An unusual supplemental vehicle restraint-induced injury: Report of case and review of literature

J Oral Maxillofac Surg 60:1062-1066, 2002

An Unusual Supplemental Vehicle Restraint-Induced Injury: Report of Case and Review of Literature Barry C. Boyd, DMD, MD,* David J. Dattilo, DDS,† Joseph H. Goth, DMD, MD,‡ and Frank J. Liberto, PA-C§ Since their introduction and widespread installation in domestic and foreign vehicles, inflatable supplemental restraint systems, more commonly termed airbags, have played a significant role in the reduction of severe and fatal traffic accident–related injuries. When used properly, as a supplement to the 3-point lap-shoulder belt restraint, airbags afford significant reduction in head, facial, and thoracic injuries. However, since their introduction to automobile fleets, numerous airbag-related injuries have been encountered and reported in the literature. An interesting trend has emerged in the patterns of injury seen before the use of airbags compared with those seen after the mass production and installation of these inflatable devices. Just as seatbelts have been associated with specific restraint-induced injuries, airbags also are associated with certain specific restraint-induced injuries with both proper and improper use. A variety of serious nonfatal and fatal injuries have been reported in out-of-position drivers positioned within close proximity to the airbag module who are often of

*Formerly, Resident in General Surgery, Mercy Hospital of Pittsburgh, Pittsburgh, PA; Currently, Assistant Professor, Department of Oral and Maxillofacial Surgery, State University of New York at Buffalo School of Dental Medicine, Attending Physician, Erie County Medical Center and Kaleida Health Hospitals, Buffalo, NY. †Chief, Division of Oral and Maxillofacial Surgery, Department of Surgery, Mercy Hospital of Pittsburgh and Private Practice, Pittsburgh, PA. ‡Attending Surgeon, Division of Oral and Maxillofacial Surgery, Department of Surgery, Mercy Hospital of Pittsburgh and Private Practice, Pittsburgh, PA. §Physician’s Assistant, Division of Oral and Maxillofacial Surgery, Department of Surgery, Mercy Hospital of Pittsburgh, Pittsburgh, PA. Address correspondence and reprint requests to Dr Boyd: Department of Oral and Maxillofacial Surgery, State University of New York at Buffalo, School of Dental Medicine, Squire Hall Room 112, 3435 Main St, Buffalo, NY 14214-3008; e-mail: [email protected] © 2002 American Association of Oral and Maxillofacial Surgeons

0278-2391/02/6009-0016$35.00/0 doi:10.1053/joms.2002.34421

small stature, requiring seat adjustments to far forward positions. In addition, several severe and often fatal injuries have been reported in infants and small children occupying front passenger seats in vehicles equipped with passenger airbags. The National Highway Transportation Safety Administration has mandated that automobile and child safety seat manufacturers must post visible warnings against placing infants in rear-facing car seats and small children, even when properly restrained with the lap-shoulder belts, in front passenger seats of airbag-equipped vehicles. We report the case of a driver of small stature who sustained an unusual blunt force injury after airbag deployment in a low-speed motor vehicle accident.

Report of a Case A 35-year-old unrestrained female driver was involved in a low to moderate–speed single-car motor vehicle accident in which she struck a utility pole. The late model vehicle she was operating was equipped with a driver-side airbag and was traveling between 35 and 40 miles per hour on dry pavement. The patient admitted to the consumption of alcohol earlier in the evening and had a blood alcohol level of 185 mg/dL. The paramedics first on the scene stated that the patient was conscious, complaining of right-side facial and neck pain. They also reported that there was severe frontal damage to the mid-size automobile and that the driver-side airbag had deployed. The patient was transported to a level 1 trauma facility, where she was evaluated and resuscitated by the trauma surgery service per advanced trauma life support protocol. On arrival the patient was awake, alert, and oriented to person, place, date, and time and was assigned a Glasgow Coma Scale score of 15. She complained of pain with swallowing and difficulty opening her jaw. Most notably on physical examination was extensive soft tissue edema and ecchymosis involving the right submandibular and anterior cervical region. Her trachea was midline and her breath sounds were clear. The oropharynx was patent as well. There was no associated edema or elevation of the tongue or floor of the mouth. There was a small superficial submental abrasion, and multiple small superficial facial lacerations were evident. There were no clinically detectable facial bone fractures. An axial computed tomography scan with intravenous contrast of the head and neck was obtained. The views of

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the neck were significant for extensive soft tissue swelling and hemorrhage both superficial to and within the right submandibular gland extending caudally to the level of the thyroid gland just above the thoracic inlet. Cervically, hemorrhage was also noted in the region superficial to the carotid sheath and within the longus coli and sternocleidomastoid muscles. A small amount of blood was noted within the right masseter and lateral pterygoid muscles. The hematoma appeared to cause effacement of the right pyriform sinus but did not affect the diameter of the airway. No facial fractures were visualized. Perhaps the most striking feature of this computed tomography examination of the neck was the presence of a ruptured, fragmented right submandibular gland (Fig 1). The patient was admitted for airway monitoring and was placed initially on ampicillin/sulbactam intravenously. She was discharged the next day on oral antibiotics with follow-up arranged with the oral and maxillofacial surgery service as an outpatient. The patient was followed after discharge for several months with resolution of the hematoma. At follow-up, she was free of submandibular swelling or submandibular salivary gland dysfunction. She had no signs of potential complications of submandibular gland rupture, including sialadenitis, sialocele development, or submandibular gland fibrosis.

Discussion Inflatable restraint systems were first developed by military engineers, with the first patent being issued in the early 1950s.1,2 Driver-side airbags were first offered as optional equipment in several large domestic automobiles in the early 1970s but were not well received. The first federal government legislation regarding airbag installation took place in 1984, when then Secretary of the Department of Transportation mandated phase-in of automatic seat belts or airbags beginning with the 1987 car models, with the goal of reaching 100% of all automobiles in 1994.3 Given the protection afforded front seat occupants in frontal and offset near frontal collisions, driver-side inflatable restraints became mandatory equipment for all domestic passenger cars beginning with the 1997 model year. The following year airbags were made mandatory for light trucks as well. Upward of 57 million cars and 32 million light trucks were equipped with airbags as of October 1999. When properly used in conjunction with the 3-point lap-shoulder belt restraint, it has been estimated that driver-side airbags have been associated with a 24% to 31% reduction of fatalities in frontal collisions and a 16% to 19% reduction in all types of collisions.4,5 Similar reductions have been appreciated in the incidence and severity of accident-related injuries with proper use of the lap-shoulder belt in conjunction with the supplemental restraint system. Passenger-side airbags are responsible for a 14% to 32% reduction in fatalities in frontal crashes.5,6 A variety of European automobile manufacturers have recently made various configurations of side airbag systems available. Many also in-

FIGURE 1. Noncontrast CT scan showing fragmentation of right submandibular gland with associated edema and hematoma (arrows).

clude additional devices designed to protect the heads of vehicle occupants. At the present time, no automobile manufacturers offer inflatable restraints for rear seat occupants. The inflatable supplemental restraint system is the most recent of numerous safety enhancements made by domestic and foreign automobile manufacturers. They are designed to enhance the protection afforded by the 3-point lap-shoulder belt restraint, which alone accounts for a reduction in fatalities of 41% to 45% and a reduction in the incidence of moderate to critical injuries by 50%.5,7,8 In frontal collisions, the airbag is designed to reduce contact of front seat occupants with hard surfaces of the automobile’s interior in synergy with the protection given by the 3-point restraint. Airbags are not designed to prevent ejection, nor are they designed to take the place of the lapshoulder belt.7,8 Crash sensors located within the front bumper and passenger compartment are activated by deceleration of 10 to 12 mph. This activation incites a signal, which results in ignition of a propellant consisting of sodium azide (NaN3) within a cartridge in the airbag module. The modules located within the center of the steering wheel and within the dashboard for driver and passenger, respectively, are designed with weak

1064 points along which the covers break open as the airbag is inflated. The airbag is then rapidly inflated within 35 to 50 milliseconds after impact by combustion of the NaN3, resulting in the generation of nitrogen, carbon dioxide, and fine particulate matter. This particulate matter consists of an alkaline mixture of sodium hydroxide, sodium bicarbonate, and metallic oxides.2 Talcum powder residue may be released as this is used in bag packaging by some manufacturers. The rate of airbag deployment reaches velocities of 140 to 200 mph. The airbag itself provides “ride down” of the vehicle occupants by controlling their deceleration as the airbag deflates after impact.9 The airbag begins to deflate about 200 milliseconds after impact. During the 1 to 2-second deflation phase, gases at high temperature are vented from the back side of the airbag.3,10 Airbags are packed within the airbag modules in folding patterns ranging from pleated to accordion style and combinations of the 2. The fully inflated airbag reaches a volume of 50 to 60 L. Two designs of driver side airbag exist: tethered and untethered. Tethered bags are restricted in excursion by internally placed straps, which create a slight central concavity within the facing of the inflated bag. The untethered variant typically presents a fully rounded surface with deployment and comes in contact with a larger area of the driver’s face when fully inflated.10,11 In a study by Huelke et al,10 a greater incidence of facial injuries was seen in collisions involving vehicles equipped with untethered driver-side airbags. Since the introduction of safety restraint devices in motor vehicles, fatality rates have declined significantly. In addition to this decline in fatalities resulting from motor vehicle accidents, severe and life-threatening injuries have been substantially reduced, especially with the introduction of the current 3-point systems properly used in combination with the airbag supplemental restraint systems. It has been estimated that of 3.8 million airbag deployments recorded since the late 1980s, 4,758 lives have been saved as of 1999.5 The original lap belt restraint required of all vehicles starting with those manufactured in the early 1960s provides modest protection in motor vehicle collisions. Perhaps the major benefit in fatality reduction occurs via reduction of the occurrence of ejection from vehicles. Ejection is associated with a markedly high incidence of fatal and near-fatal injuries.7,9 In front seat positions, the lap belt does little to reduce bodily contact with hard surfaces of the decelerating vehicle, primarily the steering wheel, windshield, and dashboard.7-9 The 3-point lap-shoulder belt was designed to reduce contact of the vehicle occupants with hard surfaces of the vehicle and thus reduce the incidence of

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and severity of collision-related injuries. Unfortunately, the 3-point design does less to reduce injuries or fatalities associated with side-impact collisions. The 3-point design became mandatory equipment in all US vehicles in 1974. These devices have been shown to have an overall effectiveness of 42% in reducing fatalities in front seat occupants.7,8 As of 1999, 49 US states have adopted safety belt laws that carry significant penalties if violated. Among studies on belt use following adoption of mandatory restraint use laws, compliance rates range from 69% to 74%.5,7 Seat belt compliance rates reported for occupants of vehicles equipped with airbags range from 66% to 74%.7,11 All states have child restraint laws in effect that carry similar penalties for violators. In 1999, it was estimated that the compliance rate was 91% for restraints for children under the age of 5.5 The inflatable supplemental restraint device or airbag was designed to further mitigate forces generated by contact of vehicle occupants with interior surfaces during rapid deceleration as occurs in collisions. Used without the 3-point restraint, the airbag does not prevent ejection, nor does it provide protection against impacts that may occur after deflation. They do, however, provide substantial force distribution and reduction of impact with hard interior surfaces used in conjunction with the 3-point restraint. Viano8 estimated an overall effectiveness of 47% in fatality reduction with use of the lap-shoulder belt in combination with airbags for front seat occupants. In their study, Sutyak et al12 found an overall greater incidence of severe thoracic and abdominal injuries in patients involved in collisions in airbag-equipped vehicles without application of the 3-point restraint. These victims required more surgical procedures and lengthier hospital stays and rehabilitation than those involved in collisions with airbag-equipped vehicles that used 3-point restraints. INJURY PATTERNS OF UNRESTRAINED/RESTRAINED DRIVERS AND PASSENGERS BEFORE AIRBAGS

In their study of facial injuries in motor vehicle collisions, Huelke and Compton13 examined the frequency and severity of facial injuries in vehicles before the introduction of airbags. Contact with a variety of vehicle interior surfaces was responsible for injuries, with glass surfaces being the most frequent followed by those occurring due to contact with the steering wheel and spokes. The most striking feature of this study was perhaps the comparison of facial injuries in restrained versus unrestrained occupants. A reduction in the incidence of all facial injuries of 25% was seen in restrained occupants. Facial injuries of a moderate to severe nature as reflected in the Abbreviated Injury Scale were reduced by 66% in restrained compared with

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unrestrained occupants. The incidence of facial injuries of minor severity was greater in restrained occupants; however, restraints were associated with an overall reduction in the occurrence of all types of injuries combined. Of those facial injuries occurring in restrained occupants, half were caused by contact with the steering wheel or spokes, with fewer caused by contact with the windshield, headliner, side glass, or dashboard.13 HEAD, FACIAL, AND CERVICAL INJURIES

Reports of airbag-induced maxillofacial injuries in the early phases of mass airbag availability were limited mainly to minor injuries such as erythema, abrasions, and contusions.7,10 Heulke et al10 found that the preponderance of these minor facial injuries occurred with the untethered as opposed to the tethered airbags. Tethered airbags have a deployment distance of 10 to 13 inches compared with 15 to 20 inches in the untethered devices, thus reducing contact with the occupant’s face and reducing the severity of restraint induced facial injuries.10,11,14 Subsequent studies documented moderate-level facial injuries, which included soft tissue lacerations, nasal fractures, and orbital wall fractures.15,16 An airbag-restrained patient with a nasal fracture and medial wall and floor fractures in association with a severe ocular injury was reported by Scott et al.17 In an early study on patterns of fractures in airbag deployment, Blacksin11 compared injuries sustained by restrained versus unrestrained occupants involved in collisions in which airbags deployed. Two unrestrained drivers experienced flexion-type injuries to the cervical spine and upper thoracic spine. Of the restrained drivers, 1 sustained a cervical extension-type injury thought to be due to close positioning to the deploying airbag. There were equal numbers of facial lacerations among restrained and unrestrained drivers.11 In a recent study of the patterns of facial injuries, Major et al18 observed marked differences between facial injuries in restrained versus unrestrained occupants. All of the unrestrained patients sustained facial injuries, with 66% having minor injury, 24% having suffering moderate injury, 7% having severe injury, and the remaining 3% having serious injury according to the Abbreviated Injury Scale adapted for use in maxillofacial injury classification by Huelke.13,18 These unrestrained patients by far experienced the most extensive facial injuries, with the only mandibular fractures and midfacial injuries occurring among this group compared with the restrained occupants. In addition, the unrestrained group had a considerably greater incidence of concomitant closed head and spinal injuries. Among the airbag-restrained victims, 50% sustained maxillofacial injuries. Of those injured, 86% had minor injuries such as abrasions, contusions, or

1065 lacerations. The remaining 14% sustained moderate maxillofacial injuries consisting of orbital wall fractures and a single nondisplaced zygoma fracture. There were no severe or serious injuries among the airbag-restrained group. Among the seat belt only– restrained victims, 79% had minor injuries, whereas 12% sustained moderate and 9% sustained severe maxillofacial injuries. None of the seat belt only–restrained victims sustained maxillofacial injuries of the highest or serious category. Interestingly, a high proportion of airbag only–restrained drivers in this series had associated lower extremity injuries thought to result from the mechanism of “submarining” beneath the deployed airbag and subsequently having an impact against the dashboard and floor pan of the decelerating vehicle.11,18 Temporomandibular joint injury resulting from airbag deployment has been described in 2 separate publications. Garcia19 reported a restrained driver who sustained minor facial soft tissue injuries in addition to blunt injury to the mandible resulting in bilateral effusions and disc displacement without reduction. More recently, 2 instances of airbag-induced temporomandibular injury were described. One of the victims sustained blunt force mandibular impact resulting in pain, restricted opening, and magnetic resonance imaging findings consistent with unilateral anterior disc displacement. The second patient had an intracapsular condylar fracture and developed myofascial pain dysfunction. The authors theorized that these and several other airbag-related temporomandibular joint injuries occur as a result of complex summation of forces generated by the inertia of the occupant traveling in a forward direction at impact, as well as by forces oriented in rearward and upward directions by the deploying airbag as it makes contact with the victim’s mandible.1 Garcia19 suggests that temporomandibular joint injuries may occur either through posterior displacement of the condyles with anterior displacement of the menisci and compression of retrodiscal tissues in a closed or nearly closed mandible or, alternatively, via airbag impact with an extended mandible adding to the mandibular whiplash mechanism. Six cases of otologic injuries resulting from airbag impulse noise were reported in the otolaryngology literature. Rapid release of gas into the deploying airbag is associated with a short-duration, high-amplitude pressure pulse consisting primarily of low-frequency noise followed by low-amplitude high-frequency noise produced by turbulence and bag unfolding. The high-frequency noise burst is thought to be responsible for producing temporary threshold shifts. Airbag deployment noise is capable of reaching 168 dB sound pressure level, which, although potentially damaging to hearing, is below the threshold for

1066 tympanic membrane rupture. Of the 6 patients reported with otologic symptoms, 5 had documented hearing loss, 1 had persistent tinnitus, and 2 had dysequilibrium. Three of the 5 patients with hearing impairments had premorbid hearing loss, which may have served to lower the threshold for impulse noiseinduced hearing loss.20 The current case is an example of an unexpected injury resulting in an out-of-position driver involved in a motor vehicle collision with airbag deployment. There have been several prior reports of minor facial and neck soft tissue injuries, but on careful review of the literature, submandibular gland rupture has not been reported. Perhaps more remarkable is the fact that the patient had no clinical evidence of adverse sequelae of her submandibular gland injury with ample salivary flow and resolution of submandibular swelling and discomfort at follow-up. Automotive manufacturing engineers are currently focusing attention on the design and implementation of “smart airbag” devices. These devices work in conjunction with a variety of sophisticated sensors within the front bumper and front seats of the vehicle. Adjustments in airbag deployment parameters given certain collision conditions and occupant characteristics would be the benefits of smart airbag technology. Adjustments in the inflation thresholds upward for minor collisions, reduction of deployment forces, or inactivation of the devices if seat sensors detect an occupant weighing less than a predetermined minimum safe weight are but a few of the current goals of this technology.21-23

References 1. Levy Y, Hasson O, Zeltser R, et al: Temporomandibular joint derangement after air bag deployment: Report of two cases. J Oral Maxillofac Surg 56:1000, 1998 2. Mohamed A, Banerjee A: Patterns of injury associated with automobile airbag use. Postgrad Med J 74:455, 1998 3. Jagger J, Vernberg K, Jane J: Air bags: Reducing the toll of brain trauma. Neurosurgery 20:815, 1987

UNUSUAL VEHICLE RESTRAINT-INDUCED INJURY 4. Lund A, Ferguson S: Driver fatalities in 1985-1993 cars with airbags. J Trauma 38:469, 1995 5. National Highway Traffic Safety Administration: Safety Fact Sheet (NHTSA Web Site). Available at http://www.nhtsa.gov/ airbags/factsheets/numbers.html. 1999. Accessed February 8, 2001 6. Braver E, Ferguson S, Greene M, et al: Reductions in deaths in frontal crashes among right front passengers in vehicles equipped with passenger air bags. JAMA 278:1437, 1997 7. Hendey G, Votey S: Injuries in restrained motor vehicle accident victims. Ann Emerg Med 24:77, 1994 8. Viano D: Restraint effectiveness, availability and use in fatal crashes: Implications to injury control. J Trauma 38:538, 1995 9. King A, Yang K: Research in biomechanics of occupant protection. J Trauma 38:570, 1995 10. Huelke D, Moore J, Ostrom M: Air bag injuries and occupant protection. J Trauma 33:894, 1992 11. Blacksin M: Patterns of fracture after air bag deployment. J Trauma 35:840, 1993 12. Sutyak J, Passi V, Hammond J: Air bags alone compared with the combination of mechanical restraints and air bags: Implications for the emergency evaluation of crash victims. South Med J 90:915, 1997 13. Huelke D, Compton C: Facial injuries in automobile crashes. J Oral Maxillofac Surg 41:241, 1983 14. Duma S, Kress T, Porta D, et al: Airbag-induced eye injuries: A report of 25 cases. J Trauma 41:114, 1996 15. Newman L, Hopper C: Driver’s airbags and facial injuries. B J Oral Maxillofac Surg 34:480, 1996 16. Cacciatori M, Bell W, Habib N: Blow-out fracture of the orbit associated with inflation of an airbag: A case report. B J Oral Maxillofac Surg 35:241, 1997 17. Scott I, John G, Stark W: Airbag-associated ocular injury and periorbital fractures. Arch Ophthalmol 111:25, 1993 18. Major M, MacGregor A, Bumpous J: Patterns of maxillofacial injuries as a function of automobile restraint use. Laryngoscope 110:608, 2000 19. Garcia R: Air bag implicated in temporomandibular joint injury. J Craniomandib Pract 12:125, 1994 20. Saunders J, Slattery W, Luxford W: Automobile airbag impulse noise: Otologic symptoms in six patients. Otolaryngol Head Neck Surg 118:228, 1998 21. Cunningham K, Brown T, Gradwell E: Airbag associated fatal head injury: Case report and review of the literature on airbag injuries. J Accid Emerg Med 17:139, 2000 22. Graham J, Goldie S, Segui-Gomez M, et al: Reducing risks to children in vehicles with passenger airbags. Pediatrics 102:1, 1998 23. National Highway Traffic Safety Administration: Occupant protection program update. (NHTSA Web Site). Available at http:// www.nhtsa.gov/people/injury/airbags/oppu_december/ airbags.html. 1999. Accessed February 8, 2001