ORIGINAL CONTRIBUTION motor vehicle crashes; safety belts

Prospective Study of the Effect of Safety Belts in Motor Vehicle Crashes Trauma resulting from motor vehicle crashes (MVCs) is the leading cause of death in persons I to 38 years old. The following prospective study was undertaken to assess the effect of safety belts on the types of injuries sustained in MVCs. A total of 1,364 patients from four Chicago-area hospitals were evaluated prospectively during a six-month period. Safety belts reduced the incidence of head, facial, thoracic, abdominal, and extremity injuries sustained in MVCs. Spinal injuries comprised the only group in which safety belt wearers sustained injuries more frequently than safety belt nonwearers. Further research on the different safety belt designs and effects of air bags is needed to reduce the incidence of cervical and lumbar strain in restrained patients. [Orsay EM, Dunne M, Turnbull TL, Barrett JA, Langenberg P, Orsay CP: Prospective study of the effect of safety belts in motor vehicle crashes. Ann Emerg Med March 1990;19:258-261.] INTRODUCTION Injuries sustained in motor vehicle crashes (MVCs) are a major challenge to our health care system and an enormous societal burden. In 1982, an estimated 3.2 million persons were involved in MVCs, of whom approximately 1.4 million were treated in emergency departments and 350,000 required hospitalization. 1 Statistically, an individual in the United States can expect to be involved in an MVC every ten years and has a 33% chance of sustaining a disabling injury during a lifetime of driving. 2 This prospective study was undertaken to assess the effect of safety belt use on the types of injuries sustained in MVCs. MATERIALS A N D M E T H O D S Data were collected from MVC victims who presented to one of four Chicago-area hospital EDs from January 1 through June 30, 1986. Throughout the study period, a mandatory safety belt use law for front-seat passengers was in effect in Illinois. The four hospitals receive patients from a wide geographic area within Cook C o u n t y and from a broad socioeconomic spectrum. Two of the hospitals (Mercy Hospital and Medical Center and Illinois Masonic Medical Center) are urban community hospitals; one (Cook County Hospital) is a public inner-city hospital; and one (Lutheran General Hospital) is a suburban community hospital. All patients who presented within 24 hours after an MVC were eligible for inclusion. Pedestrians, bicyclists, motorcyclists, bus passengers, and riders in trucks with more than two axles were excluded. The patient logs of each ED or trauma unit were reviewed each weekday to identify any missed cases; these medical records were resubmitted to the examining physician for data retrieval and inclusion in the study. Initial data were collected prospectively for all study subjects by the examining physician. The structured questionnaire that was used included determination of safety belt use, position of subject in the vehicle, mechanism of injury (front-end, rear-end, or broadside collision), posted speed limit at MVC site, and mode of transport to hospital. Whenever possible, independent confirmation of data was sought from paramedics, police, or others. Access to police reports was not available in Cook County at this time. The medical records (ED and inpatient, if hospitalized) of all subjects

19:3 March 1990

Annals of Emergency Medicine

Elizabeth Mueller Orsay, MD, FACEP* Park Ridge, Illinois Mary Dunne, MDt Timothy L Turnbull, MD, FACEP* John A Barrett, MD, FACS§ Patricia Langenberg, PhDII Charles P Orsay, MD, FACS# Chicago, Illinois From the Division of Emergency Medicine, Lutheran General Hospital, Park Ridge, Illinois;* Department of Emergency Medicine, Illinois Masonic Medical Center;i- Department of Emergency Medicine, Mercy Hospital and Medical Center;* Trauma Unit, Cook County Hospital;§ and School of Public HealthII and Department of Surgery,# University of Illinois, Chicago. Received for publication April 10, 1989. Revision received September 18, 1989. Accepted for publication October 20, 1989. Presented at the University Association for Emergency Medicine Annual Meeting in Cincinnati, Ohio, May 1988. This study was supported in part by the Illinois Safety Belt Coalition. Address for reprints: Elizabeth Mueller Orsay, MD, FACER Lutheran General Hospital, 1775 Dempster Street, Park Ridge, Illinois 60068.

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were s u b s e q u e n t l y reviewed by a member of the research team for collection of demographic data and delineation of injuries sustained. All injuries were coded by diagnosis using the Abbreviated Injury Scale manual 3 and recorded. The simple, descriptive statistics that were recorded included means and proportionsi Pearson X~ tests were used to compare proportions. All analyses were performed using the SAS statistical software package in the University of Illinois at Chicago IBM mainframe computer. RESULTS

A total of 1,364 patients were entered into the study. The mean patient age was 33.03 ___ 0.42 years (+ SEM); 52.5% were men. Of the study p o p u l a t i o n , 63.6% were drivers, 24.6% were front-seat passengers, 11.3% were back-seat passengers, and 0.5% were in an unrecorded position. No significant variation was noted in the number of cases per month. There was a significant difference noted in time of registration: 42.1% registered between 3:00 PM and 11:00 PM, 37.1% between 7:00 AM and 3:00 PM, and 20.8% between 11:00 PM and 7:00 AM (P < .001). Fifty-eight percent of the subjects (791) reported wearing safety belts at the time of the MVC, and 42% (573) reported that they had not. Of those wearing safety belts, 76.2% (603) wore a three-point restraint, 15.3% wore a lap belt only, and 8.5% (67) wore an unreported type of safety belt. As a group, safety belt wearers were slightly older (35 vs 31.9 y~rs), more often female (50.3% of wearers vs 44.2% of nonwearers), and more often involved in rear-end collision (40.8% of wearers vs 26.2% of nonwearers). Fewer safety belt wearers than nonwearers had used alcohol (5.6% vs 19.5%), and fewer were transported by ambulance (36.4% vs 57.6%). No significant differences were noted between the groups with respect to the reported speed limit where the MVC occurred. Sixty-seven percent of safety belt nonwearers sustained head and facial injuries compared with 30% of safety belt wearers (P < .001). Overall, 61 patients suffered head injury with loss of consciousness; 75% of these were patients who had been unrestrained. Of the two patients with 68/259

TABLE 1. Spinal injuries resulting from MVCs Strain

Fracture

With SB* (N = 547)

Without SB (N = 316)

With SB (N = 12)

Without SB (N = 5)

Cervical Thoracic

414 24

239 18

2 1

3 1

Lumbar

109

59

9

1

*SB, safety belts.

skull fractures, four with subdural hematomas, and five with epidural hematomas, none had worn a safety belt. Of the 59 facial and dental fractures, 85% occurred in unrestrained patients. Four hundred seventy-six patients suffered facial skin or scalp injuries (contusion, abrasions, lacerations); 65% of these were patients who had been unrestrained. Spinal injuries occurred in 49% of unrestrained patients compared with 61.6% of restrained patients (P < .001). The majority of these injuries were cervical and lumbar strain. The specific injuries w i t h respect to safety belt use are outlined (Table 1). No patient suffered a cord transection in this series. One restrained patient was diagnosed with "neuropraxia" of the upper extremity. One unrestrained patient sustained "bracial plexus syndrome" and another a sacral alar fracture with nerve root injury. None of the spinal fractures or dislocations were associated with n e u r o l o g i e deficit in this series. Safety belt wearers sustained eight compression or vertebral body fractures/one cervical, one thoracic, and six lumbar), one cervical spinous process fracture, two lumbar transverse process fractures, and one lumbar laminar fracture. Safety belt nonwearers had only three compression or vertebral body fractures (one cervical, two thoracic, and one lumbar). However, they suffered more severe cervical-spine injuries: one cervical dislocation, a cervical-spine pedical fracture, and a fractured odentoid. T h o r a c i c i n j u r i e s o c c u r r e d in 20.6% of unrestrained patients and 11.8% of restrained patients (P < .001). The one aortic tear in the study was sustained by an unrestrained patient. Nine patients, six of whom had been unrestrained, were discharged with a diagnosis of cardiac c o n t u Annals of Emergency Medicine

sion. Of the five patients with pulm o n a r y contusions, four had been unrestrained. Two hundred two patients, 55% of whom had been unrestrained, sustained rib fractures. The two patients with sternal fractures had worn safety belts. A b d o m i n a l injury was seen in 3.I% of unrestrained patients and 0.6% of restrained patients (P < .001). The three splenic injuries and one h e p a t i c injury o c c u r r e d in unrestrained patients. Of the seven patients with renal injuries, five had been unrestrained. Upper extremity injury was sus rained by 23.6% of unrestrained patients and 14.5% of restrained patients (P < .001). Of the 46 patients with upper extremity fractures, 63% had been unrestrained. Lower extremity injury occurred in 32.3% of unrestrained patients and 18.7% of restrained patients (P < .001). Of 199 patients with lower extremity fractures, 53% had been unrestrained. Three restrained patients sustained safety belt-related injuries: two with sternal fractures and one with a clavicular fracture. No significant difference was noted in the incidence of chest wall c o n t u s i o n (91 in unrestrained vs 79 in restrained patients) or rib fractures (111 in unrestrained vs 91 in restrained patients) between the two groups. The greatest benefit from safety belt use was seen in front-end collisions, p a r t i c u l a r l y in p r o t e c t i o n against head, facial, and extremity injuries (Table 2). In broadside and rearend collisions, safety belt wearers were better protected from head and facial injuries than were safety belt nonwearers. Spinal injury was more frequent in safety belt wearers regardless of the mechanism of injury but was seen m o s t frequently in safety belt wearers after rear-end 19:3 March 1990

TABLE 2. Patients with injuries resulting from MVCs according to mechanism of impact Mechanism of Impact Front-End Collision With SB*

Type of Injury

Head and face (N = 871) Spine (N = 768) Thorax (N = 296) Abdomen (N = 23) Upper extremity (N = 259) Lower extremity (N = 349) *SB, safety belt.

Broadside Collision

Rear-End Collision

Without SB

With SB

Without SB

With SB

(°/o)

(%)

(°/4

(%)

104 (11.9) 83 (10.8) 57 (19.3) 1 (4.3) 24 (9.3) 50 (14.3)

278 (31.9) 77 (10) 73 (24.7) 6 (26.1) 50 (19.3) 90 (25.8)

112 (12.9) 138 (18) 56 (18.9) 2 (8.7) 56 (21.6) 64 (18.3)

144 (16.5) 83 (10.8) 40 (13.5) 7 (30.4) 51 (19.7) 58 (16.6)

Unknown

Without SB

With SB

Without SB

(%)

(°/4

(°/4

(%)

59 (6.8) 254 (33.1) 23 (7.8) 2 (8.7) 33 (12.7) 30 (8.6)

107 (12.3) 105 (13.7) 28 (9.5) 2 (8.7) 27 (10.4) 33 (9.5)

15 (1.7) 12 (1.6) 5 (1.7) 0 (0) 5 (1.9) 7 (2)

52 (6) 16 (2.1) 14 (4.7) 3 (13) 13 (5) 17 (4.9)

TABLE 3. Patients with injuries resulting from MVCs according to position in vehicle Position in Motor Vehicle Driver Type of Injury

Head and face (N = 871) Spine (N = 768) Thorax (N = 296) Abdomen (N = 23) Upper extremity (N = 2 5 9 ) Lower extremity (N = 349) *SB, safety belt.

Back-Seat Passenger

Unknown

With SB*

Without SB

With SB

Without SB

With SB

Without SB

With SB

Without SB

(%) 185 (21.2) 363 (47.3) 104 (35.1) 4 (17.4) 86 (33.2) 106 (30.4)

(%) 301 (34.6) 157 (20.4) 98 (33.1) 9 (39.1) 71 (27.4) 101 (28.9)

(%) 80 (9.2) 96 (12.5) 31 (10.5) 0 (0) 25 (9.7) 38 (10.9)

(%) 183 (21.0) 77 (10.0) 38 (12.8) 5 (21.7) 39 (15.1) 57 (16.3)

(%) 22 (2.5) 21 (2.7) 3 (1.0) 1 (4.3) 7 (2.7) 7 (2.0)

(%) 88 (10.1) 45 (5.9) 16 (5.4) 2 (8.7) 30 (tl.6) 40 (11.5)

(%) 3 (0.3) 7 (0.9) 3 (1.0) 0 (0) 0 (0) 0 (0)

(%) 9 (1.0) 2 (0.3) 3 (1.0) 2 (8.7) 1 (0.4) 0 (0)

collisions. Regardless of their position in the m o t o r vehicle, restrained p a t i e n t s sustained fewer head and facial injuries than unrestrained patients (Table 3). Restrained front- and back-seat passengers suffered fewer upper and lower extremity injuries than their unrestrained counterparts. Spinal injury occurred more frequently in re-

19:3 March 1990

Front-Seat Passenger

strained drivers and front-seat passengers.

DISCUSSION This study demonstrates a significant benefit of safety belt use in protection from specific injuries sustained in MVCs and is, to our knowledge, the first study using data from the United States that evaluate speAnnals of Emergency Medicine

cific patterns of injuries associated with safety belt use compared with n o n u s e in MVCs. Overall, unres t r a i n e d p a t i e n t s had m o r e t h a n twice the number of head and face injuries, almost twice the number of thoracic injuries, five times the number of abdominal injuries, and one and one half to two times the number of extremity injuries. If anything,

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our methodology may m i n i m i z e the benefits of restraints as it examined only patients who presented for examination to a hospital ED. There!ore, r e s t r a i n e d p a t i e n t s m a y have l~ad fewer i n j u r i e s , and f e w e r restrained patients may have come to an ED than patients who were not restrained. • Spinal injury was the only category in Which s a f e t y b e l t w e a r e r s h a d more f r e q u e n t i n j u r i e s t h a n n o n Wearers; this is in agreement w i t h previously published reports.4-6 However, Burke reported a decrease in the number of spinal cord injuries and Severity of neurologic injury after the Introduction of mandatory safety belt Use in Australia.7 In our study, the Vast m a j o r i t y of spinal i n j u r y was Cervical or l u m b a r strain. There are s u r p r i s i n g l y l i t t l e d a t a from the U n i t e d States on injuries SUstained in MVCs. T h i s s t u d y is Unique in its use of p a t i e n t h i s t o r y and medical records as data sources covapared w i t h the use of police or government reports. D a t a regarding safety belt use were based on patient Port, p a r a m e d i c o b s e r v a t i o n , or th. Actual use m a y have been ap-

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preciably different from that reported because it was not always possible to obtain objective evidence of restraint use. While paramedics were asked to verify whether patients had been restrained, frequently subjects were already out of the v e h i c l e w h e n the ambulance arrived. For only 23 of the 618 MVC v i c t i m s transported by ambulance was there a d i s c r e p a n c y in the reports of the patients and paramedics. The greatest difference between safety belt wearers and n o n w e a r e r s was noted in the frequency of head and facial injuries. This study evaluated acute injuries only. T h e effect of safety belt use in reducing long-term disability is an i m p o r t a n t issue and warrants further research. Furthermore, the effect of passive restraint systems, such as air bags and antomatic belts, on injuries sustained in MVCs m e r i t s investigation. CONCLUSION This prospective s t u d y e v a l u a t e d the effect of safety belts on the types of injuries sustained in MVCs. Safety b e l t w e a r e r s suffered s i g n i f i c a n t l y fewer head and facial, thoracic, ab-

Annals of Emergency Medicine

dominal, and e x t r e m i t y injuries than safety belt nonwearers. A n increased i n c i d e n c e of spinal i n j u r i e s was obs e r v e d in r e s t r a i n e d m o t o r v e h i c l e occupants. Further research m safety belt design as w e l l as on the effect of passive restraint s y s t e m s is needed to reduce the incidence of cervical and l u m b a r strain in safety belt wearers.

REFERENCES

1. Committee on Trauma Research: Injury in America. Washington, DC, National Research

Council and the Institute of Medicine, 1985. 2. Sleet DA: Motor vehicle trauma and safety belt use in the context of public health pliorities. J Trauma 1987;27:695-702. 3. Committee on Mury Scaling: The AbbrevL ated Injury Scaling, 1985 Revision. Arlington Heights, Illinois, American Association for Automotive Medicine, 1985. 4. Allen MJ, Barnes MR, Bodiwala GG: The elfeet of seat belt legislation on injuries sustained by car occupants. In/ury 1985;16:471-476. 5. Freedman LS: Initial assessment of the effect of the compulsory use of seat belts on car occupants injuries, and the trauma department work load. Infury 1984~16:6& 6. Deans GT, McGaBiard JN, Rutherford WH: Incidence and duration of neck pain among patients injured in car accidents. Br Med ] 1986; ~92:94-95. 7. Burke DC: Spinai cord injuries and seat belts. Med [ Aust 1973;2:801-806.

19:3 March 1990

Prospective study of the effect of safety belts in motor vehicle crashes.

Trauma resulting from motor vehicle crashes (MVCs) is the leading cause of death in persons 1 to 38 years old. The following prospective study was und...
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