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Forensic medicine > Injury patterns and mechanisms > Flashcards

Injury patterns and mechanisms Flashcards

1
Q

Legal definition of wound?

A

breach of full thickness of skin or lining of lip (excludes bruising, abrasions and fracture)

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2
Q

Medical definition of a wound?

A

disruption in the continuity of the tissues produced by external mechanical force

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3
Q

What are the 7 forms of mechanical trauma?

A 
impact
angulation
compression
traction
torsion
shearing 
acceleration/deceleration
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4
Q

Degree of force applied is a physical factor that must be considered in injury patterns. What other physical factors must be considered (4)?

A

Area of application of force
duration of application
direction of application
tissue properties (elasticity, viscosity, plasticity)

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5
Q

In kinetic energy, which carries more power, velocity or mass?

A

velocity

e.g. a bullet travels at several hundred mph but is only a few grams

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6
Q

skin is elastic and resists stretching - true or false

A

true

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7
Q

blood vessels are vulnerable to stretching - true or false

A

true

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8
Q

the semi-fluid brain is vulnerable to which type of mechanical injury?

A

semi fluid brain is vulnerable to shearing/rotation injury

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9
Q

bone is vulnerable to torsion - true or false

A

true

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10
Q

hollow organs are vulnerable to which mechanical injury type?

A

compression

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11
Q

list the 3 injuries categorised as blunt force injury.

A

abrasion
bruising
laceration

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12
Q

list the 2 injuries under sharp force injury

A

stabs and incisions

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13
Q

“Leakage of blood from ruptured small vessels into surrounding tissues”

A

bruising

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14
Q

site of bruise is always the site of impact - true or false

A

false - tracking can occur along path of least resistance

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15
Q

the haemorrhage in bruising usually originates from subcutaneous venules/arterioles - true or false

A

true - not capillaries since these are too small for visible haemorrhage

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16
Q

what are the exceptions to consider in bruising injury pattern?

A

intra-dermal bruise e.g. footwear
seatbelt bruise
tramline
doughnut

areas are compressed and won’t bleed hence pattern of e.g. footprint can be seen

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17
Q

severity of bruising can depend on the victim’s age, gender and body habitus - true or false

A

true - the young and old bruise more, females bruise more and so do obese people

fatty tissue bruises more than bone, more bruising in bleeding disorders and in alcoholics

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18
Q

difference between senile purpura and normal bruising?

A

sharp/well demarcated edges in senile purpura

blood vessels are very vulnerable to shearing

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19
Q

age of a green bruise (roughly)

A

4-5 days (biliverdin)

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20
Q

rough age of a dark purple bruise

A

minutes (deoxyHb)

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21
Q

rough age of a yellow bruise

A

7-10 days (bilirubin)

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22
Q

after how long does a bruise typically disappear?

A

7-14 days

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23
Q

describe fingertip bruising e.g. around upper arm

A

consistency in distance between bruises and also the ages of the bruises.
location can indicate forceful restraint

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24
Q

“a portion of body surface from which the skin or mucous membrane has been removed by rubbing”

A

abrasion

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25
Q

abrasions are a full thickness injury - true or false

A

false - superficial or partial thickness

crushing or scraping of dermis/epidermis

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26
Q

what are the 2 mechanisms behind abrasions?

A

crushing - vertical force (imprint)

scraping - tangential force

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27
Q

describe abrasions (bleeding, healing, scarring?)

A

minimal bleeding, heals quickly, no scar

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28
Q

what are the most forensically useful of all injuries? and why?

A 
ABRASIONS
always occur at site of impact
often reflect pattern of causal object 
often indicate direction of impact
possible trace evidence transfers
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29
Q

what type of injury is a bite mark?

A

combination of abrasion, bruising and laceration

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30
Q

an animal bite mark is deeply arched - true or false

A

true + laceration

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31
Q

a human bite mark is circular or a shallow oval - true or false

A

true

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32
Q

“full thickness tearing of the skin or tissue due to stretching, pinning and crushing by blunt force trauma”

A

laceration

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33
Q

what are the 2 mechanisms underlying lacerations?

A

crushing/splitting - where skin overlies bone

stretching/tearing - where skin is stretched beyond its elastic limit

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34
Q

what wound features are associated with lacerations?

A 
ragged edges
tissue bridges in base
associated bruising and abrasions
bleeding is less than expected (spasm/retraction of vessels)
trace evidence possible
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35
Q

someone is hit on the back of the head with a hammer -> laceration with circular abrasion. why is the abrasion more useful?

A

abrasion gives the shape and hence the weapon

lacerations are less distinctive

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36
Q

falls from height onto concrete show which external injury pattern?

A

stellate laceration

initial central area of impact fractures skull in comminuted pattern causing laceration to extend in stellate pattern

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37
Q

the bleeding in lacerations is often profuse - true or false

A

false - external haemorrhage is often slight in lacerations

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38
Q

a laceration heals with a scar - true or false

A

true

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39
Q

“clean division of the full thickness of the skin or tissue under the pressure of a sharp-edged instrument”

A

incision

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40
Q

Is there any bruising, abrasion or tissue bridges in an incision?

A

no

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41
Q

an incision is longer than it is deep - true or false

A

true

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42
Q

an incision has minimal bleeding - true or false

A

false - profuse bleeding since blood vessels are left cut open, they don’t spasm

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43
Q

what signs would suggest an incision is self-inflicted?

A 
site of election (accessible)
clothes drawn aside
hesitation wounds
handedness
1 or 2 wounds potentially fatal
repetition in wound track
44
Q

what signs would suggest that an incision/ stab is from assault?

A

aimed at target sites but scattered
clothing is cut
most are deep and forceful
defence injuries

45
Q

what types of injury pattern is a chop wound?

A

a variant of incision

46
Q

What are some features of a chop wound?

A

marginal abrasion due to wide blade (“trails off”)
bruising
longer than it is deep

47
Q

“penetrating injury caused by separation of the skin and tissues under the pressure of a sharp or blunt pointed instrument”

A

stab wound

48
Q

Which is the greatest dimension of a stab wound?

A

its depth - goes deeper into the body than its length on body surface

49
Q

on removal of a blade, what happens to the dimensions of a stab wound?

A

widens and shortens on removal blade due to skin elasticity

50
Q

what offers most resistance against a stab wound?

A

clothes and skin

51
Q

wound depth indicates stabbing force - true or false

A

false - wound depth does not indicate force, force is difficult to quantify and easily overestimated.

52
Q

which 3 factors effect the required stabbing force?

A

sharpness of tip of blade
speed of approach
anatomical site (chest vs. abdomen)

53
Q

List the 9 things to describe in relation to documenting a stab wound.

A 
damage to clothing
site
shape
size
alignment
direction
depth
underlying damage
effects
54
Q

what can the shape of a stab wound indicate?

A

cross sectional shape of blade
direction of insertion
movement of victim and/or assailant

55
Q

what distorts the shape of a wound and in which situation would a wound heal with a large scar?

A

Langer lines distort the shape of a wound
If parallel to LL, wound gapes slightly and heals with a small scar.
If at right angles to LL, wound gapes widely and heals with large scar.

56
Q

a boat-shaped incision indicates which type of blade?

A

single-edged blade

57
Q

blade length = wound x?

A

blade length = wound depth

58
Q

blade width = wound ?

A

blade width = wound length

59
Q

blade thickness = wound x ?

A

blade thickness = wound width

60
Q

If a stab wound length > blade width, what does this indicate?

A

wound length > blade width when there is rocking of the knife.

61
Q

If a stab wound length < blade width, what does this indicate?

A

wound length < blade width when skin is stretched prior to penetration (or if blade is not fully inserted).

62
Q

If wound track depth and blade length are not equal, what does this indicate?

A

blade not fully inserted

63
Q

if wound track depth > blade length, what does this indicate?

A

the tissues were compressed

64
Q

when there are multiple wound dimensions, which wound is the most accurate indicator of the blade dimensions?

A

the wound which is deepest but shortest in length

deepest = fully inserted and shortest = no rocking of blade

65
Q

what might cause a laceration to the eyebrows in an assault?

A

kicks/stamps targets at face

66
Q

What are some early complications of injury?

A

haemorrhage (intra-cranial/thoracic/abdominal)
loss of function
fat and air embolism

67
Q

What primary injury are you looking for in a pedestrian RTA?

A

bumper strikes legs - height above heel is important and can indicate acceleration/decel from site of abrasion.

check soles of feet/shoes for pedal parks to see if driver pressing on brake/gas

68
Q

What secondary injuries can be seen in pedestrian RTA?

A

bonnet - strikes thigh, pelvis, chest

windscreen + pillars strike chest and head

69
Q

what tertiary injuries can be seen in pedestrian RTA?

A

victim thrown onto road surface, roadside objects, other vehicles

victim thrown forward if height of vehicle impacts above person’s centre of gravity

70
Q

What signs might you see in a pedestrian that has been run over?

A

patterned imprint abrasions from tyres / underneath of vehicle
flaying lacerations w/ minor bruising
oil/dirt staining of skin

71
Q

List the 5 pedestrian injury patterns from a RTA.

A 
Wrap around
Forward projection
Wing top
Roof top
Somersault
72
Q

a car bonnet lowers on braking - true or false

A

true

rises on acceleration

73
Q

What causes ‘wrap around’ injury?

A

bumper striking leg

74
Q

throw distance suggests speed of impact if vehicle is braking hard - true or false

A

true

throw distance = 1st impact w/ car to 1st impact w/ ground

75
Q

What causes ‘forward projection’?

A

pedestrian struck at or above centre of gravity -> thrown forwards and down.
risk of running over.
adult by high fronted vehicle, child by car

76
Q

A person who is carried over the wing and falls off to the side of a car, will have which injury pattern?

A

‘wing top’

pedestrian struck by front wing

77
Q

a pedestrian hit at high speed is likely to have which injury pattern?

A

‘roof top’ - secondary impact with roof of vehicle
OR
‘somersault’ - thrown high into air so no secondary impact but tertiary impact with road

78
Q

the car bumper strikes the adult femur - true or false

A

false - upper tibia of adult, femur of child

79
Q

The usual height of a car bumper is 40-50cm, if the bumper abrasion is higher or lower on the pedestrian, what does this mean?

A 
higher = car was accelerating
lower = car was braking

height of abrasion measured from heel

80
Q

What are the 2 tibial fractures common to pedestrian RTA?

A

wedge fracture - at point of impact from angulation

spiral fracture - at weakest point from rotational impact

81
Q

When a car has a frontal impact, which direction do the occupants move?

A

move towards point of impact - knees hit dashboard, show soles marked by pedals

continue upwards and forwards - head hits windscreen/roof; chest hits wheel or dashboard

82
Q

List some protective mechanisms of seatbelts.

A

restrain body during deceleration
spread area of decel force + duration of impact
reduce impact w/ steering wheel + dash
prevent ejection during rollover

83
Q

List some protective mechanisms of airbags.

A

restrain upper torso during deceleration
spread are of decel force + duration of impact
reduce impact w. steering wheel, dash & car interior

84
Q

What are some airbag injuries?

A

neck hyperextension, bag-slap

85
Q

What is a classic deceleration injury?

HINT: related to one of the great vessels

A

transection of the aorta

can be isolated or due to (e.g.) sternal fracture

86
Q

If a person is denying driving the culprit car, what injuries will you look for to match them to the car?

A

Diagonal seatbelt injuries
Dicing injuries from tempered side window glass
Transfer of trace material onto windscreen, dash, Seatbelt, airbag
Footwear impressions from pedals

87
Q

What signs indicate vehicular suicide?

A

single vehicle impact, stationary object
no seatbelt worn, no sign of avoidance
intoxication

88
Q

What type of injuries is the head vulnerable to (4)?

A

Impact, rotation, acceleration/ deceleration, swelling

89
Q

GCS totals 15 points, how are these divided?

A

MOTOR - 6; obey commands, localising, normal flexion, abnormal flexion, none.
VERBAL - 5; orientated, confused, words, sounds, none.
EYES - 4; spontaneous, to sounds, to pressure, none.

90
Q

the falx cerebra and tentorium cerebelli

A

falx cerebri - dual membrane that divides right and left hemispheres
tentorium cerebelli - divides cerebellum from cerebral hemispheres

91
Q

What causes a hinge (skull) fracture?

A

at base of skull, impact strikes jaw and transmitted to base of skill - typical in motorcyclists

92
Q

What skull fracture pattern would you see in a fall from height?

A

comminuted radiating fracture

comminuted >2 fragments

93
Q

extradural haematoma is associated with a lucid interval - true or false

A

true

often due to a blow to the temple; may have LOC

94
Q

In 85% of extradural haematomas, a skull fracture tears an artery within the skull, which artery is this?

A

middle meningeal artery inside temporal bone
arterial bleeding strips dura off skull
localised enlarging haematoma by dura

95
Q

a subdural haematoma is often seen in which patients?

A

common in alcoholics, elderly and children since due to a fall or (trivial) blow

96
Q

which vessels are affected most in subdural haemorrhage?

A

bridging veins in subdural space are sheared - blood spreads widely over brain surface

97
Q

Describe the pathogenesis behind natural and traumatic subarachnoid haemorrhages.

A

natural - ruptured berry aneurysm (circle of Willis)

traumatic - arises from contusion or laceration to brain surface, e.g. blow to chin (traumatic basal SAH)

98
Q

Where is the danger area for traumatic basal SAH?

A

the area around the jaw line which extends from lower corner of ear

e.g. due to blow to chin or angle or jaw jerks the head

99
Q

Which artery is the cause of immediate collapse and death in traumatic basal SAH?

A

vertebral artery
strong assoc. with alcohol intoxication
death comes as a surprise to all
culpable homicide

100
Q

which kind of brain haemorrhage is common in hypertension?

A

intracerebral

101
Q

contre-coup contusion is diagonally opposite the point of impact - true or false

A

true

often extensive and due to a fall (backwards)
occur where the brain glides over rough interior skull

102
Q

in a backwards fall, the contre-coup injury is roughly where?

A

rough frontal area

103
Q

which mechanical forces cause diffuse traumatic axonal injury (DTAI)?

A

rotation and acceleration/ deceleration forces

RTA, blows/kicks to mobile head

104
Q

Which microscopic finding would you see 12-24hrs after DTAI?

A

thickened axons seen with silver stains

105
Q

Which microscopic findings can you seen 2-4hrs after DTAI?

A

beta-amyloid precursor protein in immunostains

106
Q

Which microscopic findings can you seen 1 days+ after DTAI?

A

axonal retraction bulbs in white matter

107
Q

concussion causes anterograde amnesia - true or false

A

false - concussion is associated with retrograde amnesia, transient LOC, temporary nerve dysfunction due to impact but no residual structural damage

Forensic medicine (10 decks)

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