Forensic Pathology Chapter 4 - The pathology of wounds

Definition of a wound

a wound or injury can best be defined as "damage to any part of the body due to the application of mechanical force"

Mechanism of wounding

the body usually absorbs external force either by the resilience and elasticity of its soft tissues or the rigid strength of its skeletal framework

it is only when the intensity of the applied force exceeds the capability of the tissues to adapt or resist that a wound or injury occurs

Classification of wounds

abrasions - informally "grazes or scratches"

contusions - informally "bruises"

lacerations - informally "cuts or tears"

incised wounds - informally "cuts, slashes, or stabs"

Forensic anatomy of the skin

most superficial is the keratinized dead layer of cells (stratum cornea) - varies greatly in thickness from one part of the body to another

that on the soles and palms is the thickest

this has forensic relevance in the amount of injury that is needed to penetrate the skin and allow bleeding from the underlying tissues

Abrasions

the most superficial of injuries and, in the most restrictive of definitions, is one that does not penetrate the full thickness of the epidermis

the pure abrasion does not bleed

when death ensues soon afterward, the abrasion becomes stiff, leathery, and of a parchment-like brown color as a result of the drying of the moist exposed surface

Antemortem vs postmortem abrasion

antemortem abrasion - red to purple color, wet "weeping", and inflamed

postmortem abrasion - yellow to brain color, dry

Tangential or brush abrasions

most abrasions are caused by a lateral rubbing action rather than vertical pressure

when this tangential component is marked, the direction of the force can often be determined by skin tags of the epidermis dragged to the terminal end of the abrasion

visual examination, using a lens if necessary, can indicate the direction of movement of the body

similarly, if a victim is struck a glancing blow with a rough object, similar epidermal skin tags may indicate the direction of the blow

Crushing abrasions

where the impact is vertical to the skin surface, no scraping or tangential marks occur

instead, the epidermis is crushed, and an imprint of the impacting object is stamped on the surface

patterned injuries occur when the force is applied at or near a right angle to the skin surface, rather than with the skidding impact of a graze

if a weapon with a patterned surface strikes the skin the abrasion of the epidermis follows the ridges of the object if it has a profile of varying height

not only may the epidermis be damaged, but the skin may be compressed into the cavities of the pattern, with consequent capillary damage leading to an intradermal bruise

Postmortem abrasions

other damage may be caused following autopsy - as the postmortem interval increases, the skin becomes more fragile

even the normal procedures of post-autopsy reconstruction and handling in the mortuary may cause dermal damage

if the pathologist returns for a later examination, or if they are retained to perform a second autopsy for the defense, the appearances should be checked with the original description or photographs, if some injuries suggest a postmortem origin

Contusions or bruises

although often combined with abrasions or lacerations, a pure bruise lies beneath an intact epidermis and consists of an extravascular collection of blood that has leaked from blood vessels damaged by mechanical impact

an extravasation of blood that is larger than a few mm in diameter, is usually termed a "bruise" or contusion - the size overlaps the older and now little used term "ecchymosis" witch is a really small bruise

even smaller is the "petechial hemorrhage," which is the size of a pin head or less - both ecchymoses and petechiae aren't usually caused by direct mechanical trauma and are often seen on serous membranes and conjunctivae as well as on skin

bruises are caused by damage to veins, venues, and small arteries - capillary bleeding would be visible only under a microscope and even petechiae originate from a larger order of blood vessel than a capillary

Intradermal bruises

the usual bruise from a blunt impact is situated in the subcutaneous tissues, often in the fat layer - when viewed through the overlying corium and epidermis, the bruise is somewhat blurred, especially at the edge

when a bruise is made by impact with a patterned object, however, the hemorrhage may be far more sharply defined, if it lies in the immediate sub-epidermal layer - the amount of blood is relatively small, but because of its superficial position and the translucency of the thin layer that overlies it, the pattern is distinct

Color of bruises - timeline

red, swollen/tender - 0-2 days

blue/purple - 2-5 days

green - 5-7 days

yellow - 7-10 days

brown - 10-14 days 

Factors affecting the prominence of a bruise

several factors influence the apparent size and prominence of a bruise:

         as it is a leakage of blood from a vessel, there must be sufficient space outside that vessel for free blood to accumulate - this explains the ease with which bruising appears in lax tissues such as the eye socket or scrotum and its rarity in the sole of the foot or palm of the hand

the size of the hemorrhage depends partly, but not entirely, on the intensity of the injuring force

resilient areas, such as the abdominal wall and buttocks, bruise less with a given impact than a region where underlying bone acts an anvil with the skin between the bone and the inflicting force

the depth at which the bruise is placed affects the apparent severity - a bruise may be placed superficially in the dermis to form the well-patterned intradermal bruise, a minute amount of blood will be obvious

most bruises are in the subcutaneous tissues above the deep fascia and will therefore be fairly obvious, but others can be confined below deeper fascial membranes

for a given impact, the volume of blood lost into the tissues can depend upon the fragility of the blood vessels and the coagulability of the blood

Movement of bruises

a bruise may appear at a different place on the surface from the point of impact

when the bruise is superficial, especially intradermal bruising, the lesion appears immediately and is at the point of infliction

when blood extravasates in the deep tissues, however, it may take time to reach the surface, and this may be some distance away because of deflection and obstruction by fascial planes and other anatomical structures

Alteration of bruises with time

bruises often become more prominent some hours or days after infliction because red cells or hemoglobin diffuse closer to the translucent epidermis

in racially pigments victims, a bruise may sometimes be undetectable from the surface, apart from swelling caused by a hematoma and tissue edema

Bruising of special significance - part 1

if several bruises are present and are of markedly different colors, then they couldn't have been inflicted at the same time - this is particularly important in suspected child abuse, where intermittent episodes of injury have important diagnostic significance

clusters of small discoid bruises of about a cm in diameter are characteristic of fingertip pressure from either gripping or prodding - these groups are often seen in child abuse, when an adult hand grips the infant by a convenient "handle"

when the skin surface is stuck by a rod or rectangular sectioned object, the consequent bruising may be of the "tram-line" or "railway line" type - this appears as 2 parallel lines of bruising with an undamaged zone in the center

the mechanism of this double line is that the weapon sinks into the skin on impact so that the edges drag the skin downwards and the traction tears the marginal blood vessels

the so-called "love bites" are often bruises, with or without associated abrasions, being a show of small petechial lesions caused by oral suction on the skin

Bruising of special significance - black eyes

not all black eyes are true bruising from a blow in the orbit - some are from fractured orbital roofs and others are the result of gravitational movement of a forehead injury

Raccoon eyes indicate that there is a skull fracture

a bruise below the ear in a death from subarachnoid hemorrhage needs careful examination of the upper cervical spine and basil-vertebral arteries

the skull is made up of more than 20 different bones - the basilar bones at the base of the skull protect the following structures:

       eyes, nerves to the head and neck, ears, brain stem, cerebellum or coordination and balance center

when one of the basilar bones is broken, blood may pool behind the ear, creating the Battle's sign bruise - while Battle's sign may look like an ordinary bruise, it is not a result of direct injury behind the ear; instead it is a sign that one or more of the skull's bones have been broken

Kicking

the shod foot may leave a patterned bruise on the body, most often on the abdomen or chest, though it may be recognizable on the neck or face

a glancing kick is more likely to cause scuffed abrasions and bruising, and a kick from a toecap, a curved abrasion or even laceration

a vertical stomping action may imprint an intradermal bruise corresponding to the sole pattern, especially in these days of rubber "trainer" shoes

as with a motor tire, the skin can be forced into the slots in the sole, creating an accurate pattern of superficial bruising

Lacerations 

the third major type of blunt injury is the laceration, in which the full thickness of the skin is penetrated - lacerations differ from incised wounds in that the continuity of the tissues is disrupted by tearing rather than clean slicing, but the distinction is often blurred because some lacerations are caused by jagged projections ripping into the skin in much the same manner as a blunt knife or axe

acerations are caused when trauma exceeds intrinsic tissue strength

it is unusual for a blunt impact to lacerate the abdomen or buttocks, but the scalp, shins, shoulder, face, and the thorax are all prone to lacerated injury

because of the crushing and tearing components of a laceration there is usually associated abrasion and bruising, though these may be minimal if the lacerating force acts at right angles to the surface

Lacerations - difference between laceration and incised wound

a laceration can be distinguished from an incised wound by:

• the bruising and crushing of the margins, though this may be a very narrow zone, requiring inspection through a lens

• the persistence of tissue strands across the interior of the wound, including fascial bands, vessels and nerves; in a wound from a sharp weapon these are divided

• the absence of a sharply linear injury in the underlying bone, especially if it is in the skull; a knife or axe is likely to chip or score the base of the wound 

• if the area is covered with hair, as on the scalp, intact hairs will survive to cross the wound; an incised injury would divide them

firearm wounds are a special form of laceration

Blunt penetrating injuries

these "puncture wounds" are a hybrid between lacerations and incised wounds - and have more features of the latter

such injuries can occur from metal spikes, wooden stakes, garden or farm forks, and a variety of vehicular and industrial accidents

they are occasionally seen in homicides or suicides when weapons like screwdrivers are used as daggers

Incised wounds

injuries caused by sharp objects are classified as "incised" wounds

the term "incised wound" usually covers all types of injury from, a knife, sword, razor, glass, or sharp axe

the essential feature of all incised wounds is the clean division of the skin and underlying tissues so that the margins are almost free from any damage

Cuts or slashes

when an incised wound is longer than it is deep, it may be referred to as a "cut" or "slash" - such slashes inflicted by a sharp object are typical in a fight, when the assailant strikes out with a swiping action, rather than the thrust of a stabbing attack

slashed wounds are less dangerous than stabs, as the relative shallowness of the wounds is less likely to affect vital organs - especially as the arms and face are the common targets

a stab wound is an incised wound that is deeper than it is wide

The nature of stabbing weapons

knives are the weapons most frequently involved and their physical characteristics are important in shaping the wound

a pathologist called upon to examine a knife that may have been used in an assault should not and measure:

• the length, width, and thickness of the blade

• whether it is single or double-edged

• the degree of taper from tip to hilt

• the nature of the back edge in a single-edged knife

• the face of the hilt guard adjacent to the blade

• any grooving, serration, or forking of the blade

• most importantly, the sharpness of the edge and especially of the extreme tip of the blade

The characteristics of a stab wound

the surface and internal appearances of a stab wound allow the pathologist to offer an opinion upon:

• the dimensions of the weapon

• the type of weapon

• the taper of the blade

• movement of the knife in the wound

• the depth of the thrust

• the direction of the thrust

• the amount of force used

Dimensions of the weapon

when suspect weapons are recovered, the inspection of them may indicate whether or not they are consistent with having caused the wounds in question

as always in forensic medicine, however, caution must be employed and the cardinal sin of over-interpretation avoided

Type of weapon

the type of blade usually refers to whether it had a single or double cutting edge - most knives have a single sharp edge the back edge being blunt or otherwise machined

a few dagger-like weapons have both edges ground to sharpness, some have only the distal part of the back of the blade sharpened

on inspecting the skin wound, the pathologist frequently finds that both ends of the defect appear sharply cut, coming to a fine "V-point" at the extremities - unfortunately, this does not necessarily indicate that a knife with 2 sharp edges was used, as the skin often splits behind the blunt edge to produce a symmetrical appearance

Depth of the thrust

the death of a stab wound may be important in attempting to assess the length of a missing weapon - again there are pitfalls to be avoided

first, if a knife is driven in up to the hilt, the depth of the wound as measured at autopsy may be greater than the true length of the blade - this is common in the abdomen and to a lesser extent in the chest, because the impact of a forceful stab may momentarily indent the abdominal or chest all so that the tip of the knife penetrates tissues that apparently should have been out of reach

Measuring the depth of a wound

the recommended method for measuring depth is to use a sterile cotton tip swab, gently insert it into the area of undermining, then grasping it at the wound edge measure against a ruler

Direction of the thrust

the direction of a stab wound is often a matter of contention in homicides, especially as trial lawyers sometimes tend to over-interpret the facts when trying to reconstruct the scene of the fatal assault

a stabbing incident is often moving and dynamic, and the victim is rarely in a static, anatomical position

all that the pathologist can do is to determine the direction of the wound relative to the axis of the body - it is then a matter of non-medical evidence to relate that to the posture of the victim when struck

more information about direction comes from careful examination of the track of the stab wound - this is an anatomical exercise during autopsy, the layers of tissue being examined in sequence from the surface downwards and damage to deep structures and organs compared with the position of the surface wound

attempts have been made to delineate the track of a stab wound before dissection either by filling the defect with a radio-opaque fluid before taking X-rays, or by filling with a plastic or even metallic substance that will harden to form a cast - in practice, these methods appear to have little advantage over careful dissection

when radio-opaque liquids or pastes are used, there is often leakage from the stab wound into the thoracic or abdominal cavities, leading to a confusing radiological picture

Estimation of the degree of force used in stabbing

the amount of force required to inflict any given stab wound is often a matter of extensive debate in criminal trials - the prosecution naturally gains from showing that a stabbing was inflicted with "considerable force," sometimes even using pejorative terms such as "violent" or "frenzied;" this tends to confirm the intention to stab, whereas the defense proposition is often that the victim inadvertently fell or was pressed against a weapon held passively by the accused

an expert medical witness has difficulty in replying to the almost inevitable question by counsel - "what amount of force was necessary to cause this wound"

assessment of force is subjective and cannot be quantified in any satisfactory way that is meaningful to the court

physical units mean nothing to a judge and jury

Estimation of the degree of force using in stabbing - what we know

apart from bone or calcified cartilage, the tissues most resistant to knife penetration is the skin, followed by muscle where large muscle bundles underlay the fascia

the sharpness of the extreme tip of the knife is the most important factor in skin penetration - the cutting edge of the knife, once the tip has penetrated, is of relatively minor importance

stretched skin is easier to penetrate than lax skin - the chest wall, where skin tends to be intermittently supported by underlying ribs, is relatively easy to puncture with a sharp knife as the skin and tissues are stretched over intercostal spaces in the manner of a drum membrane

the skin of aged, or women, is not appreciably resistant to a sharp point than that of men or young people

when a knife-point impacts the skin, the latter dimples and resists until penetration suddenly occurs - the tension developed in the stretched skin appears to act as an "elastic reservoir" and, when the threshold of resistance is exceeded, the knife "falls" through the subcutaneous tissue without any further force being imparted to it unless impeded by bone or cartilage

Injuries by weapons other than knives

glass is almost invariably radio-opaque, even though this is either unknown or even denied by the doctor

numerous civil actions for negligence have occurred though usually in non-fatal circumstances but, on occasion, the first person to find a deep fragment of glass in a vital position has been a forensic pathologist

Defense wounds

in assaults of any kind, the natural reaction of the victims is to protect themselves - the limbs used for protection can themselves be injured and these defense wounds may be considerable medico-legal significance, as they indicate that the victim was conscious, at least partly mobile and not taken completely by surprise

the classic position for them is on the forearms and hands, which are instinctively raised to protect the eyes, face, and head - other defense injuries may be inflicted on the thighs, when attempts are made to shield the genitals

with attacks from blunt instruments or fists, bruises are the hallmark of defense attempts

the most obvious defense injuries are seen in knife attacks, as the victim often attempts to ward off the thrusts by seizing the weapon - when the fingers are closed around the blade, its withdrawal cuts across the flexures of the fingers, slicing through the skin and perhaps tendons, or sometimes all four fingers

Chronological histological changes after wound infliction - part 1

30 mins - 4 hours:

• margination of polymorph leukocytes in dilated small vessels may occur, a feature which is often completely absent

4-12 hours:

• leukocyte infiltration is likely to be more definite, still mostly polymorphs, but some mononuclear cells as well; a scanty mixed population of lymphocytes and poorly differentiated "monocytes" appears usually after 12 hours

• tissue edema and swelling of vascular endothelium occurs, in small wounds involving the skin, the start of epithelial regeneration may be seen at the sides at the level of the basal layer of epidermis

12-24 hours:

• leukocytes tend to demarcate the area of the wound by forming a marginal palisade, the polymorph response declines and the macrophage and mononuclear cell population increases from now on

• removal of necroses tissue begins, with macrophages evident and a basophilic tinge to the ground substance, mitoses are visible in fibroblasts from about 15 hours; the epidermis beings to spread across the surface of the scab and down the sides of a cut into the wound

Chronological histological changes after wound infliction - part 2

24-72 hours:

• eukocyte infiltration reaches a peak at about 48 hours; repair begins concurrently with many fibroblasts appearing, but rarely before 72 hours; new capillaries then begin to bud from vessels, the vascular, infiltrated storm becoming "granulation tissue"

3-6 days:

• repair is proceeding apace - collagen begins to form and giant cells may be visible around necrotic debris and foreign matter

10-15 days:

• cellular reaction subsides in small wounds, vascularity decreases and the cell population drops, especially in leukocytes; fibroblasts are most active, with collagen being laid down

two weeks to several month, depending on size and other factors

• consolidation of the healing tissue continues, the inflammatory response has vanished, unless the wound has become infected; collagen and elastin increase and a vascular scar is formed, which gradually becomes more dense and non-vascular

Survival period after wounding

a pathologist is often asked either by police during an investigation, or by counsel at trial, what was the probably interval between the fatal injuries and death; a supplementary query is how long would the victim have been active, even if still alive?

these are extremely difficult questions to answer, as a number of variables enter the estimation, the doctor should never give a dogmatic answer, unless the nature and severity of injuries are obviously incompatible with continued life or activity