Sharp Force Injury Flashcards
Define an incision
Clean division of the full thickness of the skin or tissue under the concentrated pressure of a sharp edged instrument
Key that the edge divides tissue not the tip
What causes an incision
Sharp edge drawn along skin surface
The tissue divides as the pressure is focused on a narrow edge - clean division
As concentrated pressure the force doesn’t need to be great
Can be a knife, broken glass or any keen edge
Describe the appearance of an incision
It will be longer than it is deep
May see underlying fat and muscle if deep enough
Usually a gaping wound - skin elasticity pulls it open
No bruising, abrasion or tissue bridges - clean cut
Will be profuse bleeding - cut vessels tend not to constrict/spasm
What are dicing incisions
Many small incisions caused by shattering glass
Some are linear, some L shaped, some Y
Glass forms small cubes with sharp edges and corners which cause incisions when they impact the occupants
Which features suggest an incision are self-inflicted
Accessible chosen sites (at blood vessels such as wrist or neck)
Clothes drawn aside - can see what they are doing
Associated “hesitation wounds” - superficial incisions to gain confidence
Handedness - right handed person usually injures themselves on the left
1 or 2 potentially fatal wounds rather than many
Repetition in wound track
What are the common sites of self-inflicted incisions
wrist
cubital fossa
neck
All have good access to blood vessels
Are self-inflicted wounds more likely to be blunt or sharp force
Sharp force
Less force and pain required to cause injury
Why do incisions gape
The elastic properties of the skin pull the edges apart
What does an up and down blood spray pattern suggest
Pulsatile pattern of blood spray which suggests an arterial bleed - usually a major one like carotid
What are the features of assault incisions/stabs
Aimed at target sites, but scattered - victim may try and dodge so some miss or glance
Clothing is cut - usually kept in the way
Most are deep and forceful as perpetrator can carry on with same force for longer
Many of the wounds are potentially fatal
Associated defense injuries - ward off blows or grab knife
Where are defensive wounds typically found
Flexor aspect of fingers or palmar hand if they’ve tried to grab the knife
Forearms if they raise arms to protect themselves
When do defensive wounds typically occur
Tends to occur earlier in attack before victim is overwhelmed
They show that the victim was conscious and mobile at the time- active attempt to stop attack
What are the differences between laceration and incision
Laceration are blunt force but incision are due to sharp edge
Laceration will have slight bleeding but incision are profuse bleeding
Laceration may have trace evidence in wound but incision have no trace evidence (unless blade breaks which is very rare)
List some signs of incision by serrated blade
Small, curved and evenly placed lines/cuts at edge of incision or in glancing wounds
Lines will match the serrations (peaks and troughs)
Spacing between lines may change as knife changes angle during movement
What is a chop wound
Variant of incision
Caused by a wide blade such as an axe
The width of the blade causes traction and abrasions at the margins as it crushes the surrounding skin
What are the features of a chop wound
Incision with marginal abrasion and bruising
Will be longer than it is deep
Abrasions trailing away from the main incision may be caused by handle
What is the definition of a stab wound
Penetrating injury caused by separation of the skin and tissues under the pressure of a sharp or blunt pointed instrument
Created with the tip of the weapon (usually a sharp point such as knife, needle or blunt instrument like screwdriver)
Not the edge - this is an incision
What is the greatest dimension of a stab wound
It’s depth
It goes deeper into the body than its length on the body surface (often small on surface)
It is this internal damage that makes them so dangerous
What kind of instrument causes a puncture style stab wound
Blunt, long and rigid
Such as a spike or screwdriver
Describe how stab wounds occur
Sharp tip thrust into skin and tissues
Clean division of skin and tissues under concentrated pressure of sharp tip
Why can’t you accurately estimate weapon dimension from resting wound
It will have changed shape as tissues move
The elasticity of the skin will cause the wound to gape wider but also shorten slightly
Can push the skin together to reconstruct the dimension - more accurate representation so should be done
Describe the anatomy of a knife
Handle at top Tang - portion of blade within handle Guard - may leave mark Hilt Blunt edge is called the spine Ricasso is the thicker, unsharpened area at top of blade Kick - flick out between ricasso and blade Heel - first portion of cutting edge Blade - sharp, cutting edge Tip
What is a bowie knife
Single edged knife with serration on the back of the blade
What is a dagger
A double edged blade
What determines the force required for a stabbing
Sharpness of tip of blade - main one
Speed of approach - quick jab more likely to penetrate than a slow sustained push
Anatomical site (chest easily penetrated)
When might the tip of the knife break off
Can occur if it strikes bone
May embed in the bone - trace evidence
Which areas are easy to penetrate with a knife
Chest
Skin is held taut over the ribs so doesn’t have much room to compress and resist penetration
Which areas are difficult to penetrate with a knife
Abdomen
It is very compressible (has a lot of give) so more resistant to penetration
Requires more force
Describe the forces involved in stabbing
Difficult to quantify force and is often overestimated (doesn’t actually take much force)
Skin and clothing are more resistant to penetration
Once you have broken this the underlying tissue penetrate easily - sudden give due to energy in compressed tissue and energy in assailant arms building up
Why are partial thickness stab wounds rare
Once the skin in broken the tissues underneath are easily penetrated - knife pretty much slides in
The energy required to break the skin is the same as that required to get it in up to the hilt
Would have to deliberately remove force to only push in partially
Therefore wound depth doesn’t necessarily = force
List the features used to describe stab wounds
Damage to clothing - do holes match up? Site Shape - elliptical or boat etc. Size Alignment - horizontal/vertical Direction - 3D direction Depth Underlying damage - which structures have been affected Effects - e.g. external blood loss, internal blood loss, damage to nerves
How do Langer’s lines of skin tension affect stab wounds
Wounds parallel to LL only gape slightly and heal with small scar (go with tension) - surgeons use these lines
Wounds at right angles to LL gape widely and heal with large scar - line of tension pulls it out of shape
How can pathologists use Langer’s line
They can pull the lines back into place to allow better visualisation of the true wound shape and therefore better estimation of knife
Measured an photographed in this position
What is a stab wound in the middle of the back suggestive of
Homicide
Inaccessible for suicide or accident
What is a V shaped stab would suggestive of
Suggests the knife has been twisted or moved within the body
When can a stab wound become an incision
Stab wound can trail off into an incision as the knife is pulled back out at an angle
Blade ends up dragging across tissue
How can stab wound length be extended
If the knife is rocked/tipped and comes out at a different angle it will make the wound longer
Length of wound would be greater than the width of the blade itself
Sometimes surgeons will use the wound as a start point for their incision which disguises original dimension
What effect do pegs or bolts on a knife have on the wound
They will leave corresponding abrasions
Can help determine knife - common in flip knives
How can scissor stab wound vary
The wound depends on how open the blades are
May have a small notch caused by overlap of blades
What wound dimension does blade length correspond to
Wound depth
What wound dimension does blade width correspond to
Wound length
What wound dimension does blade thickness correspond to
Wound width
Why might the stab wound length be less than the blade width
Skin is stretched on penetration
It can contract back when knife is removed making the wound shorter
Will also be shorter than the widest part of the knife if it is not fully inserted
Why might wound depth be less than the blade length
If it is not fully inserted
Why might wound depth be more than the blade length
If the tissue is compressed the wound depth can be longer as knife goes in further but then tissues will decompress once removed and rise back out
Common in the abdomen
Also organs may have been affected by the stabbing but fall back deeper when body is on back for examination which makes it artificially longer
If you have multiple stab wounds which is the best indicator of weapon dimension
Typically they vary in length and depth so you use:
The deepest - as you get full blade length
The shortest - this suggest no rocking and extension
How are wounds numbered on pathology photos
By region not in order of event
Describe the wound shape left by single edged blade
They leave a boat shaped wound
Flatter at one side and pointed at the other (edge with the blade)
If back is significantly blunt it can cause tearing that makes it look fishtailed or may create another single point
Describe the wound shape left by a double edged blade
Will leave an elliptical shaped wound
Sharp at both sides as both have blades
What does a concentrated attack to the face suggest
It often aims to depersonalise and disfigure the victim
What does direction of blood flow indicate
The position the victim was in when injured
Will move with gravity
Flows down when upright and off to each side when lying down
What can the shape of a stab wound indicate
The cross sectional shape of the blade
Direction of insertion
Movement of the victim or assailant
When do you get a hilt mark
When there is full penetration of the blade
May come from the kick (small rectangular abrasion), guard, the handle or the assailants hand
What shape would a bayonet stab wound be
Shallow T shape
Does the shape of the stab wound suggest the shape of the weapon
Typically - it may indicate cross sectional shape of weapon
May also show direction of insertion and movement of victim
Must however take into account tearing at edges or gaping due to tension lines
What pattern would a stab wound made by a blunt instrument make
Would be bruised and abraded as well as a penetrating injury
