Percentage of patients with facial fractures following a motor vehicle crash with regard to use of restraining devices.
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Simoni P, Ostendorf R, Cox AJ. Effect of Air Bags and Restraining Devices on the Pattern of Facial Fractures in Motor Vehicle Crashes. Arch Facial Plast Surg. 2003;5(1):113–115. doi:
Copyright 2003 American Medical Association. All Rights Reserved.
Applicable FARS/DFARS Restrictions Apply to Government Use.2003
Objective To examine the relationship between the use of restraining devices and the incidence of specific facial fractures in motor vehicle crashes.
Design Retrospective analysis of patients with facial fractures following a motor vehicle crash.
Setting University of Alabama at Birmingham Hospital level I trauma center from 1996 to 2000.
Patients Of 3731 patients involved in motor vehicle crashes, a total of 497 patients were found to have facial fractures as determined by International Classification of Diseases, Ninth Revision (ICD-9) codes. Facial fractures were categorized as mandibular, orbital, zygomaticomaxillary complex (ZMC), and nasal.
Results Use of seat belts alone was more effective in decreasing the chance of facial fractures in this population (from 17% to 8%) compared with the use of air bags alone (17% to 11%). The use of seat belts and air bags together decreased the incidence of facial fractures from 17% to 5%.
Conclusions Use of restraining devices in vehicles significantly reduces the chance of incurring facial fractures in a severe motor vehicle crash. However, use of air bags and seat belts does not change the pattern of facial fractures greatly except for ZMC fractures. Air bags are least effective in preventing ZMC fractures. Improving the mechanics of restraining devices might be needed to minimize facial fractures.
THE US Air Force first engineered air bags in 1952. Federal mandates required air bag placement in cars as standard equipment in 1987, and dual air bags were required in 1998.1-2
Rapid deceleration of the vehicle is detected by sensors that trigger a primer in the air bag canister to ignite 70 g of sodium azide. This liberates nitrogen, carbon dioxide, and a fine alkaline aerosol, which inflate the air bag in 10 milliseconds with a velocity of 110 to 210 mph (176-336 km/h). The air bag deflates immediately through venting holes or porous fabric under the occupant's weight, absorbing the impact.2-4
Murphy et al5 have shown that drivers whose air bags have been deployed sustain significantly fewer facial fractures. They were not able to show that the use of seat belts provides any additional protection from facial fractures when air bags are deployed. Murphy et al included in their study patients involved in motor vehicle crashes who were admitted to the intensive care unit and hospitalized for more than 72 hours, without focusing on the severity or pattern of the fractures. The effect of air bags on the severity of facial fractures was addressed by Major et al,6 who used the Abbreviated Injury Scale to assess the severity of injuries with respect to air bag and seat belt use. They showed that the use of air bags is associated with less severe facial fractures compared with the use of seat belts alone or no restraint. Their study did not compare the effect of using seat belts in conjunction with air bag deployment with the use of each alone.
Air bags protect motor vehicle passengers by providing a cushioning barrier between the passenger and hard surfaces inside the vehicle. Using the air bags in conjunction with 3-point seat belts has been shown to reduce fatalities by 45%, compared with 18% with air bags alone.7 An unrestrained driver accelerating toward the air bag produces a flexion of the upper spine accepting blunt impact to the chest area. However, in the case of a restrained driver, an air bag inflates upward, hyperextending the cervical spine. In this case the chin, neck, and face area receive the maximum impact of the air bag.8 A study by Sutyak et al9 showed how unbelted crash victims who were protected only by air bags sustained more severe thoracoabdominal injuries.
The difficulty in conducting a double-blind prospective study is one of the major problems in assessing the effect of air bags and seat belts in motor vehicle crashes. The major literature on the use of restraining devices studied patients presenting with fractures to medical facilities following motor vehicle crashes. Also, there are no tools to measure the severity of each crash individually. As a result, some studies have concluded that the use of air bags increases some injuries without considering the severity of the collision as a confounding factor.10 One may argue that patients using restraining devices such as air bags and sustaining fractures may have been involved in a more severe crash than others without such devices.
This study focuses on the role of restraining devices on the pattern of facial fractures. The main objective of this study was to answer 3 questions: Does the use of air bags and seat belts affect the pattern of the facial fractures secondary to motor vehicle crashes? Does the use of restraining devices alter the pattern of bilateral fractures? Does the use of air bags and seat belts affect the need for repair once the facial fracture has occurred?
A retrospective analysis was performed on patients involved in motor vehicle crashes treated by the trauma surgery team at University of Alabama at Birmingham level I trauma center between 1996 and 2000. For a patient involved in motor vehicle crashes to be treated by the trauma surgery team, certain criteria must be met (Table 1). The International Classification of Diseases, Ninth Revision (ICD-9) codes were used to select and group patients with facial fractures. Computed tomographic scan reports were used to categorize patients' fractures and identify patients with bilateral fractures. Fractures were categorized as nasal, mandibular, zygomaticomaxillary complex (ZMC), and orbital. Operating reports and clinical visit reports were used to identify which of these fractures were repaired. Patients were grouped into 4 groups based on the use of restraining devices: unrestrained, only air bag, only seat belt, both seat belt and air bag.
Nominal variables were assessed using the χ2 test of association. P<.05 was considered statistically significant.
The institutional review board for human use reviewed and approved this project.
A total of 3731 patients were treated by trauma surgery following motor vehicle crashes at the University of Alabama at Birmingham Hospital from 1996 to 2000. A total of 497 patients sustained facial fractures that could be grouped into nasal, mandibular, ZMC, or orbital fractures. A total of 2295 cases did not use any restraining devices; of these, 380 (17%) sustained facial fractures. Seat belts were used by 1147 patients; of these, 97 (8%) sustained facial fractures. A total of 84 patients had an air bag deployed; of these, 9 (11%) sustained facial fractures. Air bag deployment in conjunction with seat belt was used by 205 patients; of these, 11 patients (5%) sustained facial fractures. The χ2 test of association showed a global significant difference among the 4 groups (χ2 = 56, P<.001) (Figure 1).
The 4 groups were compared based on the 4 variables of nasal, mandibular, ZMC, and orbital fractures (Table 2). There was a statistically significant difference among the 4 groups in relation to ZMC fractures (χ2 = 16.3, P<.001). There were no statistically significant differences among the 4 groups in relation to nasal, mandibular, and orbital fractures.
The 4 groups were compared with regard to bilaterality and fracture repair. Nasal fractures were omitted from the bilateral comparison secondary to ambiguity in segregating bilateral from unilateral fractures. There was no statistically significant difference among these groups with regard to bilaterality and fracture repair.
To more effectively study the protective effect of restraining devices in motor vehicle crashes, a prospective double-blind study is necessary. However, a prospective double-blind study is impractical. Using the available data, there is no way to control for severity of the crash. One could always argue that restrained patients presenting with facial fractures to medical facilities could have been involved in a more severe crash than nonrestrained ones. Comparing these 2 groups to estimate the efficacy of vehicle restraints is not statistically sound without taking the severity of the crash into account.
The patients in this study were involved in motor vehicle crashes with a level of severity necessitating trauma surgery consultation, which means certain criteria were met (Table 1). Using this population somewhat narrows the range of severity of the crashes. Of patients involved in motor vehicle crashes in which trauma surgery was consulted, 13% experienced facial fractures. Use of seat belts alone was found more effective in decreasing the chance of facial fractures in this population from 17% (no restraints) to 8% than air bags alone (17% to 11%). The use of seat belts and air bags together, however, was found to be most effective in reducing facial fractures in our studied population (17% to 5%) (Figure 1).
In our study, nasal fractures were the most common facial fractures at 50%, with ZMC fractures second at 46%. Mandibular fractures were the least common (27%). Use of restraining devices was found to affect the pattern of only ZMC fractures. In patients presenting with facial fracture(s), use of seat belts alone decreased the chance of ZMC fractures from 49% (no restraints) to 37%. Interestingly, 45% of patients presenting with facial fractures with air bag deployment had ZMC fractures. Use of seat belts in conjunction with air bags did not seem to change this pattern. At first glance, one might speculate that use of air bags increases the chance of ZMC fractures compared with the use of seat belts alone. Considering severity of the crash as a confounding factor, this conclusion is not statistically sound. One could always argue that patients involved in motor vehicle crashes with air bag–equipped vehicles were involved in more severe crashes. At best, we could conclude that even though use of air bags decreases the incidence of facial fractures, they are least protective of ZMC fractures.
The purpose of this study was not to quantify the effect of air bags in prevention or even causing the specific facial fractures but rather to evaluate patterns of protection air bags and seat belts offer for facial fractures. Based on the initial part of the study, air bags, especially if they are used in conjunction with seat belts, greatly reduce the incidence of facial fractures. However, if a crash is severe enough to cause facial fractures, air bags do not change the pattern of facial fractures greatly. They seem to be least protective for the ZMC fractures. One could explain this finding by considering the force direction of a deployed air bag on the facial skeleton. Air bags inflate at very high velocity (up to 210 mph [336 km/h]) toward the weakest parts of the facial skeleton, ie, nose and ZMC. Air bag designers have decreased the velocity of inflating air bags during the past few years. If further studies can confirm this pattern, the air bag design might be altered to divert forces from the weaker part of the face to more stable parts of the body or to decease the velocity vector of air bag deployment toward the face.
When a crash is severe enough to cause facial fractures, the use of restraining devices does not increase or decrease the chance of bilateral fractures. Also, once the fracture occurs, the chance of fracture(s) needing surgical repair would not be altered by the use of restraining devices.
Use of seat belts and air bags, especially together, offers a statistically significant reduction in facial fractures in severe motor vehicle crashes. Nasal and ZMC fractures are the most common facial fractures following motor vehicle crashes; however, the pattern of facial fractures is not greatly altered by the use of restraining devices. If a crash is severe enough to cause a facial fracture, air bags are least protective of the ZMC. Perhaps a change in the mechanics of air bags might be needed to provide more protection for weaker areas of the face.
Corresponding author and reprints: Payman Simoni, MD, Division of Otolaryngology–Head and Neck Surgery, 1501 Fifth Ave S, Birmingham, AL 35233.
Accepted for publication July 31, 2001.
This study was presented at the spring meeting of the American Academy of Facial Plastic and Reconstructive Surgery, Palm Desert, Calif, May 13, 2001.
We thank Charles Katholi, PhD (Department of Public Health, University of Alabama at Birmingham), for statistical consultation.