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Forensic Medicine > Blunt Force Injury > Flashcards

Blunt Force Injury Flashcards

1
Q

What is the definition of trauma

A

Bodily harm due to transfer of energy from whatever source to the tissues
+/- structural damage and/or physiological effects

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2
Q

What is meant by structural damage in trauma

A

Damage to the underlying body structure

Includes bruising, laceration and breaking the underlying bone

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3
Q

What is meant by physiological effects in trauma

A

Usually a neurological reaction to the trauma such as damaging or effecting the nerves below
Can occur without any outward injury
E.g. Blunt force to the neck can cause reflex cardiac arrest by stimulating the nerves

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4
Q

What is the medical definition of a wound

A

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

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5
Q

What is the legal definition of a wound

A

Breach of the full thickness of the skin or lining of the lip
Less useful than medical definition
Excludes bruising, abrasions and closed fractures

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6
Q

Which types of blunt force trauma are not legally considered wounds

A

Bruises
Abrasions
Fractures (unless open)

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7
Q

Does every blunt force impact cause an injury

A

No

A punch can lead to bruising etc but can also have little/no effect on the tissue

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8
Q

What is the definition of an injury

A

Synonymous with wound but a broader term and therefore more useful
Also includes damage caused by heat, cold, electricity, chemicals and radiation

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9
Q

What is the definition of lesion

A

Used to describe any area of injury, disease (e.g. wart or tumour) or local degeneration in a tissue causing a change in its structure or function
May be used by pathologist if they are not sure the exact nature of the area

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10
Q

How does electricity cause a burn

A

Electricity flows through the body and damages the tissue and can cause injury

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11
Q

How can a ‘blast’ cause an injury

A

Changes in atmospheric pressure cause tissue damage

Particularly to the lungs and internally

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12
Q

What are the 3 types of mechanical force injuries

A

Blunt force trauma
Sharp force trauma
Explosive/firearms force

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13
Q

List the 7 main ways that mechanical force can damage tissue

A

Impact
Angulation - tissue is bent
Compression
Traction - tissues are pulled apart
Torsion - twisting force
Shearing -sliding one layer of tissue over another (chinese burn)
Acceleration/Deceleration- seen in falls from height or RTA

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14
Q

How does degree of force affect injury

A

Greater the force the greater the likelihood of injury

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15
Q

How does tissue area affect injury

A

Energy will be spread out over the area making contact

If larger area the tissues can disperse the energy and leads to less injury

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16
Q

How do you calculate kinetic energy

A

half the mass of the object multiplied by the speed of the object squared
Higher mass and higher speed = greater force

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17
Q

How does duration of force affect injury

A

Quicker duration gives greater sudden energy

Slow push of knife less likely to penetrate than quick stab

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18
Q

What physical factors affect a forces’ ability to cause injury

A 
Degree of force applied 
Area of application of force 
Duration 
Direction - glancing vs direct blows 
Tissue properties - viscosity, plasticity and elasticity
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19
Q

What is meant by tissue viscosity

A

How fluid the tissue is

Protective factor

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20
Q

What is meant by tissue plasticity

A

How the tissue copes with change (how its bends etc)

Protective factor

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21
Q

What is meant by tissue elasticity

A

How quickly the tissue goes back to its natural state - how springy it is
Protective factor

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22
Q

How does direction of force affect injury

A

Direct, resting impact will deliver all of its energy and therefore cause greater injury
Glancing blows do not give up all energy so injure less

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23
Q

How do you calculate energy of a vehicle crash

A

mph2 x 0.034

Divided by stopping distance (use consistent units)

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24
Q

Why is stopping distance so important in a vehicle crash

A

If the car is able to slow down over a large distance then there is less energy on impact - less injury
If you hit an object at high speed the car stops immediately and a lot of energy is transferred - occupants and car absorb a lot of energy = more injury

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25
Q

What is the benefit of a large crumple zone in your car

A

Greater the crumple zone in the car the more energy the vehicle can absorb and the less the occupants do
Reduces injury

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26
Q

What biological factors can influence injury

A

Mobility of body part
Anticipation and coordination
The biomechanical properties of tissues

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27
Q

How does mobility of the body part affect injury

A

If the body part impacted is able to move with the direction of force it absorbs less energy directly and therefore is less injured

e. g. moving with a punch is less likely to injure than staying still
e. g. more likely to injure a standing/stationary leg than swinging/moving leg

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28
Q

How does anticipation and coordination affect injury

A

Being able to anticipate force will reduce injury

e.g. learn how to impact safely by spreading the energy (roll on falling)

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29
Q

Which biomechanical factors protect us from injury

A

Skin is very elastic and resists stretching

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30
Q

Which biomechanical factors make us vulnerable to injury

A

Blood vessels vulnerable to stretch - burst easily
Semi-fluid brain is vulnerable to shearing/rotation - delicate nerves get damaged
Bone is vulnerable to torsion (twisting)
Hollow organs vulnerable to compression

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31
Q

What are the 3 main types of blunt force injury

A

Bruises
Abrasions
Lacerations

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32
Q

In which layer of the skin are blood vessels found

A

Subcutaneous fat

Branches come up to the surface

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33
Q

When does a bruise occur

A

When an object strikes the skin and the blood vessels below are torn and stretched beneath it
Skin in not broken

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34
Q

What is a laceration

A

A more severe, full thickness injury

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35
Q

What is a stab

A

Short and deep wound

Weapon is plunged into the tissue - deeper in body than width/length on surface

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36
Q

What is an incision

A

Wide lesion on skin surface but not very deep
Weapon dragged across
Causes a full thickness injury

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37
Q

What is a cerebral contusion

A

A bruise to the brain

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38
Q

Do bruises occur in death

A

Not usually

The heart isn’t pumping so there isn’t enough pressure for the blood to leak out and spread

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39
Q

What is a vital phenomenon

A

Something that only occurs within life

Such as a bruise

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40
Q

Where do bruises most commonly occur

A

Within the subcutaneous fat

Some may leak into the dermis

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41
Q

Describe how bruises ‘track’

A

Bruising can track/move with gravity and muscle movement as the blood moves
e.g. impact to the forehead or a skull fracture can lead to a black eye

This can take time so bruises may appear over a few days and then become bigger and darker (develop)

42
Q

Do bruises usually match the shape of impact/weapon

A

This is rare
The blood that leaks out will spread out in 3 dimensions
Edges will be blurry so not a distinct shape

43
Q

Describe how a tramline bruise forms

A

Usually due to the impact of a rod shaped object
The vessels in the site of impact are compressed forming a central pale area
Vessels either side rupture due to stretch and from the 2 parallel tramline bruises

44
Q

What may an intradermal bruise show

A

As this is more superficial it may show the pattern of the object
Example: stamp bruise
However, seeing the exact tread is rare - requires very localised bleeding

45
Q

What can seatbelt bruises tell you

A

Which side of the car the person was on - direction of bruise
Useful if there is suspicion of swapping drivers

46
Q

What causes a donut bruise

A

Caused by impact of a circular object such as a ball

Central pale area where vessels are compressed and circular bruise around

47
Q

What does a curved bruise suggest

A

Weapon that has mobility such as a hose

Flexible weapons will also move around any convexities of the body

48
Q

What should be included in the documentation of an injury

A

Site
Precise location - usually in relation to an anatomical landmark
Type of injury
Shape - relation to common object (circle, pear, boat)
Size - length, width, depth
Associated features - injury to underlying/surrounding structure
Clinical effects - haemorrhage, was it fatal, how did it affect patient

49
Q

What is haemorrhage

A

The escape of blood from any part of the vascular system - veins, artery, heart
Can be external - onto surface
Internal - into a body cavity
Or into tissues which is a bruise

50
Q

What is the definition of a bruise

A

Leakage of blood from ruptured small vessels into the surrounding tissues - seen as discolouration through intact skin
Due to blunt force trauma

51
Q

What is a haematoma

A

A swollen bruise within a confined space

52
Q

Which tissues can bruise

A

Any tissue can bruise

53
Q

Are bruises tender

A

Yes typically

Tenderness can be elicited by pressing on the bruise

54
Q

What is the difference between an internal and external bruise

A

External - visible on skin surface
(may be masked on darker skin)

Internal - not visible on skin surface
too deep

55
Q

List some of the difficulties with bruise interpretation

A

Site of bruise isn’t always site of impact - tracking
Appearance may be delayed
Shape rarely reflects causal object
Size rarely reflects severity of impact - e.g. minor impact can cause large bruise, especially in the elderly or alcoholics
Accurate ageing is hard

56
Q

Where do bruises track

A

Along the planes of least resistance

This can be natural or traumatic planes

57
Q

What is the severity of a bruise dependent on

A

Degree of force
Site of impact - loose fatty tissue bruise easily as vessels are poorly supported
Age of victim - very young and very old
Sex of victim - females bruise more easily as greater subcutaneous fat
Obesity
Natural disease - blood disorders
Alcohol intake - alcoholics bruise easily and often, fall risk and clotting issues due to liver damage

58
Q

Why do the elderly bruise easily

A

Connective tissues degenerate with age so blood vessels are less supported
They tear very easily so everyday impacts can cause bruising
Skin is thinner so bruises are more obvious - clear edges
Called senile purpura

59
Q

List the colour changes seen as a bruise ages

A

dark red - immediate - due to oxyHaemoglobin
Dusky purple - after minutes - due to deoxyhaemoglobin
Brown - after 1-3 days
Green - after 4-5 days - due to biliverdin (Hb breakdown product)
Yellow - after 7-10 days - due to bilirubin
Disappears after 7-14 days

Lots of variation between individuals

60
Q

What is senile purpura

A

Distinct, well defined bruising in the elderly

Dark purple

61
Q

Are bruises easy to age

A

No

Lots of individual variation so not an accurate process

62
Q

Bruises on the face and ears are suggestive of what

A

Punching and kicking assaults

May also see bruising on the inside of the lips

63
Q

Bruises on the upper neck are suggestive of what

A

Strangulation

May see fingertip marks

64
Q

Bruises on the limbs are suggestive of what

A

Forceful restraint

65
Q

Bruises on the back are suggestive of what

A

Counter pressure - being pressed against a hard flat surface such as wall/the floor etc
Most common in spine or shoulder blades
Or if patient has been lying down for a long period - tracking

66
Q

Bruises of various ages are suggestive of what

A

Repeated assaults or abuse

Useful in child abuse cases

67
Q

Resuscitation may cause bruising - where

A

Face, neck and chest

68
Q

Are bruises on the shins normal or abnormal in children

A

Normal

Often occur through normal play, activity and falls

69
Q

Describe the appearance of fingertip bruises

A

Similar size and age

Spacing between matches finger spread

70
Q

Fingertip bruises on the thighs may be suggestive of what

A

Sexual assault

Even with absence of genital injury

71
Q

What is lividity

A

Post-mortem phenomenon where blood pools in the vessels due to gravity and causes skin discoloration
Can be confused with bruising but is not the same

72
Q

What is the definition of an abrasion

A

A portion of the body surface from which the skin or mucous membrane has been removed by rubbing/friction
Superficial or partial thickness injury - only involves epidermis and/or dermis
Includes imprints and scraping/grazes

73
Q

What causes an abrasion

A

Crushing or scraping of the epidermis/dermis
Crushing is a vertical force - imprints into the skin
Scraping is a tangiential force across the skin surface

74
Q

What is the difference between a graze and a scratch

A

Graze is a scraping abrasion over a large area - such as road rash
A scratch is a scraping abrasion over a fine point - e.g. from a fingernail

75
Q

Do abrasions bleed a lot

A

No - bleeding is usually slight as the vessels are lower down in the skin
They will heal quickly and won’t leave a scar

76
Q

Are abrasions clinically significant

A

Not really

Often overlooked by doctors as not usually severe

77
Q

Describe an imprint abrasion

A

Underlying skin is crushed from the outside

Often leaves an imprint of the causal object or overlying clothing

78
Q

What happens to an abrasion after death

A

It dries out
Leaves an orange/brown, leathery appearance
May look like parchment

79
Q

What can cause an imprint abrasion

A 
Footwear
Tyre impressions 
Clothing weave 
Ligature weaves 
Seatbelts 
Vehicle parts in a RTA 
Weapon itself 
Hilt of knife
80
Q

Describe a scrape abrasion

A

Object dragged across skin causes the epidermis to be scraped off and pushed to the ‘finishing edge’ - leaves skin tags
Can show direction of scrape
May bleed slightly is some dermal papillae are disrupted

81
Q

What type of abrasion is road rash

A

Scrape abrasion

82
Q

What is the forensic importance of abrasions

A

Most useful injury type

Always occur at site of impact
Often reflect the pattern of the causal object/surface
Often indicate the direction of impact
Possible transfer of trace evidence - grit or dirt

83
Q

Can abrasions be aged

A

Not really
Can tell if its healing but not really age it
Will dry out and pucker

84
Q

Bite marks are suggestive of what

A

May be seen in sexual assault and child abuse

Can be a result of young siblings, pets, sporting collisions as well as assault or self-inflicted injury

85
Q

What type of injury is a mouth mark

A

May be a combination of bruising, abrasion and laceration
Teeth cause abrasions and bruising
Laceration if sharp like an animal bite
Suction leaves a central bruise - hickey

86
Q

Why is mouth mark a better description than bite mark

A

Not just the teeth involved
Also tongue, lips and suction force - tissue is drawn into the mouth
Suction leaves a bruise - hickey

87
Q

Describe the appearance of an animal bite

A

Will be deeply arched

Sharper teeth cause lacerations

88
Q

Describe the appearance of a human bite

A

Circular or oval in shape

Shallow

89
Q

What is the definition of laceration

A

Full thickness tearing of the skin due to stretching, pinning and crushing by blunt force trauma
Irregular edges
Can occur in any tissue

90
Q

What are the 2 mechanisms of laceration

A

Crushing or splitting

Stretching or tearing

91
Q

Where do crushing/splitting lacerations typically occur

A

Areas where skin overlies bone such as the scalp, eyebrow, cheek, knees, elbows and knuckles
Blunt force in these areas - blows to head or falls
Punches in the case of the knuckles

92
Q

When do stretching/tearing laceration occur

A

When skin is stretched past its elastic limit

93
Q

What are the physical features of a laceration

A

Ragged edges
Tissue bridges in base - skin splits unevenly
Associated bruises and abrasions - often on margins
Minor bleeding despite size - associated with spasm/retraction of vessels
Don’t usually indicate shape of causal object - skin stretched or tears irregularly
May hold trace evidence - splinters, paint chip from care

94
Q

How might a laceration from a hammer strike appear

A

Circular laceration with abrasions
Stellate splitting of laceration
Glancing blows may have more of a moon shape

95
Q

What is flaying

A

A type of stretching laceration

Seen in RTA - tires split skin then tear it off as they spin

96
Q

What causes post-mortem lacerations

A

Oedematous or elderly skin can split when handled

Fingers can tear it when lifting the body

97
Q

What is the clinical significance of lacerations

A 
Haemorrhage is usually slight 
Often require suturing 
Foreign bodies and infection are common 
Heals by scarring 
May be confused with incision
98
Q

What are the main differences between lacerations and incisions

A

Lacerations are blunt force - have tissue bridges, bruising in base and marginal abrasion
Incisions are sharp force and so have no tissue bridges, bruises or abrasions

Bleeding is slight in lacerations but profuse in incisions

Trace evidence is often found in lacerations but is rare with incisions

99
Q

In which layer of the skin are hair follicles and sweat glands found

A

Dermis

100
Q

How can you differentiate between a bruise and lividity if unsure

A

Make an incision
If there is blood in the tissue itself it is a bruise
If not it is lividity

Forensic Medicine (13 decks)

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