality rates. The higher the Charlson index, the higher the shortterm complication rate in patients undergoing primary THA or THA following a fracture, including mortality [25,26]. One possible reason for the statistically significant finding of increased inpatient mortality with increasing patient age is that elderly patients tend to have more comorbidities that will make them less able to withstand the stresses of anesthesia and surgery [27,28]. Interestingly, the presence of obesity resulted in decreased mortality rates when compared to patients who did not have these co-morbidities. The results of this study cannot discern why the presence of obesity resulted in decreased mortality rates; however one potential hypothesis is that patients with obesity are more closely evaluated before, during and after their procedure; however this association has not been documented in the literature. It is reasonable to assume that surgeons may more closely select healthier patients in the setting that their patient is obese and may even refuse operated management on obese patients with significant co-morbidities. Not only will patient selection be stricter, but intra-operative care and care during their hospital course may be heightened due to the concern of inpatient complications. Patients undergoing a THA in a southern hospital region had significant increase in mortality compared to patients in a western hospital region (OR 2.36 CI [1.86–2.99]). The southern regions tend to have more rural areas than other parts of the country. These patients often live at a significant distance from the closest big city and will seek care in local hospitals in the rural areas. The local hospitals are equipped to take care of basic medical needs of these patients. Patients seeking a THA tend to be older and have multiple co-morbidities, and care for these patients necessitates proper facilities, personnel, and equipments that might be in shortage in rural hospitals. In addition, the more rural hospitals tend to have lower surgical volumes compared to more urban areas and several studies have shown the association between low volume institutions and higher mortality rates. Patients with income quartile less than 38,999$ had a significant increase in mortality compared to patients with income quartile of more than 63,000$ (OR 1.87 CI [1.49–2.36]). Wealthy patients have better access to healthcare, and are more willing to seek medical care earlier when their disease is in its early stages. These patients are even prepared to travel to more specialized centers seeking better healthcare. On the other hand, patients with lower income tend to have limited access to healthcare and they try to defer taking care of their health as long as possible. Eventually, these patients are forced to seek medical attention in order to improve on their quality of life, but they present in a less than optimal health status with multiple associated comorbidities that put them at a disadvantage and increases their risk of morbidity and mortality following any kind of medical or surgical management, which includes THA. For patients who suffered inpatient mortalities, the majority of them died within the first 4 hospital days (344 out of 660). This suggests an acute cause of inpatient mortality and is consistent with the findings that the most significant predictors of mortality after
K.D. Illingworth et al. / The Journal of Arthroplasty 30 (2015) 369–373
primary THA were the presence of inpatient complications. Pulmonary (OR 63.90 CI [54.56–74.83]) and cardiovascular (OR 42.24 CI [35.99–49.56]) complications had the largest impact on inpatient mortality after THA. Studies have shown that the leading causes of mortality in patients undergoing TJA involve the cardiovascular system, including pulmonary embolus, myocardial infarction, congestive heart failure, and arrhythmias [4,8,16]. This is consistent with the findings of this study with the presence of myocardial infarctions, pneumonia and/ or pulmonary emboli being associated with the highest inpatient mortality rates. A higher American Society of Anesthesiologists (ASA) score, which reflects on the overall health of the patient, have also been shown to correlate highly with higher mortality rates in THA [6,29]. These studies support our findings that both the pulmonary and cardiovascular inpatient complications have the most significant impact on inpatient mortality rates after primary THA. This current study is not without its own limitations. First, this study uses a large national database that only looks at hospital inpatient stays by ICD-9 codes. For this reason patients are not able to be followed longitudinally. Limitations of this study are mainly related to the choice of and the accuracy of information of the database. However, the database undergoes periodic quality checks with internal and external validation regarding this key feature of NIS database. Second, the study only looked at inpatient mortality rates, which might be different than the 30-day, 90-day, and long-term mortality rates following THA. Other studies report that the mortality rates increased in the first 30 days after THA, but decrease gradually after that [30–32]. Third, mortality rates might be related to readmission rates following THA, a factor that was not reported in the database and therefore could not be analyzed. Readmission to hospitals is related to the various complications following surgery including cardiovascular complications, infection, and thromboembolic events, and these might cause an increase in the immediate short-term and long-term mortality rates after THA. This particular study was unable to determine the etiology of OA necessitating the need for a primary THA. It is possible that degenerative OA inpatient mortality rates may differ from those with secondary causes of OA (RA, post-traumatic, etc.). Unfortunately, 70% of the patients in this study were classified in the NIS database as “unspecified” when referring to their etiology of OA. Conclusion Mortality rates following total hip arthroplasty were significantly affected by multiple factors, with the most significant factors being inpatient complications, weekend admission, increasing age, and Medicare payer provider status. These variables that have an impact on inpatient mortality after primary THA should be taken into account when counseling patients on surgery as well as for when taking care of THA patients during their medical management of primary THA. Future studies should further delineate the longitudinal effect of these variables on mortality after primary THA. References 1. Reginster JY. The prevalence and burden of arthritis. Rheumatology (Oxford) 2002; 41(Suppl 1):3. 2. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007; 89:780.
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Inpatient Mortality After Primary Total Hip Arthroplasty: Analysis from the National Inpatient Sample Database Kenneth D. Illingworth, MD a, Youssef F. El Bitar, MD a, Devraj Banerjee, MD a, Steven L. Scaife, MS b, Khaled J. Saleh, MD, MSc, FRCS(C) a a b
Division of Orthopaedics and Rehabilitation, Department of Surgery, Southern Illinois University School of Medicine, Springfield, IL Center for Clinical Research, Southern Illinois University School of Medicine, Springfield, IL
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Article history: Received 16 January 2014 Accepted 4 August 2014 Keywords: total hip arthroplasty mortality inpatient complications age payer status
a b s t r a c t Although inpatient mortality rates following total hip arthroplasty are low, understanding factors that influence inpatient mortality rates is important. Discharge data from the 2007–2008 HCUP Nationwide Inpatient Sample database were used in this study. Patients were identified based on whether they were admitted for a primary total hip arthroplasty and grouped based on their mortality status. All hip and acetabular fracture patients were excluded. Discharge data revealed 508,150 primary total hip arthroplasties with an inpatient mortality rate of 0.13%. The most significant pre-operative predictors of inpatient mortality were increasing age, weekend admission, increased Charlson co-mobidity score, Medicare payer status, race and a Southern hospital region. The two most significant complications post-operatively leading to increased mortality were pulmonary and cardiovascular complications. Published by Elsevier Inc.
Degenerative joint disease affects approximately 43 million Americans, often resulting in debilitating pain and decreasing functional capacity. The economic impact of degenerative joint disease is estimated to be $60 billion per year [1]. As the numbers of total joint arthroplasties (TJA) have increased, there has been little debate as to the clinical merits of these procedures. Few orthopedic surgical procedures can claim to treat adult end-stage disease with quite the same degree of consistent clinical success. With 572,000 primary total hip arthroplasties (THA) projected annually by 2030, the societal impact of THA is undeniable [2]. As technology, education, pre-operative management, and surgical techniques have improved over the last few decades, the mortality rates after THA have decreased [3–5]. However, along with such advancements, and an ever-increasing age of the general population, older and more medically-complicated patients are undergoing joint arthroplasty [5–8]. Additionally, with the improvement of implant technology and increased survivorship of modern joint arthroplasty, younger and more active patients are seeking earlier intervention for debilitating joint pain and therefore expanding the demographics of utilization of THA [8–10]. Although considered to be a safe and effective procedure, complications following THA exist and include infection, dislocation, and
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.08.002. Reprint requests: Khaled J. Saleh, MD, MSc, FRCS(C), MHCM, Division of Orthopedics and Rehabilitation, Chairman, Director of Clinical and Translational Research, Southern Illinois University School of Medicine, P.O. Box 19679, Springfield, IL 62794-9679. http://dx.doi.org/10.1016/j.arth.2014.08.002 0883-5403/Published by Elsevier Inc.
pulmonary embolism [11]. Complication rates following THA have been reported to be up to 3.9% of patients [12,13] with the most concerning of these complications being mortality [4,6,7,14–19]. Inpatient mortality rates after THA in the literature have been reported to range from 0.1 to 0.8% over the last couple of decades [4–6,8,20], lower than the older reported rates in the 1970s of 1 to 2% [3]. Technological advances, better pre-operative care and patient optimization have all impacted the decrease in inpatient mortality rates. With an increasing number of THA being performed in all age groups, identification of factors that may influence mortality would be important both for individual patient care and societal health care cost burden, and therefore it is more important than ever to identify risk factors associated with increased inpatient mortality following THA [2,6,7]. The purpose of this study was to use a large national database in order to determine what variables affect inpatient mortality rates following primary TJA. Specifically the relationships between mortality, patient demographics, hospital demographics, inpatient complications, co-morbidities and weekend admissions were assessed. We hypothesized that the most significant factors in inpatient mortality following THA will be an increasing patient age and inpatient complications. Materials and Methods A large national database was used to identify patients who had inpatient hospital stays after a primary THA. Patients were grouped by inpatient mortality and statistical analysis was done to determine the association between mortality, patient demographics, hospital demographics, inpatient complications, co-morbidities and weekend admission.
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Investigational review board approval was obtained by the Committee for Research Involving Human Subjects for this study. Discharge data from the 2007 and 2008 Nationwide Inpatient Sample (NIS), were used in this study. Data were accessed in July of 2011 [21,22]. The 2007 and 2008 NIS databases utilize longitudinal hospital inpatient information from over 40 states, and contains information on approximately 16 million inpatient stays in 1000 hospitals, reflecting 20% of U.S. hospitals. The information in the NIS database includes sources and types of admissions, diagnoses and procedures, discharge statuses, and patient demographics [21]. At the time of analysis the 2008 NIS database was the most current database available. The outcome of interest was THA and their respective inpatient mortality rates. Inclusion criteria for this study were inpatient stay for primary THA using the International Classification of Diseases, Ninth Edition (ICD-9) code 81.51. Exclusion criteria were admission for femoral neck fracture (ICD-9 codes 820.00, 820.01, 820.02, 820.03 and 820.09) and or/acetabular fracture (ICD-9 code 808.00). All identifying patient information was removed prior to analysis. The variables of interest are listed in Table 1 and included age, gender, ethnicity, primary payer type, hospital location, hospital length of stay (LOS), mean income quartile, co-morbidities, Charlson co-morbidity index, weekend admission, hospital region and hospital teaching status, patient location and inpatient complications. Mean income quartile and patient location were based off the patients' 6 digit zip code. Obesity was defined as a body mass index above 30. The presence of diabetes was determined based on subjective patient disclosure at admission. The Charlson co-morbidity index score predicts the 10-year mortality for a patient who may have a range of co-morbid conditions such as heart disease, AIDS, or cancer (a total of 22 conditions). Each condition is assigned with a score of 1, 2, 3 or 6
Table 1 Independent Variables for Inpatients Undergoing Primary THA. Age b64 65–79 N80
Location Urban Rural b
Gender Male Female Race White Black Hispanic Other Primary Payer Type Medicare Medicaid Private All othersd
c
Median household income 38,999 or less 39,000 to 47,999 48,000 to 62,999 63,000 or more Inpatient complications Cardiovascular Cerebrovascular Pulmonary Mechanical wound Infection Systemic
b
Patient location Urban Rural
depending on the risk of dying associated with this condition. Scores were divided into one of three groups for analysis; 0, 1 or 2 and greater than 3 [23]. The Charlson score was directly provided by the NIS database and was not individually calculated. Patient location was designated as rural or urban based on the National Council for Health Statistics (NCHS) 2006 rural urban classification scheme for counties [19]. This 6 level classification is scaled from most urban category with large metropolitan central counties, to the most rural with nonmetropolitan noncore counties. Micropolitan and non core areas were considered rural for the purpose of this study. Inpatient complications were categorized into 6 groups based on ICD-9 codes. The cardiovascular group included ICD-9 codes for acute myocardial infarctions; Cerebrovascular group included ICD-9 codes for cerebral infarction; pulmonary group included ICD-9 codes for pneumonia and pulmonary embolus; Mechanical wound group included ICD-9 codes for surgical wound dehiscence and hematoma; infection group included ICD-9 codes for post-operative infection; and systemic group included ICD-9 codes for systemic shock. The specific ICD-9 codes for each group are listed below Table 1. Statistical Analysis The data were weighted using the discharge weights included in the NIS. The discharge weights were calculated to permit extrapolation of the NIS sample discharges to provide national estimates. Each weighted value was rounded to the nearest whole number for statistical analysis. Univariate analyses, specifically chi-square tests, were conducted to determine significant differences between groups. The primary analysis focused on pre-operative predictors of inpatient mortality using a logistic regression analysis with odds ratios and 95% confidence intervals. The secondary analysis focused on mortality as it related to inpatient complications using a logistic regression analysis with odds ratios and 95% confidence intervals. All analysis was done on SAS version 9.2.
Co-morbidities Diabetes Obesity a Charlson Index Score 0 1 or 2 N3
Source of Funding
Weekend admission
There were 508,150 primary THAs performed from 2007 to 2008 with an overall inpatient mortality rate of 0.13%. The mortality rate after inpatient THA for the pre-operative variables is listed in Table 2. Weekend admission was associated with the highest rate of mortality, 0.86%. Patients greater than 80 years of age had a mortality rate of 0.42%. A primary payer of Medicare was associated with a mortality rate of 0.20%; while a private (including HMO) primary payer had a mortality rate of 0.05%. Patient co-morbidities and inpatient mortality rates are listed in Table 3. A Charlson co-morbidity score of N3 was associated with a mortality rate of 0.30%. Mortality rates for inpatient complications are listed in Table 4. Pulmonary and cardiovascular inpatient complications were associated with the highest mortality rates of the inpatient complications, 4.79 and 3.40%, respectively. The hospital length of stay for all inpatient THA mortality patients is presented in Fig. 1. Three hundred forty four patients died with the first 4 days after surgery, 147 died from 5 to 9 days and 169 died in the hospital greater than or equal to 10 days. Odds ratios and 95% confidence intervals for the pre-operative variables are listed in Table 5. The most significant pre-operative variables related with an increase in inpatient mortality were age N 80, weekend admission, Medicare payer type, a Charlson co-morbidity score greater than 3 and operation at a hospital in the southern region. Odds ratios and 95% confidence intervals for inpatient complications are listed in Table 6. The two most significant inpatient complications resulting in increased
Hospital length of stay Hospital region Northeast Midwest South West Hospital type Rural Urban non-teaching Urban Teaching
Cerebrovascular included occlusion and stenosis of precerebral arteries (ICD-9 codes 433.00–433.91). Pulmonary included pneumonia (ICD-9 Codes 480.00–486.00, 997.31–997.39), acute respiratory failure following trauma or surgery (ICD-9 codes 518.51–518.53) and pulmonary embolus (ICD-9 codes 415.11–415.19). Mechanical wound included hematoma complicating a procedure and disruption of operation wound (ICD-9 codes 998.12–998.13, 998.30–998.33). Infection included postoperative infection (ICD-9 codes 998.51–998.59, 999.31–999.39, 996.66). Systemic included septic shock and hemorrhage (ICD-9 codes 998.00–998.09, 998.11). a Co-morbidity was quantified using the nine disease conditions used in Charlson comorbidity index [23]. b Determined by patient zip code. c Cardiovascular included acute myocardial infarctions (ICD-9 codes 410.00–410.92). d Self pay, no charge and others were combined in a single category.
No external source of funding was necessary for completion of this study. Results
K.D. Illingworth et al. / The Journal of Arthroplasty 30 (2015) 369–373 Table 2 Pre-Operative Variables for Inpatients Undergoing Primary THA. Pre-Operative Variables
Table 4 Inpatient Complications for Patients Undergoing Primary THA.
Mortality (no) Mortality (yes) % Mortality n = 507,490 n = 660 0.13%
Age b64 235,869 65–79 206,494 N80 64,517 Gender Male 223,158 Female 282,435 Ethnicity White 322,186 Black 25,043 Hispanic 10,684 Other 12,383 Primary payer Medicare 261,834 Medicaid 15,714 Private (and HMO) 210,524 Other 18,530 Location Urban 395,381 Rural 97,696 Median household income per zip code b38,999 93,688 39,000–47,999 128,520 48,000–62,999 129,681 N63,000 145,872 Weekend admission No 504,590 Yes 2,900 Elective No 30,650 Yes 474,663 Hospital region Northeast 102,022 Midwest 139,077 South 156,124 West 110,267 Teaching status Rural 51,834 Urban non-teaching 221,393 Urban teaching 233,769
371
99 288 273
0.04 0.14 0.42
388 322
0.17 0.11
410 48 18 34
0.13 0.19 0.17 0.28
518 14 113 15
0.20 0.09 0.05 0.08
495 144
0.13 0.15
160 166 182 133
0.17 0.13 0.14 0.09
636 25
0.13 0.86
111 544
0.36 0.12
105 168 298 89
0.10 0.12 0.19 0.08
84 268 308
0.16 0.12 0.13
inpatient mortality after primary THA were pulmonary and cardiovascular complications. Discussion
Inpatient Complication Cardiovascular No Yes Cerebrovascular No Yes Pulmonary No Yes Mechanical wound problem No Yes Infection No Yes Systemic No Yes
Mortality (no)
Mortality (yes)
% Mortality
500,581 6,909
417 243
0.08 3.40
505,206 2,285
633 27
0.13 1.17
502,215 5,276
395 265
0.08 4.79
505,277 2,213
626 35
0.12 1.55
506,364 1,126
641 20
0.13 1.74
502,695 4,795
588 73
0.12 1.49
one of the most successful surgeries in terms of cost-effectiveness, decreasing pain, and improving quality of life [7,14,17,24]. Inpatient mortality after primary THA is low, however the ever-increasing number of patients needing THA in the near future makes understanding these factors that contribute to inpatient mortality rates a must for both surgeons and patients. The most significant predictor of increased inpatient mortality after primary THA was a patient age greater than 80 years. Patients over 80 years of age had a significant increase in mortality over patients less than 64 years of age (OR 10.07, CI [8.00–12.68]). Patients 65–79 years of age also had a significant increase in mortality over patients less than 64 years of age (OR 3.32, CI [2.64–4.17]), however not to the extent of the patients over 80 years of age. The findings of increased age and increased risk of mortality are consistent with the literature, with literature findings indicating that the older the patient, the higher the risk of mortality [5,6,24]. Healy et al found that in the United States, the rate of acute mortality after inpatient orthopedic surgical procedures is approximately 1% for all patients, 3.1% for patients with a hip fracture, and 0.5% for patients without a hip fracture [5]. A study by Blom et al stratified the risk of mortality in relation to age in patients undergoing THA and found that the 90-day mortality rate increased with increasing age of the patient, reaching 2.5% for patients older than 80 years [19].
The most important finding of this study is that multiple preoperative variables and post-operative inpatient complications were identified that contributed to a statistically significant increase in inpatient mortality rates after primary THA. The variables that were highly associated with an increase in inpatient mortality after primary THA were presence of inpatient complications, weekend admission, an increasing patient age and Medicare payer status. THA remains
Table 3 Co-Morbidities for Inpatients Undergoing Primary THA. Co-Morbidities
Mortality (no)
Mortality (yes)
% Mortality
No Yes
437,955 69,535
590 71
0.13 0.10
No Yes Charlson score 0 1 or 2 N3
449,651 57,930
630 30
0.14 0.05
311,856 152,451 43,183
267 263 131
0.09 0.17 0.30
Diabetes
Obesity
Fig. 1. Hospital length of stay for all inpatient mortalities occurring after primary total hip arthroplasty.
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Table 5 Odds ratios and 95% Confidence Intervals for the Pre-Operative Variables in Patients Undergoing THA. Odds Ratio Race (compared to white) Black Hispanic Other Payer status (compared to private/HMO) Medicaid Medicare Other Income quartile (compared to N$63,000) b$38,999 $39,000–$47,999 $48,000–$62,999 Charlson score (compared to score of 0) 1 or 2 3 or more Hospital region (compared to West) Midwest Northeast South Hospital type (compared to urban teaching) Urban non-teaching Rural Age (compared to b65) 65–79 N79 Female (compared to male) Rural patient location (compared to urban) Diabetes Obesity Weekend admission Non-elective
95% CI
1.52 1.35 2.18
(0.79–2.93) (0.85–2.16) (1.54–3.09)
1.65 3.68 1.52
(0.94–2.87) (3.00–4.51) (0.89–2.60)
1.87 1.41 1.54
(1.49–2.36) (1.12–1.77) (1.23–1.92)
2.02 3.54
(1.70–2.39) (2.87–4.36)
1.49 1.27 2.36
(1.15–1.93) (0.96–1.69) (1.86–2.99)
1.24 0.92
(0.97–1.57) (0.78–1.08)
3.32 10.07 0.75 1.17 0.76 0.37 6.76 3.18
(2.64–4.17) (8.00–12.68) (0.65–0.88) (0.97–1.41) (0.59–0.97) (0.25–0.53) (4.52–10.13) (2.60–3.90)
Weekend admission was associated with a significant increase in morality when compared with weekday admissions (OR 6.76 CI [4.52– 10.13]). THA performed for hip or acetabular fractures were excluded from this study, therefore, theoretically the mortality associated with hip or acetabular fractures for non-elective procedures was not a confounding factor. The database only reports on the admission day, and does not clarify if the surgery was actually done on a weekend or a weekday. Patients can be admitted on a weekend, but have their surgery done on a weekday following a few days of stay in the hospital. Elective admission of a patient for a THA is usually done on a weekday, and usually the surgery is performed the same day. Some patients with more health-related risk factors might be admitted to the hospital for medical optimization on a weekend prior to surgery in order to undergo surgery during the early weekdays. Some patients are admitted for anticoagulation bridges during the weekend in preparation for surgery at the beginning of the week. These patients necessarily have cardiovascular comorbidities that increase their mortality risk. This might be one explanation as to why mortality in these patients was higher than patients who were admitted on weekdays. Another reason as to why patients might be admitted on a weekend is the tight operating room (OR) schedule in the hospitals. In order to maximize the use of the OR, some surgeons elect to perform their elective operations on a weekend where they have more available surgical time. During the weekends, the operating room staff is at a minimum with staff from different specialties Table 6 Odds ratios and 95% Confidence Intervals for Inpatient Complications in Patients Undergoing Primary THA. Inpatient Complication Cardiovascular Cerebrovascular Pulmonary Mechanical wound Infection Systemic
Odds Ratio
95% CI
42.24 9.48 63.90 12.74 13.99 12.95
(35.99–49.56) (6.44–13.95) (54.56–74.83) (9.04–17.96) (8.93–21.94) (10.13–16.55)
covering all the cases of that same day. Although the exact reason that weekend admission increases the risk of inpatient mortality after primary THA cannot be deduced from this study, it is reasonable to assume that some of these factors play a role. There were 30,650 cases of non-elective THA reported in the NIS database. Non-elective primary THA are usually THA performed for fractures in the hip of acetabulum. However, fractures were excluded in this study, and despite that, there were still non-elective primary THAs performed. One explanation might be that surgeons label the primary THA as “non-elective” just to be able to add the case to the surgery schedule on a weekend or during a day where there is not much operating room time available except in the room dedicated to emergency cases. Another explanation might be inaccuracies in coding the procedure type as being elective or not. The literature has shown that a high Charlson co-morbidity index reflects on the overall health of patients and gives an estimate of their 10year mortality rates. The higher the Charlson index, the higher the shortterm complication rate in patients undergoing primary THA or THA following a fracture, including mortality [25,26]. One possible reason for the statistically significant finding of increased inpatient mortality with increasing patient age is that elderly patients tend to have more comorbidities that will make them less able to withstand the stresses of anesthesia and surgery [27,28]. Interestingly, the presence of obesity resulted in decreased mortality rates when compared to patients who did not have these co-morbidities. The results of this study cannot discern why the presence of obesity resulted in decreased mortality rates; however one potential hypothesis is that patients with obesity are more closely evaluated before, during and after their procedure; however this association has not been documented in the literature. It is reasonable to assume that surgeons may more closely select healthier patients in the setting that their patient is obese and may even refuse operated management on obese patients with significant co-morbidities. Not only will patient selection be stricter, but intra-operative care and care during their hospital course may be heightened due to the concern of inpatient complications. Patients undergoing a THA in a southern hospital region had significant increase in mortality compared to patients in a western hospital region (OR 2.36 CI [1.86–2.99]). The southern regions tend to have more rural areas than other parts of the country. These patients often live at a significant distance from the closest big city and will seek care in local hospitals in the rural areas. The local hospitals are equipped to take care of basic medical needs of these patients. Patients seeking a THA tend to be older and have multiple co-morbidities, and care for these patients necessitates proper facilities, personnel, and equipments that might be in shortage in rural hospitals. In addition, the more rural hospitals tend to have lower surgical volumes compared to more urban areas and several studies have shown the association between low volume institutions and higher mortality rates. Patients with income quartile less than 38,999$ had a significant increase in mortality compared to patients with income quartile of more than 63,000$ (OR 1.87 CI [1.49–2.36]). Wealthy patients have better access to healthcare, and are more willing to seek medical care earlier when their disease is in its early stages. These patients are even prepared to travel to more specialized centers seeking better healthcare. On the other hand, patients with lower income tend to have limited access to healthcare and they try to defer taking care of their health as long as possible. Eventually, these patients are forced to seek medical attention in order to improve on their quality of life, but they present in a less than optimal health status with multiple associated comorbidities that put them at a disadvantage and increases their risk of morbidity and mortality following any kind of medical or surgical management, which includes THA. For patients who suffered inpatient mortalities, the majority of them died within the first 4 hospital days (344 out of 660). This suggests an acute cause of inpatient mortality and is consistent with the findings that the most significant predictors of mortality after
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primary THA were the presence of inpatient complications. Pulmonary (OR 63.90 CI [54.56–74.83]) and cardiovascular (OR 42.24 CI [35.99–49.56]) complications had the largest impact on inpatient mortality after THA. Studies have shown that the leading causes of mortality in patients undergoing TJA involve the cardiovascular system, including pulmonary embolus, myocardial infarction, congestive heart failure, and arrhythmias [4,8,16]. This is consistent with the findings of this study with the presence of myocardial infarctions, pneumonia and/ or pulmonary emboli being associated with the highest inpatient mortality rates. A higher American Society of Anesthesiologists (ASA) score, which reflects on the overall health of the patient, have also been shown to correlate highly with higher mortality rates in THA [6,29]. These studies support our findings that both the pulmonary and cardiovascular inpatient complications have the most significant impact on inpatient mortality rates after primary THA. This current study is not without its own limitations. First, this study uses a large national database that only looks at hospital inpatient stays by ICD-9 codes. For this reason patients are not able to be followed longitudinally. Limitations of this study are mainly related to the choice of and the accuracy of information of the database. However, the database undergoes periodic quality checks with internal and external validation regarding this key feature of NIS database. Second, the study only looked at inpatient mortality rates, which might be different than the 30-day, 90-day, and long-term mortality rates following THA. Other studies report that the mortality rates increased in the first 30 days after THA, but decrease gradually after that [30–32]. Third, mortality rates might be related to readmission rates following THA, a factor that was not reported in the database and therefore could not be analyzed. Readmission to hospitals is related to the various complications following surgery including cardiovascular complications, infection, and thromboembolic events, and these might cause an increase in the immediate short-term and long-term mortality rates after THA. This particular study was unable to determine the etiology of OA necessitating the need for a primary THA. It is possible that degenerative OA inpatient mortality rates may differ from those with secondary causes of OA (RA, post-traumatic, etc.). Unfortunately, 70% of the patients in this study were classified in the NIS database as “unspecified” when referring to their etiology of OA. Conclusion Mortality rates following total hip arthroplasty were significantly affected by multiple factors, with the most significant factors being inpatient complications, weekend admission, increasing age, and Medicare payer provider status. These variables that have an impact on inpatient mortality after primary THA should be taken into account when counseling patients on surgery as well as for when taking care of THA patients during their medical management of primary THA. Future studies should further delineate the longitudinal effect of these variables on mortality after primary THA. References 1. Reginster JY. The prevalence and burden of arthritis. Rheumatology (Oxford) 2002; 41(Suppl 1):3. 2. Kurtz S, Ong K, Lau E, et al. Projections of primary and revision hip and knee arthroplasty in the United States from 2005 to 2030. J Bone Joint Surg Am 2007; 89:780.
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