a b s t r a c t

Background: The populations of many developed countries have been aging in recent years, resulting in increas- ing numbers of elderly-related injuries. Conventionally regarded as minor, injuries from ground-level falls are now associated with a higher risk of death for Elderly people.

Methods: The subjects of this study were 15662 adult patients with injuries from ground-level falls who were registered in the Japan Trauma Data Bank between 2007 and 2013. Logistic regression analysis was used to eval- uate the effects of age, sex, Injury Severity Score, and Revised Trauma Score on Inhospital mortality. Pa- tients aged 60 years or older were further categorized into 4 subgroups by age and sex, and the effect of the presence of injuries of Abbreviated Injury Scale greater than or equal to 3 in each region on inhospital mortality was analyzed.

Results: Logistic regression analysis for inhospital mortality showed significant interactions between sex and age and between sex and RTS, and subgroup analysis by sex was, therefore, performed. The odds ratio (95% confi- dence interval) for inhospital mortality compared with patients older than 60 years was 2.75 (1.90-3.96) for men aged 60 to 79 years and 5.44 (3.77-7.85) for men 80 years or older and 1.46 (0.83-2.58) for women aged 60 to 79 years and 2.32 (1.35-4.01) for women 80 years or older. The odds ratios (95% confidence interval) for RTS less than 7.840 was 6.89 (5.56-8.55) for men and 9.97 (7.59-13.10) for women.

Conclusions: The effects of age and RTS on inhospital mortality of patients after ground-level falls differed by sex.

(C) 2015

1. Introduction

The populations of many developed countries have been aging in re- cent years, resulting in an increasing number of injuries to elderly peo- ple [1,2]. This is particularly evident in Japan, where more than 32% of the population was aged 60 years or older in the 2012 fiscal year, higher than the 20% in the United States and the 27% in Germany [3]. Studies in the United States have shown that fall-induced injuries in the broad sense, including those caused by falls from heights, falling off objects, or ground-level falls, are more frequent in elderly people than in youn- ger individuals, and injuries from ground-level falls account for 80% or more of these cases [1,4]. Generally speaking, injuries from ground- level falls have conventionally been regarded as minor injuries with a low risk of death, but it is now reported that, in patients 70 years or older, the crude mortality rate has increased to 3 times higher than that for those younger than 70 years, and the odds ratio of mortality

? Conflicts of interest and source of funding: The authors have no conflicts of interest to disclose. No corporate funding was received for the preparation of this paper.

* Corresponding author at: Department of Emergency and Critical Care Medicine, Tokai University School of Medicine, 143 Shimokasuya, Isehara City, Kanagawa 259-1193, Japan. Tel.: +81 90 6775 1569; fax: +81 463 95 5337.

E-mail addresses: [email protected] (T. Taira), [email protected] (S. Morita), [email protected] (R. Umebachi), [email protected] (N. Miura), [email protected] (A. Icimura), [email protected] (S. Inoue), [email protected] (Y. Nakagawa), [email protected] (S. Inokuchi).

at age 70 years or older is 2.75 times higher than for those at age youn- ger than 70 years, indicating that injuries from ground-level falls should not be regarded as minor for elderly people [5]. In the future, population aging is projected to continue to intensify in developed countries [3], and the evaluation of the severity of fall-induced injuries in elderly peo- ple is an important task for the near future.

In this study, risk factors for inhospital mortality after ground-level falls were analyzed in patients registered in the Japan Trauma Data Bank (JTDB), the trauma database for the nation that currently has the world’s most aging population, Japan.

1. Methods
   1. Study design and patient enrollment and characteristics of baseline

There were 144048 cases registered in the JTDB between 2007 and 2013. Of these, cases with missing data on Abbreviated Injury Scale coding, sex, outcome, age, cause of injury, Glasgow Coma Scale score, respiratory rate, pulse rate, and systolic blood pressure on arrival at hospital as well as those with penetrating injury, injury due to burn or Electric shock, or explosions; those in cardiopulmonary arrest on arrival at hospital; those transported from other hospitals; and those aged 16 years or younger were excluded, leaving a total of 70487 cases. Of these, 15662 who had suffered injuries as the result of a ground-level fall were the subjects of this study (Figure).

http://dx.doi.org/10.1016/j.ajem.2015.01.052

0735-6757/(C) 2015

Figure. Flow diagram of blunt trauma patients from among the 144048 trauma patients included in the JTDB (2007-2013).

Table 1 shows the clinical features of the subjects: GCS, respiratory rate and systolic blood pressure on arrival at hospital, Revised Trauma Score (RTS), duration (days) of hospitalization, mortality rate, Injury Se- verity Score (ISS), and the presence of injury of AIS greater than or equal to 3 in each region (regions 1-8). The subjects were 6350 men and 9312 women, who were divided into 3 categories by age (b 60, 60-79, and

>=80 years). Table 2 shows a comparison of their clinical features.

Outcome measures and statistical analysis

In this study, the degree to which age constituted a risk factor for inhospital mortality was investigated first. A logistic regression model of analysis with inhospital mortality of subjects as the target variable and sex, age, RTS, and ISS as explanatory variables was used. Because the RTS distribution was skewed, it was divided into 2 categories: 7.840 (maximum score) and les than 7.840. The addition of interaction terms between the parameters to this model revealed significant inter- actions between sex and age and between sex and RTS, and the subjects were, therefore, divided into male and female subgroups, for which lo- gistic regression analyses were performed with inhospital mortality as the target variable and age, RTS, and ISS as explanatory variables.

Logistic regression analysis was then used to analyze the effect of in- jury in each region on inhospital mortality for the 13692 subjects aged 60 years or older. The addition of interaction terms between the param- eters to this model revealed significant interactions between age, sex, and head injury of AIS greater than or equal to 3. The subjects were, therefore, divided into 4 subgroups according to sex (men and women) and age (60-79 and >=80 years), and logistic regression analy- sis was performed with the presence of injury of AIS greater than or equal to 3 in each region as an explanatory variable. Because the inci- dence of injury of AIS greater than or equal to 3 in region 2 (face) and region 3 (neck) was extremely low and both ISS and RTS exhibited col- linearity with head AIS, they were not included as explanatory variables in the model.

SPSS software (Windows version 22.0) (SPSS, Chicago, IL) was used for data analysis. Categorical variables were compared using the ?² test, and continuous variables were compared using the Mann-Whitney U test or the Kruskal-Wallis test. Categorical variables are reported as sig- nificant figures and percentages, and continuous variables are reported as means and SDs, with P b .05 regarded as significant.

The JTDB data were used for this study with the permission of Japan Trauma Care and Research. Patient data were all anonymized, and indi- viduals were not identifiable.

1. Results

Table 3 shows the logistic regression model for inhospital mortality and the logistic regression model incorporating interaction terms between sex and age and between sex and RTS. There were significant interactions between sex and age and between sex and RTS. Table 3 shows the results of logistic regression analyses for inhospital mortality with men and women divided into 2 subgroups. For men, the odds ratio (95% confidence interval [CI]) for inhospital mortality in each age category compared with patients younger than 60 years increased greatly with increasing age, at

2.75 (1.90-3.96) for subjects aged 60 to 79 years and 5.44 (3.77-7.85) for those aged 80 years or older. For women, however, it was not a significant independent risk factor for subjects aged 60 to 79 years, at 1.46 (0.83- 2.58), and at age 80 years or older, the odds ratio was 2.32 (1.35-4.01), lower than that for men. Revised Trauma Score and ISS were significant in- dependent risk factors for both male and female subgroups, with the odds ratio (95% CI) for patients with RTS less than 7.840 being somewhat higher for women, at 8.62 (6.63-11.21), compared with 6.14 (4.95-7.62) for men, and the odds ratio for ISS was somewhat higher for women, at 1.12 (1.10- 1.14), compared with 1.09 (1.07-1.10) for men.

Table 4 shows the results of logistic regression analyses for inhospital mortality with injury of AIS greater than or equal to 3 in each region as the explanatory variable when the 13692 subjects 60 years or older were divided into 4 subgroups by age category and sex. Head injury of AIS greater than or equal to 3 was a significant

Table 1

Characteristics of all patients and by sex

Table 2

Characteristics of each age category

Sex (female %) 9312 (59.5) Arrival vital signs

All cases		Female	Male			Age
(n = 15662)		(n = 9312)	(n = 6350)			b60 y 60-79 y >=80 y
Age (y)	79 (69-86)	83 (75-88)	73 (62-82)	(n = 1970)			(n = 5862)	(n = 7830)

GCS

<=3 (%)	285 (1.8)	82 (0.9)	203 (0.2)
4-5 (%)	176 (1.1)	67 (0.7)	109 (1.7)
6-8 (%)	486 (3.1)	162 (1.7)	324 (5.1)
9-12 (%)	819 (5.2)	321 (3.4)	498 (7.8)
13-15 (%)	13896 (88.7)	8680 (93.2)	5216 (82.1)

Respiratory rate (beats/min)

<=5 (%)	20 (0.1)	8 (0.1)	12 (0.2)
6-9 (%)	51 (0.3)	27 (0.3)	24 (0.4)
10-29 (%)	14910 (95.2)	8911 (95.7)	5999 (94.5)
>=30 (%)	681 (4.3)	366 (3.9)	315 (5.0)

Systolic blood pressure (mm Hg)

<=49 (%)	38 (0.2)	14 (0.2)	24 (0.4)
50-75 (%)	111 (0.7)	38 (0.4)	73 (1.1)
76-89 (%)	246 (1.6)	107 (1.1)	139 (2.2)
>=90 (%)	15267 (97.5)	9153 (98.3)	6114 (96.3)

Hospitalization (d)a	19 (8-31)	21 (12-31)	16 (5-30)
Mortality (%)	817 (5.2)	310 (3.3)	507 (8.0)
ISS	9 (9-16)	9 (9-9)	10 (9-16)
RTS

b7.840	2618 (16.7)	1089 (11.7)	1529 (24.1)
7.840	13044 (83.3)	8223(88.3)	4821 (75.9)
TRISSPs	0.97 (0.94-0.97)	0.97 (0.96-0.97)	0.97 (0.94-0.97)

Each region of AIS (>=3) (%)

Region 1 (head)	4227 (27.0)	1502 (16.1)	2725 (42.9)
Region 2 (face)	32 (0.2)	18 (0.2)	14 (0.2)
Region 3 (neck)	9 (0.1)	3 (0.01)	6 (0.1)
Region 4 (chest)	608 (3.9)	196 (2.1)	412 (6.5)
Region 5 (abdomen)	108 (0.7)	45 (0.5)	63 (1.0)
Region 6 (spine)	1090 (7.0)	324 (3.5)	766 (12.1)
Region 7 (upper limb)	520 (3.3)	387 (4.2)	133 (2.1)
Region 8 (lower limbs and pelvis)	7880 (50.3)	6218 (66.8)	1662 (26.2)

^a n = 15430.

Sex (female %) 633 (32.1) 2,937 (50.1) 7033 (73.3)

Arrival vital signs GCS

<=3 (%)	50 (2.5)	126 (2.1)	109 (1.4)
4-5 (%)	20 (1.0)	74 (1.3)	82 (1.0)
6-8 (%)	104 (5.3)	207 (3.5)	175 (2.2)
9-12 (%)	142 (7.2)	331 (5.6)	346 (4.4)
13-15 (%)	1654 (84.0)	5124 (87.4)	7118 (90.9)

Respiratory rate (beats/min)

<=5 (%) 6 (0.3) 7 (0.1) 7 (0.1)

6-9 (%)	7 (0.4)	14 (0.2)	30 (0.4)
10-29 (%)	1860 (94.4)	5589 (95.3)	7461 (95.3)
>=30 (%)	97 (4.9)	252 (4.3)	332 (4.2)

Systolic blood pressure (mm Hg)

<=49 (%) 6 (0.3) 16 (0.3) 16 (0.2)

Hospitalization (d)a	10 (3-22)	19 (7-31)	22 (13-32)
Mortality (%)	57 (2.9)	309 (5.3)	451 (5.8)

50-75 (%)	17 (0.9)	58 (1.0)	36 (0.5)
76-89 (%)	48 (2.4)	99 (1.7)	99 (1.3)
>=90 (%)	1899 (96.4)	5689 (97.0)	7679 (98.1)

ISS RTS	9 (9-16)	9 (9-16)	9 (9-9)
b7.840	442 (22.4)	1060 (18.1)	1116 (14.3)

7.840	1528 (77.6)	4802 (81.9)	6714 (85.7)
TRISSPs	0.99 (0.97-0.99)	0.97 (0.94-0.97)	0.97 (0.96-0.97)

Each region of AIS (>=3) (%)

Region 1 (head)	766 (38.9)	1,929 (32.9)	1532 (19.6)
Region 2 (face)	10 (0.5)	11 (0.2)	11 (0.1)
Region 3 (neck)	2 (0.1)	5 (0.1)	2 (0.01)
Region 4 (chest)	142 (7.2)	260 (4.4)	206 (2.6)
Region 5 (abdomen)	37 (1.9)	40 (0.7)	31 (0.4)
Region 6 (spine)	227 (11.5)	596 (10.2)	267 (3.4)
Region 7 (upper limb)	108 (5.5)	232 (4.0)	180 (2.3)
Region 8 (lower limbs and pelvis)	363 (18.4)	2307 (39.4)	5210 (66.5)

^a n = 15430.

independent risk factor for inhospital mortality in all 4 subgroups, but the odds ratios varied between subgroups at 5.95 (2.74-12.91) for women aged 60 to 79 years, 9.43 (5.48-16.22) for women 80 years or

older, 11.72 (6.55-20.98) for men aged 60 to 79 years, and 6.67 (3.94- 11.31) for men 80 years or older. For men aged 60 to 79 years, the odds ratio (95% CI) of inhospital mortality was 2.12 (1.05-4.26) for pel- vic or leg injury of AIS greater than or equal to 3 in each region, whereas for women aged 60 to 79 years, Abdominal injury was an independent risk factor with an odds ratio of 8.19 (1.51-44.56). For men 80 years or older, the odds ratio was 6.15 (1.48-25.63) for abdominal injury and

2.38 (1.20-4.73) for vertebral or spinal cord injury, whereas for the sub- group of women 80 years or older, injury of AIS greater than or equal to 3 in any region other than the head was not a significant independent risk factor.

1. Discussion

Generally speaking, injury in elderly patients is of low ISS and has low rates of other Abnormal vital signs [6-10]. It has been found, howev- er, to have a high mortality rate and a long duration (days) of hospital- ization, and the patients in the present study were no exception (Table 2) [1,2,6-8,11-14]. Taylor et al [15] investigated the effect of age on mortality among patients hospitalized for blunt injury and reported that the mortality rate increased with age, being 5.2% among those aged 65 to 74 years, 6.7% among those aged 75 to 84 years, and 9.22% among those aged 85 years or older. They also reported that logistic regression analysis showed that the odds ratio of mortality for elderly patients 65 years or older was 1.87 (95% CI, 1.06-2.18) compared with patients younger than 65 years. In a study by Sampalis et al [11], the mortality

rate among elderly patients 65 years or older was higher as a result of in- juries due to falls in the broad sense than as a result of traffic injuries. Spaniolas et al [5] studied injuries resulting only from ground-level falls, and they found that elderly patients 70 years or older spent a longer dura- tion (days) in hospital and in the intensive care unit compared with those younger than 70 years, and that being male, age 70 years or older, and GCS less than 15 were significant independent risk factors for mortality. These studies all showed that increasing age is an independent risk factor for mortality, whether from blunt injury, injuries due to falls in the broad sense, or ground-level falls. Being male is also an independent risk factor for mortality in fall-induced injuries, but differences in the effect of age on inhospital mortality according to sex have not been reported.

The present study showed that the effect of age on inhospital mor- tality among patients with injuries from ground-level falls differed ac- cording to sex. The odds ratio of inhospital mortality was 2.75 (95% CI, 1.90-3.96) for men aged 60 to 79 years and 5.44 (3.77-7.85) for men 80 years or older, but for women aged 60 to 79 years, it was not a signif- icant risk factor, and for women 80 years or older, the odds ratio was

2.32 (1.35-4.01). When treating patients with injuries from ground- level falls in emergency departments (EDs), the effect of age should be considered separately for each sex, with particular attention to the fact that the odds ratio of inhospital mortality for men 80 years or older was more than 5 times higher than that for men younger than 60 years. The reason for the differences in the effect of age on mortality ac- cording to sex is unclear, but it may be associated with the fact that the mean lifespan at birth for a Japanese woman is 86.4 years, 6.5 years higher than the 79.9 years for men [16,17]. Weakening of muscle strength and changes in activity levels due to aging also vary by sex, and it is conjectured that this may be one reason. Stevens et al [18] conjectured

Table 3

Multivariate logistic regression for survival of each sex category

	All cases	All casesa	Females	Males
	Odds ratio (95% CI)
Sex (male)	1.65? (1.40-1.96)	2.15? (1.41-3.30)
Age (y)
b60	Ref
60-79	2.32? (1.71-3.16)	2.75? (1.90-3.96)	1.46 (0.83-2.58)	2.75? (1.90-3.96)
>=80	4.22? (3.10-5.72)	5.44? (3.77-7.85)	2.32? (1.35-4.01)	5.44? (3.77-7.85)
RTS, 7.840 RTS, b 7.840	Ref 7.13? (6.03-8.44)	6.14? (4.95-7.62)	8.62? (6.63-11.21)	6.14? (4.95-7.62)
ISS	1.10? (1.09-1.11)	1.08? (1.07-1.09)	1.12? (1.10-1.14)	1.09? (1.07-1.10)
Sex x age (b60)		Ref
Sex x age (60-79) Sex x age (>=80)		0.53 (0.27-1.05) 0.43?? (0.22-0.82)
Sex x RTS (7.840) Sex x RTS (b7.840) Sex x ISS		Ref 1.41?? (1.00-1.97) 1.03?? (1.01-1.05)
a With interaction term.
* P b .01.

?? P b .05.

that, although elderly men have high levels of activity, their leg muscle strength is actually liable to become weaker compared with that of women, and they are more frequently injured outdoors, contributing to their higher mortality rate. Other reports, however, have found that elderly women‘s leg muscle strength is more liable to become weaker compared with that of elderly men and that they are at higher risk for falling inside and for being more severely injured [19] and also that women’s sense of balance is more liable to deteriorate than that of men in old age, meaning that they are prone to having ground-level falls [20]. The database used in this study did not include detailed descriptions of the circumstances of inju- ry or activity levels before injury, and it was, therefore, difficult to analyze the circumstances of injury. There may also be a wide variety of relevant factors other than muscle strength and activity levels, and further investiga- tion of the differences in risk according to sex is required.

Glasgow Coma Scale less than 15 is also known to be a significant in- dependent risk factor for mortality after ground-level falls [5]. In the present study, the odds ratio was high for patients with RTS less than 7.840 for mortality from ground-level falls for both women, at 8.62 (95% CI, 6.63-11.21), and men, at 6.14 (4.95-7.62). Patients with ground-level fall-induced injuries who present to EDs with an RTS below the maximum score, that is, with even one of the following, ab- normal consciousness level, abnormal respiration rate, or abnormal sys- tolic blood pressure, should, therefore, be treated as high-risk patients. Organ damage, which is a risk factor for mortality from blunt injury, has been the subject of numerous previous studies, and intracranial hem- orrhagic lesions, cervical spinal cord damage, hemothorax, pneumotho- rax, intra-abdominal organ injury, and leg fractures have been reported to constitute independent risk factors for mortality [2,5,7,14,21-23]. Stud- ies of ground-level falls have also identified high AIS in the head, thoracic, abdominal, pelvic, and leg areas in cases of death [5]. In the present study, patients were divided into 4 subgroups comprising men and women aged

60 to 79 years and 80 years or older, respectively, and it was found that the injury regions that constituted risk factors for inhospital mortality dif- fered between men and women. Head injury of AIS greater than or equal to 3, however, was a significant risk factor for mortality in all subgroups. Other risk factors were abdominal injury for women aged 60 to 79 years, leg and pelvic injury for men aged 60 to 79 years, and abdominal injury and vertebral or spinal cord injury for men 80 years or older. A meta-analysis of mortality rates after Hip fracture in those 50 years or older found that the relative hazard ratio for death up to 3 months after injury compared with a control cohort was higher for men (7.95, 6.13- 10.30) than for women (5.75, 4.94-6.69) [24]. The mortality rate up to 30 days after hip fracture has also been found to be higher for men than for women, and multivariate Cox regression analysis identified respiratory infection, heart failure, deep venous thrombosis, and other postoperative complications as independent risk factors for death [25]. From these re- sults, it may be conjectured that the short-term mortality rate after hip fracture in elderly patients may be higher for men because they are more likely to have complications such as respiratory infection. This sug- gests that the reason that pelvic or leg injury was found to be only a risk factor for death in men in the present study may have been the vulnerabil- ity of elderly men to postoperative complications.

Several studies have investigated sex differences in injury regions among elderly injured patients [26,27], but no studies have previously addressed the effect of sex on mortality for different injury regions in ground-level falls, and this is a topic for further research.

1. Limitations

This study had the following limitations. Patients with missing data were excluded from the present study, which meant that only around

Table 4

Multivariate logistic regression for survival of each sex and age category (>=60 years)

Females Males

60-79 y >=80 y 60-79 y >=80 y Odds ratio (95% CI)

Each region of AIS (>=3)

Region 1 (head) 5.95? (2.74-12.91) 9.43? (5.48-16.22) 11.72? (6.55-20.98) 6.67? (3.94-11.31)

Region 4 (chest) 1.09 (0.23-5.09) 2.00 (0.88-4.55) 1.77 (0.89-3.54) 1.04 (0.45-2.43)

Region 5 (abdomen) 8.19?? (1.51-44.56) 3.95 (0.96-16.17) 3.19 (0.67-15.12) 6.15?? (1.48-25.63)

Region 6 (spine) 0.35 (0.05-2.74) 1.74 (0.69-4.41) 1.76 (0.89-3.45) 2.38?? (1.20-4.73)

Region 7 (upper limb) 0.56 (0.13-2.50) 0.84 (0.25-2.81) 0.96 (0.12-7.45) 0.41 (0.05-3.15)

Region 8 (lower limbs and pelvis) 0.89 (0.39-2.03) 0.90 (0.51-1.58) 2.12?? (1.05-4.26) 1.32 (0.75-2.34)

* P b .01.

?? P b .05.

1 in 10 of the patients registered was included; this may have resulted in selection bias. Almost all subjects in this study were Japanese, and inter- racial differences were not addressed. functional outcomes at the time of hospital discharge were not recorded, and it was, therefore, impossi- ble to evaluate outcomes other than survival. Data on previous medical histories and oral anticoagulant use were missing in many cases, and these factors could, therefore, not be included in the models. Only sub- jects who had been admitted to Japanese trauma centers were included, and the possibility of selection bias cannot, therefore, be ruled out.

1. Conclusion

In conclusion, the effects of age and RTS on inhospital mortality of patients after ground-level falls differed by sex. In particular, male pa- tients 80 years or older and those that scored lower than the maximum score on the RTS were at higher risk for inhospital mortality. Head injury was also a risk factor for patients 60 years or older.

Author contribution statement

The authors were solely responsible for all aspects related to this arti- cle, including the literature search, study design, data collection, data analysis, and writing. Sadaki Inokuchi and Seiji Morita designed the study; Rimako Umebachi, Naoya Miura, Atsushi Ichimura, and Yoshihide Nakagawa researched the data; Shigeaki Inoue analyzed the data.

Acknowledgment

The author would like to thank Prof Hiroyuki Kobayashi for com- ments and suggestions related to the statistical analysis.

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