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1.  Risk Factors for Early Revision After Primary TKA in Medicare Patients 
Background
Patient, surgeon, health system, and device factors are all known to influence outcomes in total knee arthroplasty (TKA). However, patient-related factors associated with an increased risk of early failure are not well understood, particularly in elderly patients.
Questions/purposes
The purpose of this study was to identify specific comorbid conditions associated with increased risk of early revision in Medicare patients undergoing TKA.
Methods
A total of 117,903 Medicare patients who underwent primary TKA between 1998 and 2010 were identified from the Medicare 5% national sample administrative database and used to determine the relative risk of revision within 12 months after primary TKA as a function of baseline medical comorbidities. Cox regression was used to evaluate the impact of 29 comorbid conditions on risk of early failure controlling for age, sex, race, census region, socioeconomic status, and all other baseline comorbidities.
Results
The most significant independent risk factors for revision TKA within 12 months were chronic pulmonary disease, depression, alcohol abuse, drug abuse, renal disease, hemiplegia or paraplegia, and obesity.
Conclusions
This information could be valuable to patients and their surgeons when making shared medical decisions regarding elective TKA and for risk-stratifying publicly reported outcomes in Medicare patients undergoing TKA.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-013-3045-0
PMCID: PMC3889408  PMID: 23661301
3.  A Population-Based Study of Trends in the Use of Total Hip and Total Knee Arthroplasty, 1969-2008 
Mayo Clinic Proceedings  2010;85(10):898-904.
OBJECTIVE: To study the rates of use of total hip arthroplasty (THA) and total knee arthroplasty (TKA) during the past 4 decades.
METHODS: The Rochester Epidemiology Project was used to identify all Olmsted County, Minnesota, residents who underwent THA or TKA from January 1, 1969, through December 31, 2008. We used a population-based approach because few data are available on long-term trends in the use of THA and TKA in the United States. Rates of use were determined by age- and sex-specific person-years at risk. Poisson regression was used to assess temporal trends by sex and age group.
RESULTS: The age- and sex-adjusted use of THA increased from 50.2 (95% confidence interval [CI], 40.5-59.8) per 100,000 person-years in 1969-1972 to 145.5 (95% CI, 134.2-156.9) in 2005-2008, whereas TKA increased markedly from 31.2 (95% CI, 25.3-37.1) per 100,000 person-years in 1971-1976 to 220.9 (95% CI, 206.7-235.0) in 2005-2008. For both procedures, use was greater among females, and the rate generally increased with age.
CONCLUSION: In this community, TKA and THA use rates have increased steadily since the introduction of the procedures and continue to increase for all age groups. On the basis of these population-based data, the probable need for TKA and THA exceeds current federal agency projections.
In Olmsted County, Minnesota, use rates of total hip arthroplasty and total knee arthroplasty have increased steadily since introduction of the procedures and continue to increase for all age groups.
doi:10.4065/mcp.2010.0115
PMCID: PMC2947961  PMID: 20823375
4.  Estimating Risk in Medicare Patients With THA: An Electronic Risk Calculator for Periprosthetic Joint Infection and Mortality 
Background
Although risk factors for periprosthetic joint infection (PJI) and mortality after total hip arthroplasty (THA) have been identified, interactions between specific patient risk factors are poorly understood. Therefore, it is difficult for surgeons to counsel patients on their individual risk of PJI or mortality after THA.
Questions/purposes
We evaluated the interaction between patient clinical and demographic factors on the risk of PJI and mortality after THA and developed an electronic risk calculator for estimating the patient-specific risk of PJI and mortality in Medicare patients with THA.
Methods
We used the Medicare 5% sample claims database to calculate the risk of PJI within 2 years and mortality within 90 days after THA in 53,252 Medicare patients with primary THAs between 1998 and 2009. Logistic regression using 29 comorbid conditions, age, sex, race, and socioeconomic status were used as inputs to develop an electronic risk calculator to estimate patient-specific risk of PJI and mortality after THA.
Results
The overall 2-year risk of PJI and 90-day risk of mortality after primary THA were 2.07% and 1.30%, respectively. White women aged 70 to 74 years with alcohol abuse, depression, electrolyte disorder, peptic ulcer disease, urinary tract infection, rheumatologic disease, preoperative anemia, cardiopulmonary (cardiac arrhythmia, congestive heart failure, ischemic heart disease, chronic pulmonary disease) comorbidities, and peripheral vascular disease were at highest risk for PJI. White women aged 65 to 69 years with electrolyte disorder, hemiplegia/paraplegia, hypertension, hypothyroidism, metastatic tumor, preoperative anemia, coagulopathy, cardiopulmonary (congestive heart failure, chronic pulmonary disease) and psychiatric (psychoses, depression) comorbidities, malignancies, and peripheral vascular disease were at highest risk for mortality. An electronic risk calculator was developed to estimate the risk of PJI and mortality in Medicare patients with THA.
Conclusions
This electronic risk calculator can be used to counsel Medicare patients regarding their patient-specific risks of PJI and mortality after THA.
Level of Evidence
Level II, prognostic study. See the Instructions for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2605-z
PMCID: PMC3549162  PMID: 23179112
5.  Gamma-irradiation Sterilization in an Inert Environment: A Partial Solution 
Background
In the mid to late 1990s, to sterilize UHMWPE bearings, manufacturers changed from gamma-irradiation-in-air (gamma-air) sterilization, which initiated oxidation leading to bearing fatigue, to gamma-irradiation sterilization in an inert environment (gamma-inert). The change to gamma-inert sterilization reportedly prevented shelf oxidation before implantation but not in vivo oxidation.
Questions/purposes
We asked: (1) Has the change to gamma-inert sterilization prevented shelf oxidation that led to early in vivo fatigue damage in gamma-air-sterilized tibial inserts? And (2) has the change to gamma-inert sterilization prevented the occurrence of fatigue secondary to in vivo oxidation?
Methods
We rated 183 retrieved gamma-air- and 175 retrieved gamma-inert-sterilized tibial inserts for clinical fatigue damage and analyzed 132 gamma-air- and 174 gamma-inert-sterilized tibial inserts for oxidation by Fourier transform infrared spectroscopy.
Results
Oxidation led to decreased mechanical properties in shelf-aged gamma-air-sterilized tibial inserts. Barrier packaging prevented shelf oxidation in gamma-inert-sterilized tibial inserts. Gamma-air- and gamma-inert-sterilized inserts oxidized in vivo. Fatigue damage (delamination) occurred more frequently in inserts retrieved after longer time in vivo. Longer in vivo time correlated with higher oxidation and more accumulated cycles of use.
Conclusions
Published oxidation projections suggest gamma-inert-sterilized tibial inserts would reach the critical oxidation for the onset of fatigue after 11 to 14 years in vivo. These retrievals appear to follow the projected oxidation trends. Frequency of fatigue damage increased with increasing oxidation.
Clinical Relevance
Fatigue of tibial inserts becomes more likely, especially in active patients, after more than a decade of good clinical performance.
doi:10.1007/s11999-011-2150-1
PMCID: PMC3369088  PMID: 22033874
6.  Knee Wear Measured in Retrievals: A Polished Tray Reduces Insert Wear 
Background
Polyethylene wear is often cited as the cause of failure of TKA. Rotating platform (RP) knees show notable surface damage on the rotating surface raising concerns about increased wear compared to fixed bearing inserts.
Questions/purposes
We therefore addressed the following questions: Is wear in RP inserts increased compared to that in fixed bearing inserts? Does the surface roughness of the tibial tray have a measurable impact on in vivo wear of modular knees? And does wear rate differ between posterior stabilized (PS) and cruciate retaining (CR) knees?
Methods
We compared wear in two series of retrieved knee devices: 94 RP mobile bearings with polished cobalt-chrome (CoCr) trays and 218 fixed bearings with both rough titanium (Ti) and polished CoCr trays. Minimum implantation time was 0.4 months (median, 36 months; range, 0.4–124 months) and 2 months (median, 72 months; range, 2–179 months) for the RP and fixed bearing series, respectively.
Results
Wear rate was lower for RP inserts than for fixed bearing inserts. Backside wear rate was lower for fixed bearing inserts mated to polished CoCr trays than for inserts from rough Ti trays. Inserts against polished trays (RP or fixed bearing) showed no increase in wear rate increase over time. Wear rate of PS knees was similar to that of CR knees.
Conclusions
We found mobile bearing knees have reduced wear rate compared to fixed bearings, likely due to the polished CoCr tibial tray surface. Fixed bearing inserts in polished CoCr trays wear less than their counterparts in rough Ti trays, and the wear rate of inserts from polished CoCr trays does not appear to increase with time.
doi:10.1007/s11999-012-2248-0
PMCID: PMC3369101  PMID: 22314963
7.  Patient-related Risk Factors for Postoperative Mortality and Periprosthetic Joint Infection in Medicare Patients Undergoing TKA 
Background
The impact of specific baseline comorbid conditions on the relative risk of postoperative mortality and periprosthetic joint infection (PJI) in elderly patients undergoing TKA has not been well defined.
Questions/purposes
We calculated the relative risk of postoperative mortality and PJI associated with 29 comorbid conditions in Medicare patients undergoing TKA.
Patients and Methods
The Medicare 5% sample was used to calculate the relative risk of 90-day postoperative mortality and PJI as a function of 29 preexisting comorbid conditions in 83,011 patients who underwent primary TKA between 1998 and 2007.
Results
The independent risk factors for 90-day postoperative mortality (in decreasing order of significance) were congestive heart failure, metastatic cancer, renal disease, peripheral vascular disease, cerebrovascular disease, lymphoma, cardiac arrhythmia, dementia, pulmonary circulation disorders, and chronic liver disease. The independent risk factors for PJI (in decreasing order of significance) were congestive heart failure, chronic pulmonary disease, preoperative anemia, diabetes, depression, renal disease, pulmonary circulation disorders, obesity, rheumatologic disease, psychoses, metastatic tumor, peripheral vascular disease, and valvular disease.
Conclusions
We believe this information important when counseling elderly patients regarding the risks of mortality and PJI after TKA and risk-adjusting publicly reported TKA patient outcomes.
Level of Evidence
Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-011-2043-3
PMCID: PMC3237966  PMID: 21874391
8.  Failed Metal-on-Metal Hip Arthroplasties: A Spectrum of Clinical Presentations and Operative Findings 
Background
A number of recent reports have described novel failure mechanisms of metal-on-metal bearings in total and resurfacing hip arthroplasty. Hip arthroplasties with metal-on-metal articulations are also subject to the traditional methods of failure seen with different bearing couples. There is currently little information in the literature to help guide timely clinical evaluation and management of these patients.
Questions/purposes
We therefore describe the (1) clinical presentations; (2) reasons for failure; (3) operative findings; and (4) histologic findings in patients with failed metal-on-metal hip arthroplasties.
Methods
We retrospectively identified all 37 patients (37 hips) with metal on metal total hip or resurfacing arthroplasties who underwent revision over the past 3 years at our institution. Relevant clinical, radiographic, laboratory, intraoperative, and histopathologic findings were analyzed for all patients.
Results
Of the 37 patients, 10 were revised for presumed hypersensitivity specific to the metal-on-metal articulation. This group included eight patients with tissue histology confirming chronic inflammation with lymphocytic infiltration, eight with aseptic loosening of a monoblock screwless uncemented acetabular component, two with iliopsoas impingement associated with a large-diameter femoral head, and three with femoral neck fracture after resurfacing arthroplasty; the remainder of the patients were revised for infection, instability, component malposition, and periprosthetic fracture.
Conclusions
Increased awareness of the modes of failure will bring to light the potential complications particular to metal-on-metal articulations while placing these complications into the context of failures associated with all hip arthroplasties. This novel clinical information should be valuable for the practicing surgeon faced with this patient population.
Level of Evidence
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1419-0
PMCID: PMC2919884  PMID: 20559767
9.  Risk of Complication and Revision Total Hip Arthroplasty Among Medicare Patients with Different Bearing Surfaces 
Background
To address the long-term problems of bearing surface wear and osteolysis associated with conventional metal-polyethylene (M-PE) total hip arthroplasty (THA), metal-metal (M-M), and ceramic-ceramic (C-C) bearings have been introduced. These bearing surfaces are associated with unique risks and benefits and higher costs. However the relative risks of these three bearings in an older population is unknown.
Questions/purposes
We compared the short-term risk of complication and revision THA among Medicare patients having a primary THA with metal-polyethylene (M-PE), metal-metal (M-M), and ceramic-ceramic (C-C) bearings.
Methods
We used the 2005 to 2007 100% Medicare inpatient claim files to perform a matched cohort analysis in three separate cohorts of THA patients (M-PE, M-M, and C-C) who were matched by age, gender, and US census region. Multivariate Cox proportional-hazards models were constructed to compare complication and revision THA risk among cohorts, adjusting for medical comorbidities, race, socioeconomic status, and hospital factors.
Results
After adjusting for patient and hospital factors, M-M bearings were associated with a higher risk of periprosthetic joint infection (hazard ratio, 3.03; confidence interval, 1.02–9.09) when compared with C-C bearings (0.59% versus 0.32%, respectively). There were no other differences among bearing cohorts in the adjusted risk of revision THA or any other complication.
Conclusions
The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface. Hard-on-hard THA bearings are of questionable value in Medicare patients, given the higher cost associated with their use and uncertain long-term benefits in older patients.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1262-3
PMCID: PMC2914292  PMID: 20165935
10.  Risk of Complication and Revision Total Hip Arthroplasty Among Medicare Patients with Different Bearing Surfaces 
Background
To address the long-term problems of bearing surface wear and osteolysis associated with conventional metal-polyethylene (M-PE) total hip arthroplasty (THA), metal-metal (M-M), and ceramic-ceramic (C-C) bearings have been introduced. These bearing surfaces are associated with unique risks and benefits and higher costs. However the relative risks of these three bearings in an older population is unknown.
Questions/purposes
We compared the short-term risk of complication and revision THA among Medicare patients having a primary THA with metal-polyethylene (M-PE), metal-metal (M-M), and ceramic-ceramic (C-C) bearings.
Methods
We used the 2005 to 2007 100% Medicare inpatient claim files to perform a matched cohort analysis in three separate cohorts of THA patients (M-PE, M-M, and C-C) who were matched by age, gender, and US census region. Multivariate Cox proportional-hazards models were constructed to compare complication and revision THA risk among cohorts, adjusting for medical comorbidities, race, socioeconomic status, and hospital factors.
Results
After adjusting for patient and hospital factors, M-M bearings were associated with a higher risk of periprosthetic joint infection (hazard ratio, 3.03; confidence interval, 1.02–9.09) when compared with C-C bearings (0.59% versus 0.32%, respectively). There were no other differences among bearing cohorts in the adjusted risk of revision THA or any other complication.
Conclusions
The risk of short-term complication (including dislocation) and revision THA were similar among appropriately matched Medicare THA patients regardless of bearing surface. Hard-on-hard THA bearings are of questionable value in Medicare patients, given the higher cost associated with their use and uncertain long-term benefits in older patients.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-010-1262-3
PMCID: PMC2914292  PMID: 20165935
11.  Midterm to Long-term Followup of Staged Reimplantation for Infected Hip Arthroplasty 
Most reports on two-stage reimplantation have focused on the short-term cure rate of infection, but little is known about long-term reinfection-free survival or mechanical durability. We retrospectively reviewed 168 patients (169 hips) with infected arthroplasty, all of whom had two-stage reimplantation for the treatment of an infected total hip arthroplasty between 1988 and 1998. In the second stage, the femoral component was fixed with antibiotic-loaded bone cement in 121 hips; the remaining femoral components and all acetabular components were uncemented. The minimum followup time was 2 years (mean, 7 years; range, 2–16 years). At most recent followup, 12 hips (7.1%) were reoperated on for reinfection and 13 hips (7.7%) were revised for aseptic loosening or osteolysis. Apparently aseptic loosening occurred on one or both sides of the joint in 24 hips (14.2%). The 10-year survivals free of reinfection and mechanical failure were 87.5% and 75.2% respectively. Nineteen hips dislocated and eight underwent revision surgery for instability. The method of femoral component fixation, either with or without cement, did not correlate with risk of infection, loosening, or mechanical failure. Based on these results, the method of fixation used for the femoral component during two-stage reimplantation surgery should be based on the surgeon’s preference for fixation combined with the assessment of femoral bone stock.
Level of Evidence: Level IV, case series. See the Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-008-0480-4
PMCID: PMC2600996  PMID: 18813895
12.  The 2008 Frank Stinchfield Award: Variation in Postoperative Pelvic Tilt May Confound the Accuracy of Hip Navigation Systems 
Most computer navigation systems used in total hip arthroplasty integrate preoperative pelvic tilt to calculate the anterior pelvic plane assuming tilt is constant; however, the consistency of pelvic tilt after THA has never been proven. Therefore, using a modern comprehensive gait analysis before and after arthroplasty we sought to compare (1) dynamic pelvic tilt changes and (2) pelvic flexion/extension range-of-motion changes. Twenty-one patients who underwent unilateral THA were prospectively studied. Quantitative pelvic tilt changes (in the sagittal plane) and pelvic range of flexion/extension motion relative to a laboratory coordinate system were compared using a computerized video motion system. Mean gait pelvic tilt was 13.9º ± 4.8º (range, 1.73º–23.1º) preoperatively, 12.5º ± 4.5º (range, 1.4º–18.7º) 2 months postoperatively, and 10.5° ± 5.5º (range, –2.36º–19.2º) 12 months postoperatively. A significant proportion (31%) of patients had more than a 5° difference between preoperative and 12-month postoperative measurements and the variability was spread over 20°. Significant dynamic changes in pelvic tilt occurred after THA. While navigation clearly improves the anatomical position of the component during THA, the functional position of the component will not always be improved because of the significant change between preoperative and postoperative pelvic tilt.
doi:10.1007/s11999-008-0521-z
PMCID: PMC2600967  PMID: 18830796
13.  The Epidemiology of Revision Total Knee Arthroplasty in the United States 
Understanding the cause of failure and type of revision total knee arthroplasty (TKA) procedures performed in the United States is essential in guiding research, implant design, and clinical decision making in TKA. We assessed the causes of failure and specific types of revision TKA procedures performed in the United States using newly implemented ICD-9-CM diagnosis and procedure codes related to revision TKA data from the Nationwide Inpatient Sample (NIS) database. Clinical, demographic, and economic data were reviewed and analyzed from 60,355 revision TKA procedures performed in the United States between October 1, 2005 and December 31, 2006. The most common causes of revision TKA were infection (25.2%) and implant loosening (16.1%), and the most common type of revision TKA procedure reported was all component revision (35.2%). Revision TKA procedures were most commonly performed in large, urban, nonteaching hospitals in Medicare patients ages 65 to 74. The average length of hospital stay (LOS) for all revision TKA procedures was 5.1 days, and the average total charges were $49,360. However, average LOS, average charges, and procedure frequencies varied considerably by census region, hospital type, and procedure performed.
Level of Evidence: Level II, economic and decision analysis. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-009-0945-0
PMCID: PMC2795838  PMID: 19554385
14.  The Epidemiology of Revision Total Knee Arthroplasty in the United States 
Understanding the cause of failure and type of revision total knee arthroplasty (TKA) procedures performed in the United States is essential in guiding research, implant design, and clinical decision making in TKA. We assessed the causes of failure and specific types of revision TKA procedures performed in the United States using newly implemented ICD-9-CM diagnosis and procedure codes related to revision TKA data from the Nationwide Inpatient Sample (NIS) database. Clinical, demographic, and economic data were reviewed and analyzed from 60,355 revision TKA procedures performed in the United States between October 1, 2005 and December 31, 2006. The most common causes of revision TKA were infection (25.2%) and implant loosening (16.1%), and the most common type of revision TKA procedure reported was all component revision (35.2%). Revision TKA procedures were most commonly performed in large, urban, nonteaching hospitals in Medicare patients ages 65 to 74. The average length of hospital stay (LOS) for all revision TKA procedures was 5.1 days, and the average total charges were $49,360. However, average LOS, average charges, and procedure frequencies varied considerably by census region, hospital type, and procedure performed.
Level of Evidence: Level II, economic and decision analysis. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-009-0945-0
PMCID: PMC2795838  PMID: 19554385

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