Lower extremity injuries in side-impact vehicle crashes

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Lower extremity injuries in side-impact vehiclecrashesN Arndt & R H Grzebietaa Department of Civil Engineering, PO Box 60, Monash University, Vic., 3800, Australiab Department of Civil Engineering, PO Box 60, Monash University, Vic., 3800, Australia

Version of record first published: 08 Jul 2010.

To cite this article: N Arndt & R H Grzebieta (2003): Lower extremity injuries in side-impact vehicle crashes,International Journal of Crashworthiness, 8:5, 495-512

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© Woodhead Publishing Ltd 0255 495 IJCrash 2003 Vol. 8 No. 5 pp. 495–512

Corresponding Author:R H Grzebieta, Associate Professor (Structures), Civil EngineeringMonash University, PO Box 60, Monash University 3800Tel 61 3 9905 4970 Fax +61 3 9905 4955Email [email protected]. edu.au

INTRODUCTION

Vehicle crashes are a major cause of LE injuries to motorvehicle occupants. Occupant protection regulations arelimited with regard to the lower extremity. There are noregulations regarding the knee, lower leg or ankle/foot inside-impact. Neither the EuroSID nor the US-SID (side-impact dummies) have the capability of measuring therisk of injury to the lower extremity below the pelvis.Crash-induced LE injuries are common, costly anddebilitating. In the case of frontal impacts, reduction inthe risk of head injuries was achieved by the introductionof the seat belt, the pretensioning retractor, the airbagand by the reduction of the intrusion of the steering wheelinto the passenger compartment by means of structuralimprovements [36]. This reduction in head injury riskhas now brought to prominence the importance of LE

injuries. LE injuries are second only to head injuries infrequency [27] and severity [15].

UK data reveals that lower limb injuries account for37% of all injuries sustained by front seat occupants infrontal, side and rear impacts [25]. According to Gibson[10] there were more LE injuries in 1990 as a result ofroad injury diagnosed in Australian hospitals than injuriesto any other body region. Several researchers [2, 19, 35]concluded that injuries of the ankle and foot were themost common types of injuries to the regions below theknee. Crandall and Martin [2] have stated that “Morethan half the more severe LE injuries occurring in frontal-crashes were of regions below the knee. The foot andankle constitute the most frequently injured regions with30% to 40% of severe LE injuries”.

Automobile crashes cause higher energy injuries thanslips and falls and therefore have poorer prognoses. LEinjuries resulting from motor vehicle crashes are the mostfrequent cause of permanent disability and impairment[4, 9, 18, 27]. These injuries are debilitating due to theloss of weight bearing function. Fractures of the knee andankle joints are far more difficult to treat than femoralshaft fractures [13].

Lower extremity injuries in side-impactvehicle crashes

N Arndt and R H GrzebietaDepartment of Civil Engineering, PO Box 60, Monash University, Vic., 3800, Australia

Abstract: Lower extremity (LE) fractures and dislocations resulting from car crashes are costly anddebilitating. In particular, occupant safety regulations for side-impact crashes are deficient in protectingthe knee, lower leg and ankle/foot. Hence further side-impact research is required to understandinjury mechanisms of these parts of the LE. In addition, side-impact dummies so far cannot measureforces and injury criteria in these lower parts of the LE. The aim of this paper is to identify andcharacterise LE fractures and dislocation injuries in side-imacts and propose some injury mechanisms.There appears to be some consensus on mechanisms describing how fractures and/or dislocations ofthe LE occur in frontal crashes. However, as far as the authors are aware, the mechanisms for side-impact have yet to be described and published. This paper presents some preliminary results of casestudies of LE injuries incurred in vehicles subjected to side-impact crashes in Australia between 1989and 2002. A summary of the findings to date is presented. Three basic injury mechanisms have beenidentified. They are: (1) Intrusion causing entrapment resulting from leg area volume reduction witha bending side-force, acting alone or together; (2) High-energy, side-impact, striking force resultingfrom being in direct contact with the struck portion of the vehicle; and (3) Inertial movement of thebody causing loading of the LE resulting from its interaction with the vehicle interior and whereintrusion is not the cause of the injury. This paper also proposes some injury mitigation strategies.

Keywords: Vehicle Crashworthiness, Side Impacts, Lower Limb Injuries, Lower Leg Fractures and Dislocations

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N Arndt and R H Grzebieta

IJCrash 2003 Vol. 8 No. 5 496 0255 © Woodhead Publishing Ltd

Miller et al. (1995, cited in Manning et al. [19]) reportedthat in the US in 1993, lower limb injuries amounted to$21.5 billion in passenger-vehicle occupant injury costs.Forty percent of the total annual motor vehicle traumatreatment costs in Maryland in 1994 were for LE injuries[18].

Gibson et al. [11] assessed that of the ten injury priorityareas relating to body regions, LE injuries came third inpriority in terms of harm after the head and thorax inAustralia. Morgan et al. [21] reported that injuries to thethigh have been reduced to around 10% but knee injuriesstill account for 20% to 30% of LE injuries in frontal-crashes.

The commonness and cost of injuries of these lower,weight-bearing segments indicate that attempts shouldbe made to reduce the harm associated with these injuries.In order for countermeasures to be developed for side-impact, it is important to understand the types andmechanisms of injury resulting from these types of crashes.

Side-impacts constitute between 17% and 38% ofcrashes in Australia, Europe and the USA [8, 16, 26, 17].Vehicle occupants are particularly vulnerable in side crashes[30]. They are the second most frequent injury causingcrash configuration after frontal-impacts [5]. Near-sideimpacts are 2.3 times more common than far-side impacts[12]. Stolinski et al. [30] reported more injuries to near-side occupants compared with far-side (60% near-sidecompared to 40% far-side).

In regards to LE injuries in side-impact crashes, littlework has been reported regarding statistical data andresearch work has yet to be described and published. Hence,this paper is attempting to provide some understandingof the injury mechanisms of lower extremity (LE) injuriesin both far and near-side impact crashes and, as a result,proposes some injury mitigating countermeasures. It isthe hope of the authors that the work described in thispaper may aid future developments in regulating LE injurycriteria in side-impact vehicle crashes.

RESEARCH OBJECTIVES

The following objectives were pursued when carrying outthe research presented in this paper.

• To identify any associations between occupant, crashand vehicle characteristics and fracture and dislocationmechanisms of the LE in side-impacts;

• To identify the types and mechanisms of fractures anddislocations of the Knee, Lower Leg and Ankle/Footoccurring in side-impacts.

SIDE-IMPACT SAMPLE STUDIED ANDMETHODOLOGY

Data used in this study have been taken from MonashUniversity Accident Research Centre’s (MUARC) twoCrashed Vehicle File (CVF) databases. The first CVF

database contains information about crashes collectedbetween 1989 and 1992 and the second CVF, from April2000 (CVF2000). A third database used in this study isthe ANCIS (Australian National Crash In-depth Study).The CVFs include information about real-world Australiancrashes where an occupant was killed or injured severelyenough to be hospitalised. The ANCIS database containsdata taken from injured occupants of crashes where thevehicle had to be towed from the crash site.

The databases contain details about the crash (includingdelta-V, angle of impact, location of impact, impactingobject/vehicle), vehicle (including mass, speed, make,model, year) and occupant (including the injuriessustained, the injury severity, location of injury) as wellas other variables. The information about the occupantsalso included seating position (driver or passenger), height,weight and age. The number of occupants in the vehicleswas also included.

For the CVFs, a nurse surveyed the hospitals for patientsand interviewed them. The nurse also contacted the coronerfor patients who were admitted to hospital or who died asa result of a vehicle crash. For the ANCIS data tow-truckcompanies notified MUARC for vehicles which weredamaged and towed from the crash site.

The occupants of the vehicles who were injured in thevehicles were contacted. After signing a consent form(stating that their vehicle and medical information can beused for research purposes but would remain confidential)their medical records were examined and their vehicleinspected. If the vehicle was involved in a two car crash,the other (bullet) vehicle was inspected whenever possible.

The injuries

A nurse at MUARC was responsible for interviewing anysurviving injured occupants and also examined all themedical records, including X-rays and reports. For fatalcrashes, the coroner’s reports were examined for thoseinjured, who died. The nurse described, recorded andcoded every injury using the Abbreviated Injury Scale(AIS, a threat to life scale from 0-6, 0 being least severe).Detailed descriptions of each injury were recorded andadded into the databases.

Out of the 24 crashes and 25 injured occupants, 19fracture or dislocation injuries were classified as havingseverity of AIS 3 and 18 injuries had a severity rating ofAIS 2. Figure 6 shows the AIS’ of the injuries of the knee,lower leg and ankle/foot regions for each case in the studyreported here. The details in the case report includedtype and location information about each fracture and/ordislocation. Fracture descriptions and diagrammatic vehicledamage descriptions were more detailed for the CVFs. Inthe ANCIS database, there were fewer crashes in which aLE fracture and/or dislocation was reported comparedto the CVF to date when this paper was written.

The possible fracture mechanisms were deduced froma detailed reconstruction of each crash using the range ofinformation available for each case and examination of

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Lower extremity injuries in side-impact vehicle crashes

© Woodhead Publishing Ltd 0255 497 IJCrash 2003 Vol. 8 No. 5

and side-impacts combined). The CVF2000 had 309injured occupants in side-impacts out of 1040 cases in theentire CVF2000, including frontal, rear and side-impacts.The entire ANCIS database was not available, however, 7side-impacts with 7 injured occupants were available foranalysis.

The number of crashes was graphed against the impactangles for each crash. The mass ratios were calculated for22 of the 24 crashes. Two crashes had unknown vehiclesrecorded so their mass ratios could not be calculated. Thenumber of crashes by the mass ratio of each crash wasplotted. The cumulative percent of LE injuries was plottedagainst maximum intrusion for the crashes. The delta-Vcumulative distribution was plotted for the crashes whereit could be calculated. The impact objects involved in theside-impact crashes analysed were also graphed. Thesewere also divided into specific injuries by impact object,showing the injury distribution for the knee, lower legand ankle/foot regions.

The occupants

For this study, only cases in which there was a LE fractureand/or dislocation of the knee, lower leg or ankle/footincurred in a side-impact were identified and analysed.Only front seat occupants were investigated in this studyas the only rear seat passenger with a LE fracture ordislocation was lying down (not in a typical position) andthus not included in this study. If one person had morethan one fracture and/or dislocation of the LE, they werecounted as one case (occupant). (Four people had lowerleg and ankle/foot fractures/dislocations and one had kneeand lower leg fractures/dislocations. These cases were allresulting from two-vehicle crashes).

Twenty-four crashes, 25 injured occupants sustaining37 lower extremity fractures and/or dislocations of oneor more of the knee, lower leg and ankle/foot regionswere analysed. There were 20 near-side cases (injuredoccupants) and 4 far-side cases. For near-side impactsthere were 33 injuries incurred by 20 occupants. Therewere 4 far-side occupants injured with one LE injuryeach, all in the CVF. There was only one crash in which

the detailed records of the injuries including x-ray reportswhich the nurse in the study had examined. Anunderstanding of biomechanics, anatomy, physics andengineering was utilised. The number of injuries for eachLE body region analysed was graphed. The number ofinjuries by the identified injury mechanisms was alsographed to see the proportions of each type of injurymechanism for the knee, lower leg and ankle/foot, andfor the LE in general. The injury severity distributionwas also plotted.

The crashed vehicles

The information about the crashed vehicles includedphotographs, diagrams of the intrusions inside and outsidethe vehicles and the Collision Deformation Codes usedto give information about the location, extent and angleof impact. The vehicle was also inspected by an engineerfor interaction of the occupant with the vehicle, the contactsources of injury (where there was visible deformation ofthe vehicle caused by contact of the occupant with it).Details were noted and recorded.

The masses of vehicles in this study were also recordedand classified into under 900 kg for small vehicles, 900-1200 kg for medium vehicles and over 1200 kg for largevehicles. The near-side sample comprised the followingnumber of cars: 6 small, 5 medium and 9 large. The far-side sample comprised 2 small and 2 medium sized cars.

The crashes

The three databases analysed in this study included twoCVFs and the ANCIS database. The earlier two (CVFs)were data which was collected from crashes in which anoccupant was severely injured enough to be hospitalisedor killed. The ANCIS database was collected later, andthe criteria for which crashes were included were that thecrashes had to be severe enough to require vehicle towingfrom the crash scene. The inspection engineer examinedthe crashed vehicle and in the ANCIS cases the crash siteas well. Intrusion was measured as well as crush, frominside and outside the vehicle. He reported without havingknowledge of the injuries, any possible contact sources ofinjury. The CRASH3 program was then used to calculatedelta-V in cases where it was possible to do so. The vehiclein which the injured occupant was situated was denotedas vehicle A and the impacting vehicle, vehicle B. Wherepossible, vehicle B was also inspected. Any injuredoccupants in vehicle B were not included in the study.

The crash’s principle direction of force, PDOF (impactangle) was determined from the crush deformation patternby the engineer. The impact angle, θ is shown in Figure 1.It is defined as the angle clockwise from the 12 o’clockposition around to the principle direction of impactingforce.

All side-impact cases were available for analysis for theCVF database (1989–1992) (which comprised 198 side-impacts and 234 injured occupants in the entire databaseof 501 crashes and 606 injured occupants in frontal, rear

Figure 1 Impact angle (θ) definition.

Crush profile

-near-sideoccupant

θ

PDOF

θ - angle ofimpact

×

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fractures and/or dislocations was 41 years as shown inFigure 2. There was a fairly evenly distributed range ofages of people with a LE fracture and/or dislocation inside-impact crashes.

GenderThere were more females injured with a fracture and/ordislocation of their knee, lower leg or ankle/foot in theside-impact crashes analysed (15 females, 60%) comparedto males (10 males, 40%). In near-side crashes 10 femalesand 10 males, and in far-side crashes, 5 females and nomales incurred knee, lower leg or ankle/foot fracturesand/or dislocations. Every front left passenger (FLP)injured except one was female (n = 7 females, 1 male).

Crash and vehicle factors which affect LE injury inside-impact

Impact angleFigure 3 indicates the distribution of impact angles for allLE fracture and/or dislocation cases studied (knee, lowerleg and ankle/foot) for near-side (15°–80° and 90°–120°)and far-side impacts (270°–315°). It shows that mostinjuries occurred at impact angles less than 90°, where

both the driver and front left passenger were injured.This was in a severe collision with a pole and both occupantswere unrestrained. There were 17 drivers and 8 front leftpassengers in this study. Three of the 25 people wereunbelted. The age distribution of the injured occupantswas graphed.

So far there are not enough data for meaningful statisticalanalyses, however, trends are discernible and presented here.

RESULTS

This section is divided into the effect of crash char-acteristics on LE injury and the case study analysis inwhich the preliminary findings and the identifiedfundamental fracture/dislocation mechanisms aredescribed. Many factors may effect the risk of LE fracturesand dislocations in side-impacts. Not all can be examinedhere so a few in which some trends were discernible havebeen reported here.

Occupant factors which affect LE injury in side-impact

Injured occupant ageThe median age for those in the databases, with LE

Figure 2 Cumulative percent of injured occupant age (with a LE fracture and/or dislocation).

Cumulative distribution of occupant age

15 20 25 30 35 40 45 50 55 60 65 70

Occupant age

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15–80 90–120 270–315 (Farside)

Impact angle (degrees)

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Figure 3 Distribution of impact angles for all LE fracture and/or dislocation cases studied (knee, lower leg and ankle/foot) for near-side (15°–80° and 90°–120°) and far-side (270°–315°) impacts (n = 37 injuries).

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there is a frontal component of force, and where it waslikely for some forward displacement of the occupant insidethe vehicle to occur. LE injuries tend to occur morefrequently in near-side crashes [12], [30]. Six crashes (25%)of those analysed were pure near-side impacts (90°). Therewere 21 near-side crashes and 4 far-side in the combineddata. The impact angles observed and their frequencies inthe sample studied included: 1*15°, 3*30°, 5*45°, 3*60°,1*80°, 6*90°, 1*100° and 1*120° for near-side and 2*270°,1*285° and 1*315° for far-side crashes

When examining the data, 16.7% of crashes were far-side compared with 83.3% near-side. The 4 far-side injurieswere sustained in crashes with poles/trees except for one,which was sustained in a crash with no intrusion.

Figure 4 shows that lower leg and ankle/foot injuriesoccurred mostly in crashes with low impact angles (inoblique angled crashes). Fewer lower leg and ankle/footinjuries occurred in 90°–120° (near-perpendicular) crashes.Knee injuries were evenly distributed in crashes with allimpact angles in this study, however numbers are small.More cases are required for the identified trends to beverified.

Mass ratioFigure 5 displays the mass ratios (target vehicle mass/bullet vehicle mass) for the side-impact crashes analysedwhere there was a knee, lower leg or ankle/foot fractureand/or dislocation. Most injuries occurred in crashes wherethe mass ratio of the target vehicle was less than 1.0, i.e.where the target vehicle had a smaller mass than the bulletvehicle or where the target vehicle impacts with a fixedobject (most often a pole/tree), as expected.

Frequency of injuries by LE regionFigure 6 shows that there were 16 ankle/foot fractures,15 lower leg fractures/dislocations and 6 knee fractures/dislocations. All the knee fractures/dislocations observedwere in the older database (CVFs) which comprised crashesof older vehicles. Most ankle/foot fractures occurred inthe newest database (ANCIS). There were more lower legfractures/dislocations in the CVF than the ANCIS studybut there were also more cases analysed in the CVF databasethan those in the ANCIS database. The proportions oflower leg fractures/dislocations of all LE fractures/dislocations were the same in both databases. However,

Figure 4 No. of injuries of the knee, lower leg and ankle/foot by impact angle.

No. of Injuries by impact angle

15–80 90–120 270–315

Impact angle (degrees)

12

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No.

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KneeLower legAnkle/Foot

Figure 5 Mass Ratio (target vehicle mass/bullet vehicle mass) of impacts for cases in which there was a knee, lower leg orankle/foot fracture and/or dislocation (n = 22 crashes, 2 crashes had unknown bullet vehicles so mass ratio could not becalculated).

No. of crashes by mass ratio category

<1.0 1 >1.0Mass ratio category

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only small numbers of data were analysed. In the samplestudied the breakdown of the data were; knee cases: 6CVF, 0 ANCIS, lower leg cases: 9 CVF and 4 ANCIS andankle/foot cases: 5 CVF and 5 ANCIS.

Injury severity (AIS)Figure 7 shows the frequency of injury by injury severityclassified according to the AIS. This chart shows thatmost injuries were of the ankle/foot and these were moreof the AIS 2 severity (11 injuries), being less serious thanAIS 3 (7 injuries). The second most common injury wasof the lower leg of the AIS 3 severity (8 injuries). Thiswas followed by lower leg injuries of the AIS 2 severity (7injuries). The least common injury type was AIS 2 kneeinjuries (2 injuries) and AIS 3 knee injuries (4 injuries).

Maximum intrusionFigure 8 shows the cumulative percentage of fracturesand/or dislocations of the knee, lower leg and ankle/footincurred in side-impacts. This graph shows that 50% offractures and/or dislocations occurred at intrusion levels

greater than 38.5 cm and 20% occurred at intrusions greaterthan 61 cm. In a small percentage of cases (8.3%) therewas injury without intrusion (2 crashes).

Delta-VThe collision delta-V, reported in km/h (collision severity)was recorded for 16 out of the 24 crashes analysed (69.5% of crashes). Figure 9 shows the cumulative percent ofcases with a LE fracture and/or dislocation by delta-V.The delta-V values were calculated using the CRASH-3computer program. Based on these cases 80 % of caseshad delta-Vs under 42 km/h and half the cases had delta-Vs under 33 km/h. These speeds are relatively low yetcause significant injury.

Impact objectFigures 10 and 11 show the types of impact objects thatwere involved in the crashes in which an occupant sustaineda LE fracture and/or dislocation. Of the 24 crashes therewere 9 with poles or trees (33.3%), 13 with other passengervehicles (54.2%) and 2 with trucks/buses (8.3%). Of the

Figure 6 Number of fractures/dislocation injuries by LE body region for each of the knee, lower leg or ankle/footinjuries (n = 37 injuries).

Knee Lower legLE region

Ankle/foot

No. of injuries by LE region16

14

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KneeLower legAnkle/foot

No. of injuries by AIS10

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AIS2 3

Figure 7 Frequency of injury by AIS for the knee, lower leg and ankle/foot.

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4 far-side crashes, there were 2 pole/tree crashes (50%)and two car-to-car crashes (50%). There were 21 fractures/dislocations in 13 two-vehicle crashes, 13 fractures/dislocations in 8 vehicle-pole/ tree crashes and 3 fractures/dislocations in 2 collisions with a truck or bus. Figure 10also shows the number of injuries sustained in each type

of crash. These are in relative proportion to the numberof crashes in each category.

Table 1 shows that there were very few crashes withtrucks/buses in the data analysed. The percentages inTable 1 were calculated from Figure 11 for car, pole/treeand truck/bus crashes

Cumulative % fractures/dislocations by maximum intrusion

0 20 40 60 80 >80Maximum intrusion (cm)

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/dis

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Figure 8 Graph showing cumulative percentage of fractures and/or dislocations incurred to the knee, lower leg andankle/foot from all side-impacts in this study (n = 37 injuries).

Figure 9 Cumulative percent of cases with a LE fracture and/or dislocation incurred by Delta-V (n = 16 crashes).

Cumulative % cases by Delta-V(n=16)100

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15 20 25 30 35 40 45 50 55

Delta-V (km/h)

No. of injuries (n=37)

No. of crashes (n=24)

Number of fractures/dislocations by impact object

Car Pole/TreeImpact object

Truck/Bus

24

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Figure 10 No. of fractures/dislocations by impact object.

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(1) Intrusion causing entrapment resulting from leg areavolume reduction with bending side-force, acting aloneor together; This mechanism was identified as occurringpredominantly to near-side occupants of obliqueangled, 15°–80° impacts.

(2) High-energy, side-impact, striking force resulting frombeing in direct contact with the struck portion of thevehicle. This mechanism was identified as occurringpredominantly to near-side occupants where thestriking vehicle hits the struck vehicle at 90°–120°,i.e. the striking vehicle is perpendicular to the struckvehicle (T bone crash).

(3) Inertial movement of the body causing loading of the LEresulting from its interaction with the vehicle interiorand where intrusion is not the cause of injury. Thismechanism was identified as occurring predominantlyto far-side occupants i.e. in 270°–315° impacts.However, it can also occur in near-side oblique angledcrashes (15°–80°) where the occupant slides forwardand sideways during deceleration and their LE strikesthe vehicle interior. Likewise wedge entrapment canoccur because of the (design) geometry of the vehicleinterior, i.e. the lower extremity wedges into anincreasingly confining space.

Figures 12 and 13 show the proportions of injuries causedby the three different identified mechanisms. Theproportions of injuries as seen in Figure 3 is similar tothose in Figure 12, indicating the mechanisms of fractureand/or dislocation are somewhat related to the angle ofthe crash. Most injuries were caused by Mechanism (1),less by Mechanism (2) and least by Mechanism (3).Mechanism (1) occurs mainly in near-side oblique angledcrashes, Mechanism (2) in near-side perpendicular crashesand Mechanism (3) mainly in far-side crashes.

Figure 13 shows that most ankle/foot injuries wereincurred by Mechanism (1) (compression and bending inoblique angled crashes), lower leg injuries by Mechanism(2) (high-energy side-impact forces causing bending) and

Figure 11 Number of fractures/dislocation injuries by impact object for each of the knee, lower leg or ankle/foot injuries(n = 37 injuries, from 24 crashes).

KneeLegAnkle/foot

TruckPoleImpact object

Circle

No. of fracture/dislocations by impact angle for Knee,Lower Leg and Ankle/Foot (n=37 fractures/dislocations)

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Table 1 Number of injuries of the LE by impact object

Impact No of injuries Knee Lower/ Ankle/object for each impact leg foot

object

Car 21 2 (10%) 10 (48%) 9 (43%)Pole/Tree 13 4 (31%) 4 (31%) 5 (38%)Truck/Bus 3 0 (0%) 1 (33%) 2 (66%)

The pole/tree crashes can be compared with the car-to-car crashes as follows: There were three times as manyknee injuries in pole/tree crashes compared with car-to-car crashes (31% : 10%) whereas lower leg fractures weremore common as a result of car-to-car crashes as comparedwith car-to-pole crashes (48% : 31%). Percentages ofankle/foot injuries were similar as a result of car-to-carcrashes and for car-to-pole crashes. The numbers of truck/bus collisions was too small to consider in this regard.More cases are required to verify the observed trends.

Side-impact injury mechanism findings

In order to understand how LE injuries are occurring inside-impact crashes, a detailed case-by-case study wascarried out. Three fundamental fracture and/or dislocationmechanisms were identified and are proposed here afterdetailed examination of crash and medical records andreconstruction of 24 side-impact crashes (25 injury cases).

This paper outlines some of the preliminary findingsfrom the analysis. It was felt that similar to the statisticalanalysis some trends were observable and worthy ofreporting. The three fracture and/or dislocation injurymechanisms proposed are yet to be verified using crashsimulation programs and crash tests where occupantkinematics, forces, moments and accelerations can bemonitored and compared to published injury tolerancedata.

The three fundamental mechanism categories identifiedfrom this study are:

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knee injuries by Mechanism (2) (high-energy side impactcontact forces at knee). There were some lower leg injuriesby Mechanism (1) as expected in oblique angled crasheswhere compression and entrapment can occur, and someknee injuries caused by Mechanism (3) where the kneeimpacts with the interior of the vehicle in far-sidecrashes.

Fundamental Mechanism (1): Intrusion causingentrapment resulting from leg area volume reductionwith bending side-force, acting alone or together

This fundamental mechanism is caused by toepan intrusionwith the knee being trapped at the dash. It includes threepossible loading types: axial compression, bending from aside force and torsion. Axial compression, bending and/or torsion can occur together or alone.

Axial compression (P) and bending side force (S)This mechanism was observed in near-side occupants, atimpact angles between 15° and 80°. Figures 14 and 15show how such an impact can cause axial compression (P)in the lower leg and ankle from toepan intrusion withknee trapping at the dash, further exacerbated by a forward

component of force. A side force (S) can occur in such acrash when there is intrusion of the vehicle’s side structuresuch as the door or lower portion of the A-pillar. Themaximum intrusions observed in these cases ranged from10 cm to 85 cm.

Knee ligament disruption, tibial plateau fractures,fibular/tibial shaft fractures, malleolar fractures and pilonfractures were noted. In particular, one knee, five lower

No. of fractures/dislocations by injury mechanism

Mech 1 Mech 2Mechanism type

Mech 3

20

16

12

8

4

0

No

of f

ract

ures

/dis

loca

tions

Figure 12 Number of fracture and/or dislocations (knee, lower leg and ankle/foot) for Mechanism 1, 2 and 3 (n = 37injuries, 25 injured occupants, 24 crashes).

Figure 13 Frequency of injury by injury mechanism for the knee, lower leg and ankle/foot.

Mech 1 Mech 2Mechanism type

Mech 3

16

14

12

10

8

6

4

2

0

No.

of

inju

ries

KneeLower legAnkle/foot

No. of injuries by mechanism of injury

Driver’s side–driver

θ-angle of impact

θ

Crushprofile

Axial compression (p)along lower leg from floorand toepan intrusion andknee entrapment.

Toe pan intrusion

Side force (S) (lower‘A’ pillar door and sidepanel intrusion)

Knee entrapment atdash

Figure 14 Diagram showing how the LE is injured byMechanism (1).

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The limbs are usually free to move, i.e. entrapment doesnot occur. There were no ankle/foot injuries observed inthis mechanism category.

The injuries caused by such a high energy, impulseforce included tearing of the ligaments of the knee leadingto dislocation of the joint, indented femoral condyle, fibularhead fracture and tibial plateau fracture. The lower leginjuries included comminuted fractures of the tibia/fibula.

Fundamental Mechanism (3): inertial movement of thebody causing loading of the LE resulting from itsinteraction with the vehicle interior and where intrusionis not the cause of injury.

In this mechanism the occupant is thrown against thevehicle’s interior as a result of inertia loading when thevehicle suddenly decelerates. This mechanism wasidentified as occurring predominantly to far-side drivers,involving impact angles between 270° and 315°. However,it can also occur to near-side drivers in oblique angledcrashes (15°–80°) where the occupant slides forward duringdeceleration and their LE strikes the vehicle interior butthere is no intrusion or high-energy contact force. Thereare two main mechanisms involving such inertia loading.One is where the knee impacts internal parts of the vehiclestructure, i.e. steering column, centre console and dash.The other is where the foot is inverted/everted as it slipsoff a pedal. Both knee and foot cases were without intrusion.

Impact with internal parts of the vehicle structureDuring deceleration, the driver’s knees swing towards thestruck side. The right knee hits the steering column anddash as shown in Figures 18 and 19 and the left knee thecentre console and dash. Injuries incurred to the kneeincluded tibial plateau fracture and ruptured cruciateligaments leading to dislocation. The steering column anddash apply significant forces perpendicular to the proximaltibia (knee end), sometimes leading to shearing of the

leg and four ankle/foot fractures and/or dislocation caseswere identified under this category.

Torsional loadingIntrusion of the footwell/toepan area was also associatedwith spiral fractures of the distal tibia/fibula in thismechanism category. Internal rotation of the foot (awayfrom the struck side of the vehicle) caused by toepanintrusion combined with rotation of the knee and bodytowards the struck side occurred. This mechanism isillustrated in Figure 16. The spiral fractures observed inthe CVF generally occurred at an impact angle of 45°.Maximum intrusions of the toepan and the lower A-pillarwere both of the order of 45 cm.

Fundamental Mechanism (2): High-energy, side-impact,striking force resulting from being in direct contact withthe struck portion of the vehicle.

This mechanism was observed in 3 knee and 4 lower legfracture and/or dislocation cases. It was identified asoccurring predominantly to near-side occupants wherethe striking vehicle, often with greater mass than the onehit, is perpendicular to the struck vehicle (T bone crash)as shown in Figure 17. Such loads can also occur whenthere is an impact with intruding objects such as a pole ortree. In this mechanism, there is a direct impact loadtransmitted to the occupant from the side, often by theencroaching door or A-Pillar.

A high-energy impulse force is directly transmitted tothe knee or lower leg, which is in direct contact with thestruck portion of the car interior. The maximum intrusionsin these cases ranged between 35 cm and 80 cm. An exampleof this mechanism is shown in Figure 17 where, in thiscase, it is a passenger’s knee being injured by the intrudingdoor and subsequently deformed dash. The broken lineindicates how the leg can move immediately after impact.

SL

P

PToe pan and floor intrusioncausing axial compressionalong tibia/fibula

Side force caused bylower A pillar and/ordoor intrusion

Passenger’s left leg ordriver’s right leg

Vertical component of dash forcecaused by entrapment

Figure 15 Diagram showing how the LE is fractured byMechanism (1).

Front θ -angle of impact 45°

- driver

Crush profile Knee rotation with bodymoving towards struck side

Internal rotation &dorsiflexion fo footfrom toepan intrusion

Knee

Foot

Person’s body rotatestowards struck side

Before

After

Torsion in lower leg(tibia/fibula) causes spiralfractures

θ

Figure 16 Diagram showing how spiral fractures can occurin the tibia and fibula in mechanism (1).

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tibial plateau. In the case of a passenger the right kneecan be thrown against the centre console and in somecases (non-intrusion) entrapment can occur when the kneeis thrown sideways and upwards wedging under the dash.

Foot slip-off-pedal mechanismIn vehicle crashes, the ankles and feet can be injured.Pedals have been known to be a contributor to the injuriesincurred [2, 14, 22, 27, 30, 31]. In the data analysed,interaction with pedals was noted as injury sources in theside-impacts. The types of fractures observed help indicatehow the injuries occurred. In the data examined, manyfractures of the ankles were of the malleoli. Inversion andeversion movements are known to cause these types of

fractures. These movements can occur either from slippingoff pedals or from an intruding footwell deforming underthe foot.

There are a number of ways in which left and rightankles and feet can be injured in side-impacts. The leftfoot can slip off the clutch towards the struck side as aresult of vehicle deceleration, and hence invert, leadingto fractures of the ankle (malleoli) as indicated in Figure20. There can also be inversion of the left foot as the bodyrotates to the left. A similar mechanism can occur withthe right foot as it slips off the brake pedal, leading toeversion injuries. In bending inversion, there is tension atthe lateral malleolus (distal fibula) and compression ofthe medial malleolus (distal tibia).

Figure 17 Diagram showing how a 270° impact force causes intrusion of the door and dash into the occupantcompartment resulting in knee fractures, by Mechanism (2). (Note: the knee is in direct contact with the portion of thestruck door and subsequently intruding dash immediately on impact).

θ Door

dash

After

Before

θ - angle of impact = 270°

- front left passenger

Struck Side

Force from impactwith centre console& dash (left knee)

Knees movetowards struckside

Force from impactwith dash andsteering column(right knee)

Before

After

Figure 18 Diagram showing how in a far-side crash for a driver the knees can be fractured and/or dislocated by, forexample, the right knee hitting the steering column and left knee hitting the centre console in Mechanism (3).

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DISCUSSION

Occupant factors which affect LE fracture and/ordislocation

Some trends were identified from analysis of the factorsin the previous results section. However, in order to fullyverify these trends, more data is required to be collectedand analysed. The factors analysed appear to have effectson the LE fractures and dislocations incurred in this side-impact study.

The following is a discussion of some of the findingsand their relevance to other research work.

AgeThe median age for those injured with a LE fractureand/or dislocation in side-impacts for the crashes analysedfrom the CVF and ANCIS databases was 41 years. Therewere slightly more people in the age group between 45

and 50 years of age than any other age group analysed. Inother words, older people more prone to injuries thanyoung fit people are over represented in the data. Theproperties of the padding of the interior of the vehiclemay have to be altered in order to protect the LE bonesfrom injury if people of an older age group are at mostrisk of injury.

Gender of driversIn this study females were more commonly driving smallcars and medium cars and males more commonly drovelarge cars. This is similar to the findings of others (Tingvall(1990), cited in [12]) who found women in general drivesmaller cars than men. In their study 45% of women and51% of men drove cars in the weight range 950-1250 kg.For cars below 950 kg 33% of drivers were women and19% were men and for larger cars 23% were women and30% were men.

θ

Crush profile

θ° - angle

- driver

Medial side of leg

Femur

Movement of right leg toleft towards struck sideresulting in impact withsteering column.

Tibia

Fibula

Lateral side of leg

Tibial plateaufracture

Load fromsteering column

Axial componentforce from dash

Figure 19 Diagram showing how the tibial plateau can shear in a far-side crash. Also showing how the femoral condylecan fracture from dash force and shear from the steering column in Mechanism (3).

Figure 20 Tension fractures at the lateral malleolus (distal fibula) and compression at the medial malleolus (distal tibial)by inversion movements as seen in Mechanism (3) and (1).

Fibula

Lateralmalleolus

Talus

Medialmalleolus

Tibia

Tension infibula

Talus moves right

Compression intibia

Inversion (of left foot) - malleoli fractures

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Crash and vehicle factors which affect LE fractureand/or dislocation

Impact angleIn this study, most crashes in which a LE fracture and/ordislocation occurred had impact angles between 15° and80°. These angles correlated with Mechanism (1) wherethe injuries were caused predominantly by entrapmentcausing compression in the LE and/or bending.

In a study by Stolinski et al. [30] most cases also hadimpact angles predominantly with frontal components offorce (<90°). Even though the same database was used(CVF 1989–1992) different cases were looked at byStolinski et al. as they examined all injuries and far-sidecases only.

Mass ratioMost crashes in this study had mass ratios less than 1.0.This is where the bullet vehicle has greater mass than thetarget vehicle. In such crashes one would expect injury tobe more likely where intrusions and delta-Vs wouldgenerally be greater.

The mass ratio findings from this study correlatewith the mass ratio trend found by Stolinski et al. [30]where “the distribution is skewed towards low massratios”.

Frequency of injury by LE regionThere were no knee injuries observed in the ANCISdatabase. The CVF is a database, which is comprised ofcrashes of older vehicles. The ANCIS database, withpredominantly newer vehicles analysed, possibly reflectsdesigns where the shape and padding of the dash weredifferent from those of older vehicles. These newer carsmay have designs where the knee is deflected away fromthe dash to prevent entrapment. Even though the datashow more ankle/foot fractures to have occurred in thenewer database, and more lower leg injuries in the CVF,more data would have to be analysed in order for anyconclusions to be drawn as to the types of injuries innewer and older vehicles.

The data comprised the following fractures/dislocations:16.2% knee, 40.5% lower leg and 43% ankle/foot.

Morgan et al. [21] reported that injuries to the kneeaccount for 20% to 30% of LE injuries in frontal-crashes.This is much higher than those in side-impacts. The reasonfor this could be due to the knee hitting the dash in afrontal impact being quite common. In side-impacts, theknee is more likely to be injured from impact with thedoor when it intrudes.

Thomas and Bradford (1989, cited in [34] (studying)side-impacts, reported injuries to the lower legs comprised49% of LE injuries. This is of the same order as injuriesto the lower leg reported in this paper.

However, injuries of the ankle/foot are common inmost studies. Crandall and Martin [2] found from frontalstudies that the foot and ankle constitute the mostfrequently injured regions with 30% to 40% of severeLE injuries. This also is similar to the results reported in

this paper with ankle/foot injuries being the most common.Ward et al. (1992) [35] in their frontal study of impactsurvivors reported that 31% of LE injuries occurred atthe ankle. Begeman et al. [1] also reported ankle fracturesto be the most common intra-articular fracture of a weight-bearing joint.

However, significant conclusions cannot be drawn fromthe results of this analysis, as there is an insufficient numberof cases.

Injury severityThe distribution of the severities of the injuries in thesample is likely to be due to the different injury mechanismsin the crashes and crash characteristics such as the impactangle. The greater number of ankle/foot injuries is probablydue to the greater number of oblique angled crashes andgreater number of crashes exhibiting the first injurymechanism, where intrusion resulted in compressive andbending forces being applied to the feet. The number ofAIS 2 and 3 lower leg injuries are likely to be caused byMechanism (2) in which a high-energy side-force causesfracture, or in crashes with Mechanism (1) in whichcompressive and bending forces cause the fractures. Thelarger number of AIS 3 knee injuries is the result ofMechanism (1) and (2) crashes where the compressiveand contact loads were higher than those resulting frominertia loads in Mechanism (3). AIS 2 injuries occurredin Mechanism (3) crashes, from impacts with the interiorof the vehicle.

Maximum intrusionIn this study, 50% of the injuries occurred at intrusionsbelow 38.5 cm and 20% at intrusions greater than 61 cm.As most cases were near-side impacts, one would expectedthat many of the injuries would have occurred in crasheswith lower intrusions and where the occupant injuredwas close to the intruding vehicle part. The cases in whichinjury occurred without any intrusion evident (8.3% ofcases analysed), were caused by inertial forces where theoccupant hit the vehicle interior.

In the study by Stolinski et al. [30] 20% of cases hadno intrusion. However, it is expected that, in a purely far-side sample, inertia would have been the cause of most ofthe injuries sustained without intrusion. When consideringthe cases in which intrusion was associated with injury, ingeneral, the findings of Stolinski et al. [30] were similarto those in the study reported in the results section.Stolinski et al. [30] reported that 50% of injuries occurredwith intrusions of 40 cm and 20% greater than 62.5 cm (n= 45, all injuries).

Delta-VIn half the cases examined in this paper, the delta-Vswere less than 33 km/h whereas in 80% of the cases, thedelta-Vs were less than 42 km/h. In a study of side-impactsby Thomas and Bradford (1989, cited in [34]) the mediandelta-V was 31 km/h for seriously injured near-sidesurvivors and 43 km/h for fatalities in car-to-car crashes.Cesari and Dolivet (1989, cited in [34]) found similar

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results in a side-impact study, where the mean delta-V forAIS 3-5 injuries of survivors was 30 km/h. Mackay (1989,cited in [34]) described typical delta-V resulting in AIS3+injuries to be in the region of 30 km/h with the 75th %ileat 38 km/h. These values of delta-V as found by otherresearchers concur with the values recorded in this study.In the study of all side-impacts by Fildes et al. (2001) [7]the median range of delta-Vs was between 25 to 30 km/h (pole and car-to-car crashes) and in 67% of pole crashesthe delta-Vs were less than 40 km/h.

In half the cases in the far-side impact study by Stolinskiet al.’s (1998) [30] the delta-Vs were less than 40 km/h.In eighty percent of cases, the delta-Vs were less than 60km/h. The values of delta-V for [30] far-side studies weregreater than the values for this study. This suggests thatgreater delta-Vs are required to injure occupants on thefar-side than near-side.

The delta-Vs in the side-impacts in this study werehigher than those in Fildes et al.’s (1997) [6] frontal impacts.This trend is similar to that of intrusion, that being:intrusion values are lower in frontal impacts than in theside-impacts. However it could also be that in “all injury”studies for frontal impacts, lower delta-Vs are required tocause an injury than when only LE fractures/dislocationsas examined, as in this study. No other studies of side-impacts could be found that reported delta-Vs associatedwith LE fractures/dislocations.

Impact objectIn this study, there were more car-to-car crashes (54.2%),followed by pole-to-car crashes (33.3%) and in the smallestgroup truck-to-car crashes (8.3%). The EuropeanTransport Safety Council (1993) [5] reported that in theirstudy, two-car crashes were the most common type ofcrash in the USA. These are similar to the findings ofStolinski et al. (1998) [30] who classified poles and treesseparately and 4WDs separate from cars. However, mostcrashes were with other cars and collisions with trees andpoles were less common. In a study of Australian crashesin 1990, by Ginpil et al. (1990, cited in [28]) 40% of side-impact crashes resulted from a crash with a fixed objectsuch as a tree or pole rather than being hit by anothervehicle. This figure is close to but slightly higher thanthat found in this study. This could be as Ginpil et al.’s(1990) study was for all injuries as compared to only LEfractures and dislocations considered in this study. Somepole crashes result in injuries which are not related to legfractures/dislocations. Thomas and Bradford (1989, citedin [34]) found 31% of near-side occupants with seriousinjuries had experienced a tree or pole crash. This is similarto 33% as found in this study. Most injuries in this studywere to near-side occupants.

Mechanisms of injury and contact sources

Identified in this study were mechanisms of injuryincluding axial loading, bending, torsion of long bonesand dorsiflexion (Mechanism (1)), inversion/eversion (in

Mechanism (1) and (3) and inertial injuries such as theknee impacting the steering column and centre consoleand dash and feet rolling off the pedals (Mechanism (3)).Other researchers have also reported these as occurringin crashes. The following findings of researchers relate tothe findings of this study.

In Mechanism (1) contact of the knee with the dashand feet with the toepan as well as LE contact with thedoor and A-pillar (causing bending) were reported asmechanisms of injury in this study. The mechanismincorporated axial loading from entrapment at the dashand toepan intrusion, with or without a bending side-force. This type of mechanism has been reported by severalresearchers.

In separate studies by Manning et al. [19] and Tamuraet al. [33], axial compression with bending caused lowerleg injuries. They showed how the tibia could sustain ashaft fracture during a frontal car crash. They stated thatit can occur when the proximal end (knee end) of the tibiais constrained while the distal end (ankle end) of the tibiais loaded as a result of excessive toeboard (toepan) intrusion.This loading mechanism could induce bending of the tibiaalong its natural bowing curvature and make it vulnerableto fracture [33]. A similar mechanism was also reportedby States et al. (1986) in their study of frontal impacts,where the occupant’s knee was trapped at the instrumentpanel and the foot was fractured when the toepan waselevated under it. This mechanism is common and likelyto cause axial loading in the tibia and ankle. Nagel et al.[23] also stated in their study that lower leg entrapmentbetween the dash and the floor/toepan is a commonlyreported lower leg fracture mechanism. Manning et al.[19] similarly reported in their study that in half the below-knee injuries in their study, entrapment between the floorand facia (dash) occurred.

Fildes et al. [6] in their study reported that lower legfractures could be caused by perpendicular loading andtorsion from floor and toepan interaction. Thesemechanisms were also reported when there was contactwith the instrument panel. In this study, in Mechanism(1), these were also identified.

Most tibial/fibular fractures in a study by Dischingeret al. [4] involved axial loading and eversion.

In Mechanism (2), the sources of injury in this studywere reported as including the door, A-pillar, dash andexternal object such as a tree/pole. In the study by Fildeset al. [7] the main causes of injury in side-impacts werecontact with the door, an external impacting object or, toa lesser extent, the dashboard. Again, there was similaritybetween the contact sources in this study and Fildes’ study.Strother et al.’s [32] study reported the following sourcesas injury mechanisms, as also found in the study reportedin the results section: contacting the (deformed orundeformed) side structure of the occupied vehicle; directlycontacting the striking object or vehicle; and beingcompressed between the impacted side structure and otherparts of the occupant compartment.

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In Mechanism (3) in this study, inertial forces were acause of injury. Stolinski et al. [29] also reported inertialforces and dynamic contact with interior vehicle com-ponents caused injury in their far-side study.

Similar to the findings in this research, Stolinski et al.[30] reported the centre console, steering wheel and steeringcolumn to be sources of LE injury in far-side crashes.Knee interaction with the dash combined with inertialforce can contribute to knee injuries according to Manninget al. [19].

Nagel et al. [23] reported tibial plateau fracturesoccurring as a result of a perpendicular force being appliedto the proximal tibia. They reported these injuries occurredwhen the knee impacted a rigid steering column supportor an instrument. This occurred in one of the far-sidecases in this study. This type of injury can also occur in afrontal crash, as reported by Fildes et al. [6] where theyreported the mechanism of fracture of the knee to becaused by perpendicular loading from steering columncontact.

In Mechanisms (1) and (3) injury to the ankles hasbeen demonstrated to have been caused by inversion/eversion (from toepan intrusion in Mechanism (1), andfrom interaction with pedals, and from the feet slippingoff the pedals in Mechanism (3)). In general, abductionand adduction (eversion and inversion) are the mostfrequently reported causes of ankle fractures. Crawford-Adams [3] and Moore [20] reported these movements,which can occur in side-impacts, to cause malleolarfractures. Begeman et al. [1] found in laboratory tests ofthe ankle/foot complex that the most common injurieswere of the malleoli and feet. They reported inversion/eversion and excessive dorsiflexion to be the most commonmechanisms of injury as a result of toeboard intrusion.

Interaction with pedals, as can occur in Mechanism(3), was reported as an ankle/foot fracture mechanism byCrandall et al. [2], Morris et al. [22] and Manning et al.[19]. Manning et al. reported 34% of malleolar fracturesto be caused by the foot being on the pedal on impact andthen rolling off the pedal to one side due to the crashpulse.

Possible LE injury countermeasures

Analysis of the data and classification of the observed LEinjuries into the three proposed mechanisms has alloweddifferent injury-mitigating countermeasures to beconsidered. However, as in the case of identifying theinjury mechanisms, these strategies are only preliminarysuggestions and require more research, such as crash tests,to determine their effectiveness.

SeatbeltsIn the case of frontal impacts, belts reduce upper bodyinjuries and when combined with airbag use further suchinjuries are prevented. However, belts do not have mucheffect in preventing LE injuries in near-side impacts [2].Their main role is frontal restraint and preventing ejection[12, 30]. Belts can reduce pelvis/thigh injuries including

femoral fractures but not knee, lower leg and ankle/footinjuries in frontal-impacts [2, 24].

Two people with LE fractures and/or dislocations inthe sample studied in the CVF were unbelted. A greaternumber of cases is required to determine the effect ofbelts on LE fractures and/or dislocations in side-impacts,but it is likely that there will be little difference betweenLE injuries of belted and unbelted occupants. In near-side impacts and severe far-side crashes it is likely thatthe intrusion will cause injury before the belt would haveany effect.

Strengthening the toepan, door and lower A-pillar regionFundamental Mechanism (1): Initial consideration of thecases of this study suggests that strengthening the toepancould reduce over 50% of LE injuries caused by entrapmentfrom the deforming footwell. However, toepan streng-thening may increase other (head, neck, and chest) injuriescaused by increasing the vehicle crush stiffness. Thusthe effect of such changes to the vehicle structure needsto be further investigated to determine if overall harm isreduced.

Fundamental Mechanism (2): Strengthening the door andA-pillar in combination with padding can reduce thetransfer of high energy impulse forces to the knee andlower leg.

Airbags and paddingFundamental Mechanism (2): Lower door airbags mayreduce knee and lower leg injuries from high-energy, side-impact loads, where there is direct contact with that portionof the vehicle interior that has been directly struck by thebullet vehicle or when it hits an object. When the occupantis effectively punched by the encroaching vehicle interior,padding can provide a “earlier and prolonged contact periodfor the occupant, and hence provide a greater distance todissipate the kinetic energy” [14].

Fundamental Mechanism (3): Airbags and padding on thesteering column, centre console and dash may reduce inertialoads, thus reducing injury caused by knee contact withthese structures. Floor airbags could help reduce foot slip-off-pedal injuries.

Future work

Further research is underway as part of this study withthe following tasks in mind:

• To validate the identified fracture and/or dislocationmechanisms using computer simulation crash tests; and

• To examine possible injury countermeasures formitigating LE injuries in side-impact crashes.

The following would be useful for improving LE fracture/dislocation research:

• Collection of data from injured who have not beenadmitted to hospital or killed, i.e. those seen inemergency rooms and discharged.

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• Hospital emergency room personnel (triage nurses)should be requested to approach injured occupants witha LE fracture/dislocation for permission for data to bereleased for research and to agree to have the crashedvehicle inspected.

• More accurate, detailed information concerning injurysites and types and copies of radiology reports in allcases.

• More detailed engineers drawings of the crashed vehiclesfor all cases.

CONCLUSIONS

Associations between some occupant, crash and vehiclecharacteristics and fracture mechanisms of the LE in side-impacts have been identified. More data are required toverify these trends. Nevertheless, the following trends wereevident:

1. The majority of LE injuries occurred in oblique angledimpacts (15°–80°, in Figures 3 and 4).

2. Most injuries occurred in crashes where the massratio of the target vehicle to bullet vehicle was lessthan 1.0.

3. Eighty percent of LE injuries occurred in crashes withintrusions of 60 cm or less.

Analysis of the CVF and ANCIS databases has enabledpreliminary identification of three fundamental mech-anisms of fracture and/or dislocation of the knee, lowerleg and ankle/foot:

1. Intrusion causing entrapment resulting from leg areavolume reduction with bending side-force, acting aloneor together;

2. High-energy, side-impact, striking force resulting frombeing in direct contact with the struck portion of thevehicle.

3. Inertial movement of the body causing loading of theLE resulting from its interaction with the vehicle interioror entrapment and where intrusion is not the cause ofinjury.

However, more data and work in regards to modellingand testing is required in order to validate that knee, lowerleg and ankle/foot fractures and dislocations in side-impacts can indeed be categorised into the above threeproposed fundamental mechanisms. Crash testing isrequired to determine that the proposed injury counter-measures would be effective.

ACKNOWLEDGEMENTS

The authors would like to thank Prof. Brian Fildes from MonashUniversity’s Accident Research Centre for providing access tocrash data and Dr. Laurie Sparke from Holden’s AutomotiveLtd. for initial sponsorship of the research program. Theauthors would also like to thank the ANCIS committee forproviding access to de-identified ANCIS crash data. Assistance

with the drawings provided by Mr Robert Alexander from theCivil Engineering Department at Monash University isgratefully acknowledged.

REFERENCES

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2. CRANDALL, J R and MARTIN, P G. ‘Lower limb injuriessustained in crashes and corresponding biomechanicalresearch’, International Symposium on Real World CrashInjury Research, UK, 1997 p. 3.5.1–3.5.16.

3. CRAWFORD-ADAMS, J. ‘Outline of fractures’, 4th Edition ed,E & S Livingston Ltd, 1964.

4. DISCHINGER, P C, SCHMIDHAUSER, C B, BURGESS, A R, HO, SM, Cushing, B M, O’QUINN, T D, JULIANO, P J and BENTS,F D. ‘Lower extremity trauma in vehicular front seatoccupants: patients admitted to a level 1 trauma centre’,SAE international congress and exposition. In depthaccident investigation: trauma team findings in late modelvehicle collisions, SAE Paper No. 940710, ISBN 1-56091-494–7, Detroit, Michigan, SAE, 1994 p. 11–18.

5. European Transport Safety Council, Reducing TrafficInjuries Through Vehicle Safety Improvements – The Roleof Car Design, in Technical Annexes, Annex C, EuropeanTransport Safety Council, 1993 p. 55–193.

6. FILDES, B, Lenard, J, Lane, J, Vulcan, P and Seyer, K.‘Lower limb injuries to passenger car occupants’, AccidentAnalysis and Prevention., 1997 Nov; 29(6) 785–91.

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Documents

Lower extremity injuries in side-impact vehicle crashes