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Ten‐year trends of adult trauma patients in Central Denmark Region from 2010 to 2019: A retrospective cohort study

Abstract Background Trauma causes significant economic and societal burdens, and the trauma patient population and their prognosis change over time. This study aims to analyze 10‐year trends of trauma patients at a major trauma center in Central Denmark Region. Methods Five thousand three hundred and sixty‐six patients aged ≥16 years with Injury Severity Score (ISS) > 0 admitted by trauma team activation at a major trauma center between January 1, 2010, and December 31, 2019, were included. An annual percent change with a 95% confidence interval was used to estimate trends in the mechanism of injuries. Multiple logistic regression with mortality as the outcome was adjusted for age, sex, and ISS. Admission year was used as continuous variable in logistic regressions. Results The median age increased from 37 in 2010 to 49 in 2019, and the proportion of patients aged ≥65 doubled. The annual incidence of minor injuries (ISS 1–15) decreased from 181.3/105 inhabitants in 2010 to 112.7/105 in 2019. Severe injuries (ISS > 15) increased from 10.1/105 inhabitants in 2010 to 13.6/105 in 2019. The proportion of patients with ISS > 15 increased from 18.1% in 2010 to 31.1% in 2019. Multivariable logistic regression indicates lower 30‐day mortality for all trauma patients over the study period when adjusting for age, sex, and ISS (odds ratio: 0.94, 95% CI: 0.90–0.99). The 30‐day mortality for severely injured patients with ISS > 15 seems to decrease during the study period when adjusting for age, sex, and ISS (Odds ratio: 0.92, 95% CI: 0.87–0.97). Fall injuries increased by 4.1% annually (95% CI: 2.3%–6.1%). Conclusions Ten‐year trends of trauma patients at a major trauma center show an increasing median age, injury severity, and number of fall injuries. The 30‐day mortality of trauma patients decreased slightly for both minor injuries and severe injuries when adjusting for age, sex, and injury severity.


Editorial Comment
A trauma center in Denmark reports an increase in age and injury severity of admitted patients over the last 10 years. A higher proportion of cases had falling as the injury mechanism, and there appears to have been a decrease in mortality when adjusting for patients characteristics.

| INTRODUCTION
Injuries and trauma account for 8% of global mortality and significantly reduce quality of life. [1][2][3][4] Trauma is the leading cause of death among young people and creates a substantial economic and societal burden from subsequent disabilities and loss of potential life years. 2,5 Injuries in Scandinavia are predominantly traffic-related, falls, and blunt trauma, with lower rates of gunshot wounds and penetrating injuries than other countries. [6][7][8] In 2018, trauma patients accounted for 2405 admissions to major Danish trauma centers, of whom 6.8% died within 30 days. 3 Common causes of death in Denmark among trauma patients have been identified as damage to the central nervous system, exsanguination and multiple organ failure. 8,9 Characterizing and analyzing trauma patients regarding epidemiology, patient demographics, interventions, and outcomes may lead to improved trauma care, identify preventable injuries and describe tendencies over time. 6 To date, several studies have investigated long-term trauma trends in the USA, Japan, and UK. [10][11][12] Previous studies have highlighted the changes in the mechanism of injury, mortality and demographics; particularly, a rise in fall injuries and increasing age were among the compelling findings. 11,12 Moreover, trauma mortality is changing due to demographic alterations and the increasing proportion of elderly trauma patients with higher mortality. 6,13 In recent years, the impact of long-term changes in the Danish trauma population has not been explored. Trauma registries can facilitate analysis, injury prevention, comparison and benchmarking across regions and countries. 6 Hence, this study's aim is to analyze 10-year trends of trauma patients admitted to the major trauma center in Central Denmark Region focusing on annual incidence, severity, mortality, and the mechanism of injury (MOI). We will further investigate the subgroup of patients with severe injuries (Injury Severity Score [ISS] > 15).

| METHODS
This is a 10-year (2010-2019) retrospective cohort study conducted at a major trauma center in Denmark. The study followed the STROBE guidelines. 14

| Setting and data collection
Our Trauma Registry (TR) is the trauma registry of Aarhus University Hospital Trauma Center (AUH-TC). AUH-TC is a tertiary trauma center with highly specialized surgery and critical care. The catchment area for minor injuries covers the municipality (population 350,000) and major trauma patients from the region (population 1.3 million).

| Outcome
Danish trauma centers use the Abbreviated Injury Scale (AIS) to score each injury sustained by trauma patients. 15,16 The ISS is calculated based on the assigned AIS scores done by AIS-certified physicians and medical students. To avoid interpersonal discrepancies between AIS scores assigned, the coding team regularly discussed cases and reviewed the process of assigning codes to assure consistency. Severe injuries were defined as ISS > 15. Data for 30-day mortality were retrieved from patients' medical records using the Danish Civil Registration number (CRS). The Danish Civil Registration System contains a vital status for all Danish citizens and non-citizens who reside in Denmark. 17

| Patients
Trauma patients admitted with TTA to AUH-TC with an ISS > 0 and aged ≥16 were included in the analyses. Figure 1 shows patient inclusion and exclusion for the study. Patients with major trauma initially admitted to an acute-care hospital with secondary transfer to AUH-TC within 24 h were also included.

| Statistics
Descriptive data were reported as numbers and percentages. Continuous data were reported as mean and standard deviation for normally distributed data, and median and interquartile range (IQR) for nonnormal distributed data. Nonparametric comparisons over time for ISS and age were performed using the Kruskal-Wallis test. The annual incidence rates were calculated using the catchment area population count separately for the municipality (ISS 1-15) and Central Denmark Region (ISS > 15). 4 An average linear trend in the change in sex, ISS > 15 and MOI proportions during the 10-year study period was calculated using logistic regression with year as a continuous independent variable. This computed the estimated annual percent change (APC) with a 95% confidence interval. Logistic regression with 30-day mortality as outcome adjusted for age, sex, and ISS were calculated and admission year was used as continuous independent variable.
STATA version STATA/IC 17.0 (StataCorp. 2019, Texas) was used for all statistical analyses. A two-sided p value of <.05 was considered statistically significant.

| Ethics and approvals
This study was a registry study and exempted from trial registration following Danish law due to the data anonymity. The hospital board of directors approved the study.   Kruskal-Wallis test.

| DISCUSSION
In this study, we investigated 10-year trends in demographics, injury severity, 30-day mortality, and MOI among trauma patients admitted to AUH-TC. We found an increase in the median age, and the proportion of patients aged ≥65 doubled. The annual incidence and proportion of severely injured patients (ISS > 15) increased throughout the study period. The crude 30-day mortality of all patients including those severely injured did not change despite an increased injury severity but did, however, decrease marginally when adjusting for age, sex, and ISS. Long-term trends in the mechanism of injuries displayed a significant increase in fall injuries. Another study from Germany found increased mortality independent of ISS from age ≥ 56 in severely injured elderly trauma patients. 21 A nationwide study of death causes in Sweden reported a decline in injury-related mortality among working-age but an increase among elderly patients. 13 Several studies highlighted the frailty and excess mortality of elderly trauma patients and the need for increased focus on this age group. 13,22 The aging population and possibly more active elders results in a changing trauma patient population.

| Injury severity
We found an increasing injury severity, and the proportion of severely

| Mechanism of injury
We found a significant APC increase in fall injuries of 4.1%. We found a decreasing APC in pedestrian injuries of À4.7% and scooter injuries of À6.0%. Many studies have also reported increasing numbers of falls, especially in patients aged ≥65. [10][11][12]20 In the UK, the proportion of fall injuries <2 m among severely injured patients increased from 4.7% in 1990 to 39.1% in 2013. 12 Ten-year trends from 2005 to 2014 in a statewide trauma registry in Oklahoma, USA, found the APC of fall injuries to increase by 4.0% (95% CI: 3.1%-4.9%), and the number of fall injuries among patients ≥65 more than doubled. Furthermore, the APC of pedestrian injuries decreased by À1.5% during the 10-year study period in that trauma patient population. 10 31 The centralization of trauma care may improve survival but the effect of centralization remains unclear.

| Strengths and limitations
We included long-term trends in mortality. The percentage of missing patients is low, and most major trauma patients in Central Denmark Region (22% of the Danish population) are admitted to AUH-TC. 32 Our study, however, has potential limitations that affect the interpretation. We found significant changes in MOI, but the number of patients in each category of MOI was limited and we did not include minor injuries treated in the ED, thus complicating the identification of long-term trends in MOI. The level of undertriage in our region is unknown. Studies have shown inter-rater discrepancies in AIS scores; however, these discrepancies rarely affect the ISS. 33 Although the TTA criteria remained the same, the emergency physician's threshold to activate the trauma team could have changed during the study period. The implementation of national HEMS in 2014 and centralization of trauma care may have changed the referral pattern. In 2018, Weile et al. 34 found a heterogeneous composition of the trauma team and TTA criteria and poor registration practice at regional trauma facilities in Denmark and some unknown number of major trauma patients may still be treated at acute-care hospitals in Central Denmark Region. Therefore, a national benchmark study including the entire Danish trauma patient population is warranted.

| CONCLUSION
In this single-center 10-year retrospective cohort study, we observed increasing injury severity and proportion of elderly but unchanged crude 30-day mortality. The annual incidence of minor injuries with TTA decreased contrary to the rise in the annual incidence of severe injuries.