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Comparison of motor vehicle occupant injuries in restrained and unrestrained 4- to 14-year-olds
Accid. Anal. & PET. Vol. 24. No. 4. pp. 349-355. Printed in Great Britain.
1992
WXll-4575192 0 1992 Pergamon
S5.00+ .W Press Ltd.
COMPARISON OF MOTOR VEHICLE OCCUPANT INJURIES IN RESTRAINED AND UNRESTRAINED 4- to 14-YEAR-OLDS” Department
PHYLLIS F. AGRAN of Pediatrics, Public Policy Research Organization. Irvine, CA 92717, U.S.A.
University of California,
DAWN N. CASTILLO and DIANE G. WINN Public Policy Research Organization, University of California, Irvine, Irvine, CA 92717, U.S.A. Abstract-This study compares injuries of restrained and unrestrained 4- to 14-year-olds in nine emergency rooms and the Coroner’s office in Orange County, California from 1983 to 1989. Analyses were performed separately for 4- to 9- and lo- to 14-year-olds because of differences related to the fit of the seat belt. Significantly fewer intracranial injuries and a significantly lower mean Injury Severity Score (ISS) were seen between the restrained and unrestrained for lo- to 14-year-olds in the front passenger and back seats; but for 4- to 9-year-olds in the back seat only. These same differences were noted between restrained 4- to 9-year-olds in the back compared with those in the front passenger seat. Except for 4- to 9-year-olds in the front passenger seat, our findings are consistent with similar studies of occupants of all ages. Our results suggest that lap-shoulder belts (primary restraint in front seat) may provide less protection for 4- to 9year-olds than for lo- to 14-year-olds and adults.
INTRODUCTION
Many studies have demonstrated the effectiveness of seat belts in reducing motor vehicle occupant morbidity and mortality (Campbell 1987; Evans 1987; Iowa Safety Restraint Assessment 1988; Orsay et al. 1988; Reath et al. 1989). These evaluations, however, have grouped children with adults in the analyses. Because of marked differences in anatohic and physical features between children and adults, the effectiveness of seat belts for children separate from adults warrants evaluation (Agran et al. 1989; Snyder and O’Neill 1975) especially in consideration of current federal standards for the construction of seat belts (FVMSS 208). The minimum dimensions the lap belt are required to fit are those of a fiftieth percentile 6-year-old-child. However, the lap-shoulder belt, which is considered superior to the lap belt and will be standard equipment in rear outboard seats, has different specifications. The minimum dimensions the lap-shoulder belt is required to fit are those of a fifth percentile adult female (Code of Federal Regulations 1989). The general assumption that adult seat belts are as effective for young children as for adults should be evaluated. The present study utilizes a multihospital and coroner’s office monitoring system to compare body region and severity of injury of restrained and unrestrained 4- to lCyearold occupants. The rationale for this study design is that the effectiveness of seat belts in mitigating and preventing injury should be manifested in different body regions of injury and less severe injuries among the restrained in comparison to the unrestrained. This methodology has been utilized by others with the expected positive results of altered patterns and less severe injuries among the restrained in comparisori with the unrestrained (Iowa Safety Restraint Assessment 1988; Orsay et al. 1988; Reath et al. 1989). The primary difference between our study and the aforementioned studies was the analysis of a specific age-group; the aforementioned studies included occupants of all ages, with adults constituting the majority.
*Presented in part at the 117th Annual Meeting of the American Public Health Association, October 2226, 1989, Chicago, IL. This study was supported in part by the California State Office of Traffic Safety (Peter O’Rourke, director), the US Department of Transportation, and a grant from the Centers for Disease Control. The opinions expressed in this article are those of the authors and not necessarily those of the funding agencies. 349
3.50
P. E AGRAN et al.
In the present study, analyses are performed separately for children aged 4-9 and lo-14 years because of anatomic and structural differences between these two age-groups related to the fit of the seat belt. The anchor point for the lap portions of the belt-the anterior iliac crests-are not fully developed until approximately ten years of age. Further, the smaller rib cage and bony pelvis of the younger child are less protective of abdominal viscera (Burdi et al. 1969). Behavioral characteristics may also influence the protective effects of seat belts, e.g. the young child may be more likely than an older child to adjust his/her seating position, lean forward and move about, or engage in activities that alter the “fit” of the belt system. METHODS
A monitoring system to identify children through the age of 14 years injured as motor vehicle occupants was utilized. The surveillance system consisted of nine of 38 hospitals and the coroner’s office in Orange County, California. The system included a major health maintenance organization hospital, the children’s .hospital, and three of the County’s four trauma centers. One of the trauma centers in the surveillance system is also the major healthcare facility in the County utilized by the medically indigent. Regular audits of emergency department and coroner’s office logbooks were conducted to identify cases. Information from medical records of child occupants involved in motor vehicle crashes and non-crash events was abstracted onto a standardized interview schedule. Diagnosed injuries were recorded and assigned codes. The Abbreviated Injury Scale (AIS-85), which ranks severity of injury on a scale from 1 to 6, with 1 representing a minor injury and 6 corresponding to a virtually unsurvivable injury, was utilized. The Injury Severity Score (ISS), which sums the squares of the highest AIS for the three body regions with most severe injury, was calculated to assess overall injury severity (American Association for Automotive Medicine 1985). An interviewer contacted the parent(s) or guardian within 4 to 6 weeks after the injury event and administered a standardized telephone interview, soliciting information on the circumstances of the injury event. Sixteen hundred and forty-nine children injured as motor vehicle occupants between January 1, 1983 and March 31, 1989 were eligible for inclusion in the study. Forty-three children were excluded because restraint use was not determined; 12 because the child was restrained by a toddler seat; 100 because the child was sitting in a location for which seat belts are not standard (i.e. back of pickup trucks, cargo areas); and five because of an intentional ejection (i.e. the child stepped out before the car was completely stopped.) To minimize erroneous reporting of seat belt use by the parent, questions regarding circumstances of the crash, including what happened to the child to cause his/her injuries, were asked first. Information on restraint use was usually volunteered by the parent prior to direct inquiry. For those indicating restraint use, additional questions were asked regarding the type of restraint (lap belt or lap/shoulder) and what happened to the child and the restraint during the crash. All cases in which restraint use was indicated were reviewed by the research team, using hospital records, police reports (when available), and available newspaper reports. Eight cases in which there was doubt regarding restraint use were further excluded from the analysis. Two-sided t-tests were used for comparisons of means of continuous variables and chi-square tests for drawing inferences concerning proportions. Differences were considered statistically significant if the p-value was .05 or less. RESULTS
to 9-year-olds A total of 755 4- to 9-year-olds were included in the study-382 restrained by a seat belt, 373 unrestrained (Table 1). There was one fatality among the restrained and four
4
Injuries in restrained and unrestrained
4- to 14-year-olds
351
Table 1. Location and restraint use of front and back seat 4- to 9-yearold passengers
Seat location Driver’s Middle Passenger Unspecified Restraint use Unrestrained Restrained
Front seat (n = 371)
Back seat (n = 384)
2 46 295 28
101 43 136 104
197 174
176 208
among the unrestrained. Forty-eight percent of the restrained were male compared with 45% of the unrestrained (difference not statistically significant). Slightly more children were seated in the back than the front seat. Because of the heterogeneous environment of the front seat by location (driver’s, middle, passenger), we did not aggregate the three locations when examining effects of restraint use in the front seat. The majority of children were in the front passenger location. The small numbers of children in the driver’s and middle locations of the front seat precluded separate analyses for these locations. The primary type of restraint for the front passenger seat was lap/shoulder. Seat location was aggregated for examination of the effects of restraint use in the back seat; the lap belt was the principal type of restraint (Table 2). As shown in Table 3, the most frequent type of injury was soft tissue (contusions, lacerations, and nonspinal strains). Restrained children experienced significantly fewer soft tissue injuries and significantly more spinal strains than unrestrained children. When the analyses were stratified by seat location (Table 3)) there were no significant differences between restrained and unrestrained in the front passenger seat. In contrast, significant differences seen in the crude analysis (decreased soft tissue injuries and increased spinal strains in restrained compared to unrestrained) were found for the back seat, as well as significantly fewer intracranial injuries in the restrained compared with unrestrained in the back seat. Injuries were also compared between restrained children in the front passenger and back seats. Restrained children in the front passenger seat experienced significantly more intracranial injuries than restrained children in the back seat, p-value = .043. The reader should be cautioned that while significant differences were noted, the absolute numbers were small, 14 vs 9. There were no significant differences between restrained in the front passenger and back seat for the other injury types. The mean ISS for restrained and unrestrained children in the crude analysis (all seat locations) was not significantly different. However, restrained children in the back seat had a significantly lower mean ISS than unrestrained children in the back seat (Table 4). Further, the mean ISS of restrained children in the back seat was significantly lower than that of restrained children in the front seat, p = .034.
Table 2. Restraint use by seat location for 4- to 9-year-old passengers Restraint use Unrestrained Restrained Lap/shoulder Lap Unspecified
Front passenger seat* (n = 295)
Back seat (n = 384)
150 145 120 12 13
176 208 10 155 43
*The front passenger seat is analyzed separately from the driver’s and middle seat locations because of the heterogeneous environment of the front seat by location. The small numbers of children seated in the driver’s and middle seat locations precluded separate analyses for these locations.
P. F. AGRAN et al.
352
Table 3. Types of injuries for restrained and unrestrained 4- to 9-year olds All seats (n) Intracranial Restrained Unrestrained Eye injury or facial fracture Restrained Unrestrained Spinal strains Restrained Unrestrained Spinal fractures or cord injuries Restrained Unrestrained Intrathoracic or intraabdominal Restrained Unrestrained Extremity or bony pelvis injury (other than sprain) Restrained Unrestrained Soft Tissue (contusions, lacerations, and nonspinal strains) Restrained Unrestrained
Front passenger (n)
p*
p Back seat (n)
p
6% 9%
(23) (35)
ns**
10% 7%
(14) (11)
n.s
4% 12%
(9) (21)
3% 5%
(11) (17)
ns
3% 6%
(5) (9)
Its
3% 3%
(6) (6)
16% 8%
(61) (29)
,001
15% 9%
(22) (14)
ns
17% 7%
(35) (13)
1% 1%
(2) (3)
ns
2%
(0) (3)
M
2% 2%
(8) (6)
ns
3% 2%
(5) (3)
ns
1% 2%
(3) (3)
ns
6% 6%
(22) (22)
ns
6% 3%
(8) (5)
ns
6% 9%
(12) (15)
ns
87% (126) 89% (134)
ns
86% (327) 91% (339)
.024
.oo6
ns
.005
ns
83% (173) 92% (162)
.009
*p-value, chi-square test **not significant, alpha = .05
IO- to 14-Year-olds A total of 726 lo- to 14-year-olds were included in the study-293 restrained and 433 unrestrained. There were two fatalities among the restrained and eight among the unrestrained. Forty-three percent of the unrestrained were male compared with 41% of the restrained (difference not statistically significant). More children were seated in the front than in the back seat (Table 5). Most of the children in the front seat were known to be seated on the passenger’s side. As with the 4- to 9-year-olds, analysis of the effects of restraint use in the front seat were restricted to children in the front passenger location. The majority of restrained children in the front passenger seat used a lap/shoulder belt, while those restrained in the back seat primarily used a lap belt (Table 6). Table 7 demonstrates that the most frequent type of injury was soft tissue. Restrained children experienced significantly fewer intracranial, soft tissue, and facial injuries and more spinal strains than unrestrained children. Analysis by front passenger and rear seat locations produced the same results with the exception that eye injuries or facial fractures were not significantly more frequent among the unrestrained than the restrained in the back seat. There were no significant differences between restrained children in the front passenger and those in the back seat.
Table 4. Mean
injury
severity
score (KS) for restrained 9-year-olds
Restrained
All seat locations Front passenger Back seat *two-tailed r-test **not significant,
and unrestrained
4- to
Unrestrained
x 2 SEM (n)
x + SEM (n)
p-value*
2.01 IL .15 (382) 2.48 2 .32 (145) 1.75 2 .14 (208)
2.67 ? .34 (373) 2.93 t .73 (150) 2.57 !z .33 (174)
ns**
alpha
= .05
.:;2
Injuries in restrained and unrestrained
4- to lCyear-olds
353
Table 5. Location and restraint use of front and back seat lo- to 14year-old passengers
Seat location Driver’s Middle Passenger Unspecified Restraint use Unrestrained Restrained
Front seat (n = 396)
Back seat (n = 330)
8 16 348 24
89 53 130 58
251 157
176 136
The mean ISS for restrained was significantly lower than for the unrestrained in all seat locations, the front passenger and back seats (Table 8). The mean ISS was not significantly different for restrained lo- to 14-year-olds in the front seat compared with those in the back seat.
DISCUSSION
Previous studies have documented the effectiveness of seat belts in reducing occupant injuries. The extent to which this applies to children has not been well documented. Children have unique anatomic and physiological characteristics that may impact on the protective effects of seat belts that were not specifically designed for children. This study compares injuries between restrained and unrestrained child occupants utilizing a multihospital-based monitoring system and the coroner’s office in Orange County, California. Restrained lo- to 14-year-olds sustained a significantly lower mean ISS and significantly fewer intracranial injuries than unrestrained lo- to lCyear-olds. These results were similar to those reported by Iowa Safety Restraint Assessment 1988, Orsay et al. 1988, and Reath et al. 1989. Restrained 4- to 9-year-olds in the rear seat likewise sustained a significantly lower mean ISS and significantly fewer intracranial injuries in comparison with unrestrained 4- to 9-year-olds in the back seat. However, these same differences were not found between restrained and unrestrained 4- to 9-year-olds in the front passenger seat. Our data suggest that existing belt systems in the front passenger seat may provide inadequate protection for 4- to 9-year-olds. As 83% of the 4- to 9-year-olds restrained in the front passenger seat were known to be restrained by lap/shoulder belts, we hypothesize that the lap/shoulder belt may be inadequate for 4- to 9-year-olds. This hypothesis is plausible-the lap/shoulder belt is not required to fit the different anatomy and size of a child (Code of Federal Regulations 1989). Further, misuse of lap/shoulder belts by 4- to 9-year-olds may reduce their effectiveness. Thirteen percent (17/130) of lap/shoulder-restrained 4- to 9-year-olds in this study placed the shoulder portion of the Table 6. Restraint use by seat location for lo- to 14-year-old passengers Restraint use Unrestrained Restrained Lap/shoulder Lap Unspecified
Front passenger seat* (n = 348)
Back seat (n = 330)
202 146 126 12 8
176 136 2 116 18
*The front passenger seat is analyzed separate from the driver’s and middle seat locations because of the heterogeneous environment of the front seat by location. The small numbers of children seated in the driver’s and middle seat locations precluded separate analyses for these locations.
P. E AGRAN et al.
354
Table 7. Types of injuries for restrained and unrestrained
lo- to 14-year-olds
Front passenger (n)
p
All seats (n)
p*
3% (10) 10% (42)
.OOl
3% 9%
(5) (19)
.030
4% 10%
(5) (19)
,035
1% (4) 6% (27)
,002
1% (1) 6% (13)
.007
2% 6%
(3) (12)
rrs**
39% (113) 20% (85)
.OOl
40% 20%
(58) (41)
.OOl
37% 20%
(50) (39)
.OOl
ns
:z
$1
ns
1%
(0) (1)
ns
ns
3% 2%
(5) (4)
ns
1% 4%
(1) (7)
ns
ns
7% 7%
(9) (14)
ns
Intracranial Restrained Unrestrained Eye injury or facial fracture Restrained Unrestrained Spinal strains Restrained Unrestrained Spinal fractures or cord injuries Restrained Unrestrained Intrathoracic or intraabdominal Restrained Unrestrained Extremity or bony pelvis injury (other than sprain) Restrained Unrestrained Soft Tissue (contusions, lacerations, and nonspinal strains) Restrained Unrestrained
‘:T 0
(!:,’
2% 3%
(6) (13)
5%
(15) (36)
8%
69% (203) 85% (368)
69% (101) 87% (175)
,001
Back seat (n)
69% (94) 83% (161)
,001
p
,003
*p-value, chi-square test **ns = not significant at alpha = .05
belt behind them. Misuse is likely a function of misfit; children complain that the shoulder portion is uncomfortable because it lies across the neck or face. Further, parents may place the shoulder portion behind the child because of concern about the potential for a neck injury. A potential bias in the data is overreporting of restraint use by parents. The presence of restraint laws in California may have influenced parent reporting of seat belt utilization. Children under 4 years or 40 pounds have been required to ride in a child safety seat since 1983. A mandatory seat belt use law for all occupants was enacted in 1986. Enforcement of the latter law is secondary; a citation can be issued only if the vehicle is pulled over for another reason. As discussed in the methods section, steps were taken to minimize false reporting of seat belt use. Overreporting of restraint use by parents could result in an underestimation of the effectiveness of seat belts. Because 4- to 9year-olds in the front passenger seat were the only group for which differences between restrained and unrestrained were not seen, this is the only group for which misclassification of restraint use would be an issue. There is no reason to believe that overreporting of restraint use was specific to this subgroup of subjects. Additional limitations to the study are absence of data on uninjured occupants and crash severity. Seat belts are intended to mitigate and prevent injuries; thus, enumerating the ultimate seat belt success (no injury) is important. Unfortunately, this is not possible using a hospital monitoring system. Another limitation of the study is lack of data on crash severity. The possibility
Table 8. Mean injury severity score (ISS) for restrained and unrestrained 14-year-olds Restrained x + SEM All seat locations Front passenger Back seat *Two-tailed I-test
(n)
1.94 ? .22 (293) 2.00 r .34 (146) 1.93 * .31 (136)
lo- to
Unrestrained x
2
SEM (n)
3.46 + .39 (433) 3.72 * .65 (202) 3.39 2 .54 (194)
p-value* ,001 ,019 .020
Injuries in restrained and unrestrained
4- to 14-year-olds
355
exists that crash severity differed between compared groups. In order for this to impact our conclusions, restrained 4- to 9-year-olds in the front passenger seat would need to be in more serious collisions than their unrestrained counterparts. There is no reason to believe that more severe crashes among the restrained in comparison with the unrestrained was peculiar to 4- to 9-year-olds in the front passenger seat. Effective December 11, 1989, new passenger cars sold in the United States are required by a federal standard to have rear outboard lap/shoulder belts. This mandate was extended to vans and light trucks September 1, 1991. Acknowledging that the environment and lap/shoulder systems in the back differ from those in the front passenger seat, we feel our results highlight the need to critically evaluate the implications of these mandates and closely monitor the effects. Based on the results of this study, current lap/shoulder belt systems may not provide adequate protection for the young child. Child safety seats were designed for infants and toddlers because of their special needs with respect to occupant protection. Once children outgrow these devices, they are customarily placed in belt systems designed for adults. However, the young child continues to have special needs for occupant protection. Though booster seats have been developed for children 4- to 7-years-old, they have limited availability and most parents are uneducated about the need for their use. Further, the effectiveness of boosters in real world crashes needs to be evaluated. We feel that in addition to further investigation of the effectiveness of lap/shoulder belts and boosters for the young child, new technologies should be investigated towards addressing the special needs of young children and provision of optimal protection. REFERENCES Agran. P. E; Winn. D. G.; Dunkle. D. E. Injuries among 4- to 9-year-old restrained motor vehicle occupants by seat location and crash impact site. Am. J. Dis. Child. 143:1317-1321; 1989. American Association for Automotive Medicine: The abbreviated injury scale 1985 revision. Arlington Heights, IL: American Association for Automotive Medicine; 1985. Burdi. A. R.; Huelke. D. F.; Snyder, R. Cl.; Lowrey, G. H. Infants and children in the adult world of automobile safety design: Pediatric and anatomical considerations for design of child restraints. Biomechanics 2:267-280; 1969. Campbell, B. J. Safety belt injury reduction related to crash severity and front seated position. J. Trauma 271733-739; 1987. Code of Federal Regulations: Transportation (49): Parts 400 to 999. Office of the Federal Register, National Archives and Records Administration as a Special Edition of the Federal Register. Washington. DC: U.S. Government Printing Office: 1989. Evans. L. Fatality risk reduction from safety belt use. J. Trauma 27:746-749; 1987. Iowa Safety Restraint Assessment. A Study of Motor Vehicle Crash Injuries and Hospital Charges in Belted and Unbelted Victims. November 1987-March 1988. Des Moines, IA: Iowa Methodist Medical Center; December 198X. Orsay. E. M.; Turnbull. T. L.; Dunne, M.; Barett, J. A.: Langenberg, P.; Orsay, C. P. Prospective study of the effects of safety belts on morbidity and health care costs in motor vehicle accidents. JAMA 260:35983603; 1988. Reath. D. B.; Kirby. J. K.; Lynch. M.; Maull. K. I. Injury and cost comparison of restrained and unrestrained motor vehicle crash victims. J. Trauma 29: 1173-l 177: 1989. Snyder. R.; O’Neill. B. Are 1974-1975 automotive belt systems hazardous to children? Am. J. Dis. Child. 129:946-949: 1975.
1992
WXll-4575192 0 1992 Pergamon
S5.00+ .W Press Ltd.
COMPARISON OF MOTOR VEHICLE OCCUPANT INJURIES IN RESTRAINED AND UNRESTRAINED 4- to 14-YEAR-OLDS” Department
PHYLLIS F. AGRAN of Pediatrics, Public Policy Research Organization. Irvine, CA 92717, U.S.A.
University of California,
DAWN N. CASTILLO and DIANE G. WINN Public Policy Research Organization, University of California, Irvine, Irvine, CA 92717, U.S.A. Abstract-This study compares injuries of restrained and unrestrained 4- to 14-year-olds in nine emergency rooms and the Coroner’s office in Orange County, California from 1983 to 1989. Analyses were performed separately for 4- to 9- and lo- to 14-year-olds because of differences related to the fit of the seat belt. Significantly fewer intracranial injuries and a significantly lower mean Injury Severity Score (ISS) were seen between the restrained and unrestrained for lo- to 14-year-olds in the front passenger and back seats; but for 4- to 9-year-olds in the back seat only. These same differences were noted between restrained 4- to 9-year-olds in the back compared with those in the front passenger seat. Except for 4- to 9-year-olds in the front passenger seat, our findings are consistent with similar studies of occupants of all ages. Our results suggest that lap-shoulder belts (primary restraint in front seat) may provide less protection for 4- to 9year-olds than for lo- to 14-year-olds and adults.
INTRODUCTION
Many studies have demonstrated the effectiveness of seat belts in reducing motor vehicle occupant morbidity and mortality (Campbell 1987; Evans 1987; Iowa Safety Restraint Assessment 1988; Orsay et al. 1988; Reath et al. 1989). These evaluations, however, have grouped children with adults in the analyses. Because of marked differences in anatohic and physical features between children and adults, the effectiveness of seat belts for children separate from adults warrants evaluation (Agran et al. 1989; Snyder and O’Neill 1975) especially in consideration of current federal standards for the construction of seat belts (FVMSS 208). The minimum dimensions the lap belt are required to fit are those of a fiftieth percentile 6-year-old-child. However, the lap-shoulder belt, which is considered superior to the lap belt and will be standard equipment in rear outboard seats, has different specifications. The minimum dimensions the lap-shoulder belt is required to fit are those of a fifth percentile adult female (Code of Federal Regulations 1989). The general assumption that adult seat belts are as effective for young children as for adults should be evaluated. The present study utilizes a multihospital and coroner’s office monitoring system to compare body region and severity of injury of restrained and unrestrained 4- to lCyearold occupants. The rationale for this study design is that the effectiveness of seat belts in mitigating and preventing injury should be manifested in different body regions of injury and less severe injuries among the restrained in comparison to the unrestrained. This methodology has been utilized by others with the expected positive results of altered patterns and less severe injuries among the restrained in comparisori with the unrestrained (Iowa Safety Restraint Assessment 1988; Orsay et al. 1988; Reath et al. 1989). The primary difference between our study and the aforementioned studies was the analysis of a specific age-group; the aforementioned studies included occupants of all ages, with adults constituting the majority.
*Presented in part at the 117th Annual Meeting of the American Public Health Association, October 2226, 1989, Chicago, IL. This study was supported in part by the California State Office of Traffic Safety (Peter O’Rourke, director), the US Department of Transportation, and a grant from the Centers for Disease Control. The opinions expressed in this article are those of the authors and not necessarily those of the funding agencies. 349
3.50
P. E AGRAN et al.
In the present study, analyses are performed separately for children aged 4-9 and lo-14 years because of anatomic and structural differences between these two age-groups related to the fit of the seat belt. The anchor point for the lap portions of the belt-the anterior iliac crests-are not fully developed until approximately ten years of age. Further, the smaller rib cage and bony pelvis of the younger child are less protective of abdominal viscera (Burdi et al. 1969). Behavioral characteristics may also influence the protective effects of seat belts, e.g. the young child may be more likely than an older child to adjust his/her seating position, lean forward and move about, or engage in activities that alter the “fit” of the belt system. METHODS
A monitoring system to identify children through the age of 14 years injured as motor vehicle occupants was utilized. The surveillance system consisted of nine of 38 hospitals and the coroner’s office in Orange County, California. The system included a major health maintenance organization hospital, the children’s .hospital, and three of the County’s four trauma centers. One of the trauma centers in the surveillance system is also the major healthcare facility in the County utilized by the medically indigent. Regular audits of emergency department and coroner’s office logbooks were conducted to identify cases. Information from medical records of child occupants involved in motor vehicle crashes and non-crash events was abstracted onto a standardized interview schedule. Diagnosed injuries were recorded and assigned codes. The Abbreviated Injury Scale (AIS-85), which ranks severity of injury on a scale from 1 to 6, with 1 representing a minor injury and 6 corresponding to a virtually unsurvivable injury, was utilized. The Injury Severity Score (ISS), which sums the squares of the highest AIS for the three body regions with most severe injury, was calculated to assess overall injury severity (American Association for Automotive Medicine 1985). An interviewer contacted the parent(s) or guardian within 4 to 6 weeks after the injury event and administered a standardized telephone interview, soliciting information on the circumstances of the injury event. Sixteen hundred and forty-nine children injured as motor vehicle occupants between January 1, 1983 and March 31, 1989 were eligible for inclusion in the study. Forty-three children were excluded because restraint use was not determined; 12 because the child was restrained by a toddler seat; 100 because the child was sitting in a location for which seat belts are not standard (i.e. back of pickup trucks, cargo areas); and five because of an intentional ejection (i.e. the child stepped out before the car was completely stopped.) To minimize erroneous reporting of seat belt use by the parent, questions regarding circumstances of the crash, including what happened to the child to cause his/her injuries, were asked first. Information on restraint use was usually volunteered by the parent prior to direct inquiry. For those indicating restraint use, additional questions were asked regarding the type of restraint (lap belt or lap/shoulder) and what happened to the child and the restraint during the crash. All cases in which restraint use was indicated were reviewed by the research team, using hospital records, police reports (when available), and available newspaper reports. Eight cases in which there was doubt regarding restraint use were further excluded from the analysis. Two-sided t-tests were used for comparisons of means of continuous variables and chi-square tests for drawing inferences concerning proportions. Differences were considered statistically significant if the p-value was .05 or less. RESULTS
to 9-year-olds A total of 755 4- to 9-year-olds were included in the study-382 restrained by a seat belt, 373 unrestrained (Table 1). There was one fatality among the restrained and four
4
Injuries in restrained and unrestrained
4- to 14-year-olds
351
Table 1. Location and restraint use of front and back seat 4- to 9-yearold passengers
Seat location Driver’s Middle Passenger Unspecified Restraint use Unrestrained Restrained
Front seat (n = 371)
Back seat (n = 384)
2 46 295 28
101 43 136 104
197 174
176 208
among the unrestrained. Forty-eight percent of the restrained were male compared with 45% of the unrestrained (difference not statistically significant). Slightly more children were seated in the back than the front seat. Because of the heterogeneous environment of the front seat by location (driver’s, middle, passenger), we did not aggregate the three locations when examining effects of restraint use in the front seat. The majority of children were in the front passenger location. The small numbers of children in the driver’s and middle locations of the front seat precluded separate analyses for these locations. The primary type of restraint for the front passenger seat was lap/shoulder. Seat location was aggregated for examination of the effects of restraint use in the back seat; the lap belt was the principal type of restraint (Table 2). As shown in Table 3, the most frequent type of injury was soft tissue (contusions, lacerations, and nonspinal strains). Restrained children experienced significantly fewer soft tissue injuries and significantly more spinal strains than unrestrained children. When the analyses were stratified by seat location (Table 3)) there were no significant differences between restrained and unrestrained in the front passenger seat. In contrast, significant differences seen in the crude analysis (decreased soft tissue injuries and increased spinal strains in restrained compared to unrestrained) were found for the back seat, as well as significantly fewer intracranial injuries in the restrained compared with unrestrained in the back seat. Injuries were also compared between restrained children in the front passenger and back seats. Restrained children in the front passenger seat experienced significantly more intracranial injuries than restrained children in the back seat, p-value = .043. The reader should be cautioned that while significant differences were noted, the absolute numbers were small, 14 vs 9. There were no significant differences between restrained in the front passenger and back seat for the other injury types. The mean ISS for restrained and unrestrained children in the crude analysis (all seat locations) was not significantly different. However, restrained children in the back seat had a significantly lower mean ISS than unrestrained children in the back seat (Table 4). Further, the mean ISS of restrained children in the back seat was significantly lower than that of restrained children in the front seat, p = .034.
Table 2. Restraint use by seat location for 4- to 9-year-old passengers Restraint use Unrestrained Restrained Lap/shoulder Lap Unspecified
Front passenger seat* (n = 295)
Back seat (n = 384)
150 145 120 12 13
176 208 10 155 43
*The front passenger seat is analyzed separately from the driver’s and middle seat locations because of the heterogeneous environment of the front seat by location. The small numbers of children seated in the driver’s and middle seat locations precluded separate analyses for these locations.
P. F. AGRAN et al.
352
Table 3. Types of injuries for restrained and unrestrained 4- to 9-year olds All seats (n) Intracranial Restrained Unrestrained Eye injury or facial fracture Restrained Unrestrained Spinal strains Restrained Unrestrained Spinal fractures or cord injuries Restrained Unrestrained Intrathoracic or intraabdominal Restrained Unrestrained Extremity or bony pelvis injury (other than sprain) Restrained Unrestrained Soft Tissue (contusions, lacerations, and nonspinal strains) Restrained Unrestrained
Front passenger (n)
p*
p Back seat (n)
p
6% 9%
(23) (35)
ns**
10% 7%
(14) (11)
n.s
4% 12%
(9) (21)
3% 5%
(11) (17)
ns
3% 6%
(5) (9)
Its
3% 3%
(6) (6)
16% 8%
(61) (29)
,001
15% 9%
(22) (14)
ns
17% 7%
(35) (13)
1% 1%
(2) (3)
ns
2%
(0) (3)
M
2% 2%
(8) (6)
ns
3% 2%
(5) (3)
ns
1% 2%
(3) (3)
ns
6% 6%
(22) (22)
ns
6% 3%
(8) (5)
ns
6% 9%
(12) (15)
ns
87% (126) 89% (134)
ns
86% (327) 91% (339)
.024
.oo6
ns
.005
ns
83% (173) 92% (162)
.009
*p-value, chi-square test **not significant, alpha = .05
IO- to 14-Year-olds A total of 726 lo- to 14-year-olds were included in the study-293 restrained and 433 unrestrained. There were two fatalities among the restrained and eight among the unrestrained. Forty-three percent of the unrestrained were male compared with 41% of the restrained (difference not statistically significant). More children were seated in the front than in the back seat (Table 5). Most of the children in the front seat were known to be seated on the passenger’s side. As with the 4- to 9-year-olds, analysis of the effects of restraint use in the front seat were restricted to children in the front passenger location. The majority of restrained children in the front passenger seat used a lap/shoulder belt, while those restrained in the back seat primarily used a lap belt (Table 6). Table 7 demonstrates that the most frequent type of injury was soft tissue. Restrained children experienced significantly fewer intracranial, soft tissue, and facial injuries and more spinal strains than unrestrained children. Analysis by front passenger and rear seat locations produced the same results with the exception that eye injuries or facial fractures were not significantly more frequent among the unrestrained than the restrained in the back seat. There were no significant differences between restrained children in the front passenger and those in the back seat.
Table 4. Mean
injury
severity
score (KS) for restrained 9-year-olds
Restrained
All seat locations Front passenger Back seat *two-tailed r-test **not significant,
and unrestrained
4- to
Unrestrained
x 2 SEM (n)
x + SEM (n)
p-value*
2.01 IL .15 (382) 2.48 2 .32 (145) 1.75 2 .14 (208)
2.67 ? .34 (373) 2.93 t .73 (150) 2.57 !z .33 (174)
ns**
alpha
= .05
.:;2
Injuries in restrained and unrestrained
4- to lCyear-olds
353
Table 5. Location and restraint use of front and back seat lo- to 14year-old passengers
Seat location Driver’s Middle Passenger Unspecified Restraint use Unrestrained Restrained
Front seat (n = 396)
Back seat (n = 330)
8 16 348 24
89 53 130 58
251 157
176 136
The mean ISS for restrained was significantly lower than for the unrestrained in all seat locations, the front passenger and back seats (Table 8). The mean ISS was not significantly different for restrained lo- to 14-year-olds in the front seat compared with those in the back seat.
DISCUSSION
Previous studies have documented the effectiveness of seat belts in reducing occupant injuries. The extent to which this applies to children has not been well documented. Children have unique anatomic and physiological characteristics that may impact on the protective effects of seat belts that were not specifically designed for children. This study compares injuries between restrained and unrestrained child occupants utilizing a multihospital-based monitoring system and the coroner’s office in Orange County, California. Restrained lo- to 14-year-olds sustained a significantly lower mean ISS and significantly fewer intracranial injuries than unrestrained lo- to lCyear-olds. These results were similar to those reported by Iowa Safety Restraint Assessment 1988, Orsay et al. 1988, and Reath et al. 1989. Restrained 4- to 9-year-olds in the rear seat likewise sustained a significantly lower mean ISS and significantly fewer intracranial injuries in comparison with unrestrained 4- to 9-year-olds in the back seat. However, these same differences were not found between restrained and unrestrained 4- to 9-year-olds in the front passenger seat. Our data suggest that existing belt systems in the front passenger seat may provide inadequate protection for 4- to 9-year-olds. As 83% of the 4- to 9-year-olds restrained in the front passenger seat were known to be restrained by lap/shoulder belts, we hypothesize that the lap/shoulder belt may be inadequate for 4- to 9-year-olds. This hypothesis is plausible-the lap/shoulder belt is not required to fit the different anatomy and size of a child (Code of Federal Regulations 1989). Further, misuse of lap/shoulder belts by 4- to 9-year-olds may reduce their effectiveness. Thirteen percent (17/130) of lap/shoulder-restrained 4- to 9-year-olds in this study placed the shoulder portion of the Table 6. Restraint use by seat location for lo- to 14-year-old passengers Restraint use Unrestrained Restrained Lap/shoulder Lap Unspecified
Front passenger seat* (n = 348)
Back seat (n = 330)
202 146 126 12 8
176 136 2 116 18
*The front passenger seat is analyzed separate from the driver’s and middle seat locations because of the heterogeneous environment of the front seat by location. The small numbers of children seated in the driver’s and middle seat locations precluded separate analyses for these locations.
P. E AGRAN et al.
354
Table 7. Types of injuries for restrained and unrestrained
lo- to 14-year-olds
Front passenger (n)
p
All seats (n)
p*
3% (10) 10% (42)
.OOl
3% 9%
(5) (19)
.030
4% 10%
(5) (19)
,035
1% (4) 6% (27)
,002
1% (1) 6% (13)
.007
2% 6%
(3) (12)
rrs**
39% (113) 20% (85)
.OOl
40% 20%
(58) (41)
.OOl
37% 20%
(50) (39)
.OOl
ns
:z
$1
ns
1%
(0) (1)
ns
ns
3% 2%
(5) (4)
ns
1% 4%
(1) (7)
ns
ns
7% 7%
(9) (14)
ns
Intracranial Restrained Unrestrained Eye injury or facial fracture Restrained Unrestrained Spinal strains Restrained Unrestrained Spinal fractures or cord injuries Restrained Unrestrained Intrathoracic or intraabdominal Restrained Unrestrained Extremity or bony pelvis injury (other than sprain) Restrained Unrestrained Soft Tissue (contusions, lacerations, and nonspinal strains) Restrained Unrestrained
‘:T 0
(!:,’
2% 3%
(6) (13)
5%
(15) (36)
8%
69% (203) 85% (368)
69% (101) 87% (175)
,001
Back seat (n)
69% (94) 83% (161)
,001
p
,003
*p-value, chi-square test **ns = not significant at alpha = .05
belt behind them. Misuse is likely a function of misfit; children complain that the shoulder portion is uncomfortable because it lies across the neck or face. Further, parents may place the shoulder portion behind the child because of concern about the potential for a neck injury. A potential bias in the data is overreporting of restraint use by parents. The presence of restraint laws in California may have influenced parent reporting of seat belt utilization. Children under 4 years or 40 pounds have been required to ride in a child safety seat since 1983. A mandatory seat belt use law for all occupants was enacted in 1986. Enforcement of the latter law is secondary; a citation can be issued only if the vehicle is pulled over for another reason. As discussed in the methods section, steps were taken to minimize false reporting of seat belt use. Overreporting of restraint use by parents could result in an underestimation of the effectiveness of seat belts. Because 4- to 9year-olds in the front passenger seat were the only group for which differences between restrained and unrestrained were not seen, this is the only group for which misclassification of restraint use would be an issue. There is no reason to believe that overreporting of restraint use was specific to this subgroup of subjects. Additional limitations to the study are absence of data on uninjured occupants and crash severity. Seat belts are intended to mitigate and prevent injuries; thus, enumerating the ultimate seat belt success (no injury) is important. Unfortunately, this is not possible using a hospital monitoring system. Another limitation of the study is lack of data on crash severity. The possibility
Table 8. Mean injury severity score (ISS) for restrained and unrestrained 14-year-olds Restrained x + SEM All seat locations Front passenger Back seat *Two-tailed I-test
(n)
1.94 ? .22 (293) 2.00 r .34 (146) 1.93 * .31 (136)
lo- to
Unrestrained x
2
SEM (n)
3.46 + .39 (433) 3.72 * .65 (202) 3.39 2 .54 (194)
p-value* ,001 ,019 .020
Injuries in restrained and unrestrained
4- to 14-year-olds
355
exists that crash severity differed between compared groups. In order for this to impact our conclusions, restrained 4- to 9-year-olds in the front passenger seat would need to be in more serious collisions than their unrestrained counterparts. There is no reason to believe that more severe crashes among the restrained in comparison with the unrestrained was peculiar to 4- to 9-year-olds in the front passenger seat. Effective December 11, 1989, new passenger cars sold in the United States are required by a federal standard to have rear outboard lap/shoulder belts. This mandate was extended to vans and light trucks September 1, 1991. Acknowledging that the environment and lap/shoulder systems in the back differ from those in the front passenger seat, we feel our results highlight the need to critically evaluate the implications of these mandates and closely monitor the effects. Based on the results of this study, current lap/shoulder belt systems may not provide adequate protection for the young child. Child safety seats were designed for infants and toddlers because of their special needs with respect to occupant protection. Once children outgrow these devices, they are customarily placed in belt systems designed for adults. However, the young child continues to have special needs for occupant protection. Though booster seats have been developed for children 4- to 7-years-old, they have limited availability and most parents are uneducated about the need for their use. Further, the effectiveness of boosters in real world crashes needs to be evaluated. We feel that in addition to further investigation of the effectiveness of lap/shoulder belts and boosters for the young child, new technologies should be investigated towards addressing the special needs of young children and provision of optimal protection. REFERENCES Agran. P. E; Winn. D. G.; Dunkle. D. E. Injuries among 4- to 9-year-old restrained motor vehicle occupants by seat location and crash impact site. Am. J. Dis. Child. 143:1317-1321; 1989. American Association for Automotive Medicine: The abbreviated injury scale 1985 revision. Arlington Heights, IL: American Association for Automotive Medicine; 1985. Burdi. A. R.; Huelke. D. F.; Snyder, R. Cl.; Lowrey, G. H. Infants and children in the adult world of automobile safety design: Pediatric and anatomical considerations for design of child restraints. Biomechanics 2:267-280; 1969. Campbell, B. J. Safety belt injury reduction related to crash severity and front seated position. J. Trauma 271733-739; 1987. Code of Federal Regulations: Transportation (49): Parts 400 to 999. Office of the Federal Register, National Archives and Records Administration as a Special Edition of the Federal Register. Washington. DC: U.S. Government Printing Office: 1989. Evans. L. Fatality risk reduction from safety belt use. J. Trauma 27:746-749; 1987. Iowa Safety Restraint Assessment. A Study of Motor Vehicle Crash Injuries and Hospital Charges in Belted and Unbelted Victims. November 1987-March 1988. Des Moines, IA: Iowa Methodist Medical Center; December 198X. Orsay. E. M.; Turnbull. T. L.; Dunne, M.; Barett, J. A.: Langenberg, P.; Orsay, C. P. Prospective study of the effects of safety belts on morbidity and health care costs in motor vehicle accidents. JAMA 260:35983603; 1988. Reath. D. B.; Kirby. J. K.; Lynch. M.; Maull. K. I. Injury and cost comparison of restrained and unrestrained motor vehicle crash victims. J. Trauma 29: 1173-l 177: 1989. Snyder. R.; O’Neill. B. Are 1974-1975 automotive belt systems hazardous to children? Am. J. Dis. Child. 129:946-949: 1975.