SAQ assessment Flashcards
Anisotropic meaning
It’s properties depend on direction; Bone is stronger when forces are applied to its longitudinal axis than horizontal; elastically anisotropic.
first level bone structures
1.woven bone
2.plexiform bone
3.primary osteonal cortical bone
4.secondary osteonal cortical bone
second level bone structures
structures which make up osteons
1. osteoblasts (formers)
2. osteocytes (mature cells)
3. osteoclasts (destroyers)
Two types of bone pattern
- woven; weak, haphazard organisation
- lamellar; strong, regular, parallel
Bone remodelling
- in response to mechanical stress
- dynamic rather than static loading promotes remodelling
Forces acting on bone
- tension
- compression
- torsion
- bending
- shearing
Affect of forces on femur
- Strongest: compressive longitudinal
- Weakest: tensile transverse strength
stress definition
the measure of the forces acting on a body (load)
load definition
the average force per unit area under which forces act
Strain definition
Deformation of a deformable body under the application of stress
Young’s modulus
- a measure of the intrinsic stiffness of a material
- The slope of the stress-strain curve within the elastic region/before the yield point
area under the stress-strain curve
a measure of the amount of energy needed to cause material failure; energy absorption/ modulus of toughness
Types of trauma
- blunt
- sharp
- ballistic
- burning
- explosive
displacement fracture
when two broken ends of bone no longer meet
Hinge fracture
when a break only passes through part of the bone, causing a portion to hinge off but remain attached.
Greenstick fracture
no displacement between broken ends - incomplete transverse fracture
comminuted fractures
result in multiple pieces
Tension
- Force that pulls on a bone
- usually directed along the long axis of bone
-few fracture lines/rare in bone
-Common in accidents/little forensic relevance
Compression
-Forces push down on the bone
-cause fracture lines radiating from point of impact
-most common in skull
-shape may be similar to fracturing instrument
-vertical fracture along long axis of bone
-depressed fracture (skull)
-Torus/buckling fracture; unilateral buckling of cortex at the end of long bones
Torsion
-A twisting force when one end of the bone is stationary whilst the other end is twisted
-pedestrian vs car
-Fractures spiral down the long axis of bone (spiral fractures)
-caused by accidents
Bending
-force impacts side of bone at right angles to its long axis, compression and tension occur as a result
-Butterfly fracture (apex faces tension, base compression)
-Greenstick fracture; incomplete transverse
-comminuted fracture
Shearing
-load is applied at right angles to long axis of bone whilst one end of the bone is fixed in place
-Colles’ fracture (distal radius) from fall onto outstretched arm
-common with accidents or dismemberment
Speed of force/loading rate
-Dynamic; sudden stress delivered at a high speed
-Static; stress applied slowly, builds to a point where bone breaks. Usually results in displacement without fracture
Forces causing BFT
Compression, bending, shearing
Forces causing SFT
Compression or shearing
Forces causing ballistic trauma
compressive and bending
delivery of blunt force trauma
low-energy impacts resulting from a broad instrument delivered over a relatively large surface area (vehicular accidents most common type)
smaller focus of force
less force needed to fracture
stress
the force applied to the bone
strain
the forces passing through the bone
yield point
bent but not broken, will not bounce back (plastic deformation), permanent deformation
Bone failure
the fracture of the bone
Young’s modulus of elasticity
during the initial stage of loading, elastic deformation, bone is subject to a degree of force with which the bone is able to cope competently
when does plastic deformation take place?
after the yield point is reached
sign that both elastic and plastic deformation have occurred
bone will fit back together perfectly
slow load application
more time for bone to bend, significant deformation is typical of BFT
rapid load application
minimal deformation of skeletal tissue, fragments fit together more easily; bone does not progress through the elastic/plastic stages but fails immediately = ballistic or explosive trauma from shearing force
slow loading fracture characteristics
tortuous with rougher fracture surfaces
large amounts of peripheral damage
fracture deflects along cement lines, not taking a direct path
fracture is wider and clearly marked
rapid loading fracture characteristics
straighter fractures with less peripheral damage
smoother fracture surface
fracture progresses along a single path with minimal deflection, narrower gap
difference in loading type fracture characteristics cause
rate dependent change in properties of collagen from brittle to ductile as strain rate increases
Bow fractures
plastic deformation = compression bend to bone (juvenile) - result of micro fractures/not reached point of failure
Bone bruise
Compression micro fractures = visible radiographically
Torus/buckling fracture
unilateral buckling of cortex
greenstick fracture
incomplete transverse fracture (juvenile)
Toddlers fracture
incomplete spiral or oblique fracture
vertical fracture
fracture along long axis = compressive
depressed fracture
inward pointing defect = compressive
transverse fracture
crosses diaphysis at right angles to long axis
oblique fracture
crosses diaphysis on a horizontal
spiral fracture
spirals up long axis due to excessive torsion
comminuted fracture
break resulting in production of more than 2 pieces
Butterfly fracture
wedge of bone separates from fractured ends
segmental fracture
three segments
epiphyseal fracture
occurs at ends of long bones, can separate epiphysis from diaphyseal metaphysis - can inhibit further growth
bone fails under what force?
under tension, stronger under compression
linear skull fracture
straight
diastic skull fracture
fracture along a suture line
Depressed skull fracture
hinge/crushing in of skull
Stellate skull fracture
impact site with radiating fracture lines like the sun and rays
First phase skull response to BFT
In bending at impact site with concomitant out-bending surrounding the impact site
second phase skull response to BFT
fracture lines begin at various points on the out-bent surface and progress inward to impact site and outward where they form radiating fracture lines; if force continues, causes the formation of wedge shaped pieces of bones
Third phase skull response to BFT
If force is sufficient to penetrate vault, concentric fractures occur around the area of impact as tips of the wedge are forced inwards; fractures occur from the outer table to the inner table angling away from the point of impact (hoop fractures)
Facial fracturing
Blunt forces guided by facial buttresses; breaks occur at set points to dissipate force
LeFort 1
separation of alveolar part of the maxilla from the rest of the viscerocranium; Results from blow to face from front or side
LeFort 2
separation of the mid-face from the rest of the viscerocranium; Results from a blow to the anterior mid-face
LeFort 3
separation of the entire viscerocranium from the neurocranium; Result of a blow to the upper face
ring fracture
> caused by skull being forced down onto vertebral column; fall onto head from height or onto locked legs or buttocks
begins at posterior occipital and progresses anteriorly
order of mandibular fracture
body>angle>condyles>symphysis>ascending ramus>coronoid process>temporal bone fracture
long bone BFT
> usually delivers compressive and bending forces to long bones
results in complete, simple fractures without fracture lines; can be comminuted with significant force
Rib fracture
- Can break anywhere along body but prone to break at anterior end
- Anterior or lateral blows
- Break at right angles to long axis when viewed externally
When viewed superiorly or inferiorly they are observed to break from outside to inside
Vertebrae fracture
Simple fractures of transverse or spinous processes
Pelvis fracture
- Ischiopubic ramii
Iliac crest
Scapula fracture
- Separation of glenoid
Fracture of coracoid
sequencing blunt force trauma
> intersection of fractures
energy dissipates between fractures, not enough energy present to jump fractures/sutures
SFT wound type
puncture; cone shaped focus perpendicular to bone surface
incision; force applied over long, narrow surface area
cleft; dynamic force from a long, sharp edged implement applied perpendicular to bone surface
SFT bone damage
> fracture lines (rare)
hinge fractures = green bone effct
wastage/separation
primary characteristics of SFT
> cross-sectional shape
width
depth
length
striations
secondary characteristics of SFT
> fracture lines
hinge fractures
wastage
direction of kerf (cut) can sometimes be discerned
Knife kerf formation
> straight even edges, breadth remains consistent over length of kerf.
little debris found in walls and floor
extremities of kerf are thinner and pointed
if angle differs from 90 degrees, one side of kerf will be raised and fractured (bone flakes) with the other remaining smooth.
Little/no lateral compression
Hatchet kerf formation
> width of kerf same for entire length
kerf irregular compared to knife due to blunt mechanism
smooth walls and floor = sharp edge
edges uneven with significant bone flaking and fracturing found adjacent
significant lateral compression and destruction
3 categories of SFT tool
> stabbing
cutting
chopping
3 types of marks caused by saws to bone
- superficial false start kerfs: initial low pressure draw across bone
- False start kerfs: shallow incomplete saw kerf; allows for estimation of max. width of blade
3.Sectioned bone cuts: deep kerfs
SFT entry and exit wounds
entry wound larger than exit
bullet trajectory/impact perpendicular to target
circular outline
bullet trajectory/impact not perpendicular to target
oblique outline
bevelling (ballistic trauma)
> when projectiles strikes bone, it deforms to a variable degree
causes exit defect to be larger than entry
defect adopts funnel shape = bevelling
Inward bevelling
> observed at entry site
external defect smaller than internal defect
inward bevelling seen on internal surface of entry point
outward bevelling
> observed at site of exit
internal defect smaller than external defect
Reverse bevelling
> characterised by bevelling on the external surface of an entry defect in addition to bevelling on the internal surface
Ballistic defect shapes
- round
- oval
- keyhole
- irregular
round ballistic defect
> angle of trajectory and bullet axis are perpendicular to bone surface
More likely in entry rather than exit wounds
jacketing may result in round entry and exit wound
oval ballistic defect
> occurs when; angle of trajectory is not perpendicular to bone surface or bullet is tumbling when it strikes = <90 degree angle between bone and bullet.
more common in entry wounds
Keyhole ballistic defects
> usually caused by bullet grazing bone/entering at an angle
occasionally viewed in exit wounds
commonly observed in cranial vault
originates from any bullet type
Irregular ballistic defects
> no uniform outline
result of bone shattering = high velocity projectiles
more characteristic of exit wounds but can be observed at entry where bullet has been obstructed
Ballistic fracture lines
> radiating: originate from site of impact
concentric: encircling entry point; occurs in internal cortex then external
BFT vs Ballistic
> BFT = inward bevelling concentric fractures due to tensile failure
Ballistic = externally bevelled concentric fracture due to tension on intracranial surface due to elevated pressure
sequencing ballistic trauma
> distinguish entry from exit
distinguish radiating from concentric fracture
identify radial fracture intersection
heat flux
> the rate of energy transfer through a surface per unit time, measure in watts or kilowatts
dictates what materials become involved in a fire
Heat Release Rate (HRR)
> the rate at which a fire will release energy, measure in kilowatts or mega watts
Heat of combustion
> total energy released as heat when a material undergoes complete combustion = exothermic reaction
Heat transfer
> the process by which heat energy moves from one object to another via radiation, conduction or convection
burn progression on non-combustible floor for duration of fire
Body will burn more severely on the surface that is exposed to the fire
showing less damage on the side in contact with the non-combustible floor
burn progression on top of burning items
The side of the body in contact with the burning items will burn first, proceeding up around the body.
burn progression on combustible floor that collapses during fire
The floor, if combustible, will act as fuel and burn the side of the body in contact with it.
If the floor collapses, remains could be deposited over a wide area = fragmentation
burn progression In suspension on metal framework
The car seat or mattress may initially shield the body.
If the fire then continues to burn long enough, the fragmented remains may fall through the framework and scatter.
burn progression Exposed on all sides
The body will burn on all sides, and burning will progress in a relatively predictable way.
Stages of the burning process
- Dehydration; 100-600c = black cortex
- Decomposition; removal of organic components = 300-800c, grey colour indicated leeching of organics
- Inversion; 500-1100c, Removal of carbonates = white colour of bone
- Fusion; 700-1200c, warping of crystals
Colour change in burned bone
- unaltered
- Heat line = white line
- Heat border = brown - white band
- Charred = black
- Calcined = grey-white
brown colour change association
haemoglobin or soil discolouration
Black colour change association
carbonisation of burned bone (300c)
Grey/blue colour change association
pyrolysis of organic components of bone (600c)
White colour change association
final end stage of calcination (800c)
Green/yellow/pink/red colour change association
presence of copper, bronze, zinc in surrounding environment
Heat induced fractures
- Patina
- longitudinal
- Curvilinear
- transverse
Patina fracture
> observed on surface of flat bones + long bones
fine cracks, do not penetrate marrow cavity
Longitudinal fractures (burning)
> follow long axis of bone
may penetrate marrow cavity
follow orientation of collagen fibres
curvilinear fractures
> can exhibit oblique orientation
circumscribe long bone shaft
Transverse fractures (burning)
> perpendicular to shaft
delamination fracture = peeling or flaking of bone layers, separates cortex from trabeculae
primary explosive injuries
> Causes by pressurised shock wave moving through body
characterized by the absence of external injuries
targets gas containing organs
internal injuries are frequently unrecognized and underestimated
Secondary explosive injury
> caused by the propulsion of objects into the individual
can cause penetrating trauma and hemmorrhage.
anti-personnel bombs
Tertiary explosive injuries
> when a person themselves is thrown against other objects
blunt force trauma = fractures
Quaternary explosive injuries
> includes burns, crushing and respiratory injuries
Torture definition
> any act by which severe pain and suffering is intentionally inflicted on a person, when such pain and suffering is inflicted by or at the instigation of a public official or someone acting in an official capacity
Evidence to support torture
1.comparing pattern of injuries to documented cases of torture
2.Timing of injuries (sustained over a prolonged period)
3.pathological findings consistent with detainment (untreated disease/injury)
4. Corroboration with other physical findings
istanbul protocol
manual on effective investigation and documentation of torture and other cruel treatment or punishment.
Istanbul protocol recommendations (torture)
> experts must avoid speculation
Must take into account the variability of lesions depending on the victim and the severity of the lesions themselves.
all lesions must be recorded, whole body observed in detail
Consider region specific methods
inflicted injury types
> sternal fractures
hands and feet
parry fracture = forearm, defensive
Accidental injury types
> colles fracture = distal radius
clavicle
humerus
5 types of abuse
- physical
- sexual
- neglect and negligent treatment
- emotional
- exploitation
what to look for in abuse cases:
- injuries which are unlikely to be accidental
2.injuries in different stages of healing
3.indicators of untreated injuries
4.injuries which do not fit the story given
Oral injuries = abuse
> torn labial frenum
fractured/chipped teeth
bruising to tongue, cheeks
fractured mandible/maxilla
soft tissue abuse indicators
> bruising
bite marks
burns
scalds
ligature marks
pressure sores
kwashiorkor
severe lack of protein but sufficient calorie intake.
>oedema, irritability, ulcerating dermatose, enlarged liver + hair discolouration
marasmus
> lack of protein and calories
emaciated, dehydrated, prone to infection and circulatory disorders
Harris lines
> reaction to stress (neglect)
transverse sclerotic layers in the metaphysis indicating times of reduced growth
ribs and long bones especially tibia and distal femur.
Enamel hypoplasias
> poor thin enamel, laid down in lines
linked to periods of ill-health and infection or starvation
bucket handle fractures
> metaphyseal fractures
caused by twisting or wrenching of extremities causing the metaphysis to be pulled and fractured
Heat related fracture characteristics
> occur in early stages of burning
radiate from charred black areas into buff coloured bone
will never radiate into unburnt bone
well-defined, sharp margins
Pre-existing fracture characteristics (burning)
> may extend into unburned bone
will have eroded, deformed margins due to thermal exposure
tool marks from blunt and sharp force trauma will still be visible
bevelling from ballistic trauma is retained
