Abstract
Background
Regional anesthesia has proven to be a highly effective technique for pain control after total shoulder arthroplasty. However, concerns have been raised about the safety of upper-extremity nerve blocks, particularly with respect to the incidence of perioperative respiratory and neurologic complications, and little is known about their influence, if any, on length of stay after surgery.
Questions/purposes
Using a large national cohort, we asked: (1) How frequently are upper-extremity peripheral nerve blocks added to general anesthesia in patients undergoing total shoulder arthroplasty? (2) Are there differences in the incidence of and adjusted risk for major perioperative complications and mortality between patients receiving general anesthesia with and without nerve blocks? And (3) does resource utilization (blood product transfusion, intensive care unit admission, length of stay) differ between groups?
Methods
We searched a nationwide discharge database for patients undergoing total shoulder arthroplasty under general anesthesia with or without addition of a nerve block. Groups were compared with regard to demographics, comorbidities, major perioperative complications, and length of stay. Multivariable logistic regressions were performed to measure complications and resource use. A negative binomial regression was fitted to measure length of stay.
Results
We identified 17,157 patients who underwent total shoulder arthroplasty between 2007 and 2011. Of those, approximately 21% received an upper-extremity peripheral nerve block in addition to general anesthesia. Patients receiving combined regional-general anesthesia had similar mean age (68.6 years [95% CI: 68.2–68.9 years] versus 69.1 years [95% CI: 68.9–69.3 years], p < 0.0043), a slightly lower mean Deyo (comorbidity) index (0.87 versus 0.93, p = 0.0052), and similar prevalence of individual comorbidities, compared to those patients receiving general anesthesia only. Addition of regional anesthesia was not associated with different odds ratios for complications, transfusion, and intensive care unit admission. Incident rates for length of stay were also similar between groups (incident rate ratio = 0.99; 95% CI: 0.97–1.02; p = 0.467)
Conclusions
Addition of regional to general anesthesia was not associated with an increased complication profile or increased use of resources. In combination with improved pain control as known from previous research, regional anesthesia may represent a viable management option for shoulder arthroplasty. However, further research is necessary to better clarify the risk of neurologic complications.
Level of Evidence
Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.
Electronic supplementary material
The online version of this article (doi:10.1007/s11999-013-3356-1) contains supplementary material, which is available to authorized users.
Introduction
Regional anesthesia has proven to be an effective technique for the anesthetic and analgesic management of patients undergoing shoulder surgery [14, 20]. Upper-extremity peripheral nerve block techniques frequently are utilized in combination with general anesthesia as a strategy to reduce requirement for systemic analgesics, facilitate rehabilitation, and potentially allow for earlier discharge after total shoulder arthroplasty [5, 27, 31]. However, concerns have been raised in the past regarding the safety of upper-extremity nerve blocks, owing to the occurrence of perioperative respiratory and neurologic complications [26, 30, 34, 35].
Existing studies largely agree that regional anesthesia shortens length of stay after orthopaedic surgery in general, as well as after shoulder arthroplasty [14, 17]. However, it remains controversial whether the use of peripheral nerve blocks can affect the likelihood of systemic complications (such as respiratory compromise due to hemidiaphragmatic paresis [35]) after shoulder surgery and to what extent regional anesthesia modifies outcomes such as resource utilization.
We chose a population-based approach to examine the differential impact of general anesthesia with or without addition of a peripheral nerve block in patients undergoing total shoulder arthroplasty and evaluated the following questions: (1) How frequently are upper-extremity peripheral nerve blocks added to general anesthesia in patients undergoing total shoulder arthroplasty in a large national cohort? (2) Are there differences in the incidence of and adjusted risk for major perioperative complications, including but not limited to respiratory complications, and mortality between patients receiving general anesthesia with and without nerve blocks? And (3) does resource utilization (blood product transfusion, intensive care unit [ICU] admission, length of stay) differ between groups?
Patients and Methods
Institutional Review Board Approval and Data Source
The Hospital for Special Surgery Institutional Review Board (New York, NY, USA) granted exemption of consent requirements for this study as it solely utilized deidentified data compliant with the Health Insurance Portability and Accountability Act [32]. Data were commercially obtained from Premier, Inc (Charlotte, NC, USA) for the years between January 2007 and September 2011. The Premier database is an administrative database containing discharge information from about 400 acute-care hospitals throughout the United States, covering about 20% of all discharges in the United States from this time period. It includes hospitals with diverse geographical locations across the United States, different sizes, urban/rural settings, and teaching status. Medicare, Medicaid, and uninsured patients are captured in the database, as well as those with commercial insurance. The database vendor assures a high level of database integrity by performing numerous quality and data validation checks before the data are released for analysis. Numerous earlier publications have relied on this data source for retrospective studies in a variety of clinical subspecialties [19, 22, 25]. Our group utilized the same database previously for various projects focusing exclusively on comparative perioperative outcomes and ICU utilization in patients undergoing lower-extremity joint arthroplasty [21, 29].
Dataset Creation
Patients receiving a total shoulder arthroplasty were identified in the dataset by querying for entries featuring the ICD-9-CM code (81.80) and respective billing codes for general anesthesia. This group was subdivided according to whether a peripheral nerve block was added: individuals receiving general anesthesia only or individuals receiving general anesthesia plus an upper-extremity nerve block. Patients receiving regional anesthesia only (without general anesthesia) were excluded. The groups were compared by patient- and healthcare-related demographics: age, sex, and ethnicity (white, black, Hispanic, other); admission type (emergent, elective, trauma, urgent, other); hospital size (< 299, 300–499, > 500 beds), location (urban or rural), and teaching status; and comorbid diseases including the Deyo (comorbidity) index [7]. The outcomes of interest included mortality, incidence of major perioperative complications (infection, acute renal failure, gastrointestinal complications, myocardial infarction, cardiac complications other than myocardial infarction, pulmonary embolism, pneumonia, pulmonary compromise, cerebrovascular accident), invasive ventilation, blood product transfusion, and comparative resource utilization (ICU admission, length of hospitalization). Comorbid diseases and complication variables were defined by ICD-9-CM, current procedural terminology (CPT), and billing codes (Appendix 1; supplemental materials are available with the online version of CORR®).
Statistical Analysis
Statistical analyses were performed with SAS® software (Version 9.3; SAS Institute Inc, Cary, NC, USA). Continuous and discrete variables are described as means and assessed using a two-sample t-test. For categorical variables, frequencies and percentages were determined. Pearson chi-square tests were used to measure associations between these variables. Separate multivariable logistic regressions were analyzed, with the following events defined as outcomes: combined complications, cardiac complications, pulmonary complications, invasive ventilation, transfusion, and use of ICU services. To determine the association between type of anesthesia and length of stay, we performed a multivariable negative binomial regression, which is recommended for discrete outcomes when overdispersion (variance > mean) is present [2] and has been used previously in health research for this purpose [6, 8, 16].
Composite variables were created to allow for a statistically robust comparison of adverse events. If a case had at least one of the listed events, the composite variable was positively indicated: combined complications included all complications mentioned above; cardiac complications included acute myocardial infarction and cardiac complications other than myocardial infarction; pulmonary complications included pulmonary embolism, pneumonia, and pulmonary compromise. All models controlled for age group (< 45, 45–54, 55–64, 65–74, 75+ years), sex, ethnicity, Deyo index (0, 1, 2, 3+), and presence of sleep apnea and obesity. Adjusted odds ratios (ORs) and adjusted incident rate ratios (IRRs) were calculated for multivariable logistic and negative binomial regressions, respectively, and reported with 95% CIs. Significance of findings was determined using the conventional threshold of statistical significance (ie, two-sided p < 0.05). We report 95% CIs of estimates to allow for improved interpretation of the findings, as very large sample sizes might have an undue effect on the p values.
Multiple model diagnostics were performed to assess the value of our statistical model. We calculated the variance inflation factor (VIF) as a measure of multicollinearity, where a VIF of less than 10 was defined as absence of multicollinearity. Moreover, adequate model discrimination at different levels of the outcome was evaluated using the C-statistic (area under the receiver operating characteristic curve) for multivariate logistic regressions [24]. While C-statistic values of 0.7 or higher were considered indicative of acceptable discrimination [11], lower values have previously been attributed to comparisons of cohorts with very similar characteristics, rather than necessarily representing an indicator of weak discrimination [23]. Finally, the Hosmer-Lemeshow test and the Pearson’s chi-square test were utilized to test model calibration [12] for logistic regression models and the negative binomial model, respectively. A p value of greater than 0.05 from these tests indicated good model fit.
Results
We identified 17,157 patients who underwent total shoulder arthroplasty between 2007 and 2011. Of those, 20.9% received an upper-extremity peripheral nerve block in addition to general anesthesia. Patients receiving combined regional-general anesthesia had similar mean age (68.6 years [95% CI: 68.2–68.9 years] versus 69.1 years [95% CI: 68.9–69.3 years], p < 0.0043), a slightly lower mean Deyo index (0.87 versus 0.93, p = 0.0052), and similar prevalence of individual comorbidities, compared to patients receiving general anesthesia alone (Table 1). Three comorbidities were more prevalent in the general anesthesia only group: diabetes (21.41% versus 18.91%, p < 0.001), history of myocardial infarction (6.13% versus 5.18%, p = 0.03178), and obesity (13.22% versus 11.32%, p = 0.0023) (Table 2).
Table 1.
Patient demographics and healthcare system-related data of the two groups
| Variable | General anesthesia group | General anesthesia + peripheral nerve block group | p value |
|---|---|---|---|
| Number of patients | 13,892 (79.12%) | 3665 (20.87%) | |
| Comorbidity burden | |||
| Deyo index* | 0.93 (0.91–0.95) | 0.87 (0.83–0.91) | 0.0052 |
| Deyo index category (number of patients) | 0.0168 | ||
| 0 | 7035 (50.64%) | 1920 (52.39%) | |
| 1 | 3034 (21.84%) | 825 (22.51%) | |
| 2 | 2283 (16.43%) | 571 (15.58%) | |
| ≥ 3 | 1540 (11.09%) | 349 (9.52%) | |
| Age | |||
| Age (years)* | 69.11 (68.94–69.27) | 68.57 (68.25–68.89) | 0.0043 |
| Age category (number of patients) | |||
| < 45 years | 209 (1.50%) | 52 (1.42%) | 0.0194 |
| 45–54 years | 924 (6.65%) | 280 (7.64%) | |
| 55–64 years | 2976 (21.42%) | 832 (22.70%) | |
| 65–74 years | 5276 (37.98%) | 1400 (38.20%) | |
| > 75 years | 4507 (32.44%) | 1101 (30.04%) | |
| Sex (number of patients) | |||
| Female | 7796 (56.12%) | 2057 (56.13%) | 0.9940 |
| Male | 6096 (43.88%) | 1608 (43.87% | |
| Ethnicity (number of patients) | |||
| White | 11,189 (80.54%) | 3103 (84.67%) | < 0.001 |
| Black | 541 (3.89%) | 139 (3.79%) | |
| Hispanic | 267 (1.92%) | 56 (1.53%) | |
| Other | 1895 (13.64%) | 367 (10.01%) | |
| Admission type (number of patients) | |||
| Emergent | 472 (3.40%) | 62 (1.69%) | < 0.001 |
| Elective | 12,583 (90.58%) | 3534 (96.43%) | |
| Trauma | 97 (0.70%) | 17 (0.46%) | |
| Urgent | 6 (0.04%) | 0 (0%) | |
| Other | 734 (5.28%) | 52 (1.42%) | |
| Hospital size (number of patients) | |||
| < 299 beds | 4852 (34.93%) | 1557 (42.48%) | < 0.001 |
| 300–499 beds | 5258 (37.85%) | 1538 (41.97%) | |
| > 500 beds | 3782 (27.22%) | 570 (15.55%) | |
| Hospital location (number of patients) | |||
| Rural | 1372 (9.88%) | 415 (11.32%) | 0.0010 |
| Urban | 12,520 (90.12%) | 3250 (88.68%) | |
| Hospital teaching status | |||
| Nonteaching | 9129 (65.71%) | 1971 (53.78%) | < 0.001 |
| Teaching | 4763 (34.29%) | 1694 (46.22%) | |
* Values are expressed as mean, with 95% CI in parentheses.
Table 2.
Incidence of comorbidities in the two groups
| Comorbidity | Number of patients | p value | |
|---|---|---|---|
| General anesthesia group | General anesthesia + peripheral nerve block group | ||
| Myocardial infarction | 851 (6.13%) | 190 (5.18%) | 0.03178 |
| Peripheral vascular disease | 466 (3.35%) | 141 (3.85%) | 0.14638 |
| Cerebrovascular disease | 87 (0.63%) | 33 (0.90%) | 0.07315 |
| Dementia | 30 (0.22%) | 4 (0.11%) | 0.19076 |
| COPD | 2896 (20.85%) | 733 (20.0%) | 0.26026 |
| Rheumatic disease | 1012 (7.29%) | 290 (7.91%) | 0.19689 |
| Mild liver disease | 63 (0.45%) | 18 (0.49%) | 0.76489 |
| Severe liver disease | 30 (0.22%) | 6 (0.16%) | 0.534 |
| Diabetes | 2974 (21.41%) | 693 (18.91%) | 0.00093 |
| Complicated diabetes | 264 (1.90%) | 61 (1.66%) | 0.34579 |
| Renal disease | 58 (0.42%) | 10 (0.27%) | 0.2098 |
| AIDS | 7 (0.05%) | 0 (0.0%) | 0.17408 |
| Paraplegia | 10 (0.07%) | 5 (0.14%) | 0.23493 |
| Cancer | 1138 (8.19%) | 305 (8.32%) | 0.79851 |
| Hypertension | 8786 (63.25%) | 2355 (64.26%) | 0.25802 |
| Complicated hypertension | 615 (4.43%) | 153 (4.18%) | 0.50635 |
| Pulmonary hypertension | 113 (0.81%) | 27 (0.74%) | 0.64228 |
| Sleep apnea | 1461 (10.52%) | 441 (12.03%) | 0.00863 |
| Obesity | 1836 (13.22%) | 415 (11.32%) | 0.0023 |
COPD = chronic obstructive pulmonary disease.
There were no differences in the incidence of perioperative pulmonary, cardiac, or other complications between groups (Table 3). In the multivariable logistic regression analysis (Table 4), the use of general anesthesia with a peripheral nerve block versus general anesthesia only (the referent) was not significantly associated with combined complications, cardiac complications, respiratory complications, invasive ventilation, blood product transfusion, or ICU admission.
Table 3.
Incidence of selected complications in the two groups
| Complication | Number of patients | p value | |
|---|---|---|---|
| General anesthesia group | General anesthesia + peripheral nerve block group | ||
| 30-day mortality | 5 (0.04%) | 1 (0.03%) | 0.79975 |
| Invasive ventilation | 152 (1.09%) | 31 (0.85%) | 0.18795 |
| Blood product transfusion | 843 (6.07%) | 204 (5.57%) | 0.25356 |
| ICU admission | 344 (2.48%) | 101 (2.76%) | 0.33816 |
| Infection | 410 (2.95%) | 90 (2.46%) | 0.10855 |
| Acute renal failure | 172 (1.24%) | 36 (0.98%) | 0.20287 |
| Gastrointestinal complications | 39 (0.28%) | 6 (0.16%) | 0.21262 |
| Myocardial infarction | 33 (0.28%) | 6 (0.16%) | 0.39835 |
| Cardiac complications (non-myocardial infarction) | 925 (6.66%) | 254 (6.93%) | 0.55852 |
| Pulmonary embolism | 27 (0.19%) | 5 (0.14%) | 0.46454 |
| Pneumonia | 151 (1.09%) | 33 (0.90%) | 0.3239 |
| Pulmonary compromise | 126 (0.91%) | 26 (0.71%) | 0.25076 |
| Cerebrovascular accident | 13 (0.09%) | 2 (0.06%) | 0.47215 |
| Combined complications (composite)* | 1537 (11.06%) | 398 (10.86%) | 0.72517 |
| Cardiac complications (composite)* | 943 (6.79%) | 258 (7.04%) | 0.59163 |
| Pulmonary complications (composite)* | 266 (1.92%) | 59 (1.61%) | 0.2231 |
Combined complications = all complications listed above; cardiac complications = acute myocardial infarction and non-myocardial infarction cardiac complications; pulmonary complications = pulmonary embolism, pneumonia, and pulmonary compromise; ICU = intensive care unit.
Table 4.
Results from multivariable regression analysis
| Outcome | Adjusted odds ratio (95% CI) | p value |
|---|---|---|
| Combined complications* | 1.03 (0.91, 1.16) | 0.6745 |
| Cardiac complications* | 1.09 (0.95, 1.27) | 0.229 |
| Pulmonary complications* | 0.87 (0.66, 1.16) | 0.352 |
| Invasive ventilation | 0.62 (0.33, 1.18) | 0.143 |
| Transfusion | 0.95 (0.81, 1.11) | 0.492 |
| ICU admission | 1.16 (0.93, 1.46) | 0.1938 |
| Increased length of stay† | 0.89 (0.82, 0.97) | 0.0068 |
Results are from the multivariable logistic regression model, general anesthesia + block versus general anesthesia alone (referent), adjusting for age group, sex, ethnicity, Deyo (comorbidity) index, presence of sleep apnea and morbid obesity; *combined complications = all complications listed above; cardiac complications = acute myocardial infarction and non-myocardial infarction cardiac complications; pulmonary complications = pulmonary embolism, pneumonia, and pulmonary compromise; † increased length of stay comprises entries exceeding the 75th percentile; ICU = intensive care unit.
There was no difference in mean length of stay between groups. The mean length of stay for the study cohort was 2.31 days (variance = 2.70 days). The mean length of stay was 2.27 days (95% CI: 2.21–2.30 days) in the regional-general anesthesia group and 2.32 days (95% CI: 2.29–2.35) in the general anesthesia group. The incidence rates of length of stay were similar between groups (IRR = 0.99; 95% CI: 0.97–1.02; p = 0.467). Multicollinearity was found absent (VIF < 2) from all regression models. The C-statistics were 0.7 in all multivariable logistic regression models. Tests for model fit indicated adequate model calibration for all models, except the model with transfusion as the response (p < 0.001).
Discussion
Regional anesthetic techniques have been recognized as effective for analgesic management and improved patient satisfaction after shoulder arthroplasty [14, 20]. Evidence is available that the use of regional anesthesia for orthopaedic surgery of the upper extremity conveys desirable advantages, including decreased baseline and dynamic pain, lower consumption of systemic analgesics, decrease of joint inflammation, increase in patient satisfaction, earlier mobilization, and shorter time to discharge readiness [1, 14]. However, there is little knowledge on whether incidence of systemic complications, mortality, and resource utilization beyond earlier discharge are affected by the choice of anesthetic technique. Using a large national cohort, we therefore determined (1) how frequently upper-extremity peripheral nerve blocks were added to general anesthesia in patients undergoing total shoulder arthroplasty; (2) whether there were differences in the incidence of and adjusted risk for major perioperative complications and mortality between patients receiving general anesthesia with and without nerve blocks; and (3) whether resource utilization (blood product transfusion, ICU admission, length of stay) differed between groups.
A number of limitations have to be considered when dealing with population-based data from large inpatient databases. First of all, we were not able to reliably capture peripheral neurologic damage occurring at the time of the procedure (either as a result of the nerve block or of the surgery). The Premier database only includes diagnosis codes present at discharge. However, nerve damage is frequently only encountered and/or definitely diagnosed at a later stage, and most diagnostic and therapeutic interventions are then performed in an outpatient setting. We determined the incidence of plexus injury as defined by ICD-9-CM codes 767.6, 907.x, 953.x, 955.x, 957.x and found no significant difference between the group that received a nerve block and the group that did not (0.16% versus 0.10%, p = 0.2818). However, for the reason mentioned above, this finding is likely not representative of the actual incidence of nerve damage, and we thus elected not to present it as a result of our analysis. Data from different settings and practices are integrated into the dataset, conveying considerable heterogeneity in terms of differential protocols and clinical approaches. The study has no information on how many of the blocks used the interscalene or supraclavicular approach to the brachial plexus. Interscalene block is the most widely used technique for shoulder surgery, providing reliable coverage of the entire surgical field. Supraclavicular block has recently emerged as an alternative. While risk for respiratory compromise due to phrenic nerve block is higher in the former, the latter may be associated with pneumothorax more frequently [18]. Furthermore, we could not distinguish which technique was used to locate the brachial plexus (eg, nerve stimulator, ultrasound), how much local anesthetic was injected, and whether a catheter was placed. However, the overall variability is in part accounted for by controlling for various covariates in the multivariable logistic regression. Moreover, our results originate from diverse clinical settings and are thus more likely to accurately reflect a real-world situation on a population-based level than data coming from controlled cohorts. Secondly, erroneous or ambiguous coding within the ICD-9-CM system cannot be excluded entirely; however, we used validated approaches to reliably identify various outcomes, including usage of multiple ICD-9-CM codes for each outcome. Additionally, contributing hospitals are incentivized to assure data accuracy, as the data are associated with billing operations. Numerous stringent integrity checks by the vendor lead to a generally high level of reliability in the database, as evidenced in numerous prior publications [19, 22, 25].
Described advantages of regional anesthesia for shoulder surgery include improved analgesia [27], lower intraoperative blood loss [31], better postoperative ROM of the replaced joint [15], and earlier discharge readiness [14]. The percentage of patients receiving an upper-extremity nerve block in addition to general anesthesia for total shoulder arthroplasty was about 20%. It must be stated that we did not consider the group of patients receiving regional anesthesia only so that we could more accurately compare the incidence of adverse events evoked by addition of a nerve block, rather than by avoidance of general anesthesia.
In this large cohort of patients receiving total shoulder arthroplasty, addition of an upper-extremity peripheral nerve block to general anesthesia was not associated with higher rates and risk of perioperative complications, mortality, and postoperative mechanical ventilation. Results from smaller, single-institutional trials are largely in accordance with our findings of low complication rates [5, 27, 30]. Peripheral nerve blocks predominantly used for shoulder surgery include the interscalene and supraclavicular plexus blocks, both providing good analgesic coverage of the proximal upper extremity, along with a high rate of block success [13]. However, close proximity to viable structures in the neck and thorax convey a potential risk for complications. Blockade of the recurrent laryngeal and phrenic nerves leading to stridor and hemidiaphragmatic paralysis, respectively, can necessitate mechanical ventilation and prove to be troublesome, especially in patients suffering from preexisting pulmonary morbidity [33]. Incidence of hemidiaphragmatic paralysis, along with reduction of the functional vital capacity, was reported to occur in almost all patients receiving an interscalene plexus block [10, 34]. Of note, the volume of local anesthetic injected seems to have very little influence on this outcome unless very low volumes (< 5 mL) are utilized [28]. Puncture of large vessels can result in hematoma or local anesthetic systemic toxicity [36], while puncture of the pleura can lead to pneumothorax [3]. Additionally, shoulder surgery in the sitting position was previously associated with stroke due to postural cerebral hypoperfusion [26]. However, it remains difficult to determine an exact incidence rate of these complications and their sequelae. Peripheral neurologic injury after shoulder arthroplasty remains a major concern for both surgeons and anesthesiologists. Unfortunately, we were unable to determine the incidence of peripheral nerve injury in our cohort. A study by Borgeat et al. [4] estimated the incidence of nerve damage after brachial plexus block at 0.4%; however, this number includes short-term complications up to 9 months, as well as conditions that may be related to neither surgery nor anesthesia, such as carpal tunnel syndrome. A retrospective study by Sviggum et al. [30], including approximately 1500 patients who underwent shoulder arthroplasty during a 14-year period at a single center, revealed a low overall rate of nerve injury at 2.2% but a decreased risk for nerve injury in patients who received an interscalene nerve block, compared to those who received other forms of anesthesia (OR = 0.47; 95% CI: 0.24–0.93; p = 0.031). In that study, 97% of nerve injuries resolved completely or partially until the end of documentation [30].
Unlike lower-extremity joint arthroplasty, the type of anesthesia chosen seems to have little influence on blood loss after shoulder arthroplasty [9].
In conclusion, our results suggest that the addition of an upper-extremity nerve block to general anesthesia does not affect the incidence or risk of perioperative adverse events. The good safety profile with regard to systemic complications, combined with favorable pain and satisfaction scores as reported earlier [14], support regional anesthesia as a viable option for analgesia in shoulder arthroplasty. Although the incidence of severe motor and/or sensory nerve damage is considered low, further research is required to better assess the risk of these potentially devastating complications. Moreover, the role of continuous as opposed to single-injection nerve blocks or the impact of catheters left in place after discharge could be addressed.
Electronic supplementary material
Footnotes
Each author certifies that he or she, or a member of his or her immediate family, has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. The institution of one of the authors (SGM) has received, during the study, funding from the Anna-Maria and Stephen Kellen Physician-Scientist Career Development Award provided by the Hospital for Special Surgery. One or more of the authors (RR, YLC, XS, MM) has received, during the study, funding from the Clinical Translational Science Center (Weill Medical College of Cornell University, New York, NY, USA) (RR, YLC, XS, MM); National Center for Advancing Translational Sciences (Rockville, MD, USA) (Grant UL1-RR024996) (MM); and Center for Education and Research on Therapeutics, Agency for Healthcare Research and Quality (Rockville, MD, USA) (Grant U18 HSO16-75) (MM). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Advancing Translational Sciences and Agency for Healthcare Research and Quality.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Each author certifies that his or her institution approved or waived approval for the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.
Analysis of Premier database files was performed at Weill Medical College of Cornell University, New York, NY, USA.
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