Blunt Force Injury Flashcards
What is the definition of trauma
Bodily harm due to transfer of energy from whatever source to the tissues
+/- structural damage and/or physiological effects
What is meant by structural damage in trauma
Damage to the underlying body structure
Includes bruising, laceration and breaking the underlying bone
What is meant by physiological effects in trauma
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
What is the medical definition of a wound
Disruption in the continuity of the tissues produced by external mechanical force
What is the legal definition of a wound
Breach of the full thickness of the skin or lining of the lip
Less useful than medical definition
Excludes bruising, abrasions and closed fractures
Which types of blunt force trauma are not legally considered wounds
Bruises
Abrasions
Fractures (unless open)
Does every blunt force impact cause an injury
No
A punch can lead to bruising etc but can also have little/no effect on the tissue
What is the definition of an injury
Synonymous with wound but a broader term and therefore more useful
Also includes damage caused by heat, cold, electricity, chemicals and radiation
What is the definition of lesion
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
How does electricity cause a burn
Electricity flows through the body and damages the tissue and can cause injury
How can a ‘blast’ cause an injury
Changes in atmospheric pressure cause tissue damage
Particularly to the lungs and internally
What are the 3 types of mechanical force injuries
Blunt force trauma
Sharp force trauma
Explosive/firearms force
List the 7 main ways that mechanical force can damage tissue
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
How does degree of force affect injury
Greater the force the greater the likelihood of injury
How does tissue area affect injury
Energy will be spread out over the area making contact
If larger area the tissues can disperse the energy and leads to less injury
How do you calculate kinetic energy
half the mass of the object multiplied by the speed of the object squared
Higher mass and higher speed = greater force
How does duration of force affect injury
Quicker duration gives greater sudden energy
Slow push of knife less likely to penetrate than quick stab
What physical factors affect a forces’ ability to cause injury
Degree of force applied Area of application of force Duration Direction - glancing vs direct blows Tissue properties - viscosity, plasticity and elasticity
What is meant by tissue viscosity
How fluid the tissue is
Protective factor
What is meant by tissue plasticity
How the tissue copes with change (how its bends etc)
Protective factor
What is meant by tissue elasticity
How quickly the tissue goes back to its natural state - how springy it is
Protective factor
How does direction of force affect injury
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
How do you calculate energy of a vehicle crash
mph2 x 0.034
Divided by stopping distance (use consistent units)
Why is stopping distance so important in a vehicle crash
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
What is the benefit of a large crumple zone in your car
Greater the crumple zone in the car the more energy the vehicle can absorb and the less the occupants do
Reduces injury
What biological factors can influence injury
Mobility of body part
Anticipation and coordination
The biomechanical properties of tissues
How does mobility of the body part affect injury
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
How does anticipation and coordination affect injury
Being able to anticipate force will reduce injury
e.g. learn how to impact safely by spreading the energy (roll on falling)
Which biomechanical factors protect us from injury
Skin is very elastic and resists stretching
Which biomechanical factors make us vulnerable to injury
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
What are the 3 main types of blunt force injury
Bruises
Abrasions
Lacerations
In which layer of the skin are blood vessels found
Subcutaneous fat
Branches come up to the surface
When does a bruise occur
When an object strikes the skin and the blood vessels below are torn and stretched beneath it
Skin in not broken
What is a laceration
A more severe, full thickness injury
What is a stab
Short and deep wound
Weapon is plunged into the tissue - deeper in body than width/length on surface
What is an incision
Wide lesion on skin surface but not very deep
Weapon dragged across
Causes a full thickness injury
What is a cerebral contusion
A bruise to the brain
Do bruises occur in death
Not usually
The heart isn’t pumping so there isn’t enough pressure for the blood to leak out and spread
What is a vital phenomenon
Something that only occurs within life
Such as a bruise
Where do bruises most commonly occur
Within the subcutaneous fat
Some may leak into the dermis
Describe how bruises ‘track’
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)
Do bruises usually match the shape of impact/weapon
This is rare
The blood that leaks out will spread out in 3 dimensions
Edges will be blurry so not a distinct shape
Describe how a tramline bruise forms
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
What may an intradermal bruise show
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
What can seatbelt bruises tell you
Which side of the car the person was on - direction of bruise
Useful if there is suspicion of swapping drivers
What causes a donut bruise
Caused by impact of a circular object such as a ball
Central pale area where vessels are compressed and circular bruise around
What does a curved bruise suggest
Weapon that has mobility such as a hose
Flexible weapons will also move around any convexities of the body
What should be included in the documentation of an injury
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
What is haemorrhage
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
What is the definition of a bruise
Leakage of blood from ruptured small vessels into the surrounding tissues - seen as discolouration through intact skin
Due to blunt force trauma
What is a haematoma
A swollen bruise within a confined space
Which tissues can bruise
Any tissue can bruise
Are bruises tender
Yes typically
Tenderness can be elicited by pressing on the bruise
What is the difference between an internal and external bruise
External - visible on skin surface
(may be masked on darker skin)
Internal - not visible on skin surface
too deep
List some of the difficulties with bruise interpretation
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
Where do bruises track
Along the planes of least resistance
This can be natural or traumatic planes
What is the severity of a bruise dependent on
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
Why do the elderly bruise easily
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
List the colour changes seen as a bruise ages
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
What is senile purpura
Distinct, well defined bruising in the elderly
Dark purple
Are bruises easy to age
No
Lots of individual variation so not an accurate process
Bruises on the face and ears are suggestive of what
Punching and kicking assaults
May also see bruising on the inside of the lips
Bruises on the upper neck are suggestive of what
Strangulation
May see fingertip marks
Bruises on the limbs are suggestive of what
Forceful restraint
Bruises on the back are suggestive of what
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
Bruises of various ages are suggestive of what
Repeated assaults or abuse
Useful in child abuse cases
Resuscitation may cause bruising - where
Face, neck and chest
Are bruises on the shins normal or abnormal in children
Normal
Often occur through normal play, activity and falls
Describe the appearance of fingertip bruises
Similar size and age
Spacing between matches finger spread
Fingertip bruises on the thighs may be suggestive of what
Sexual assault
Even with absence of genital injury
What is lividity
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
What is the definition of an abrasion
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
What causes an abrasion
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
What is the difference between a graze and a scratch
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
Do abrasions bleed a lot
No - bleeding is usually slight as the vessels are lower down in the skin
They will heal quickly and won’t leave a scar
Are abrasions clinically significant
Not really
Often overlooked by doctors as not usually severe
Describe an imprint abrasion
Underlying skin is crushed from the outside
Often leaves an imprint of the causal object or overlying clothing
What happens to an abrasion after death
It dries out
Leaves an orange/brown, leathery appearance
May look like parchment
What can cause an imprint abrasion
Footwear Tyre impressions Clothing weave Ligature weaves Seatbelts Vehicle parts in a RTA Weapon itself Hilt of knife
Describe a scrape abrasion
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
What type of abrasion is road rash
Scrape abrasion
What is the forensic importance of abrasions
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
Can abrasions be aged
Not really
Can tell if its healing but not really age it
Will dry out and pucker
Bite marks are suggestive of what
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
What type of injury is a mouth mark
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
Why is mouth mark a better description than bite mark
Not just the teeth involved
Also tongue, lips and suction force - tissue is drawn into the mouth
Suction leaves a bruise - hickey
Describe the appearance of an animal bite
Will be deeply arched
Sharper teeth cause lacerations
Describe the appearance of a human bite
Circular or oval in shape
Shallow
What is the definition of laceration
Full thickness tearing of the skin due to stretching, pinning and crushing by blunt force trauma
Irregular edges
Can occur in any tissue
What are the 2 mechanisms of laceration
Crushing or splitting
Stretching or tearing
Where do crushing/splitting lacerations typically occur
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
When do stretching/tearing laceration occur
When skin is stretched past its elastic limit
What are the physical features of a laceration
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
How might a laceration from a hammer strike appear
Circular laceration with abrasions
Stellate splitting of laceration
Glancing blows may have more of a moon shape
What is flaying
A type of stretching laceration
Seen in RTA - tires split skin then tear it off as they spin
What causes post-mortem lacerations
Oedematous or elderly skin can split when handled
Fingers can tear it when lifting the body
What is the clinical significance of lacerations
Haemorrhage is usually slight Often require suturing Foreign bodies and infection are common Heals by scarring May be confused with incision
What are the main differences between lacerations and incisions
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
In which layer of the skin are hair follicles and sweat glands found
Dermis
How can you differentiate between a bruise and lividity if unsure
Make an incision
If there is blood in the tissue itself it is a bruise
If not it is lividity
