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Maxillofacial injuries following steering wheel contact by drivers using seat belts
Maxillofacial belts S. Rogers, Queen
injuries following steering wheel contact by drivers using seat
J. R. Hill.
Elizabeth
G.
Hospital,
M. Mackay and Accident
Research
Unit, University
q/ Birmingham,
Birmingham
SUMMARY. Maxillofacial injuries are common sequelae in road traffic accidents. For the restrained driver, impact against the steering wheel is the most prevalent cause of injury. A sample of drivers restrained by seat belts with facial injury caused by the steering wheel was taken from data at the Accident Research Unit, University of Birmingham, UK. Two hundred and forty facial injuries occurred in 135 drivers, and these are described. Superficial contusion, laceration and nasal fractures predominated. There were 504 injuries at other body regions, and these were often caused by other vehicle components. These were, for 57% of drivers, no more serious than the facial injury caused hy steering wheel contact. The role of steering wheel design in maxillofacial trauma is discussed and new solutions briefly reviewed.
biased towards the serious injury end of the severity spectrum. In this specific analysis of restrained drivers receiving facial injuries from the steering wheel, accidents investigated between December 1983 and September 1988 (57 months) were considered. The criteria for inclusion in the study were that the driver must have been restrained by a scat belt and that facial injuries had occurred from contact with the steering wheel. The type, extent and site of each injury were recorded and the Abbreviated Injury Scale (AIS) used to classify severity (AAAM. 1985). This system rates injuries by scvcrlty on a scale of 1 to 6; examples arc given in Table 1.
INTRODUCTION The introduction of compulsory scat belt legislation for front seat occupants has reduced both the number and severity of injuries sustained following road traffic accidents (Pye & Waters, 1984: Allen et al., 1985; Rutherford et al., 1985). The face is still a common site of injury. with trauma occurring following contact with the steering wheel (I luclke & Compton, 19X3; Grattan & Ilobbs, 1985) and this can occur even in low velocity collisions (Mackay, 1987). Recent research has cmphasiscd the importance of maxillofacial trauma generated by the steering wheel (Gloyns et al., 1981; Bradford. 1986; Thomas. 1987), but little information has been rcportcd with regard to the specific details of facial injury. The aims of this study were to assess the facial injuries to drivers restrained by scat belts following contact with the steering wheel and to relate these injuries to wheel design.
PATIENTS
RESULTS A total of 1502 vehicles were imcstigatcd in the 57month period and 135 (9%) fulfilled the study criteria. The vehicles were representative of frontal 1 collisions in the West Midland region. Figure shows the cumulative frequency curve for vchiclc velocity change during the crash phase. It can be seen that 50% of the vehicles experienced a velocity change of less than 36 km/h (23 mph), cvcn though the sample is biased towards the serious injury cases. Velocity change is the best and most practical parameter used to assess the severity of an impact.
AND METHODS
The Accident Research Unit assesses accidents which arc reported to the police in the West Midlands (Mackay et al., 1985). Detailed information is obtained by examining. measuring and photographing the car in a garage within a few days of its involvement in a collision. Information is obtained on occupant injury from hospital notes and by questionnaires completed by the occupant. Only vehicles less than 6 years old are considered, and a stratified sampling scheme is employed such that accident sampling rates approximate to fatal loO%, serious S4%, and slight 14%. using the Department of Transport injury classification. The sample is thus
Injuries This sample of 135 drivers sustained 240 facial injuries attributable to steering wheel impacts. Thcrc wcrc 192 soft tissue and 48 bony injuries. Of the 192 soft tissue injuries (Table 2) 170 (8Y%) were cithcrsuperficialcontusions, abrasionsor lacerations. 23
Maxillofacial Table I - Examples
of injuries rated hy the abbreviated
injuries
following
steerin, 0 wheel
contact
by drivers
using scat belts
25
injury scale
AIS
Descriptor
Soft tissue injury
Bony injury
I 2 3 4 s 6
Minor Moderate Serious Severe Critical Virtually unsurvivable
Superficial laceration Deep facial laceration over S cm Avulscd cyc Pcrforatcd trachea Ruptured liver with tissue loss ‘l‘otal scvcrancc of aorta
Nose. teeth Zygoma, mandibular ramus Le fort II. mandibular body Lc fort III Open crush fracture IO pelvis C3 fracture with quadriplegia
.~..
2b
3b
.._
5b
Speed Change DuringCrash (Km/h) Pig. I - Speed distribution of casts. From data available. underwent a speed change of only 36 km/h or less.
speed change could be calculated
Injury detail
No of injuries
Kcpion
Injury dclail ~
Skin
EYC
Gingiva Tongue Nose Total No. of Injuries
Superficial abrasion (25 cm’ or less) Superficial contusion (2.5 cm’ or Icss) Major contusion (more than 25 cm’) Superficial Iaccration (shallow. or with length 5 cm or Icss) Deep laceration (into subcutaneous tissue and more than 5 cm long) Laceration. but details not known Pcnctration injury Subconjunctival haemorrhage Details not known Laceration Superficial laceration Deep or extensive laceration Contusion
F‘otc that SO% of vehicles
Table 3 - Hony injuries
Table 2 - Soft tissue injuries Region
in 9.5 cases (70%).
KOSC
I6 75
Teeth Mandible
I 79
Maxilla
IO I
Zygoma Orbit Total No. of Injuries
I
-
No of injuries _-
-.
Closed fracture Displaced or compound fracture Details not known I.oosencd, avulsed. or fractured Closed body or ramus fracture Displaced subcondylar fracture Details not known Closed fracture I.e fort I fracture Details not known Closed fracture
-
_
21 3 I 7 3 I 3 2 I 4 2 44
2 2 2
I I
I I92
One hundred and eighty of the injuries had an AIS of 1, an 12 an AIS of 2. Figure 2 shows the AIS distribution for the soft tissues of the fact. It can lx seen that the most common sites of trauma were the forehead (51 injuries), the nose (37 injuries). and the eyebrows (36 injuries). For the forehead, skin
contusion and minor laceration occurred in similar proportions, whilst for the nose. skin contusions were more predominant. lnjurics were moderately common at the check (23 injuries) and lips (10 injuries); 10 intra-oral injuries wcrc recorded. and eye-conjunctival trauma was rare (4 injuries). Forty eight injuries were fractures and over half of thcsc occurred to the nose (Table 3). For these injuries the AIS distribution was: AIS 1, 34 injuries; AIS 2, 13 injuries; AIS 3, 1 injury. AIS 1 bony injuries occurred typically at the nose (21 closed, 3 open or displaced), whilst AIS 2 fractures tended to
26
British
Journal
of Oral
and Maxillofacial
Sureerv
No of Injuries 30
T
25
20
15
10
5
0
Injury Location Fig. 2 - Location
and scvcrity of soft tissue injuries.
Not
With
Known
/
Other CarContact i Several Wheel Components
’
Rim Fig. 3 - ‘l‘hesteering
wheel components
responsible for injury. The number of injuries caused by each component
involve the zygoma, nose or orbit. The only AIS of 3 was assigned to a subcondylar fracture of the mandible sustained by contact with the steering wheel rim and the driver also received fatal head injuries. More than one bony injury was seen in 16 drivers. The side on which facial trauma occurred was assessed. Forty-eight (20%) were on the left and 43 (18%) on the right. For the remainder of the sample the injury involved midline structures or the detail was not available. Some drivers sustained additional facial injury by further contacts on other
arc given
parts of the car such as the window glass, or the forward roof pillar. There were only 13 such injuries. There were 504 non-facial injuries to the 135 restrained drivers. Of these drivers, 75 (55%) were injured at the torso due to loads exerted by the seatbelt, 47 (35%) had lower limb injury from facia contact, and 35 (26%) sustained Icg injury from pedals or footwell. Ilcad injury was reported in 35 drivers (26%). The majority (83%) of drivers with head injury sustained a concussive type of injury. In
Maxillol’acial
% of Drivers 100~ 90
r
iniuries
N = 32
N I 22
lollowing
stecrin g wheel
N - 21
contact
by drivers
using seat belts
27
N = 14
i Chi square = 5.17
60
0.1 < p < 0.2
I-I 60
0 Soft Material
??Hard
Material
25 steering wheels had hard 8 soft component parts; 21 were not classified.
Contusion-Abrasion of AlSl
Laceration of AIS 1
Fracture of AlSl
Any Injury of AIS 2 +
Most Severe Facial Injury Fig. 4 -- Stccrins wheel material
and injury severity.
No of Steering Wheels 40
35
30
25 0
Soft Material
20 Hard Material 15
10
51 hubs couM not be fully classified
5 I
0
-I
t
Small Hub
Large Hub
Exposed Retaining Nut Fig. 5
Steering wheel hub
Small Hub Recessed
Large Hub
Retaining Nut
types.
these cases an anatomic lesion could not be diagnosed with confidence, and the injury was coded either according to the level. or length of unconsciousness (AAAM, lOS5). Within the group coded according to concussion. 21 drivers (60% of those with head injury) were allocated an AIS of 2; 14 of these were known to be unconscious for no more than 1 h and
exhibited a ncurologic deficit, and 7 had retrograde amnesia but were awake on admission. All of the head inJuries were as a result of the fact and/or head contactmE the steering wheel. However one injury was cxaccrbatcd by fragments of window glass, and another by additional loading from a passenger. In 48% of cases the most serious injury to any area of
28
British
Journal
of Oral
and Maxillofacial
Surgery
the body had an AIS of one. Fifty seven percent of the drivers in this sample did not have other nonfacial injuries that were more serious than the facial injury.
Contacts on the steering wheel The steering wheel components causing injury are detailed in Figure 3. Eighty-one (33.8%) of injuries occurred following hub contact and 59 (24.6%) after rim contact. There was insufficient evidence to identify the contact location in 69 (28.8%) of injuries. Thus of the known contacts, 47% came from the hub and 35% came from the rim of the steering wheel.
Wheel material Steering wheel components were qualitatively assessed for hardness. In the sample, 40% of wheels were cntircly covered with soft material (classified as allowing deformation upon finger pressure), and 39% wcrc entirely hard (rigid plastic, metal and wood were put into this category), the remainder (21%) had hard and soft component parts. Although clearly a simplistic assessment, it was used to see if any correlations could be made with the injury outcome. Figure 4 describes the most severe injury sustained from steering wheels that were either entirely hard, or soft. There were a similar number of injuries with each type of wheel. Soft materials seemed to limit injury severity because more AIS 2 injuries, together with more minor lacerations, occurred after contact with hard materials. However this apparent relationship between material type and injury severity was not statistically significant.
Hub design The steering wheel hubs were clasified according to three fcaturcs: their degree of retaining nut recess, size and hardness (Fig. 5). The retaining nut was ‘recessed’ if 2 cm or more below the hub surface; the hub was ‘small’ if approximately 17.5 cm2 or less in area; and hardness was determined as described above. Small, hard hubs with exposed retaining nuts were particularly common (33%), indeed wheels with an exposed retaining nut (either in a large or small hub) constituted the greater proportion of this sample (68%). Those hubs that are large with a recessed nut were observed the least. As there were so few large hubs, with recessed nut and soft material, no correlation could be shown between these characteristics and the incidence and severity of the injuries. It was commonly observed that in higher velocity crashes the steering wheel was displaced towards the driver. Severe soft tissue and bony injuries were more common in these cases. There were 4 fatal
cases. Two of these had only minor facial lacerations but severe thoracic injuries; the others received extensive maxillofacial and cerebral trauma from the steering wheel. DISCUSSION Of the road traffic accidents investigated over the 57-month study period, 9% of drivers were restrained by seat belts, and had received facial injury from the steering wheel. The true incidence in the population would be higher than this figure suggests because of the sample selection criteria procedure. Only 14% of slight accidents are sampled from the population and Figure I shows that facial injuries from the steering wheel are common in low velocity accidents. Despite this selection bias, a broad view has been gained of the overall spectrum of facial injuries occurring following car accidents. Hospital-based studies are often more biased towards serious injury cases. Scat belt legislation has done much to reduce serious head and face injury (Perkins & Layton, 1988). The face, of drivers particularly, is still injured with significant frequency from contacts with the steering wheel. Our results in Figure 1 show that many of these occur at relatively low velocity change values. A correctly restrained driver in a present day seat belt will experience some 60 cm (2 feet) of forward motion of the head in a standard crash with a velocity change of 48 km/h (30 mph) (Mackay, 1987). As the steering wheel is normally positioned some 33 to 40 cm (13-16 inches) forward of the chest, it is inevitable that the face will reach the plane of the steering wheel in a significant frontal impact. Add to that some intrusion rearward and upward of the steering wheel during the crash, and facial contact may occur in relatively modest frontal collisions. In this context, our data in Figure 1 suggest that people in collisions have more forward movement than do the anthropomorphic dummies used for assessing the crash performance of present day cars (Svcnsson, 1978). This forward motion comes from the characteristics of the seat belt restraining the chest whilst the head arcs forwards and downwards to strike the steering wheel. The majority of injuries in this sample were relatively minor, 89% of the soft tissue injuries were superficial contusions, abrasions or lacerations, and 52% of the fractures were to the nose. Although such injuries carry a low ‘threat to life’ according to the AIS, they may cause obvious disfigurement which the AIS is not intended to assess. Forty eight per cent of drivers sustain only ‘minor’ injuries to all body regions and it is reasonable to presume that those to the face arc likely to be the least desirable in social and psychological terms. The forehead, nose, and eyebrow region were more commonly injured than the lower face. McCoy er al. (1988) suggested that the left side of the face is more prone to injury in the UK, because the driver’s torso can rotate as a result of the right shoulder being under restraint. In this study there was no particular side of the face more likely to be injured.
Maxillofacial
injuries
‘I‘his study focused specifically on facial trauma following steering wheel contacts. However, 68% of injuries occurred to other body regions: notably the thorax and lower limbs which were injured by seat belt loads. and facial and footwcll impacts rcspcctively. lnjurics to other regions were often no more serious than those sustained at the face. The seat belt reduces the number of fatalities associated with maxillofacial trauma (Arajarvi et af.. 1986) and in this sample only 2 fatalitics arose due to maxillofacial and head injunes.
Injury causation
and prevention
Relatively small forces are required to cause facial bone fracture. Nasal fractures can occur at forces of 111 to 333 newtons (25-75 lb), with loads 10 times this ncccssary to cause fractures of the mandible (lIuclke & Compton, 19X3). Such loads can occur when the face strikes a steering wheel in low speed collisions, and ideally, vehicle design should diminish these facial contacts. The effectiveness of inertia seat belts can be improved by devices which take up slack in the webbing. These pretensioning devices have a sensor which detects a crash condition, and fires a charge that tensions the belt webbing within some 30 milliseconds, well before the occupant has moved significantly forwards. A more simplistic approach to webbing tensioning uses an entirely mechanical dcvicc that utilises a torsion bar mounted under the seat (Haland & Skanberg. 1989). Rearward displaccment of the steering system is also important in vehicle safety design. Legislation limits the amount of horizontal displacement to 12.7 cm (5 inches) under 30 mph crash test conditions (EEC Directive 74/279). The Audi Pro-Con 10 system (Autocar, 1986) offers an unusual solution; on impact, rcarward engine displacement pulls the steering wheel forwards away from the driver using a cable system. It seems likely that facial contacts with the steering wheel will continue to be frequent events. Automobile design should attempt to keep the facial impact forces low. Current steering system safety legislation was developed in the 1960s to encourage designs that would limit the chest forces that an unrestrained driver experiences upon contacting a steering wheel. Consequently many current steering systems arc not designed to limit small loads that can cause facial injury. The facial load can bc reduced by improving the structure and material used in steering wheel design. In this study, soft tissue contusion/abrasions were often the only injury that occurred with soft steering wheel contacts, whilst lacerations and AIS 2 injuries were seen in greater numbers after hard material contact (Fig. 4). Hard materials may cause more lacerations bccasusc of their brittle nature which can result in sharp edges when impact damage occurs. Although soft materials reduce loads, their effcctivcness is often diminished by the presence of underlying hard components. Many of the wheels in this study had a prominent steering column nut, and
following
steerin
wheel
contact
by drivers
using scat belts
29
the majority wcrc clad with hard materials that offered little protection. Softer, deeper and more deformable material will reduce injury upon contact. This is the approach taken by the British government proposal which describes a test condition for limiting loads when a steering wheel is impacted by a honeycomb material which deforms in a manner which is correlated with facial bone fracture levels (Petty & Fenn, 1985). Supplementary airbags are now fitted to the steering wheels of the majority of new cars in the USA. Smaller and cheaper versions arc being developed in Europe and these provide a good solution because they reduce the loads on the face to very low Icvcls, and specifically solve the problem of the steering wheel rim, something that cannot bc solved adequately with static padding (Johansson el a/., 1989; Planath et al., 1989). In conclusion, the steering wheel is an important source of maxillofacial injury. Most injuries are minor, but they occur frequently and are undesirable. New technologies arc becoming available that either prevent contact on the steering wheel or limit impact forces. and these should be cncouragcd. Acknowledgements The authors thank Mr B. Spcculand for advice in the preparation of the manuscript, and arc grateful to all mcmbcrs of the Cooperative Crash Injury Project. They also acknowledge the hclpofthc sponsors: thc’l‘ransport and Road Rcxcarch Laborator! of the Department of Transport. the Ford Motor Company. the Rover tiroup. and Nissan (UK) Ltd.
References Allen. M. J.. Barnes. M. R. & Bodiwala, G. Ci. (19X.5). ‘I‘hc effect of scat belt Icgislation on injuries sustained by car occupants. Ir~jur)r, 16,471. American Association for Automotive Medicine (198.5). ‘Ihe AOhreviuted Injury SC&. 1985 Revision. Arlington I Ieiphts. II.: AAAM. Arajarvi, E., I.indqvist, C., Santarvita, S.. Toloncn. J. & Kiviluoto. 0. (1986). Maxillofacial trauma in fatally injured victims of motor vchiclc accidents. British Journul ofOral crnd Mnxiliof~~ciul SurprJ. 24, 251. Autocar. (19X6). X0 for the ninetics. Aurocar, Sept. 2&i-.12. Bradford. M. A.. Otubushin. A. ,Thomas. P.. Robertson. N. K. B. & Green, P. D. (1986). I lead and face injuries to car occupants in accidents- -field data 1983 1985. Proceedings 0.f IIKOBI Cor!ference. Scptcmbcr 1986. 85. IXC Directive 74/297 (1976) Commission uf Ihe I:‘uropmn
Communirie.s. dirccrives concernining the eliminctrion of technical barriers 10 trude in indu.wiul products, pp. 68-77. Brussels. Ciloyns. I’. F.. Rattcnbury. S. J.. Rivlin, A. Z.. Hayes. H. R. M., Hnnstcad. J. K. & Proctor, S. (1981). Steering wheel induced head and facial iniurics amongst drivers restrained by seatbclts. I’rocredings oflRCOHI Conference, Scptcmhcr I98 I. 3&48. Grattan. E. & Hobbs. J. A. (1985). Mechanisms of injury to the fact in road traffic accidents. In: Moxillofacial lnjurtk. N. L. Row XL J. Williams (cds). pp 37-41. Edinburgh & London: (Churchill 1,ivingstonc. Haland, Y. & Skanbcrg. ‘I‘. (1989). A mechanical buckle pretensioncr to improvc a three point seat belt. The 7’we(jih ESV (.‘onfercnce, May 1989. Huclkc. D. F. & Compton. C. I’. (1983). Facial injuries in automobile crashes. Journal of Orul and Muxill~~~fucictl
Surgery, 41, 241.
30
British
Journal
of Oral
and Maxillofacial
Sumcn
Johansson, I... Billig. J.. Mellander, H.. Werner. B., Hora. P. & Chcmie GmbH. B. (1989). The development of an advanced airbagconccpt. Proceedingsof Twelfih Iniernurional Technicul Conference on Experimenral Sufery Vehicle.ts. May 1989. Vol.
1.29%303. Mackay, G. M., Galer. M. D.. Ashton. S. J. &Thomas. I’. II. (1985). The methodology of in-depth studies of car crashes in Great Britain. SAE Pqw8.50.556. pp 36%390. Detroit: S.A.E. Mackav. G. M. (1987). Kinamaticsofvehiclc crashes. Advancer
in ~Trouma, 2,2
1.
McCoy. G. F., Johnstone. R. A., Nelson, I. W. & Duthic. R. B. (198X). Facial injuries to restrained drivers caused by steering wheels (letter). Lancer, 2,456. Perkins. C. S. & Lavton, S. A. (1088). ‘l‘he aetiology of maxillofacial iniurics and the seat belt law. Rrirish Journul of
Orcrl tmd Maxiliofirci*l Surgeons, 26, 353.
I’cttv. _ S. P.
F. Kr Fcnn. M. A. f1985). A modified stccrinzL wheel ~ to rcducc facial injuries and an associated test procedure. I
Prowdings of 10th Intemcrrional Technic01 C‘onference on ~$wrimentul Safety Vehicles. 342-347. Planath. I., Cesari. D. & Nilsson. S. (1989). Facial fracture protection criteria for the Hybrid 111 Load Sensing Face.
Proceedings of .?3rd A.A.
Srapp Car Crclsh Conference.
449-470.
Thomas.‘P. I‘. (1987). H&d and torso injuries to restrained drivers from the steering system. Proceedings of IRCORI
Conference.
Sepemher
1987, 7.3-89.
The Authors S. Wagers
MBChB, BDS, FDSRCS 1 louse Surgeon The Ouecn Elizabeth Hospital The Queen Elizabeth Medical Ccntre Edgbaston. Birmingham B li 2TI 1 J. R. Hill BSc Research Associate G.&l. Mackay PhD, DSc, FIMechE Professor of Transport Safety and Head of IJnit Accident Rcscarch Unit. llnwersity of Birmingham. Edgbnston. Birmingham HIS 2TT
A. hf. Conference. 3X3-397.
Pye. G. & Waters. E. A. (1984). Effect ofscat belt legislation on injuries in road traffic accidents in Nottingham. Rrirish
Mediccrl Journal, 288, 7%. Ruthorford.
J. K. (1985). The medical effects of seat hclt legislation in the llnitcd Kingdom. DltSS R~wurcl~ Repor/ NO. 13. London: I IMSO. Svensson, L. G. (1978). Means for effective improvement of the three-point scat belt in frontal crashes. I’r&edings of22nd
W. H., Greenfield.
T.. Hayes.
I-l. R. M. CGh”clson,
Correspondence
and requests for offprints to Mr J. I Ii11
Paper reccivcd 9 May 1991 Accepted 2X May 1991
injuries following steering wheel contact by drivers using seat
J. R. Hill.
Elizabeth
G.
Hospital,
M. Mackay and Accident
Research
Unit, University
q/ Birmingham,
Birmingham
SUMMARY. Maxillofacial injuries are common sequelae in road traffic accidents. For the restrained driver, impact against the steering wheel is the most prevalent cause of injury. A sample of drivers restrained by seat belts with facial injury caused by the steering wheel was taken from data at the Accident Research Unit, University of Birmingham, UK. Two hundred and forty facial injuries occurred in 135 drivers, and these are described. Superficial contusion, laceration and nasal fractures predominated. There were 504 injuries at other body regions, and these were often caused by other vehicle components. These were, for 57% of drivers, no more serious than the facial injury caused hy steering wheel contact. The role of steering wheel design in maxillofacial trauma is discussed and new solutions briefly reviewed.
biased towards the serious injury end of the severity spectrum. In this specific analysis of restrained drivers receiving facial injuries from the steering wheel, accidents investigated between December 1983 and September 1988 (57 months) were considered. The criteria for inclusion in the study were that the driver must have been restrained by a scat belt and that facial injuries had occurred from contact with the steering wheel. The type, extent and site of each injury were recorded and the Abbreviated Injury Scale (AIS) used to classify severity (AAAM. 1985). This system rates injuries by scvcrlty on a scale of 1 to 6; examples arc given in Table 1.
INTRODUCTION The introduction of compulsory scat belt legislation for front seat occupants has reduced both the number and severity of injuries sustained following road traffic accidents (Pye & Waters, 1984: Allen et al., 1985; Rutherford et al., 1985). The face is still a common site of injury. with trauma occurring following contact with the steering wheel (I luclke & Compton, 19X3; Grattan & Ilobbs, 1985) and this can occur even in low velocity collisions (Mackay, 1987). Recent research has cmphasiscd the importance of maxillofacial trauma generated by the steering wheel (Gloyns et al., 1981; Bradford. 1986; Thomas. 1987), but little information has been rcportcd with regard to the specific details of facial injury. The aims of this study were to assess the facial injuries to drivers restrained by scat belts following contact with the steering wheel and to relate these injuries to wheel design.
PATIENTS
RESULTS A total of 1502 vehicles were imcstigatcd in the 57month period and 135 (9%) fulfilled the study criteria. The vehicles were representative of frontal 1 collisions in the West Midland region. Figure shows the cumulative frequency curve for vchiclc velocity change during the crash phase. It can be seen that 50% of the vehicles experienced a velocity change of less than 36 km/h (23 mph), cvcn though the sample is biased towards the serious injury cases. Velocity change is the best and most practical parameter used to assess the severity of an impact.
AND METHODS
The Accident Research Unit assesses accidents which arc reported to the police in the West Midlands (Mackay et al., 1985). Detailed information is obtained by examining. measuring and photographing the car in a garage within a few days of its involvement in a collision. Information is obtained on occupant injury from hospital notes and by questionnaires completed by the occupant. Only vehicles less than 6 years old are considered, and a stratified sampling scheme is employed such that accident sampling rates approximate to fatal loO%, serious S4%, and slight 14%. using the Department of Transport injury classification. The sample is thus
Injuries This sample of 135 drivers sustained 240 facial injuries attributable to steering wheel impacts. Thcrc wcrc 192 soft tissue and 48 bony injuries. Of the 192 soft tissue injuries (Table 2) 170 (8Y%) were cithcrsuperficialcontusions, abrasionsor lacerations. 23
Maxillofacial Table I - Examples
of injuries rated hy the abbreviated
injuries
following
steerin, 0 wheel
contact
by drivers
using scat belts
25
injury scale
AIS
Descriptor
Soft tissue injury
Bony injury
I 2 3 4 s 6
Minor Moderate Serious Severe Critical Virtually unsurvivable
Superficial laceration Deep facial laceration over S cm Avulscd cyc Pcrforatcd trachea Ruptured liver with tissue loss ‘l‘otal scvcrancc of aorta
Nose. teeth Zygoma, mandibular ramus Le fort II. mandibular body Lc fort III Open crush fracture IO pelvis C3 fracture with quadriplegia
.~..
2b
3b
.._
5b
Speed Change DuringCrash (Km/h) Pig. I - Speed distribution of casts. From data available. underwent a speed change of only 36 km/h or less.
speed change could be calculated
Injury detail
No of injuries
Kcpion
Injury dclail ~
Skin
EYC
Gingiva Tongue Nose Total No. of Injuries
Superficial abrasion (25 cm’ or less) Superficial contusion (2.5 cm’ or Icss) Major contusion (more than 25 cm’) Superficial Iaccration (shallow. or with length 5 cm or Icss) Deep laceration (into subcutaneous tissue and more than 5 cm long) Laceration. but details not known Pcnctration injury Subconjunctival haemorrhage Details not known Laceration Superficial laceration Deep or extensive laceration Contusion
F‘otc that SO% of vehicles
Table 3 - Hony injuries
Table 2 - Soft tissue injuries Region
in 9.5 cases (70%).
KOSC
I6 75
Teeth Mandible
I 79
Maxilla
IO I
Zygoma Orbit Total No. of Injuries
I
-
No of injuries _-
-.
Closed fracture Displaced or compound fracture Details not known I.oosencd, avulsed. or fractured Closed body or ramus fracture Displaced subcondylar fracture Details not known Closed fracture I.e fort I fracture Details not known Closed fracture
-
_
21 3 I 7 3 I 3 2 I 4 2 44
2 2 2
I I
I I92
One hundred and eighty of the injuries had an AIS of 1, an 12 an AIS of 2. Figure 2 shows the AIS distribution for the soft tissues of the fact. It can lx seen that the most common sites of trauma were the forehead (51 injuries), the nose (37 injuries). and the eyebrows (36 injuries). For the forehead, skin
contusion and minor laceration occurred in similar proportions, whilst for the nose. skin contusions were more predominant. lnjurics were moderately common at the check (23 injuries) and lips (10 injuries); 10 intra-oral injuries wcrc recorded. and eye-conjunctival trauma was rare (4 injuries). Forty eight injuries were fractures and over half of thcsc occurred to the nose (Table 3). For these injuries the AIS distribution was: AIS 1, 34 injuries; AIS 2, 13 injuries; AIS 3, 1 injury. AIS 1 bony injuries occurred typically at the nose (21 closed, 3 open or displaced), whilst AIS 2 fractures tended to
26
British
Journal
of Oral
and Maxillofacial
Sureerv
No of Injuries 30
T
25
20
15
10
5
0
Injury Location Fig. 2 - Location
and scvcrity of soft tissue injuries.
Not
With
Known
/
Other CarContact i Several Wheel Components
’
Rim Fig. 3 - ‘l‘hesteering
wheel components
responsible for injury. The number of injuries caused by each component
involve the zygoma, nose or orbit. The only AIS of 3 was assigned to a subcondylar fracture of the mandible sustained by contact with the steering wheel rim and the driver also received fatal head injuries. More than one bony injury was seen in 16 drivers. The side on which facial trauma occurred was assessed. Forty-eight (20%) were on the left and 43 (18%) on the right. For the remainder of the sample the injury involved midline structures or the detail was not available. Some drivers sustained additional facial injury by further contacts on other
arc given
parts of the car such as the window glass, or the forward roof pillar. There were only 13 such injuries. There were 504 non-facial injuries to the 135 restrained drivers. Of these drivers, 75 (55%) were injured at the torso due to loads exerted by the seatbelt, 47 (35%) had lower limb injury from facia contact, and 35 (26%) sustained Icg injury from pedals or footwell. Ilcad injury was reported in 35 drivers (26%). The majority (83%) of drivers with head injury sustained a concussive type of injury. In
Maxillol’acial
% of Drivers 100~ 90
r
iniuries
N = 32
N I 22
lollowing
stecrin g wheel
N - 21
contact
by drivers
using seat belts
27
N = 14
i Chi square = 5.17
60
0.1 < p < 0.2
I-I 60
0 Soft Material
??Hard
Material
25 steering wheels had hard 8 soft component parts; 21 were not classified.
Contusion-Abrasion of AlSl
Laceration of AIS 1
Fracture of AlSl
Any Injury of AIS 2 +
Most Severe Facial Injury Fig. 4 -- Stccrins wheel material
and injury severity.
No of Steering Wheels 40
35
30
25 0
Soft Material
20 Hard Material 15
10
51 hubs couM not be fully classified
5 I
0
-I
t
Small Hub
Large Hub
Exposed Retaining Nut Fig. 5
Steering wheel hub
Small Hub Recessed
Large Hub
Retaining Nut
types.
these cases an anatomic lesion could not be diagnosed with confidence, and the injury was coded either according to the level. or length of unconsciousness (AAAM, lOS5). Within the group coded according to concussion. 21 drivers (60% of those with head injury) were allocated an AIS of 2; 14 of these were known to be unconscious for no more than 1 h and
exhibited a ncurologic deficit, and 7 had retrograde amnesia but were awake on admission. All of the head inJuries were as a result of the fact and/or head contactmE the steering wheel. However one injury was cxaccrbatcd by fragments of window glass, and another by additional loading from a passenger. In 48% of cases the most serious injury to any area of
28
British
Journal
of Oral
and Maxillofacial
Surgery
the body had an AIS of one. Fifty seven percent of the drivers in this sample did not have other nonfacial injuries that were more serious than the facial injury.
Contacts on the steering wheel The steering wheel components causing injury are detailed in Figure 3. Eighty-one (33.8%) of injuries occurred following hub contact and 59 (24.6%) after rim contact. There was insufficient evidence to identify the contact location in 69 (28.8%) of injuries. Thus of the known contacts, 47% came from the hub and 35% came from the rim of the steering wheel.
Wheel material Steering wheel components were qualitatively assessed for hardness. In the sample, 40% of wheels were cntircly covered with soft material (classified as allowing deformation upon finger pressure), and 39% wcrc entirely hard (rigid plastic, metal and wood were put into this category), the remainder (21%) had hard and soft component parts. Although clearly a simplistic assessment, it was used to see if any correlations could be made with the injury outcome. Figure 4 describes the most severe injury sustained from steering wheels that were either entirely hard, or soft. There were a similar number of injuries with each type of wheel. Soft materials seemed to limit injury severity because more AIS 2 injuries, together with more minor lacerations, occurred after contact with hard materials. However this apparent relationship between material type and injury severity was not statistically significant.
Hub design The steering wheel hubs were clasified according to three fcaturcs: their degree of retaining nut recess, size and hardness (Fig. 5). The retaining nut was ‘recessed’ if 2 cm or more below the hub surface; the hub was ‘small’ if approximately 17.5 cm2 or less in area; and hardness was determined as described above. Small, hard hubs with exposed retaining nuts were particularly common (33%), indeed wheels with an exposed retaining nut (either in a large or small hub) constituted the greater proportion of this sample (68%). Those hubs that are large with a recessed nut were observed the least. As there were so few large hubs, with recessed nut and soft material, no correlation could be shown between these characteristics and the incidence and severity of the injuries. It was commonly observed that in higher velocity crashes the steering wheel was displaced towards the driver. Severe soft tissue and bony injuries were more common in these cases. There were 4 fatal
cases. Two of these had only minor facial lacerations but severe thoracic injuries; the others received extensive maxillofacial and cerebral trauma from the steering wheel. DISCUSSION Of the road traffic accidents investigated over the 57-month study period, 9% of drivers were restrained by seat belts, and had received facial injury from the steering wheel. The true incidence in the population would be higher than this figure suggests because of the sample selection criteria procedure. Only 14% of slight accidents are sampled from the population and Figure I shows that facial injuries from the steering wheel are common in low velocity accidents. Despite this selection bias, a broad view has been gained of the overall spectrum of facial injuries occurring following car accidents. Hospital-based studies are often more biased towards serious injury cases. Scat belt legislation has done much to reduce serious head and face injury (Perkins & Layton, 1988). The face, of drivers particularly, is still injured with significant frequency from contacts with the steering wheel. Our results in Figure 1 show that many of these occur at relatively low velocity change values. A correctly restrained driver in a present day seat belt will experience some 60 cm (2 feet) of forward motion of the head in a standard crash with a velocity change of 48 km/h (30 mph) (Mackay, 1987). As the steering wheel is normally positioned some 33 to 40 cm (13-16 inches) forward of the chest, it is inevitable that the face will reach the plane of the steering wheel in a significant frontal impact. Add to that some intrusion rearward and upward of the steering wheel during the crash, and facial contact may occur in relatively modest frontal collisions. In this context, our data in Figure 1 suggest that people in collisions have more forward movement than do the anthropomorphic dummies used for assessing the crash performance of present day cars (Svcnsson, 1978). This forward motion comes from the characteristics of the seat belt restraining the chest whilst the head arcs forwards and downwards to strike the steering wheel. The majority of injuries in this sample were relatively minor, 89% of the soft tissue injuries were superficial contusions, abrasions or lacerations, and 52% of the fractures were to the nose. Although such injuries carry a low ‘threat to life’ according to the AIS, they may cause obvious disfigurement which the AIS is not intended to assess. Forty eight per cent of drivers sustain only ‘minor’ injuries to all body regions and it is reasonable to presume that those to the face arc likely to be the least desirable in social and psychological terms. The forehead, nose, and eyebrow region were more commonly injured than the lower face. McCoy er al. (1988) suggested that the left side of the face is more prone to injury in the UK, because the driver’s torso can rotate as a result of the right shoulder being under restraint. In this study there was no particular side of the face more likely to be injured.
Maxillofacial
injuries
‘I‘his study focused specifically on facial trauma following steering wheel contacts. However, 68% of injuries occurred to other body regions: notably the thorax and lower limbs which were injured by seat belt loads. and facial and footwcll impacts rcspcctively. lnjurics to other regions were often no more serious than those sustained at the face. The seat belt reduces the number of fatalities associated with maxillofacial trauma (Arajarvi et af.. 1986) and in this sample only 2 fatalitics arose due to maxillofacial and head injunes.
Injury causation
and prevention
Relatively small forces are required to cause facial bone fracture. Nasal fractures can occur at forces of 111 to 333 newtons (25-75 lb), with loads 10 times this ncccssary to cause fractures of the mandible (lIuclke & Compton, 19X3). Such loads can occur when the face strikes a steering wheel in low speed collisions, and ideally, vehicle design should diminish these facial contacts. The effectiveness of inertia seat belts can be improved by devices which take up slack in the webbing. These pretensioning devices have a sensor which detects a crash condition, and fires a charge that tensions the belt webbing within some 30 milliseconds, well before the occupant has moved significantly forwards. A more simplistic approach to webbing tensioning uses an entirely mechanical dcvicc that utilises a torsion bar mounted under the seat (Haland & Skanberg. 1989). Rearward displaccment of the steering system is also important in vehicle safety design. Legislation limits the amount of horizontal displacement to 12.7 cm (5 inches) under 30 mph crash test conditions (EEC Directive 74/279). The Audi Pro-Con 10 system (Autocar, 1986) offers an unusual solution; on impact, rcarward engine displacement pulls the steering wheel forwards away from the driver using a cable system. It seems likely that facial contacts with the steering wheel will continue to be frequent events. Automobile design should attempt to keep the facial impact forces low. Current steering system safety legislation was developed in the 1960s to encourage designs that would limit the chest forces that an unrestrained driver experiences upon contacting a steering wheel. Consequently many current steering systems arc not designed to limit small loads that can cause facial injury. The facial load can bc reduced by improving the structure and material used in steering wheel design. In this study, soft tissue contusion/abrasions were often the only injury that occurred with soft steering wheel contacts, whilst lacerations and AIS 2 injuries were seen in greater numbers after hard material contact (Fig. 4). Hard materials may cause more lacerations bccasusc of their brittle nature which can result in sharp edges when impact damage occurs. Although soft materials reduce loads, their effcctivcness is often diminished by the presence of underlying hard components. Many of the wheels in this study had a prominent steering column nut, and
following
steerin
wheel
contact
by drivers
using scat belts
29
the majority wcrc clad with hard materials that offered little protection. Softer, deeper and more deformable material will reduce injury upon contact. This is the approach taken by the British government proposal which describes a test condition for limiting loads when a steering wheel is impacted by a honeycomb material which deforms in a manner which is correlated with facial bone fracture levels (Petty & Fenn, 1985). Supplementary airbags are now fitted to the steering wheels of the majority of new cars in the USA. Smaller and cheaper versions arc being developed in Europe and these provide a good solution because they reduce the loads on the face to very low Icvcls, and specifically solve the problem of the steering wheel rim, something that cannot bc solved adequately with static padding (Johansson el a/., 1989; Planath et al., 1989). In conclusion, the steering wheel is an important source of maxillofacial injury. Most injuries are minor, but they occur frequently and are undesirable. New technologies arc becoming available that either prevent contact on the steering wheel or limit impact forces. and these should be cncouragcd. Acknowledgements The authors thank Mr B. Spcculand for advice in the preparation of the manuscript, and arc grateful to all mcmbcrs of the Cooperative Crash Injury Project. They also acknowledge the hclpofthc sponsors: thc’l‘ransport and Road Rcxcarch Laborator! of the Department of Transport. the Ford Motor Company. the Rover tiroup. and Nissan (UK) Ltd.
References Allen. M. J.. Barnes. M. R. & Bodiwala, G. Ci. (19X.5). ‘I‘hc effect of scat belt Icgislation on injuries sustained by car occupants. Ir~jur)r, 16,471. American Association for Automotive Medicine (198.5). ‘Ihe AOhreviuted Injury SC&. 1985 Revision. Arlington I Ieiphts. II.: AAAM. Arajarvi, E., I.indqvist, C., Santarvita, S.. Toloncn. J. & Kiviluoto. 0. (1986). Maxillofacial trauma in fatally injured victims of motor vchiclc accidents. British Journul ofOral crnd Mnxiliof~~ciul SurprJ. 24, 251. Autocar. (19X6). X0 for the ninetics. Aurocar, Sept. 2&i-.12. Bradford. M. A.. Otubushin. A. ,Thomas. P.. Robertson. N. K. B. & Green, P. D. (1986). I lead and face injuries to car occupants in accidents- -field data 1983 1985. Proceedings 0.f IIKOBI Cor!ference. Scptcmbcr 1986. 85. IXC Directive 74/297 (1976) Commission uf Ihe I:‘uropmn
Communirie.s. dirccrives concernining the eliminctrion of technical barriers 10 trude in indu.wiul products, pp. 68-77. Brussels. Ciloyns. I’. F.. Rattcnbury. S. J.. Rivlin, A. Z.. Hayes. H. R. M., Hnnstcad. J. K. & Proctor, S. (1981). Steering wheel induced head and facial iniurics amongst drivers restrained by seatbclts. I’rocredings oflRCOHI Conference, Scptcmhcr I98 I. 3&48. Grattan. E. & Hobbs. J. A. (1985). Mechanisms of injury to the fact in road traffic accidents. In: Moxillofacial lnjurtk. N. L. Row XL J. Williams (cds). pp 37-41. Edinburgh & London: (Churchill 1,ivingstonc. Haland, Y. & Skanbcrg. ‘I‘. (1989). A mechanical buckle pretensioncr to improvc a three point seat belt. The 7’we(jih ESV (.‘onfercnce, May 1989. Huclkc. D. F. & Compton. C. I’. (1983). Facial injuries in automobile crashes. Journal of Orul and Muxill~~~fucictl
Surgery, 41, 241.
30
British
Journal
of Oral
and Maxillofacial
Sumcn
Johansson, I... Billig. J.. Mellander, H.. Werner. B., Hora. P. & Chcmie GmbH. B. (1989). The development of an advanced airbagconccpt. Proceedingsof Twelfih Iniernurional Technicul Conference on Experimenral Sufery Vehicle.ts. May 1989. Vol.
1.29%303. Mackay, G. M., Galer. M. D.. Ashton. S. J. &Thomas. I’. II. (1985). The methodology of in-depth studies of car crashes in Great Britain. SAE Pqw8.50.556. pp 36%390. Detroit: S.A.E. Mackav. G. M. (1987). Kinamaticsofvehiclc crashes. Advancer
in ~Trouma, 2,2
1.
McCoy. G. F., Johnstone. R. A., Nelson, I. W. & Duthic. R. B. (198X). Facial injuries to restrained drivers caused by steering wheels (letter). Lancer, 2,456. Perkins. C. S. & Lavton, S. A. (1088). ‘l‘he aetiology of maxillofacial iniurics and the seat belt law. Rrirish Journul of
Orcrl tmd Maxiliofirci*l Surgeons, 26, 353.
I’cttv. _ S. P.
F. Kr Fcnn. M. A. f1985). A modified stccrinzL wheel ~ to rcducc facial injuries and an associated test procedure. I
Prowdings of 10th Intemcrrional Technic01 C‘onference on ~$wrimentul Safety Vehicles. 342-347. Planath. I., Cesari. D. & Nilsson. S. (1989). Facial fracture protection criteria for the Hybrid 111 Load Sensing Face.
Proceedings of .?3rd A.A.
Srapp Car Crclsh Conference.
449-470.
Thomas.‘P. I‘. (1987). H&d and torso injuries to restrained drivers from the steering system. Proceedings of IRCORI
Conference.
Sepemher
1987, 7.3-89.
The Authors S. Wagers
MBChB, BDS, FDSRCS 1 louse Surgeon The Ouecn Elizabeth Hospital The Queen Elizabeth Medical Ccntre Edgbaston. Birmingham B li 2TI 1 J. R. Hill BSc Research Associate G.&l. Mackay PhD, DSc, FIMechE Professor of Transport Safety and Head of IJnit Accident Rcscarch Unit. llnwersity of Birmingham. Edgbnston. Birmingham HIS 2TT
A. hf. Conference. 3X3-397.
Pye. G. & Waters. E. A. (1984). Effect ofscat belt legislation on injuries in road traffic accidents in Nottingham. Rrirish
Mediccrl Journal, 288, 7%. Ruthorford.
J. K. (1985). The medical effects of seat hclt legislation in the llnitcd Kingdom. DltSS R~wurcl~ Repor/ NO. 13. London: I IMSO. Svensson, L. G. (1978). Means for effective improvement of the three-point scat belt in frontal crashes. I’r&edings of22nd
W. H., Greenfield.
T.. Hayes.
I-l. R. M. CGh”clson,
Correspondence
and requests for offprints to Mr J. I Ii11
Paper reccivcd 9 May 1991 Accepted 2X May 1991