ABSTRACT
This study aimed to describe trends in the incidence of hip fracture hospitalizations, use of surgical procedures, and hospital outcomes among elderly patients with and without chronic obstructive pulmonary disease (COPD) in Spain (2004–2013). We selected all patients with a discharge primary diagnosis of hip fracture using the Spanish national hospital discharge database. Discharges were grouped by COPD status. From 2004 to 2013, 432,760 discharges with hip fracture were identified (6.9% suffered COPD). Incidence among COPD men increased by 2.63% per year from 2004 to 2013. There were no significant changes in tendency in the incidence among women with COPD during the study period. COPD women have almost three times higher incidence than COPD men. Incidences and hospital complications were higher among patients with COPD beside sex. The proportion of patients who underwent internal fixation increased for all groups of patients and the open reduction decreased. After multivariate analysis, in-hospital mortality (IHM) has improved over the study period for all patients. Suffering COPD was associated with higher IHM in men (odds ratio 1.45; 95% confidence interval 1.33–1.58) than women. In conclusion, hip fracture incidence is higher in subjects with than without COPD and is much higher among women than men. In COPD patients, incidence rates increased significantly in men from 2004 to 2013, but not in women. For all groups, the use of internal fixation has increased overtime and open reduction, IHM, and length of hospital stay have decreased from 2004 to 2013.
Introduction
Chronic obstructive pulmonary disease (COPD) is a common condition and its prevalence increases with increasing age. It is a leading cause of morbidity and mortality worldwide Citation(1, 2). Although COPD is primarily a lung disease, it is associated with co-morbidities, which contribute to a reduced health status, increased healthcare utilization, hospital admissions, and mortality. These include cardiovascular diseases, psychological disorders and osteoporosis Citation(3). Osteoporosis is the most common metabolic bone disease and like COPD Citation(1, 2) it is considered to be underdiagnosed and undertreated Citation(4).
The prevalence of osteoporosis in COPD ranges widely in different studies, from 23% to 83.7% Citation(5–10). The differences found may be due, at least in part, to differences in the method chosen for the diagnosis or the criteria used for the inclusion of patients. The risk factors that may contribute to its pathogenesis include older age, tobacco smoking, systemic inflammation, vitamin D deficiency, and the use of oral or inhaled corticosteroidsCitation(11, 12).
The burden of osteoporosis varies with the incidence of fracture risk. Osteoporosis-related fractures may contribute to increase the morbidity and mortality in COPD patients Citation(13). One of the most common fractures is vertebral fracture, which may further reduce the already compromisedpulmonary function in these patients Citation(14). Less attention has been given to hip fractures, which may increase mortality due to a higher operation risk related with COPD Citation(15).
Surgical options for the treatment of a proximal femoral fracture include total hip arthroplasty (THA), hemiarthroplasty (HA), and internal fixation (closed reduction of fracture [CRIF] and open reduction of fracture [ORIF]). These options depend on the fracture characteristics, the overall health of the patient, the patient's pre-fracture mobility, and the discretion of the treating surgeon Citation(16). Patients with COPD often exhibit more serious complications after hip fracture surgery. Increased risk of death, cardiopulmonary perioperative complications, and infections has been described in these patients Citation(10, 17).
Previous studies have observed changes in the incidence of hip fracture over time Citation(18). A decrease in the younger age groups and among women, and an increase in both sexes over 85 years have been demonstrated. However, there are no similar studies in COPD patients, despite the impact of this disease on mortality after hip fracture. Establishing the changes of incidence of this type of fracture and the use and outcomes of surgical procedures of hip fracture repair in patients with COPD is essential in order to implement appropriate health strategies. Also, it is necessary to find out how rates change over time in the population analyzed.
In this study, we used national hospital discharge data to examine trends in the incidence of hip fracture among hospitalized patients according to COPD status and gender between 2004 and 2013 in Spain. In particular, we analyzed trends in the use of surgical interventions (THA, HA, CRIF, and ORIF), patient co-morbidities, in-hospital complications, and in-hospital outcomes such as in-hospital mortality (IHM) and length of hospital stay (LOHS).
Methods
This retrospective, observational study was conducted using the Spanish National Hospital Database (Conjunto Minimo Básico de Datos (CMBD). This database is managed by the Spanish Ministry of Health, Social Services and Equality, and contains all public and private hospital data, hence covering more than 95% of hospital discharges Citation(19). The CMBD includes patient variables (sex and date of birth), admission date, discharge date, up to 14 discharge diagnoses, and up to 20 procedures performed during the hospital stay. The Spanish Ministry of Health, Social Services and Equality sets standards for record-keeping and performs periodic audits Citation(19). Data collected between January 1, 2004 and December 31, 2013 wereanalyzed.
Disease and procedure criteria were defined according to the International Classification of Diseases-Ninth Revision, Clinical Modification (ICD-9-CM), which is used in the Spanish CMBD.
We selected discharges for subjects whose medical diagnosis included hip fracture events code according to the ICD-9-CM: 820.xx in the primary diagnosis field. Only subjects aged 65 years or over were analyzed. Discharges were grouped by COPD status as follows: COPD (ICD-9-CM codes 490, 491, 491.0, 491.1, 491.2, 491.20, 491.21, 491.22, 491.8, 491.9, 492, 492.0, 492.8, 496) and no COPD.
Clinical characteristics included information on overall co-morbidity at the time of diagnosis, which was assessed by calculating the Charlson co-morbidity index (CCI). The index applies to 17 disease categories, and the scores of which are added to obtain an overall score for each patient Citation(20). We divided patients into three categories: low index, which corresponds to patients with no previously recorded disease or with one disease category; medium index, patients with two categories; and high index, patients with three or more disease categories. To calculate the CCI, we used 16 disease categories, excluding COPD, as described by Thomsen et al. Citation(21).
We specifically identified the following procedure: THA (ICD-9-CM code 81.51), hemiarthroplasty (ICD-9-CM code 81.52), CRIF (ICD-9-CM code 79.15), and ORIF (ICD-9-CM code 79.35). Adverse in-hospital events were also captured through query of the dataset and consisted of development of one or more of the following in-hospital complications codified in any diagnosis positions: pneumonia (ICD-9-CM codes 997.39, 486), sepsis (ICD-9-CM codes 995.91, 995.92), acute renal failure (ICD-9-CM codes 584, 584.5, 584.6, 584.7, 584.8, 584.9), surgical-site infection (ICD-9-CM codes 998.5, 998.51, 998.52, 998.53, 998.54, 998.55, 998.59, 998.50), iatrogenic pulmonary embolism and infarction (ICD-9-CMcode 415.11), deep venous thrombosis (ICD-9-CM codes 453.4, 453.40, 453.41,453.42), and urinary tract infection (ICD-9-CMcode 599.0). The proportion of patients who died during the IHM and mean LOHS were also estimated for each yearstudied.
Statistical analysis
We conducted all the analyses separately for men and women. To assess time trends, rates of hip fracture discharges for COPD and non-COPD patients were calculated in terms of 100,000 inhabitants. We calculated yearly COPD-specific incidence rates dividing the number of cases per year, sex, and age group by the corresponding number of people in that population group. In order to estimate the number of people with COPD, we used data from EPI-SCAN study (a multicenter, cross-sectional, population-based, observational study conducted in 11 sites in 10 cities in Spain, representing different geographic, climatic, and socio-economic regions) and from the National Health Surveys conducted in Spain in years 2003/2004, 2006/2007, 2009/2010, and 2011/2012. In these national representative surveys, the prevalence of chronic conditions, including COPD, is estimated. Using the estimated prevalences for sex and age group and multiplying them by the Spanish population for that same sex and age group, according to the Spanish National Institute of Statistics for each year studied, we obtained the numerator to estimate the incidence among COPD patients Citation(22, 23). We also calculated the yearly age- and sex-specific incidence rates for non-COPD patients by dividing the number of cases per year, sex, and age group by the corresponding number of people in that population group, according to data from the Spanish National Institute of Statistics, as reported on December 31 of each year Citation(24).
In our study, we used log linear joinpoint regression to identify the period in which trend changes in hip fracture rates occurred by sex and COPD status for each year, as well as to estimate the annual percentage of change (APC) in each of the periods delimited by the points of change Citation(25). The Joinpoint Regression Program, version 4.0.4, was used for the analysis Citation(26).
A descriptive statistical analysis was performed for all continuous variables and categories by stratifying discharges for hip fracture discharges according to COPD status and gender. Variables are shown as proportions or means with standard deviations. Bivariate analyses of variables according to year were using χ2 linear trend analysis (proportions) and analysis of variance (ANOVA) test (means), as appropriate.
In order to test the effect of sex in the incidence due to hip fracture events, we fitted separate Poisson regression models for patients with and without COPD, using year of discharge, age, CCI, complications, and type of repair as independent variables. A global model including the same variables and COPD status was also conducted to assess the adjusted effect of COPD in the incidence.
For IHM, logistic regression analyses were performed with mortality as a binary outcome using the same independent variables for those with and without COPD and for the entire population to assess the influence of COPD on IHM. Statistical analyses were performed using Stata version 10.1 (Stata, College Station, TX, USA). Statistical significance was set at p < 0.05 (two-tailed).
Ethical aspects
Data confidentiality was maintained at all times in accordance with Spanish legislation. Patient identifiers were deleted before the database was provided to the authors, by the Spanish Ministry of Health, Social Services and Equality, in order to maintain patient anonymity. It is not possible to identify patients on individual levels, either in this article or in the database. Given the anonymous and mandatory nature of the dataset, it was not necessary to obtain an informed consent. The study protocol was approved by the ethics committee of the Universidad Rey Juan Carlos.
Results
We identified a total of 432,760 discharges of patients aged 65 years or older, who were admitted with hip fracture as primary diagnosis in Spain from 2004 to 2013. Patients with COPD accounted for 6.90% of total (Citation29,873), mean age was 83.01 years (standard deviation (SD), 6.87 years), and 62.39% were men. In patients without COPD, mean age was 83.23 years (SD, 7.06 years) and 79.58% were women.
According to the results of joinpoint analysis, we found that age-adjusted hip fracture diagnosis in men without COPD increased by 1.24% per year from 2004 to 2013 (). For men with COPD, hip fracture diagnosis increased by 2.63% per year from 2004 to 2013 (). In women without COPD, there were no significant changes in tendency in the diagnosis of hip fracture throughout the 2004–2013 period (). Among women with COPD, the joinpoint analysis showed that incidence rate increased 0.26% per year from 2004 to 2013, with no significant changes in tendency in the incidence ().
Figure 1. Joinpoint analysis of annual hip fractures in men without COPD in Spain, 2004–2013. APC: annual percent change. Accent: APC is significantly different from 0 (two-sided, p < 0.05).
Figure 2. Joinpoint analysis of annual hip fractures in men with COPD in Spain, 2004–2013. APC: annual percent change. Accent: APC is significantly different from 0 (two-sided, p < 0.05).
Figure 3. Joinpoint analysis of annual hip fractures in women without COPD in Spain, 2004–2013. APC: annual percent change. Accent: APC is significantly different from 0 (two-sided, p < 0.05).
Figure 4. Joinpoint analysis of annual hip fractures in women with COPD in Spain, 2004–2013. APC: annual percent change. Accent: APC is significantly different from 0 (two-sided, p < 0.05).
show the annual hospital discharges rates and clinical characteristic for men and women with a hip fracture discharge diagnosis according to COPD status from 2004 to 2013. The cumulative incidence of discharges due to hip fracture in men with COPD increased significantly from 312.31 cases per 100,000 inhabitants in 2004 to 426.05 cases in 2013. In patients without COPD, the incidence increased significantly from 283.56 cases per 100,000 inhabitants in 2004 to 313.96 cases in 2013. The incidences were higher among those men with COPD than those without COPD from the years 2004 to 2013 (). For both groups of men studied, a significant increase in the mean age, CCI values, and complications were observed along the study period. Men with type COPD had significantly more co-morbidity (20.6 vs. 16.06% with two or more coexisting conditions, respectively), and more in-hospital complications (12.2 vs. 8.83%, respectively, p < 0.05) (). As can be seen in , among women with COPD with hip fracture diagnosis, the incidence of discharges was 874.53 cases per 100,000 inhabitants in 2004 and 992.34 cases in 2013, but no significant changes were detected in the trend over time. However, in women without COPD, the incidence increased from 805.91 cases per 100,000 inhabitants in 2004 to 824.32 cases in 2013(p < 0.05). The incidences were higher among women with COPD than those without COPD for the years 2004–2013 (). For both groups studied, a significant increase in the CCI values, and complications was observed along the study period. Mean age was 84.24 years (SD, 6.74 years) in women with COPD and 83.52 years (SD, 6.92 years) in those without COPD (p < 0.05). Women with COPD had significantly higher CCI values compared to those without COPD (15.23 vs. 10.33% with two or more coexisting conditions, respectively) and significantly higher in-hospital complications (9.89 vs. 7.64%) (). If we compare COPD men with COPD women, we find that women have almost three times higher crude estimated incidence than men in all the analyzed years. Women are significantly older and have lower CCI values and in-hospital complications than men along the study period.
Table 1. Incidences and clinical characteristics of hospital discharges due to hip fracture among men with and without COPD in Spain, 2004–2013.
Table 2. Incidences and clinical characteristics of hospital discharges due to hip fracture among women with and without COPD in Spain, 2004–2013.
shows the procedures and in-hospital outcomes for men and women with a hip fracture according to COPD status over the period of study. The IHM among men with COPD decreased significantly over the period of study ranging from 13.94% to 12.37%. Also, in those without COPD, crude IHM decreased significantly (8.59% in 2004 to 7.43% in 2013) (). The mean LOHS fell significantly from 12.25 days in 2004 to 9.45 days in 2013 in COPD men. In non-COPD men, the mean LOHS fell from 14.21 days in 2004 to 8.56 days in 2013(p < 0.05).
Table 3. Procedures and outcomes of hospital discharges due to hip fracture among men and women with and without COPD in Spain, 2004–2013.
Of the procedures analyzed, the most commonly used was CRIF followed by arthroplasty (HA and THA) and ORIF. A significant increase in the use of CRIF was found rising from 29.44% in 2004 to 40.45% in 2013 among COPD men and from 29.8% to 42.83% among those without the disease. As can been seen in , ORIF procedure has been decreasingly used in COPD and non-COPD men along the study period with similar figures for both groups. The IHM among COPD women with hip fracture diagnosis decreased significantly from 10.59% in 2004 to 8.01% in 2013. In those without COPD, it decreased significantly from 4.85% in 2004 to 4.31% in 2013 (). Over the 10-year study period, LOHS in women with and without COPD decreased significantly (p < 0.05). As observed for men, a significant increase in the use of CRIF from 32.97% to 44.25% in COPD women and from 30.49% to 44.58% in non-COPD women with a hip fracture was found along the study period. The most commonly used procedure was CRIF for both groups of women. However, it was used in a higher proportion among those with than without COPD. The use of CRIF has increased in COPD and non-COPD women overtime().
When we compared hospitalization outcomes between COPD men and women, we found higher crude IHM among men than women in the total study population and in all the years studied. ORIF and CRIF were used in a significantly higher proportion of COPD women than COPD men (18.64 vs. 16.99% and 38.87 vs. 35.06%, respectively), but the use of arthroplasty was lower in COPD women (30.54 vs. 32.51%).
The Poisson regression models conducted to assess the effect of sex in the incidence of hip fracture hospitalizations yielded an adjusted incidence rate ratio (IRR) for COPD patients of 2.50 [95% confidence interval (CI): 2.49–2.56]. This result shows that after adjusting for possible confounders, over the entire time period, the incidence among COPD women was 2.50 times higher than among COPD men. The IRR for non-COPD patients was 2.72 (95% CI 2.70–2.74), so the incidence among non-COPD women was 2.72 times higher than among non-COPD men. When we joined the databases of men with and without COPD, to assess the effect of the disease in the incidence of hip fracture hospitalizations, we found an IRR of 1.24 (95% CI 1.22–1.26). The corresponding figure for women was 1.14 (95% CI 1.12–1.16). This means that after adjusting for possible confounders, the incidences among COPD men and women were 24% and 14% higher than among non-COPD men and women, respectively.
summarizes the results of multivariate analysis of time trends and factors associated with IHM among men and women with and without COPD hospitalized for a hip fracture. Among men and women with COPD, IHM was significantly greater in older subjects (odds ratio [OR] 3.63, 95% CI 2.98–4.42 and OR 3.49, 95% CI 2.49–4.89 in ≥90 age group compared with reference category 65–74 years, respectively). IHM was significantly higher in COPD men and women with more co-morbidities (OR 2.23, 95% CI 1.97–2.51 and OR 2.66, 95% CI 2.22–3.19 for those with ≥2 co-morbidities, respectively) and in those with in-hospital complications (OR 2.94, 95% CI 2.62–3.30 and OR 4.01, 95% CI 3.38–4.76 for men and women, respectively). Those COPD women who did not receive an arthroplasty, ORIF, and CRIF procedure during their hospitalization had higher probability of dying (6.08-fold, 7.11-fold, and 6.63-fold, respectively) than those who underwent these procedures. Similar figures were observed in COPD men().
Table 4. Multivariate analysis of the factors associated with in-hospital mortality due to hip fracture among men and women with and without COPD in Spain, 2004–2013.
Time trend analysis showed a significant decrease in mortality from 2004 to 2013 in COPD men and women (OR 0.95, 95% CI 0.94–0.97 and OR 0.95, 95% CI 0.93–0.98). As can be seen in , the same variables were associated with IHM among those men and women without COPD. When we analyzed the entire database, and after adjusting for all covariates, suffering COPD was associated with higher IHM in men (OR 1.45; 95% CI 1.33–1.58). Among those without COPD, male gender was also associated with higher IHM (OR 1.77; 95% CI 1.72–1.84).
Discussion
Our study reveals that 6.9% of Spanish adults who suffer hip fracture have an associated diagnosis of COPD. These results are consistent with those reported by De Luise et al. Citation(15), who showed that 6.4% of patients hospitalized for a first-time diagnosis of hip fracture over a 6-year period (1998–2003) in Denmark had a history of COPD. In the same way, a longitudinal study of hip fractures in New York City during a similar time frame reported that 8.5% of the subjects had COPD Citation(27). However, these percentages are lower than those obtained by Regan et al. Citation(13), who found using data from the U.S. Department of Veterans Affairs Surgical Quality Improvement Program from 1998 to 2005, that nearly half (47.6%) of male patients undergoing acute hip fracture repair surgery had COPD. In our study, if we analyze only men, we found 18.47% of COPD among patients admitted to hospital for hip fracture. Discrepancies between the results obtained in different studies may be due to various factors, including methodological variations and differences in the criteria used to establish the diagnosis. Furthermore, Regan et al. Citation(13) conducted their investigation using data from the Veteran´s Health Affairs for years 1999–2005. We think this is a selected population that possibly has a higher history of tobacco use than the Spanish general population for years 2004–2013 and this may also explain the differences.
For patients with and without COPD, we observed a significant increase in the mean age, CCI values, and complications along the study period. We believe the possible explanations could include better health care of patients, which results in a longer life expectancy. This leads to hospitalization of patients who are older and have more co-morbidities, thereby presentation of more hospital complications Citation(28).
We found different trends by sex over time in the hospitalizations of elderly patients with and without COPD with a hip fracture diagnosis. We found an increase in hospital admissions for men with COPD and in elderly men without COPD (2004–2013). For women, there were no significant changes in tendency in the incidence of hip fracture over the study period, regardless of their COPD status. Our results are congruent with the findings of Azagra et al. Citation(16), who demonstrated a continuous rise of hip fracture rates in people of 65 years of age or more over a 14-year period (1997–2010) in Spain, but after adjustment, the rate only increased in men but decreased in women, especially in the younger groups. They explain this trend by the management of osteoporosis and prevention of osteoporotic fractures focused on analysis with dual X-ray absorptiometry and the prescription of antiresorptive drugs to women and men younger than 70 years. In Geneva, Switzerland, a significant decrease in age-adjusted incidence of hip fractures between 1991 and 2000 in women but not in men has been found Citation(29).
Our results show that after adjusting by confounders, the incidence of hospital discharge with a hip fracture diagnosis was significantly higher among men and women with COPD as compared to non-COPD subjects. Patients with COPD have a high risk of osteoporosis and fractures because of lifestyle factors (cigarette smoking and physical inactivity), systemic effects of the disease (as a result of mediators, cytokines, or activated inflammatory cells reaching the systemic circulation from inflammation in the lung), treatment (corticosteroids use) and co-morbidities (deficient calcium and vitamin D nutritional status, underweight) Citation(30, 31). In a large Danish register-based study, comparing subjects with and without COPD, suffering COPD adjusted for use of corticosteroids was associated with increased risk for hip fracture (OR 1.63, 95% CI 1.46–1.82) Citation(32). Other authors have also shown a higher risk of hip fracture in COPD patients. Indeed, it has been estimated that nearly half of patients hospitalized for COPD exacerbation have a high risk of hip fracture in the next 10 years Citation(33).
In our study, COPD patients had more concomitant co-morbidities and suffered more in-hospital complications than those without COPD as described in previous studies Citation(15, 17). After adjusting for possible confounders, the incidence among COPD men and women was 1.24 and 1.14 times higher than among non-COPD patients, respectively. Reyes et al. Citation(34) have also demonstrated that COPD is independently associated with an increased risk of hip fracture in elderly men.
We found an increase in CRIF procedure rates in patients with and without COPD from 2004 to 2013. Use of general anesthesia is a predictor of short-term mortality and complications after adjustment in patients with hip fracture treated surgically Citation(15, 35). In the United Kingdom, more than 70% of hip fracture surgeries are performed with regional anesthesia Citation(36). By contrast, a study realized in Spain reports greater than 90% of hip fracture patients receiving regional anesthesia Citation(37), suggesting the need to conduct randomized trials in patients with hip fracture with and without COPD to determine if decreased use of general anesthesia would improve hip fracture outcomes Citation(15).
In our study, LOHS was progressively reduced and overall IHM decreased over time among COPD and non-COPD patients. As previously discussed, COPD is a major factor predicting mortality in patients with hip fracture. Predictors of mortality in these patients include age, co-morbidity, worse American Society of Anaesthesiologists (ASA) class, use of general anesthesia, and delay in surgery Citation(15). It is noticeable that patients with fractures that are not operated during admission have increased mortality. It is understood that these patients for various reasons cannot be operated (including greater co-morbidities) or who die before the intervention.
Women with COPD had lower IHM than COPD men in this study. Previous studies have found that women with hip fracture have lower co-morbidities than men, possibly because they have better lifestyles and this fact could explain the lower proportion of complications Citation(28). However, further investigations are required to clarify this point. Other studies have also shown that males with hip fracture have worse outcomes than females Citation(38–40).
The strength of our investigation lies in its large sample size, its 10-year follow-up period, and its standardized methodology, which has previously been used to investigate COPD and its complications in Spain and elsewhere Citation(18, 41). Nevertheless, our study has a series of limitations. Our data source was the CMBD, an administrative database that contains discharge data for Spanish hospitalizations and uses information the physician has included in the discharge report. Therefore, an important limitation to the analysis of the current dataset is the lack of information about individual cases. However, it is the most important resource for monitoring hip fracture rates because of its size, national coverage, and relatively standardized recordingregulation Citation(42). The present study also lacks information regarding the severity of COPD and specific effects of COPD medication and osteoporosis therapy on hip fracture. Another limitation of this database is its anonymity (no identifying items such as clinical history number), which makes it impossible to detect whether the same patient was admitted more than once during the same year. In addition, patients who moved from one hospital to another would appear twice.
Nevertheless, this dataset, which was introduced in Spain in 1982, is a mandatory register, and its coverage is estimated to be greater than 95% Citation(19). Concerns have been raised about the accuracy of routinely collected datasets; however, these datasets are periodically audited. Consequently, the quality and validity of our dataset have been assessed and shown to be useful for health research Citation(18).
In conclusion, our national data show that hip fracture hospitalization rates increased from 2004 to 2013 in elderly men with and without COPD. For women, there were no significant changes in tendency in the incidence of hip fracture over the study period, regardless of their COPD status. Overall, women have almost three times higher incidence of hip fracture than men. Hip fracture incidence is higher in subjects with than without COPD. For all groups analyzed, the use of internal fixation has increased overtime and open reduction, IHM, and LOHS have decreased from 2004 to 2013. Patients who did not receive surgical procedures had much higher probability of dying during their stay than those who underwent these procedures. These findings emphasize the need to identify COPD patients at a high risk of fracture and develop fall and fracture prevention programs for elderly subjects with this disease.
Funding
This study forms part of research funded by the Grupo de Excelencia Investigadora URJC-Banco Santander N°30VCPIGI03: Investigación traslacional en el proceso de salud-enfermedad.
Declaration of interest
Javier de Miguel-Díez, Rodrigo Jiménez-García, Valentín Hernández-Barrera, Pilar Carrasco-Garrido, Luis Puente-Maestu, Laura Ramírez-García, and Ana López de Andrés declare that they have no conflict ofinterest.
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