SFI Flashcards
Define stab
Penetrating injury caused by separation of the skin and tissues under by the pressure of a sharp or blunt pointed objected
Greatest dimension is its depth - deeper into body than length on body surface
Small hole made with a sharp point
- sharp and flat (knife) = stab
- sharp and thin (needle) = needle puncture wound
- blunt, long and rigid (spike, screwdriver) = puncture wound
Anatomy of a knife
Handle - Tang - portion of blade within handle - Guard Blade - Ricasso - thicker unsharpened part of blade - Kick - Heel - Cutting edge - Tip - Spine - blunt back of knife
Features of stabbing force
Difficult to quantify Easily overestimated Clothes and skin offer most resistance Energy stored in compressed tissues Energy stored in assailants arm muscles After sudden give tissues easily penetrated Wound depth does no indicate force Force required depends on - sharpness of tip of blade - speed of approach - anatomical site - chest easily penetrated as skin taught
Parts of describing stab wound
- Damage to clothing
- Site
- Shape
- Size - length shows maximum width of the blade
- Alignment
- Direction - may suggest over/underarm
- Depth
- Underlying damage
Effects
Shape of stab wound may indicate
Cross sectional shape of blade
Direction of insertion
Movement of victim/assailant
Distorted by Langer’s lines of skin tension
Shape of stab wounds
- Shape often indicates shape of blade
- Dimensions often indicated dimension of blade
- Rounded at back end and sharp point at front of wound - boat shaped
○ If on Langer’s lines will become wide and gapping
○ Skin may split on back end giving fishtail (two pronged) appearance or irregular defect - Double edge blade can give oval shaped wound
Define Langer’s Lines
Lines of elasticity in skin
- oblique on shoulders
- horizontal and transverse across chest
- oblique in abdomen
Wounds parallel to LL gape slightly and heal with small scar
Wounds are right angles to LL gape widely and heal with large scar
Importance of Langer’s lines
Surgeons
- reduce size of scar
Pathologists
- shape/size of stab wound can be distorted
- re-oppose and tape edges to show true shape of stab wound
Relationship between knife and wound dimensions
Blade length = wound depth
Blade width = wound length
Blade thickness = wound width
Exceptions to relationship between knife and wound dimensions
- Stab wound length can be greater than blade width due to rocking of knife
- Stab wound length can be less than blade width if skin was stretched prior to penetration which recalls and relaxes
- Stab wound length can be less than blade length is blade not fully inserted
- Wound track depth less than blade length is blade not fully inserted
- Wound track depth can be greater than blade length is tissues are compressed - common in abdomen due to soft nature
Features of hilt marks
Occur with full penetration of blade Possible marks from - guard - handle - kick - assailants hand
Features of wound track depth
To work out length of blade
Exceptions
- incomplete blade insertion
- full insertion but with tissue compression
- gravitation position of organs when body is supine
Features of defensive injuries
Injuries sustained in attempting to ward off or shield against anticipated blows
- stabs and incisions in knife attack
- bruises, abrasion and lacerations in blunt force attack
Indicate victim was conscious, mobile and anticipated blows
- occur early in sequence
Determining wound dimensions in multiple wounds
Multiple wounds vary in depth/length
Most accurate indicator is wound which is deepest but shortest in length
- deepest = fully inserted
- shortest = no rocking of blade
Other penetrating wounds
- Bayonet - shallow T shape wound
- Pointed metal bar - cruciate wound
- Triangular file - 3 cornered wound
- Pitch fork - elliptical wound
- Screwdriver - shape depends on depth
- Scissors - depends on blade shape/depth
Blunt instrument - abrasions and bruising
Define incision
Sharp edge drawn along skin surface - knife, broken glass Through full thickness of skin Clean division of skin and tissue under the concentrated pressure of a sharp edge No bruising, abrasion or tissue bridges Longer than it is deep Profuse bleeding
Define dicing insisions
Small multiple y or l shaped incisions
Causes by shattered vehicle glass
Features of self-inflicted incisions
Accessible chose sites - where blood vessels located
Clothes drawn aside
Associated with hesitation wounds - shallower initial wounds
Handedness - on LHS of right handed
1 or 2 potentially fatal
Repetition in wound track
Features of assault incisions
Aimed at target sites but scattered Clothing is cut Most are deep and forceful Many wound potentially fatal Associated defence injuries
Features of chop wounds
Variation of incision
Caused by axe - wide blade causes marginal abrasion
Incision with marginal abrasion and bruising
Blade has weight and momentum
Longer than it is deep
May have associated bruising or laceration from handle
Large incision with trailing abrasion
Features of serrated knife wound
Leaves distinctive pattern
- knife bends as pulled along skin
- change in spacing of abrasions of teeth
