R O A D R E S E A R C H L A B O R A T O R Y

M i n i s t r y o f T r a n s p o r t

R . R . L . R E P O R T L R 201

M E C H A N I S M S O F S E R I O U S L O W E R L I M B I N J U R I E S T O

M O T O R V E H I C L E O C C U P A N T S

by

E. G R A T T A N , B A . , M . B . , B. C h . , F . R . C ~ S .

a n d J . A . H O B B S

R O A D R E S E A R C H L A B O R A T O R Y C R O W T H O R N E B E R K S H I R E

1968

CONTENTS

A b s t r a c t 1. I n t r o d u c t i o n 2. R e s u l t s of the I n v e s t i g a t i o n 3. D e s c r i p t i o n of C a s e s

3. 1 P o s t e r i o r d i s l o c a t i o n of the hip j o i n t 3. 2 Central fracture dislocation of the hip joint 3. 3 Fracture of the roof of the acetabulum

3.4 Single transverse fracture of the shaft of the femur

3.5 Single transverse fracture of the shaft of the femur

3. 6 Single transverse fracture of the shaft of the femur

3.7 Single comminuted fracture of the shaft of the femur

3.8 Double fracture of the femur

3. 9 Double comminuted fracture of the shaft of the femur

3. i0 Double comminuted fracture of the shaft of the femur (glancing impact)

3. iI Oblique fracture of the shaft of the femur 3. 12 Supracondylar fracture of the femur 3. 13 Fracture of the patella

3. 14 Fracture of the tibia and fibula

Page

1 I 2 6 8

12

16

20

24

28

32 36

41

45

49 53 57

61

4. Discussion of mechanisms and of directions of force 4. 1 Hip joint

4. I. 1 Posterior dislocations

4. I. 2 ~ractures of the roof of the ac etabulum

4. I. 3 Central dislocations

67 67 67

67 67

4 . 2 Shaft of the f e m u r 4. 2. 1 U p p e r 3 / 4 of the sha f t 4. 2 . 2 L o w e r 1 / 4 of the shaf t

68 68

68

4 . 3 4 . 4

P a t e l l a U p p e r 1 / 4 of the sha f t of the t i b i a and f i b u l a

69 69

5. Discussion of vehicle design in relation to injury to the lower limb

5. 1 Fractures of the upper end of the tibia and

5.2

5.3 5.4 5.5

5.6 5.7

5.8

5.9

69

fibula 70 Fractures of the patella 70 Supracondylar fractures of the femur 70

Fractures of the shaft of the femur 70 Spiral and oblique fractures of the shaft of the femur 70

Posterior dislocations of the hip joint 71 Fractures of the roof of the acetabulum 71

Central dislocations of the hip joint 71

Summary of recommended design improvements 71

.

7.

8.

9. i0.

Conclusions 72

References 73

Acknowledgements 74

Appendix I. Glossary of medical terms 75 Appendix 2. Directions of vehicle impact 76

Q CROWN COPYRIGHT 1968

Extracts from the text may be reproduced

provided the source is acknowledged

Ownership of the Transport Research Laboratory was transferred from the Department of Transport to a subsidiary of the Transport Research Foundation on l S t April 1996.

This report has been reproduced by permission of the Controller of HMSO. Extracts from the text may be reproduced, except for commercial purposes, provided the source is acknowledged.

MEOI-IANISMS OF SERIOUS LOWER LIMB INJURIES TO MOTOR

VEHICLE OCCUPANTS

A B S T R A C T

T h i s R e p o r t d e s c r i b e s t h e r e s u l t s of an i n v e s t i g a t i o n in to s e r i o u s l o w e r l i m b i n j u r i e s s u s t a i n e d by b o t h u n r e s t r a i n e d and r e s t r a i n e d v e h i c l e o c c u p a n t s in r o a d a c c i d e n t s .

The primary object of the investigation was tO determine

not only the cause of injury but, where possible, the directions in which force acts upon the human body.

The following serious injuries have been investigated:

fractures and fracture dislocations of the hip joint, fractures

of the femur, fractures of the patella and fractures of the

upper end of the tibia and fibula. This group of injuries

constitutes the main source of post-accident disability for the lower limb.

T h e r e is e v i d e n c e of a c o n s i d e r a b l e r e d u c t i o n in t h e o v e r a l l s e r i o u s i n j u r y r a t e in s e a t b e l t w e a r e r s a l t h o u g h t h e y a p p e a r to s u s t a i n t h e s a m e v a r i e t i e s of s k e l e t a l i n j u r y to t h e l o w e r l i m b a s n o n - s e a t b e l t w e a r e r s bu t w i t h r e d u c e d i n c i d e n c e , e x c e p t f o r f r a c t u r e s of t h e p a t e l l a a n d t h e u p p e r end of t h e t i b i a and f i b u l a .

Some suggestions are made as to the possible applications of this research.

A g l o s s a r y of m e d i c a l t e r m s is i n c l u d e d ( A p p e n d i x 1) a n d a d e s c r i p t i o n g i v e n of t h e m e t h o d u s e d to d e f i n e t h e d i r e c t i o n s of v e h i c l e i m p a c t ( A p p e n d i x 2).

i. INTRODUCTION

An a t t e m p t i s m a d e in t h i s r e p o r t to a n a l y s e t h e c a u s e s of s k e l e t a l i n j u r y to the l o w e r l i m b s in v e h i c l e o c c u p a n t s i n v o l v e d in r o a d a c c i d e n t s and to d e t e r m i n e t h e d i r e c t i o n s in w h i c h f o r c e a c t s to g i v e r i s e to t h e m .

T h e m e t h o d u s e d h a s b e e n to e x a m i n e b o t h c l i n i c a l l y a n d r a d i o - l o g i c a l l y i n j u r e d v e h i c l e o c c u p a n t s a d m i t t e d to h o s p i t a l f o l l o w i n g r o a d

accidents and to examine the vehicle or vehicles involved, particularly.

from the point of view of deformation of interior structures, and thus

to attempt to correlate the deformations found with the injuries

sustained. The technique of accident investigation has been described

by Hobbs I. The patients investigated were not selected in any way.

We believe them to have been a representative sample of vehicle

occupants admitted to hospital for their injuries.

To-date (July 1967) we have examined in this manner 426 occupants

of whom 355 were car occupants, and have obtained an overall

correlation rate between the injured part of the body and the interior

structure of the vehicle of about 70 percent. The remaining occupants

were mostly in commercial vehicles.

With vehicle design as it is at present it would seem that lower

limb skeletal injuries can occur both in the restrained and the unrestrained

occupant. It is therefore especially necessary to understand the precise

manner in which such injuries are caused.

2. RESULTS OF THE INVESTIGATION

.

Resulting from our investigation it would seem that the most obvious

interior design feature required is not so much the need to abolish

small projections and sharp edges, which appear to cause mainly

relatively minor surface injuries but the need to obtain optimal

energy absorption characteristics for smooth surfaces, which seem

to be responsible for most of the severe lower limb fractures and

dislocations we have observed. Table 1 shows the relatively small

number of severe, i.e. penetrating, wounds for the body as a whole

found in our series (8 out of 426 occupants) which appear to have been

caused by projecting components in vehicle interiors.

We have chosen skeletal injuries to the lower limb for the

analysis in this report. Fractures and dislocations involving these

parts of the body form the commonest type of skeletal injury in those

who survive and since there are approximately fourteen times as many

seriously injured vehicle occupant casualties in the United Kingdom

as there are deaths these forms of injury are particularly important.

In our present series there were for example out of 312 non-seat belt

seriou'sly injured front seat car occupants, 167 separately named

lower limb fractures or dislocations dompared with 59 similar

injuries for the chest, 67 for the upper limb and 50 for the head

(see Table 2).

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Similarly out of the 21 seriously injured front seat car occupants

wearing seat belts seen during the course of the same investigation there

were 17 separately named lower limb fractures or dislocations compared

with 6 similar injuries for the chest, 8 for the upper limb and 2 for the head (see Table 2).

It will be seen from this table that the various anatomical

varieties of severe lower limb injury in both unrestrained and

restrained car occupants are the same. Although the numbers are

small it will also be seen, as is to be expected (Lister and Neilson,

1966) 3 , that the greatest reduction in skeletal injury in the restrained

group is to the head, and that the proportion of lower limb skeletal

injuries appears to be less in rear seat passengers than in front seat passengers.

It is to be noted that the percentages in table 2 relate to the

distribution of skeletal injuries for each of the three categories of

injured car occupants. These categories have different risks of

receiving such injuries in accidents. The chance of injury for

belted front seat occupants, as discussed later, appears to be about

half of that for those not wearing belts. It follows from the first two

columns of Table 2 that the ratio of the chances of receiving for

example a facial or skull injury is not l0 percent to 16 percent but

approximately 5 percent to 16 percent, that is 1 to about 3 for

restrained compared with unrestrained froht seat occupants.

There is some evidence to suggest that on average the severity

of vehicle impact was greater for the seat belt cases. It will be seen

in figure 1 that the peak of incidence for numbers of vehicles damaged,

as expressed by the damage index car weight ratio (Moreland 1964)4 is

further along the damage index car weight ratio scale for the seat

belt cases (though the numbers are small) that for the non seat belt

cases. It seems probable that some cases included under seat belt

injuries if they had not been wearing belts would not have survived

and would therefore have been excluded from our sample.

A recent count of car occupants on the road wearing seat belts

in the same geographical area from which our cases were collected

suggests that about 12 percent of front seat occupants were at that

time (June 1967) wearing.belts, whereas in the series of 333 front

seat car occupants under review the proportion of cases wearing belts

was about 6 percent. If allowance is made for the apparently greater

severity of vehicle impact in some of the seat belt cases the overall

reduction of serious injury would appear to be rather more than 50 percent.

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occupants wearing belts and after allowance has been made for the

different risks of receiving'injury in the different categories of

occupant the incidence of some fractures, in particular of the patella

and of the upper end of the tibia and fibula and possibly of the femur,

would appear to be much the same whether the occupant is restrained

or unrestrained (see Table 2).

3. DESCRIPTION OF THE CASES

The examples which follow illustrate the more important types of

lower limb skeletal injury seen in this investigation.

In each case an attempt is made to demonstrate the mechanism

of injury and the probable direction in which force acted to cause the

injury.

Cases Nos. 177, 304, 338 and 176 have been quoted in earlier papers(5 and 6).

The following injuries are covered: posterior fracture

dislocations of the hip, fractures of the roof of the acetabulum,

central fracture dislocations of the hip, fractures of the shaft of the

femur, fractures of the patella and fractures of the upper end of the

tibia and fibula. A number of other skeletal injuries to the lower

limb have been seen but are not considered in detail in this report

owing either to smallness of numbers, viz impacted subcapital

fractures of the neck of the femur (2 cases, both side impacts) or to

the inadequacy of evidence of causation, viz fractures without dis-

location of the posterior wall of the acetabulum (4 cases), fractures

of the lower two thirds of the shaft of the tibia and fibula (27 cases)

and skeletal injuries to the ankle and foot i23 cases). These injuries

are however included in Table 2, which shows the general pattern

of lower limb injuries found in car occupants.

3.1 Posterior Dislocation of the Hip-Joint

Case No. 177 Male aged 66 years, weight 12 stones, height 6ft. lin.

The injured car occupant, who was not wearing a seat belt, was the driver of a 1965 Austin ii00 saloon car. This car was involved in a frontal collision with an oncoming Austin A. 50 saloon car (see figure 2).

Fig. 2.SKETCH OF ACCIDENT CASE No. 177

Glancing impact between Austin A50 and Morris1100

_ • KERB ~ I ~ l J ~ ~ I l l I ~ It SOUTH

Austin A50

~,NORTH M i / / 1 "~ KERB f Aus t in 1100

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Main impact between Austin AS0 and Austin 1100

As a result of the frontal impact (direction offside head), see Plate I,

he sustained a posterior fracture dislocation of the right hip-joint (see

Plate II). A normal X-ray of the hip joint is also shown for comparison.

The fracture dislocation appears to have been caused by the knee

striking the facia (see Plate III) the patella being fractured,the residual

force being transmitted through the femur to the hip joint, with the hip

flexed to about a right angle. The probable direction in which force acted on the hip joint is shown in the insert of Plate II.

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3. 2 Central Fracture Dislocation of the Hip-Joint

1 . C a s e No. 304 F e m a l e a g e d 23 y e a r s , w e i g h t 10 s t o n e s , h e i g h t 5ft . 5 x m s .

T h e i n j u r e d c a r o c c u p a n t , w h o w a s not w e a r i n g a s e a t b e l t , w a s the n e a r s i d e f r o n t s e a t p a s s e n g e r in a 1960 R e n a u l t D a u p h i n e s a l o o n c a r . I t w a s i n v o l v e d in a s i d e c o l l i s i o n a n d w a s s t r u c k by the f r o n t of a M o r r i s 1000 s a l o o n c a r w h i c h h a d c r o s s e d t r a f f i c l i g h t s w h e n at r e d ( s e e f i g u r e 3).

Fig 3. SKETCH OF ACCIDENT

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CASE No. 304

i i ~ i ~ i aimim

0 Traffic lights I All roads having kerbstone edges I

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ARSIDE FRONT SEAT SSENGER'S LEFT HIP Jck by incoming door causing

central fracture dislocation 'he ]eft hip joint

Plate VI INTERIOR OF RENAULT DAUPHINE SALOON

]5

3.3 Fracture of the Roof of the Acetabulum

Case No. 338 Male aged 52 years, weight 16 stones, height 6 ft.

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Fig. 4 SKETCH OF: ACCIDENT CASE No. 338

\

ROAD WIDTH 23ft

As a result of the frontal impact (direction centre head), see Plate VII, he sustained a fracture of the roof of the acetabulum of the right hip joint (see Plate VIII). A normal X-ray of the hip joint is also shown for comparison. The fracture appears to have been caused by the knee striking the facia (see Plate IX)the residual force being trans- mitted through the femur to the hip joint, with the hip flexed to less than a right angle. The probable direction in which force acted on the hip joint is shown in the insert of Plate VIII.

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3.4 Single Transverse Fracture of the Shaft of the Femur in a

Frontal Impact

Case No. 394 Male aged 52 years, weight 12 stones, height 5ft. 8ins.

T h e i n j u r e d c a r o c c u p a n t , w h o w a s n o t w e a r i n g a s e a t b e l t , w a s t h e d r i v e r o f a B e d f o r d A r t i c u l a t e d L o r r y w h i c h r a n i n t o t h e r e a r o f a p r e - c e d i n g l o r r y w h i c h h a d b e e n f o r c e d t o b r a k e i n an e m e r g e n c y ( s e e f i g u r e 5).

Fig. 5 SKETCH OF ACCIDENT CASE No. 394

KERB

• Bedford Artic. A.E.C. Artic. Path travelled by both vehicles , ~ ~ / ~ EAST ~ - - = B =B BB BBm= =B B B B B ~ l

KERB

ROAD WIDTH 33ft

As a result of the frontal impact (direction offside head), see Plate X,

he sustained a single transverse fracture of the left femur in the mid

shaft (see Plate XI). A normal X-ray of the femur is also shown for

comparison. The fracture appears to have been caused by his thigh

angulating over the rim or cross spoke of the steering wheel (see

Plate XII). The probable direction in which force acted on the femur is shown in the insert of Plate XI.

20

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23

3.5 Single Transverse Fracture of the Shaft of the Femur in a

Frontal Impact

Case No. 388 Female aged 17 years, weight I0½ stones,

height 5 ft. 7 ins.

The injured car occupant, who was not wearing a seat belt, was

the nearside front seat passenger in a 1962 Austin mini saloon car. It

was involved in a frontal collision,with a n onc.oming Hillman Minx

saloon car, whilst attempting to overtake another vehicle (see figure 6).

Fig.6 SKETCH OF ACCIDENT

KERB

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As a result of the frontal impact (direction nearside head), see

Plate XIII,she sustained a single transverse fracture of the left femur

at the junction of the upper and middle third of its shaft (see Plate XIV).

A normal X-ray of the femur is also shown for comparison. The

fracture appears to have been caused by the thigh angulating over the

parcel tray edge (see Plate XV). The probable direction in which

force acted on the femur is shown in the insert of Plate XIV.

24

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3,6 Single Transverse Fracture of the Shaft of the Femur in a Side

Impact

Case No: 95 Male aged 25 years, weight 13½ stones, height 6ft. 2 ins.

The injured car occupant, who was wearing a lap type of seat belt, was the driver of a left hand drive 1959 Renault Dauphine saloon car. The nearside of this car was struck by a Bedford Lorry which had emerged from a side turning (see figure 7).

Fig. 7 SKETCH OF ACCIDENT CASE No. 95

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As a result of the side impact (direction mid nearside).see Plate XVI~he sustained a single transverse fracture of the mid shaft

of his left femur <see Plate XVII ). A normal drawing of the femur is also shown for comparison. The fracture appears to

have been caused by angulation ol the thigh over the incoming door

(see Plate XVIII). The probable direction in which force acted on the femur is shown in the insert of Plate XVII.

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3.7 Single Comminuted Fracture of the Shaft of the Femur

Case No. 399 Male aged 21 years, weight 10st. 101bs, height 5ft. 9ins.

The injured car occupant, who was wearing a diagonal safety belt of American design, was the offside front seat passenger in a 1966

Volkswagen 1600Coupe, left hand drive model. This car was involved in a frontal collision with the front of a bus (see figure 8).

Fig. 8 SKETCH OF ACCIDENT CASE No. 399

Dotted outline shows ~ ~ M . W . final position of 1600 Volkswagon ~.,,,,~ ~ u p e

S"

As a result of the frontal impact (direction centre head), see Plate XIX,he sustained a single comminuted fracture of the right femur (see

Plate XX~. A normal X-ray of the femur is also shown for comparison. The fracture appears to have been caused by his thigh angulating over

the lower edge of the facia (see Plate XXI). The probable direction in which force acted on the femur is shown in the insert of Plate XX.

32

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CASE No. 399

Deformation caused by OFFSIDE FRONT SEAT PASSENGER'S right thigh angulating over the lower edge of the facia to cause the single comminuted fracture of the right femur

Plate XXI INTERIOR OF VOLKSWAGEN 1600 COUPE (LEFT HAND DRIVE MODEL)

3S

3. 8 Double Fracture of the Femur

Case No. 424 Male aged 32 years, weight 14 stones, height 5ft. 8ins.

The injured car occupant, who was not wearing a seat belt, was

the driver of a 1964 Morris Mini Traveller. The car was involved in

a frontal collision with an'oncoming Renault R. 8 saloon car. After

impact the Mini rotated violently clockwise (see figure 9).

Fig. 9 SKETCH OF ACCIDENT

KERB

vertaken vehicle Morris = ~

Dotted outline indicates final I I I ! position of vehicles I I_. ;

CASE No. 424

Mini pushed backwards and then rotated clockwise to reach its final position

A ~ I I = l l ~ . . .

!:i~S~:i:::~:i!:iii!!i~.:::~ EAST

m m |

f ROAD WI DT H 24 ft

As a result of the frontal impact (direction nearside head), see Plate

XXII,he sustained a double fracture of the left femur, one inter-trochanteric

(at the top of the shaft of the bone),the other a compound oblique fracture

in the lower quarter of the shaft .(see Plates XXIII and XXIV). Normal

X-rays of the femur are also shown for comparison. The lower fracture

appears to have been caused by angulation of the thigh over the parcel

tray edge and with a possible rotational element added, the upper fracture

by direct contact with the top edge of the facia (see Plate XXV). The

probable direction in which force acted on the femur is shown in the insert of Plate XXIII.

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3.9 Double Comminuted Fracture of the Shaft of the Femur

Case No. 407 Male aged 25 years, weight Ii stones, height 5ft. 7ins.

The injured car occupant, who was wearing a lap and diagonal seat belt, was the driver of a Renault R. 16 1966 Estate car. The car

was involved in a frontal collision with an oncoming M.G.B. which went

out of control on a left hand bend (see figure 10).

Fig. I0 SKETCH OFACCIDENT C A S E No. 407

,,~S~ _ ~ ..... ~. D WIDTH 1 8 f t ~ ~ g g ~ . ~ ~ y . ~ . . . . - ;.:.; ....... : . : ..................... . ............... . ....... -..~,-:-;:.;:,::::.~.:,.:;::~:!:i:~,.~ _ _ .

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As a result of the frontal impact (direction centre head),see Plate

XXVIjhe sustained a double comminuted fracture of the left femur in

the mid shaft (see Plate XXVII). A normal X-ray of the femur is also

shown for comparison. The fracture appears to have been caused by

angulation of the thigh over the lower half of the steering wheel rim and

the nearside steering wheel spoke (see Plate XXVIII). The probable

direction in which force acted on the femur is shown in the insert of P l a t e XXVII.

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3. I0 Double Comminuted Fracture of the Shaft of the Femur

Case No. 385 Male aged--25 years, weight 12 stones, h-eight 5ft. 9ins.

. ~

The injured car occupant, who was not wearing a seat belt, was

the driver of a 1966 Ford Cortina saloon car which was involved in a

glancing type of collision, the impact being frontal, with an oncoming Ford Zephyr 6 saloon car (see figure ll).

Fig. II SKETCH OF ACCIDENT CASE No. 385

J - . . . .

As a result of the glancing frontal impact (direction offside head), see

Plate XXIX~he sustained a double comminuted fracture of the right femur

(see Plate XXX). A normal X-ray of the femur is also shown for comparison. The fracture appears to have been caused by his thigh being hit progressively

by the incoming door (see Plate XXXl). The probable direction in which force acted on the femur is shown in the insert of Plate XXX.

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3. ll Oblique Fracture of the Shaft of the Femur

Case No. 232 Male aged 16 years, weight 8 stones, height 5ft. 6ins.

The injured car occupant, who was not wearing a seat belt, was the nearside front seat passenger in a 1960 Austin Mini saloon car. This car went out of control on a right hand bend and was involved

in a side collision with the front of an oncoming Ford Anglia Estate

car (see figure 12)

Fig. 12 SKETCH OF ACCIDENT CASE No. 232

. . . . :,?,:..," ~.~.'.;,-:,:.~.:~'.:'..!~:~.-~::..~ ~- . ; . . . . . . . . . ..... ->,~:~:~~:~4: , , : - ; -~. -~.<.=: , , . Dotted outhne mdtcates final

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As a result of the side impact, (direction front nearside),see

Plate XXXII,he sustained an oblique fracture of the left femur Csee

Plate XXXIII). A normal X-ray of the femur is also shown for

comparison. The impact pushed the side of the car inwards onto the

passenger, probably Wrapping the parcel tray around the left thigh

(see Plate XXXIV). The fracture appears to have been caused by the

lower left thigh being held in the deformation of the parcel tray whilst

the body rotated upwards and to the left. The probable direction in

which force acted on the femur is shown in the insert of Plate XXXIII.

It is possible that additionally the femur may have been angulated

over the deformed lower edge of the parcel tray.

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3.12 Supracondylar Fracture of the Femur

C a s e No. 176 Male aged 46 y e a r s , w e i g h t i4 s t o n e s , h e i g h t 6ft. 6 ins .

The injured car occupant, who was not wearing a seat belt, was

the nearside front seat passenger in a 1959 Morris Oxford saloon car.

This car was involved in a frontal collision with an oncoming Vauxhall

Cresta saloon car (see figure 13).

Fig. 13 SKETCH OF ACCIDENT CASENo. 176

Reflector Glancing blow between studs " ~ f w a l l and Vauxhall

. Main impact between cars "

As a result of the frontal impact (direction centre head),see Plate

XXXV, he sustained a supracondylar fracture of the right femur (see

Plate XXXVI). A normal X-ray of the femur is also shown for comparison.

The fracture appears to have been caused by impaction and angulation of

the lower thigh over the lower edge of the facia, which shows deformation

corresponding with the fracture site (see Plate XXXVII). The probable

direction in which force acted on the femur is shown in the insert of

Plate XXXVI.

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3. 13 Fracture of the Patella

Case No. 136 Male aged 21 years, weight 12 stones, height 6 ft.

The injured car occupant, who was wearing a full harness, was the

driver of an Austin A. 35 1958 saloon car which skidded out of control

on a large patch of ice. This car was involved in a frontal collision

with the corner%of abrick wall (see figure 14).

Fig. 14 SKETCH OF ACCIDENT C A S E No. 136

~ Farm Entrances

ROAD W DTH 18ft :".:':1 ::i:i::::iiii!i!iii:i:i:: ~ . . . . ~ ..... iiiiii::::ii: ~ Br ck

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. . . . . . Ice water seeping out of farm yard

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3. 14 Fracture of the Tibia and Fibula

Case No. 259 Female aged 59 years, weight 13 stones, height 5ft. llins.

The injured car occupant, who was not wearing a seat belt, was the

nearside front seat passenger in a 1965WolseleyHornet saloon car. It

was involved in a frontal collision with an oncoming Bedford Van (see

figure 15).

Fig. 15 SKETCH OF ACCIDENT CASE No. 259

. . . . . . . . . . . . . . . . . . . . . . . . . ..~__ Final position of Wolseley :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

.;:~..~:~.~.....~.~.~.~:~:.~..~.~.~t......~.~.~........~.~.~...~.~.~.~:~ [ ; ~.~.?:~.~...:;.....~.~.~..;:.:.:~;°:~:°;..~...;.;.~.~.~;~..̀ ..;:..~;~:~.~..::.~°~.~;~ K E R B ~ r n e t EAST "~

• - -

~ ~ ~ I m m m ~. WEST Parked

vehicle ROAD WIDTH 2Oft

As a result of the frontal collision (direction offside head),

see Plate XLI, she sustained bilateral plateau ~racture of the

tibia and fibula (see Plate XLII). A normal X-ray of the tibia and

fibula is also shown for comparison. The fracture appears to have

been caused by contact with the p~rcel tray which shows deformation

corresponding to the fracture sites (see Plate XLIII). The probable

direction in which force acted on the leg(s) is shown in the insert of

Plate XZII.

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TABLE 3

V A R I E T I E S OF S K E L E T A L INJURY TO T H E L O W E R L I M B S R E L A T E D TO D I R E C T I O N O F V E H I C L E

I M P A C T 426 S E R I O U S L Y I N J U R E D V E H I C L E O C C U P A N T S

T Y P E OFINJURY

H I P J O I N T

P o s t e r i o r d i s l o c a t i o n s

P o s t e r i o r f r a c t u r e d i s l o c a t i o n s

P o s t e r i o r f r a c t u r e d i s l o c a t i o n (head of f e m u r and a c e t a b u l u m )

F r a c t u r e s o f the r o o f of t he a c e t a b u l u m

F r a c t u r e of the r o o f of the a c e t a b u l u m wi th p o s t e r i o r f r a c t u r e d i s l o c a t i o n

C e n t r a l f r a c t u r e d i s l o c a t i o n

F E M U R ( U p p e r ¼ of the shaf t )

S ingle t r a n s v e r s e f r a c t u r e s

S ingle f r a c t u r e s w i t h v a r y i n g d e g r e e s of c o m m i n u t i o n

D o u b l e f r a c t u r e s w i t h v a r y i n g d e g r e e s of c o m m i n u t i o n

S ing le s p i r a l o r o b l i q u e f r a c t u r e s

F E M U R ( L o w e r ¼ of the shaf t )

S u p r a c o n d y l a r f r a c t u r e s

PATELLA

T I B I A AND F I B U L A

P l a t e a u f r a c t u r e s

NO O F CASES

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DIRECTION OF VEHICLE I M P A C T

All f r o n t a l

Al l f r o n t a l

F r o n t a l

Al l f r o n t a l

F r o n t a l

5 Side

19 F r o n t a l 5 Side

6 F r o n t a l

15 F . ron t a l 3 F r o n t a l ( g l a n c i n g

i m p a c t s )

Al l s i de i m p a c t s w i t h s m a l l e r f r o n t a l c o m p o n e n t f o r c e

Al l f r o n t a l

Al l f r o n t a l

Al l f r o n t a l

* one o c c u p a n t s u s t a i n e d h i s i n j u r y a s a r e s u l t of e j e c t i o n

+ one o c c u p a n t s u s t a i n e d h i s i n j u r y a s a r e s u l t of e j e c t i o n

65

TABLE 4

THE RELATION BETWEEN INJURY AND THE INTERIOR STRUCTURE OF THE VEHICLE

426 SERIOUSLY INJURED VEHICLE OCCUPANTS

I N J U R Y

H I P J O I N T

P o s t e r i o r d i s l o c a t i o n s a nd P o s t e r i o r f r a c t u r e d i s l o c a t i o n s

F r a c t u r e s of t h e R o o f of t h e A c e t a b u l u m

C e n t r a l f r a c t u r e d i s l o c a t i o n s

F E M U R

S i n g l e t r a n s v e r s e f r a c t u r e s w i t h o r w i t h o u t c o m m i n u t i o n

D o u b l e c o m m i n u t e d f r a c t u r e s

POINT OF CONTACT NO OF CASES

Facia

Parcel tray

Bulkhead

Centre support rear

seat

F a c i a P a r c e l t r a y H e a t e r u n i t U n k n o w n

Door

E j e c t e d

F a c i a P a r c e l t r a y D o o r S t e e r i n g w h e e l Gear lever Bulkhead

Heater unit

Seat back

E j e c t e d

14 3 1 1

19

4 2 Z

2

10

31

18

F a c i a D o o r P a r c e l t r a y Whe el R e a r s e a t b a c k U n k n o w n

S p i r a l o r o b l i q u e f r a c t u r e s F a c i a 3

S u p r a c o n d y l a r f r a c t u r e s 4

P A T E L L A

C o m m i n u t e d and N o n - C o m m i n u t e d f r a c t u r e s

F a c i a P a r c e l t r a y S e a t b a c k

TIBIA AND FIBULA

P l a t e a u fractures

F a c i a P a r c e l t r a y H e a t e r u n i t S t e e r i n g c o l u m n

S e g m e n t of f e n c e p i e r c e d c a r t h r o u g h b u l k h e a d

13

9 5 2

1

30

15 4 1

1

21

P a r c e l t r a y B u l k h e a d L o w e r e d g e f a c i a E j e c t e d

66

4. DISCUSSION O F M E C H A N I S M S AND O F D I R E C T I O N S O F F O R C E

T h e r e l a t i o n s h i p b e t w e e n s k e l e t a l i n j u r y to t h e l o w e r l i m b a n d d i r e c t i o n s of v e h i c l e i m p a c t i s s h o w n in T a b l e 3. 70 p e r c e n t of v e h i c l e i m p a c t s w e r e f r o n t a l .

From the examples quoted it will be seen, whether in

restrained or unrestrained occupants, that the probable mechanisms of

injury and the probable directions in which force acts to cause injury

to the lower limb would appear to be as follows:-

4 .1 Hip J o i n t

T h e p r o b a b l e m e c h a n i s m s of i n j u r y f o r t h e h i p j o i n t a r e d i s c u s s e d in a p r e v i o u s r e p o r t ( G r a t t a n and H o b b s 1967) 6 . P o s t e r i o r ( f r a c t u r e ) d i s l o c a t i o n s and f r a c t u r e s of t h e r o o f of t h e a c e t a b u l u m a r e u s u a l l y c l a s s i f i e d a s k n e e i m p a c t i n j u r i e s ( V o l l m a r , q u o t e d by G S g l e r (1962)) 7 . C e n t r a l d i s l o c a t i o n s a p p e a r to be p r o d u c e d by t h e d i r e c t a p p l i c a t i o n of f o r c e to t he g r e a t t r o c h a n t e r ( M c L a u g h l i n , 1959) 8

4. i. 1 Posterior dislocations and fracture dislocations. These

injuries occur in frontal impacts only. Force apears to be applied to the

knee, flexed to a right angle, direct contact being made with the facia

or more occasionally the parcel tray or bulkhead, the force being

transmi-t-t-~-d-ViK-th--d-s1~ft b-f-th-e-f~.i~lfr--t%--fh-~-hil5 j o i n t , With t h e ~ t h i g h . . . . . p r o b a b l y f l e x e d to a r i g h t a n g l e o r to m o r e t h a n a r i g h t a n g l e ( C a s e N o . 177). N i n e t e e n c a s e s h a v e b e e n s e e n . T h e p r o p o r t i o n of c a s e s c a u s e d by c o n t a c t w i t h t h e d i f f e r e n t s t r u c t u r e s of t h e v e h i c l e i n t e r i o r a r e s h o w n in T a b l e 4.

4.1.2 Fractures of the roof of the acetabulum. These injuries occur

in frontal impacts only. Force appears to be applied in the same

manner as for posterior (fracture) dislocations of the hip joint, but

with the thigh probably flexed to rather less than a right angle (Case

No. 338), the point of knee contact being lower in the vehicle, either

low on the facia or on the parcel tray or the heater unit. Ten cases

have been seen. The proportion of cases caused by contact with the

different structures of the vehicle interior are shown in Table 4.

4 . 1 . 3 C e n t r a l d i s l o c a t i o n s . T h e s e i n j u r i e s o c c u r in s i d e i m p a c t s o n l y . F o r c e a p p e a r s to be a p p l i e d in. an i n w a r d d i r e c t i o n to t h e g r e a t t r o c h a n t e r , b y c o n t a c t w i t h t he i n c o m i n g d o o r ( C a s e N o . 304) . S ix c a s e s h a v e b e e n s e e n . One o c c u p a n t w a s e j e c t e d , t h e s k i n o v e r t h e g r e a t t r o c h a n t e r b e i n g h e a v i l y b r u i s e d . T h e p r o p o r t i o n of c a s e s c a u s e d by c o n t a c t w i t h t h e d i f f e r e n t s t r u c t u r e s of t h e v e h i c l e i n t e r i o r a r e s h o w n in T a b l e 4.

67

4.2 Shaft of the femur

3 4.2. I Upper ~ of the shaft. The mechanism of fracture of the upper

three quarters of the shaft of the femur is still perhaps debatable.

GtSgler (1962) 7 states that 60 percent of femoral shafts are fractured

in car accidents by force applied through the knee, and 40 percent by

angulation. Kulowski (1960)9 quoting Ritchey et al notes that rather

more than half of their series of closed comminuted fractures of the

femoral shaft sustained by car occupants were knee impact injuries

(30 out of 52). We have been unable to demonstrate a relationship between knee impact injury and fracture of the shaft of the femur. No

case has been seen in which this mechanism was thought to have been

the cause of the fracture. We believe, from the examples seen by us

that three separate mechanisms exist to produce the different types of fracture observed, force being applied approximately at right

angles to the long axis of the bone (fracture by angulation, types l

and 2) or rotationally to the long axis (type 3). The mechanisms of fracture would appear to be as follows:-

Type I Single fractures with or without comminution - By

angulation of the shaft of the femur in frontal impacts, either over the

facia panel or parcel tray or steering wheel or occasionally over the

heater unit or bulkhead, or over the top of the seat back for rear

seat passengers, to produce single fractures with or without comminution of the shaft (Case No. 338 and Case No. 399). In side

impacts angulation seems to occur over the apex of the incoming door

or gear lever (Case No. 95). In all thirty one cases have been seen.

One occupant was ejected. The proportion of,cases caused by contact

with the different structures of the vehicle interior are shown in Table 4.

Type 2 Double fractures with or without comminution - By

angulation of the shaft of the femur, in frontal impacts, over two

separate parts of the facia or steering wheel to produce double

fractures with varying degrees of comminution of the shaft (Case No.

424 and Case No. 407). Glancing impacts upon the side of the vehicle

from a frontal direction appear to produce particularly extensive

comminution, usually of the upper shaft, the bone probably being

angulated and shattered by the progressive deformation of the in-

coming door (Case No. 358). In all eighteen cases have been seen.

The proportion of cases caused by contact with the different

structures of the vehicle interior are shown in Table 4.

Type 3 Spiral or oblique fractures - By rotation of the body, in

oblique vehicle impacts (side impacts with a smaller frontal component

force), with the knee or lower leg held in a deformation of the facia to

68

produce spiral or oblique fractures of the upper shaft (Case No. 232).

Three cases have been seen. The proportion of cases caused by

contact with the different structures of the vehicle interior are shown in Table 4.

4.2.2 Lower ¼ of the shaft (supracondylar fractures). These injuries occur in frontal impacts only. Force appears-to be appIied at right

angles to the long axis of the shaft, the femur being impacted on and angulated over the lower edge of the facia or parcel tray (Case No.

176) or occasionally for rear seat passengers on the top of the front seat back. Nine cases have been seen. The mechanism is similar to that described by Gkigler 7 for this type of fracture. The proportion

of cases caused by contact with the different structures of the vehicle interior are shown in Table 4.

4.3 Patella

Fractures of the patella occur in frontal impacts only, with

the knee flexed. Force appears to be applied to the outer surface of

the patella by direct contact with the facia panel and related structures, the parcel tray or the heater unit (Case No. i36). Some degree of

comminution is usual. Thirty cases have been seen. The proportion of cases caused by contact with the different structures of the . .~ vehicle interior are shown in Table 4.

o

1 4.4 Upper Z of the shaft of the tibia and fibula (plateau fractures)

These injuries occur in frontal impacts only. Force appears

to be applied at right angles to the long axis of the shafts of the bones

just bel~ow the knee joint, direct contact being made with the parcel

tray (Case No. 259) or more occasionally with the bulkhead or the lower edge of the facia. Twenty one cases have been seen. The

proportion of cases caused by contact with the different structures of the vehicle interior are shown in Table 4.

5. DISCUSSION OF VEHICLE DESIGN IN RELATION TO INJURY TO

THE LOWER LIMB

Firstly it should be noted that the incidence of lower limb fractures

appears to be less for rear seat occupants than for front seat occupants

(see Table 2). The energy absorption characteristics of the backs of the front seats might seem, even in their present form, more

s:atisfactory than those for the facia panel, parcel tray or steering wheel.

69

~O

Assuming that the probable directions in which force acts to

cause injury to the lower limb have been demonstrated with a

sufficient degree of accuracy it would seem that the following

preventative measures should be applicable.

5.1 Fractures of the upper end of the tibia and fibula - Parcel

trays and related structures should have adequate energy absorption

characteristics in the horizontal plane or, if seat belts are to be the

sole means of energy absorption, adequate space should be provided

to allow for belt extension and for possible backward relative move-

ment of the parcel tray due to distortion of the car.

5.2 Fractures of the patella - Facia panels, parcel trays and

heater units should have adequate energy absorption characteristics

in the horizontal plane or, if seat belts are to be the sole means of

energy absorption, adequate space should be provided to allow for

belt extension and for possible backward relative movement of the

parcel tray and facia panel.

5.3 Supracondylar fractures of the femur - The lower edge of the

facia panel or of the parcel tray should have adequate energy

absorption characteristics mainly in the vertical plane or, if seat

belts are to be the sole means of energy absorption, adequate space

should be provided to allow for belt extension and possible backward

relative movement of the facia panel.

5.4 Fractures of the shaft of the femur - For frontal impacts the

facia panel or parcel tray and the steering wheel should have adequate

energy abs6rption characteristics in both the horizontal and vertical

planes or, if seat belts are to be the sole means of energy absorption,

adequate space should be provided to allow for belt extension and

pos'sible backward relative movement of these parts of the vehicle.

For side impacts and for glancing impacts upon the side of the

vehicle, side structures, including doors, should be strengthened and

their interior energy absorption characteristics improved. Gear

levers, if floor mounted should be designed to break or preferably

bend out of the way before the femur breaks.

5.5 Spiral and oblique fractures of the shaft of the femur - It is

not possible to make a recommendation for vehicle design in respect of

this type of fracture because the leg appears to be caught in an interior

structure, viz the facia panel, which has deformed because of the

severity of the vehicle impact.

70

Q

5.6 Posterior dislocations of the hip joint - The same conditions

apply as for fractures of the patella. The optimal energy absorption

characteristics will however be different in degree.

5.7 Fractures of the roof of the acetabulum - The same conditions

apply as for posterior fracture dislocations of the hip.

5.8 Central dislocations of the hip joint - These only occur in side

impacts. The side structures of cars, including doors, should if

possible be strengthened and their interior energy absorption charac-

teristic s improved.

5.9 Summary of recommended design improvements - It can be

seen that the main design improvements required to minimise the risk

of serious injury to the lower limbs are:-

(1) To ensure adequate energy absorption characteristics of

facia panels, parcel trays, heater units and steering wheels

in both horizontal and vertical planes.

(2) To strengthen side structures including doors and to improve their interior energy absorption Characteristics.

(3) To arrange floor mounted gear levers so that they deflect

or break without inflicting serious injury.

(4) Where seat belts are to be the sole means of energy

absorption, to provide adequate space to allow for belt

extension and for possible backward relative movement

of the parcel tray and facia panel.

Although small projections and sharp edges are less

important in the context of serious lower limb injury, they

do occasionally cause severe penetrating wounds and more

commonly minor cuts or grazes, and should therefore be

eliminated.

If the interior design characteristics of cars are to be improved

from the safety viewpoint it will be necessary as a next step, knowing

the probable directions in which force acts, to determine experimentally

the loads required to cause fracture or dislocation of each of the more

important parts of the lower limb.

There would appear to be at least four separate methods of

determining the loads which different parts of the body can withstand

and thus determining the necessary strength and energy absorption

characteristics of internal car structures.

71

(a) b y e x p e r i m e n t a l c r a s h s t u d i e s u s i n g i n s t r u m e n t e d a n t h r o p o - m e t r i c d u m m i e s f r o m w h i c h t h e r e l a t i v e l o a d i n g of t h e d i f f e r e n t p a r t s o f t h e b o d y m a s s m a y b e d e t e r m i n e d a n d a t t h e s a m e t i m e c a l c u l a t i o n s m a d e f r o m a k n o w l e d g e of t h e d e c e l e r a t i o n of t h e c r a s h e d v e h i c l e o f t h e t o t a l f o r c e s i n v o l v e d . B y c o m p a r i n g t h e a m o u n t of v e h i c l e d a m a g e s u f f e r e d b y t h e c a r in w h i c h t h e i n j u r e d c a r o c c u p a n t w a s t r a v e l l i n g a t t h e t i m e o f t h e a c c i d e n t w i t h t h e d a m a g e s u f f e r e d b y c r a s h e d c a r s , o f t h e s a m e t y p e and m a k e , a r o u g h e s t i m a t i o n o f t h e m a g n i t u d e of t h e i n j u r i n g f o r c e m a y b e m a d e .

(b) by submitting cadaver specimens to static or dynamic

loading, to determine experimentally at what stage fracture or dislocation occurs.

(c) by measuring the deformation of car interior structures

caused by the impact of parts of the human body upon them,

and resulting in fractures or dislocations, and experimen-

tally reproducing the same deformations on uncrashed vehicles using known static or dynamic loads.

(d) by extending existing deformations in the car structure by

'a minimal amount, and measuring the static or dynamic load required to do so.

Methods c and d probably offer the best prospects of obtaining results which relate directly to conditions as they are found on the road.

This experimental work is already in progress at the Road Research Laboratory.

6. CONCLUSIONS

In this Report some of the mechanisms of injury occuri-ing in vehicle

occupants involved in road accidents have been investigated. A number

of patterns of skeletal injury to the lower limb have been demonstrated, both in the unrestrained and the restrained occupant. An attempt has

been made to specify the interior structures causing injury and to show

the directions in which force acted to cause the different injuries.

Two main conclusions have been drawn. ~ Firstly that in the

causation of severe lower limb injury poor energy absorption character-

istics of smooth surfaces, such as the facia panel as awhole, the parcel

tray, etc. are considerably more important than the presence of small projections or sharp edges.

72

Secondly, that the varieties of lower limb injury appear to be

similar both in the restrained and unrestrained occupant, although

there is a substantial overall reduction in serious injury in restrained

occupants. Even after allowing for the higher average severity of

vehicle impact in the seat belt cases compared with the non-seat

belt cases, the incidence of some lower limb fractures in the restrained group was higher than expected.

As a result of this investigation two alternatives have been put

forward for the better protection of the lower limbs in vehicle occupants.

Firstly, the need for improved energy absorption character-

istics of various interior structures of the vehicle. Or secondly the

need for the provision of more space in front of the occupant if belts

are to be the sole means of energy absorption.

It seems probable however that even with belted occupants it

may be useful for the lower limbs to absorb some of the energy of

deceleration in order to dissipate energy over as large a surface area

of the body as possible, and, thus, it may be preferable to provide

energy absorbing structures near the lower limbs. This is likely to

improve the injury rate of the unbelted occupants of cars as well.

Some methods of determining critical loads at which injury is

caused to the lower limb are discussed and the-f~ture programrrYe of

the Road Research Laboratory in this field reviewed. Such information

will be necessary for the redesign of the various internal components

of vehicles which have been shown in this report to be the cause of

some of the more serious varieties of lower limb injury.

7. REFERENCES

. HOBBS, J.A. The work of the accident injury group

R.R.L. Report No. i08 (1967).

. MINISTRY OF TRANSPORT AND SCOTTISH DEVELOPMENT. Road Accidents 1966.

. LISTER, R.D. and NEILSON, I.D. The effectiveness of

safety belts R.R.L. Report No. 16.

. MORELAND, J.D. Damage Index. A scale for assessing car

damage J. Inst. Auto Assess6rs Vol. XV, No.3 1964.

73

.

.

•

8.

GRATTAN, E., HOBBS, J.A., EAST, A. Mechanisms of injury to motor vehicle occupants R.R.L. Report No.109

( 1 9 6 8 )

GRATTAN, E., and HOBBS, J.A. Injuries to the hip joint in

vehicle occupants R.R.L. Report No. 126 (1968)

1 !

GOGLER, E. Road Accidents, J.R. Geigy, Basle (1962).

McLAUGHLIN, H.L. Trauma, W.B. Saunders, Philadelphia

( 1 9 5 9 )

9. KULOWSKI, J. Crash Injuries, Charles C. Thomas, Springfield, U.S.A.

8. ACKNOWLEDGEMENTS

Our thanks are due to Mr. C.M. Squire, F.R.C.S., Senior Orthopaedic Consultant Surgeon, Battle Hospital, Reading and to Mr. G.N. Golden, F.R.C.S., late Senior Orthopaedic Consultant Surgeon, Royal Surrey Hospital, Guildford, for their assistance in

the preparation of this report; to Mr. J.C. Scott,M.S. , F.R.C.S. , Surgeon in charge of the Accident Service, United Oxford Hospitals,

Radcliffe Infirmary, Oxford, to Mr. G.P. Arden, F.R.C.S., Senior Orthopaedic Consultant Surgeon, Windsor Group of Hospitals, to Mr. F.A. Simmonds, F.R.C.S., Senior Orthopaedic Consultant Surgeon, Royal Surrey Hospital, Guildford, to Mr. Graham Apley, F.R.C.S., Senior Orthopaedic Consultant Surgeon, St. Peter's Hospital, Chertsey, and to Mr. J.B. Scott, F.R.C.S., and Mr. P.J. Chesterman, F.R.C.S., Consultant Orthopaedic Surgeons, Battle Hospital, Reading, for their courtesy in allowing patients to

be examined on their wards.

Our thanks are also due to the Chief Constables and their staffs of the Berkshire, Buckinghamshire, Oxfordshire, Oxford City,

Reading Borough, Hampshire and the Surrey Constabularies for their

assistance and co-operation in this research.

We wish to thank our colleagues at the Road Research Laboratory

for their help and advice especially Mr. W. Heath of the Laboratory's Photographic Section who took the photographs included in this Report.

74

Acetabulum

Central fracture dislocation of the hip joint

Cervical spine

C omminuted fracture

C o m p o u n d f r a c t u r e

C l a v i c l e

D o u b l e f r a c t u r e o f t h e f e m u r

F e m u r

F i b u l a

G r e a t t r o c h a n t e r

Lumbo-dor sal spine

Oblique fracture

Patella

Patella tendon

Plateau fracture of the Tibia

and Fibula

Posterior fracture dislocation

of the hip joint

Sternum

Sub-capital fracture of the

neck of the femur

Suprac ondylar fracture

Tibia

Transverse fracture

9. APPENDIX 1

GLOSSARY OF MEDICAL TERMS

Hip Joint Socket

Inward dislocation of head of thigh~

bone with fracture of hip joint socket

Neck bones

Fracture in which the bone is broken

into many small fragments

Open fracture

Collar bone

Two separate and distinct fractures of

the shaft of the thigh bone

Thigh bone

Small bone of lower leg

Bony protuberance on the outer aspect

of the thigh bone at the upper end of

the shaft

Back bones

A fracture in which the fracture line

runs diagonally to the shaft of the bone

Knee cap

Knee cap ligament

Fracture of the Tibia and Fibula

immediately below the knee joint

Backward dislocation of head of thigh

bone with fracture of the hip joint socket

Breast bone

Fracture of the neck of the thigh bone

between the head and the shaft

Fracture of the shaft of the femur

immediately above the knee joint usually

with gross comminution

Shin bone

A fracture in which the fracture line

runs horizontally across the shaft of the

bone

75

10. A P P E N D I X 2

DIRECTIONS OF VEHICLE IMPACT

There are twelve basic directions of vehicle impact, three

frontal three rear and three for each of the two sides. These are named

as follows:-

Offside head )

Centre head ) Near side head )

Frontal impacts

Front offside )

Mid offside )

Rear offside )

O f f s i d e i m p a c t s

Front nearside )

Mid near side )

Rear nearside )

Nearside impacts

Offside rear )

Centre rear )

Near side rear )

Rear impacts

It is not necessarily the point at which the damage is sustained that is recorded as the direction of impact but rather the direction from which the

impact came that caused the damage. For example the offside of the vehicle

may be struck from a frontal direction or the front may be struck from a side

direction. Since the vehicle occupant moves towards the direction from which

the impact came, knowledge of the exact direction of impact is important in

considering the mechanism of that occupant's injuries.

If we consider a vehicle as being a circle, any line drawn from the

circumference of the centre can represent a direction of impact. On passing

around the circumference there is therefore an infinite number of directions

of impact. For convenience this has been simplified into twelve directions as

shown above and in Figure 16. The four central directions, centre head (C.H.)

centre rear (C. R.), mid offside (M. O. S. ) and mid nearside (M. N. S. ) are O

forces applied at 90 to the front, rear, offside and nearside of the vehicle

respectively and can only be applied at these respective sides. The other eight

directions are oblique forces varying in the magnitude of the frontal and side

components. For example the direction offside head implies a force with a

large frontal component and a smaller side component; front offside implies

a force with a large side component and a smaller frontal one and similarly

for the directions nearside head and front nearside and the oblique rear

impacts. The square in the centre of Figure 16 represents a vehicle and

t h e f o u r . - e x a m p l e s of i m p a c t s given serve to illustrate these points.

76

Mid near i i

side

IMPACT 1

IMPACT 4 e ~

Centr

e~,~e 0(~ / Of,$i(~m "

---i'~ \ 1 ~ " FRONT ~ I ~ ; .

o ~ . I REAR ~ L I

IMPACT 3 " ~. "

Centre rear

IMPACT 2

IMPACT 1 Marked thus ,i is causing damage fo the nearslde head of the vehlcJe but is actually coming from the offside head direction

IMPACT 2 Marked thus n ~ i s causing damage to the front offside of the vehicle but is actually coming from the offside rear direction

IMPACT 3 Marked thus . . . . . . . is causing damage to the centre rear of the vehicle but is actually coming from the rear nearslde dlrect|on

IMPACT 4 Marked thus . . . . is caus|ng damage to the nearslde front wing just in front of the nearside front door but is actually coming from the nearslde head direction

Mid off side

Fig. 16. APPENDIX 2 77

ATWJ 2½M 10/68 573515