Injury patterns and mechanisms Flashcards
Legal definition of wound?
breach of full thickness of skin or lining of lip (excludes bruising, abrasions and fracture)
Medical definition of a wound?
disruption in the continuity of the tissues produced by external mechanical force
What are the 7 forms of mechanical trauma?
impact angulation compression traction torsion shearing acceleration/deceleration
Degree of force applied is a physical factor that must be considered in injury patterns. What other physical factors must be considered (4)?
Area of application of force
duration of application
direction of application
tissue properties (elasticity, viscosity, plasticity)
In kinetic energy, which carries more power, velocity or mass?
velocity
e.g. a bullet travels at several hundred mph but is only a few grams
skin is elastic and resists stretching - true or false
true
blood vessels are vulnerable to stretching - true or false
true
the semi-fluid brain is vulnerable to which type of mechanical injury?
semi fluid brain is vulnerable to shearing/rotation injury
bone is vulnerable to torsion - true or false
true
hollow organs are vulnerable to which mechanical injury type?
compression
list the 3 injuries categorised as blunt force injury.
abrasion
bruising
laceration
list the 2 injuries under sharp force injury
stabs and incisions
“Leakage of blood from ruptured small vessels into surrounding tissues”
bruising
site of bruise is always the site of impact - true or false
false - tracking can occur along path of least resistance
the haemorrhage in bruising usually originates from subcutaneous venules/arterioles - true or false
true - not capillaries since these are too small for visible haemorrhage
what are the exceptions to consider in bruising injury pattern?
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
severity of bruising can depend on the victim’s age, gender and body habitus - true or false
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
difference between senile purpura and normal bruising?
sharp/well demarcated edges in senile purpura
blood vessels are very vulnerable to shearing
age of a green bruise (roughly)
4-5 days (biliverdin)
rough age of a dark purple bruise
minutes (deoxyHb)
rough age of a yellow bruise
7-10 days (bilirubin)
after how long does a bruise typically disappear?
7-14 days
describe fingertip bruising e.g. around upper arm
consistency in distance between bruises and also the ages of the bruises.
location can indicate forceful restraint
“a portion of body surface from which the skin or mucous membrane has been removed by rubbing”
abrasion
abrasions are a full thickness injury - true or false
false - superficial or partial thickness
crushing or scraping of dermis/epidermis
what are the 2 mechanisms behind abrasions?
crushing - vertical force (imprint)
scraping - tangential force
describe abrasions (bleeding, healing, scarring?)
minimal bleeding, heals quickly, no scar
what are the most forensically useful of all injuries? and why?
ABRASIONS always occur at site of impact often reflect pattern of causal object often indicate direction of impact possible trace evidence transfers
what type of injury is a bite mark?
combination of abrasion, bruising and laceration
an animal bite mark is deeply arched - true or false
true + laceration
a human bite mark is circular or a shallow oval - true or false
true
“full thickness tearing of the skin or tissue due to stretching, pinning and crushing by blunt force trauma”
laceration
what are the 2 mechanisms underlying lacerations?
crushing/splitting - where skin overlies bone
stretching/tearing - where skin is stretched beyond its elastic limit
what wound features are associated with lacerations?
ragged edges tissue bridges in base associated bruising and abrasions bleeding is less than expected (spasm/retraction of vessels) trace evidence possible
someone is hit on the back of the head with a hammer -> laceration with circular abrasion. why is the abrasion more useful?
abrasion gives the shape and hence the weapon
lacerations are less distinctive
falls from height onto concrete show which external injury pattern?
stellate laceration
initial central area of impact fractures skull in comminuted pattern causing laceration to extend in stellate pattern
the bleeding in lacerations is often profuse - true or false
false - external haemorrhage is often slight in lacerations
a laceration heals with a scar - true or false
true
“clean division of the full thickness of the skin or tissue under the pressure of a sharp-edged instrument”
incision
Is there any bruising, abrasion or tissue bridges in an incision?
no
an incision is longer than it is deep - true or false
true
an incision has minimal bleeding - true or false
false - profuse bleeding since blood vessels are left cut open, they don’t spasm
what signs would suggest an incision is self-inflicted?
site of election (accessible) clothes drawn aside hesitation wounds handedness 1 or 2 wounds potentially fatal repetition in wound track
what signs would suggest that an incision/ stab is from assault?
aimed at target sites but scattered
clothing is cut
most are deep and forceful
defence injuries
what types of injury pattern is a chop wound?
a variant of incision
What are some features of a chop wound?
marginal abrasion due to wide blade (“trails off”)
bruising
longer than it is deep
“penetrating injury caused by separation of the skin and tissues under the pressure of a sharp or blunt pointed instrument”
stab wound
Which is the greatest dimension of a stab wound?
its depth - goes deeper into the body than its length on body surface
on removal of a blade, what happens to the dimensions of a stab wound?
widens and shortens on removal blade due to skin elasticity
what offers most resistance against a stab wound?
clothes and skin
wound depth indicates stabbing force - true or false
false - wound depth does not indicate force, force is difficult to quantify and easily overestimated.
which 3 factors effect the required stabbing force?
sharpness of tip of blade
speed of approach
anatomical site (chest vs. abdomen)
List the 9 things to describe in relation to documenting a stab wound.
damage to clothing site shape size alignment direction depth underlying damage effects
what can the shape of a stab wound indicate?
cross sectional shape of blade
direction of insertion
movement of victim and/or assailant
what distorts the shape of a wound and in which situation would a wound heal with a large scar?
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.
a boat-shaped incision indicates which type of blade?
single-edged blade
blade length = wound x?
blade length = wound depth
blade width = wound ?
blade width = wound length
blade thickness = wound x ?
blade thickness = wound width
If a stab wound length > blade width, what does this indicate?
wound length > blade width when there is rocking of the knife.
If a stab wound length < blade width, what does this indicate?
wound length < blade width when skin is stretched prior to penetration (or if blade is not fully inserted).
If wound track depth and blade length are not equal, what does this indicate?
blade not fully inserted
if wound track depth > blade length, what does this indicate?
the tissues were compressed
when there are multiple wound dimensions, which wound is the most accurate indicator of the blade dimensions?
the wound which is deepest but shortest in length
deepest = fully inserted and shortest = no rocking of blade
what might cause a laceration to the eyebrows in an assault?
kicks/stamps targets at face
What are some early complications of injury?
haemorrhage (intra-cranial/thoracic/abdominal)
loss of function
fat and air embolism
What primary injury are you looking for in a pedestrian RTA?
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
What secondary injuries can be seen in pedestrian RTA?
bonnet - strikes thigh, pelvis, chest
windscreen + pillars strike chest and head
what tertiary injuries can be seen in pedestrian RTA?
victim thrown onto road surface, roadside objects, other vehicles
victim thrown forward if height of vehicle impacts above person’s centre of gravity
What signs might you see in a pedestrian that has been run over?
patterned imprint abrasions from tyres / underneath of vehicle
flaying lacerations w/ minor bruising
oil/dirt staining of skin
List the 5 pedestrian injury patterns from a RTA.
Wrap around Forward projection Wing top Roof top Somersault
a car bonnet lowers on braking - true or false
true
rises on acceleration
What causes ‘wrap around’ injury?
bumper striking leg
throw distance suggests speed of impact if vehicle is braking hard - true or false
true
throw distance = 1st impact w/ car to 1st impact w/ ground
What causes ‘forward projection’?
pedestrian struck at or above centre of gravity -> thrown forwards and down.
risk of running over.
adult by high fronted vehicle, child by car
A person who is carried over the wing and falls off to the side of a car, will have which injury pattern?
‘wing top’
pedestrian struck by front wing
a pedestrian hit at high speed is likely to have which injury pattern?
‘roof top’ - secondary impact with roof of vehicle
OR
‘somersault’ - thrown high into air so no secondary impact but tertiary impact with road
the car bumper strikes the adult femur - true or false
false - upper tibia of adult, femur of child
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?
higher = car was accelerating lower = car was braking
height of abrasion measured from heel
What are the 2 tibial fractures common to pedestrian RTA?
wedge fracture - at point of impact from angulation
spiral fracture - at weakest point from rotational impact
When a car has a frontal impact, which direction do the occupants move?
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
List some protective mechanisms of seatbelts.
restrain body during deceleration
spread area of decel force + duration of impact
reduce impact w/ steering wheel + dash
prevent ejection during rollover
List some protective mechanisms of airbags.
restrain upper torso during deceleration
spread are of decel force + duration of impact
reduce impact w. steering wheel, dash & car interior
What are some airbag injuries?
neck hyperextension, bag-slap
What is a classic deceleration injury?
HINT: related to one of the great vessels
transection of the aorta
can be isolated or due to (e.g.) sternal fracture
If a person is denying driving the culprit car, what injuries will you look for to match them to the car?
Diagonal seatbelt injuries
Dicing injuries from tempered side window glass
Transfer of trace material onto windscreen, dash, Seatbelt, airbag
Footwear impressions from pedals
What signs indicate vehicular suicide?
single vehicle impact, stationary object
no seatbelt worn, no sign of avoidance
intoxication
What type of injuries is the head vulnerable to (4)?
Impact, rotation, acceleration/ deceleration, swelling
GCS totals 15 points, how are these divided?
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.
the falx cerebra and tentorium cerebelli
falx cerebri - dual membrane that divides right and left hemispheres
tentorium cerebelli - divides cerebellum from cerebral hemispheres
What causes a hinge (skull) fracture?
at base of skull, impact strikes jaw and transmitted to base of skill - typical in motorcyclists
What skull fracture pattern would you see in a fall from height?
comminuted radiating fracture
comminuted >2 fragments
extradural haematoma is associated with a lucid interval - true or false
true
often due to a blow to the temple; may have LOC
In 85% of extradural haematomas, a skull fracture tears an artery within the skull, which artery is this?
middle meningeal artery inside temporal bone
arterial bleeding strips dura off skull
localised enlarging haematoma by dura
a subdural haematoma is often seen in which patients?
common in alcoholics, elderly and children since due to a fall or (trivial) blow
which vessels are affected most in subdural haemorrhage?
bridging veins in subdural space are sheared - blood spreads widely over brain surface
Describe the pathogenesis behind natural and traumatic subarachnoid haemorrhages.
natural - ruptured berry aneurysm (circle of Willis)
traumatic - arises from contusion or laceration to brain surface, e.g. blow to chin (traumatic basal SAH)
Where is the danger area for traumatic basal SAH?
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
Which artery is the cause of immediate collapse and death in traumatic basal SAH?
vertebral artery
strong assoc. with alcohol intoxication
death comes as a surprise to all
culpable homicide
which kind of brain haemorrhage is common in hypertension?
intracerebral
contre-coup contusion is diagonally opposite the point of impact - true or false
true
often extensive and due to a fall (backwards)
occur where the brain glides over rough interior skull
in a backwards fall, the contre-coup injury is roughly where?
rough frontal area
which mechanical forces cause diffuse traumatic axonal injury (DTAI)?
rotation and acceleration/ deceleration forces
RTA, blows/kicks to mobile head
Which microscopic finding would you see 12-24hrs after DTAI?
thickened axons seen with silver stains
Which microscopic findings can you seen 2-4hrs after DTAI?
beta-amyloid precursor protein in immunostains
Which microscopic findings can you seen 1 days+ after DTAI?
axonal retraction bulbs in white matter
concussion causes anterograde amnesia - true or false
false - concussion is associated with retrograde amnesia, transient LOC, temporary nerve dysfunction due to impact but no residual structural damage
