Chapter 3 Mechanical Injury 3 Mechanical Injury

Section 1 Brief Introduction to Mechanical Injury

Concept of injury Injury is a response of human body to external stimulating factors including physical, chemical and biological factors . Injury may cover three kinds of damages to human body: disruption of the normal structure of tissues, functional disorder and psychological disturbance

Concept of Mechanical injuries Mechanical injuries are refered to disruption of the normal structure of tissues and functional disorder caused by mechanical violence.

Classifications of the woundsClassification based on the nature of the object (1) Wounds caused by the sharp instruments The sharp instruments are those pointed or sharp-edged objects, such as knif

e, ax, dagger and scissors. (2) Wounds caused by the blunt instruments The blunt instruments are those without point or sharp edge, such as stick or

club, the bricks, stone and fist, etc. (3) Wounds caused by the firearms Firearms are refered to rifles, shotgun, explosives, etc.

Special types of wounds (1) Wounds sustained in traffic accidents (2) Wounds caused by falling from height

(3) Cerebro-cranial injuries

Classification based on the manner inflicting the wounds (1) Suicidal wounds (2) homicidal wounds (3) Accidental wounds or wounds caused by disaster

Three factors determining the developm

ent of mechanical injury:

the nature of the objects or instruments cau

sing the wound

the nature of the affected tissues

the force applied to the body

Mechanisms of wound productionMechanisms of wound production

1. The nature of the object or instruments causing the wound

With blows from pointed or sharp-edged objects or instru

ments the area of primary impact is actually limited to a poin

t or a line, causing deep penetration or clear division of the tis

sues.

With a blow from a blunt instrument, the area of body su

rface subjected to to impact may be relatively large, causing t

he localized damage.

A plastic instrument causes less damage than a rigid instr

ument.

2. The nature of the affected tissues The skin: very pliable and somewhat elastic, readily changeable

in shape when it is struck.

The subcutaneous tissues: very plastic because of their fat content and pliability of their supporting connective tissue fibers. Protect the body by cushing effect.

The muscles: frequently escape damage from blows because of their great plasticity and elasticity, but may be crushed or torn against bone or be lacerated by fragments of displaced and broken bone.

The bones: elatively rigid, but when a force is applied to a bone, it may bend without breaking, and by virtue of their elasticity, recoil to its normal shape. If a bone is bent beyond the limit of its elsticity, it fractures.

The tendons: possess great elasticity and tenacity and are not easily torn by blows, even are broken off from their attachment points.

Effects on body fluids: Fluid is virtually incompressible but as it has no shape it may be readily displaced. A blow over a hollow organ which contains fluid may set up powerful hydrostatic forces, which causes fluid to be transmitted equally and uniformly in all directions. Such transmitted forces may lead to the rupture of anatomically distant and mechanically weak tissues,

e.g. sudden compression of the abdomen may cause a retrograde displacement of blood in the great vessels – abdominal aorta and result in rupture of cardiac valves-bicuspid.

A blow to the upper left abdominal area may cause rupture of the stomach full of content.

Examination and ducumentation of the woundsExamination and ducumentation of the wounds1. Thoroughly examine the whole body and record each wound, even a minor woun

d that may be an important evidence for the medico-legal investigation.2. Record detailedly the clinical signs and manifestions of the resultant complicatio

ns, especially those transient functional disorders such as the vital signs from dyspnea and shock.

3. Because the victim may have no any sense of plea for legal process, the doctor may acquire somewhat true information regarding the case and the past medical history, e.g. changes in the vision, visual field, and auditory acuity.

4. Accurately document the site, number of the wounds and their interrelation. Record them in relation to the standard anatomical marks. Describe the wounds vividly with geometric shape such as round, oval, linear, and curved, etc. Measure the width and depth of the wound and describe the foreign bodies in the wound cavity if any.

5. Properly preserve the surgically removed organs – ruptured spleen, the attachments or residues – glass fragments, broken pieces of the instruments producing the wound, for further examination, which should be recorded in detail.

6. At autopsy, all the wounds on the body should be documented and photographied with scale. All visceral organs should be removed and carefully examined and photographied with scale. Samples should be taken for histological examintion. Blood, urine sample and stomach conten should be collected for toxicological analysis.

Section 2 The basic types of mechanical injuries

1. Abrasion

An abrasion is a destruction of the skin which usually involves the superficial layers of the epidermis only.

Abrasion is caused by friction of the skin against some rough on sharp surface resulting in the scraping away of superficial portion of the epidermis.

Abrasions are of medico-legal importance as they indicate that some force has been applied to the body.

Under certain conditions, the features of abrasions may suggest the nature, direction and cause of the force and, possibly, the purpose for which it is applied.

Abrasions are commonly found on the head and face and over bony prominence caused by blows from blunt instruments and from falls.

Abrasions are often accompanied by other injuries such as bruises, fractures or internal injuries.

They may appear either as crescentic marks or as relatively broad parallel grooves which tail away at their ends as caused by fingernails.

Abrasions may be produced after death when a body is dragged away from the scene of a crime.

It is advisable to cut off the abrasion and conduct the histological examination for determination of the antemortem abrasion.

Abrasion caused by ligature in a case of hanging

Abrasions caused by finger tips in a case of mannual strangulation

Abrasion caused by contact with a rough surface

Abrasions sustained in a traffic accident by impact agaist the windshield

Macroscopic findings of abrasions

Abrasions involving only epidermis appear yellowish in color after exudate dries, and purplish red if dermis has been involved.

Dilated subcutaneous capillaries may be seen 3-6h post-injury; scab is formed over the abrased area 12-24h after injury, begins to peel off 3d, and may peel off completely 5-7d post-injury.

2. Contusions

Contusions, also called bruises, are injuries characterized by the effusion of blood into the tissue spaces.

The extent and the degree of bruising depend upon the amount of force applied to the body, and upon other factors such as the structure and vascularity of the affected tissues.

Because of many variables, it is impossible to determine the mount of force from the extent and the degree of bruising.

In certain circumstances, the external pattern of a bruise may correspond to the form of the object or weapon, which may be of medico-legal importance and can be used as an indication for judgement of possible weapon.

When the body is struck by a round stick, linear parallel bruises separated by apparently normal tissue in the skin may occur, which is called parallel or railway-like subcutaneous hemorrhage(竹打中空 ).

The colour of bruises changes as the extravasated blood undergoes hemolysis, which is not constant and can only be used as an indication for estimating roughly its age.

Bruises-subcutaneous hemorrhages

3. Incised wound

Incised wounds are caused by sharp weapons or objects such as knives, jagged portions of metal or pieces of broken glass.

An incised wound is usually linear or spindle in shape.

The walls of the incised wound appear smooth and the edges of the wound are clean-cut.

There are usually no connecting tissues (bridges of the tissue) between the walls. The wound is often gaping.

Hemorrhage from the incised wound is usually profuse.

Bruising may or may not be present surrounding wound

edges.

The breadth of the cutting edge of a sharp weapon

cannot be determined from the width of the wound.

Incised wounds are commonly seen in cases of assault

and homicide, which are usually multiple.

Defense wounds may be found on the forearms and/or in

the palms of the hands.

Accidental incised wounds are seen in traffic injury.

Suicidal incised wounds are commonly seen in region of

the wrists and the neck. Incised wounds are sometimes

self-inflicted for the purpose of ending his or her life or

bring false charges against other persons.

Sometimes, in the cases of suicide, some superficial,

parallel cut wounds are found on the front of the left

forearm, the front and outer side of the thighs and the

side of the neck. Such cut wounds are called tentative

incisions or hesitation marks.

Suicidal incision of the throat Homicidal incision of the throat

Chop woundChop wound Chop wound is caused by weapons of certain weight w

ith sharp edge through cutting force, which is characterized by seriously destructed subcutaneous tissues, even organs.

A chop wound is usually spindle in shape and often gaping.

The walls of the incised wound appear smooth and the edges of the wound are clean-cut.

There are usually no connecting tissues (bridges of the tissue) between the walls.

Chop wounds are commonly seen in homicidal cases, which are usually distributed over the victim’s head, .

4. Stab wounds

Stab wounds are caused by long narrow instruments

with pointed end. Stab wounds are described as penetrating

when they pierce deeply into tissues and as perforating when

they transfix tissues and cause exit wounds.

The shape of stab wounds is usually linear or irregular

according to nature of weapons. The depth of a stab wound

is greater than length and width.

When a sharp weapon such as a knife has been used, the

external wound almost invariably takes the form of a split

having two pointed extremities.

The external opening of a punctured wound may have a triangular or cruciate shape if it is caused by a weapon such as a triangular file or bayonet, or by a square-sectioned instrument such as a spike.

The dimensions of the external opening of a stab wound may be smaller than the diameter or transverse dimensions of the weapon, as the elastic skin is often stretched during the process of penetration. On the other hand, the opening may be larger in cases where the weapon is withdrawn obliquely after penetration.

The depth of a punctured wound may be greater than the total length of the penetrating object or weapon due to compression of the tissues during the process of penetration.

A single wound track is usually found in relation to a single external opening in a punctured wound. In certain cases where the weapon is partially withdrawn and then reinserted in another direction, two or more tracks may be found in relation to a single external opening.

The skin surrounding the wound may be bruised by the haft of the weapon when a weapon such as a knife or a dagger is thrust into the tissue with considerable force

5. Fracture of the bones

When a force is applied to a bone directly or indirectly and the bone is bent beyond the limits of its elasticity, it fractures.

(1) Fractures of the skull

i. The types of fractures of the skull

Fissured fracture of the skull Depressed fracture of the skull Penetrated fracture of the skull Comminuted fracture of the skull

Fissured fracture of the skull

Fissured fracture of the skull may develop when inner or outer table fractures, or both inner and outer table fracture.

Patterns of fissured fracture may vary with length, width, and direction as well as the number of the lines of a fracture.

Fissured fracture of the skull is an indication of blows striking head. The number of lines of fracture is also an indication of the number and sequence of the blows.

Depressed fracture of the skull When greater force is applied to the skull,

depressed fracture of the skull may develop due to fracture of outer table or both outer and inner table.

The shape of such a fracture appears to be in the form of cone, circle or oval.

The fracture lines in a depressed-comminuted fracture tend to run radially from the central point at the apex, and at the periphery the fracture lines tend to run in a circular manner.

Penetrated fracture of the skull

When a small object strike the skull at a high speed, such as a bullet, the skull may be penetrated and penetrated fracture of the skull occurs.

Comminuted fracture of the skull When violent force is applied to the skull, some

part of skull may break into pieces or fragments to form comminuted fracture of the skull.

Comminuted fracture may develop by impact of one blow or repeated blows.

6. Injuries of the intracranial tissues

(1) Intracranial hemorrhage

Injury to the meninges and their related vessels often result in intracranial hemorrhages, including extradural, subdural, subarachnoid or subpial hemorrhages.

i. Extradural hemorrhages

(a) Definition

Extradural or epidural hemorrhages are those that occur between the inner surface of the skull and the outer surface of the dural mater.

(b) Causes of extradural hemorrhages

Extradural hemorrhages may be resulted from torn

diploic veins or from ruptured venous sinuses or

meningeal vessels.

The most important type of extradural hemorrhage is

caused by the rupture of meningeal vessels, especially

the middle meningeal vessels.

The middle meningeal vessels may be transfixed by a

spicule of bone or they may be lacerated by the edge of

a fracture.

ii.ii. Subdural hemorrhages Subdural hemorrhages

(a) Definition Subdural hemorrhages are those that happen between the inner surface of the dura mater and the outer surface of the arachnoid.

(b) Causes of subdural bleeding (hemorrhage)

Subdural hemorrhages may arise from tears in the dural venous sinuses or cortical veins, but the most common cause of the subdural bleeding is the rupture of bridging or communicating veins.

iii. Subarachnoid hemorrhage

Subarachnoid bleeding is the commonest form of traumatic intracranial bleeding which occurs between the arachnoid and the pia mater, and usually arise from the rupture of bridging veins.

In cases where the hemorrhage is the only form of the injury, the possibility of a spontaneous subarachnoid hemorrhage from natural causes must be excluded.

An important cause of spontaneous subarachnoid hemorrhage from natural causes is the rupture of a congenital or berry aneurysm of one of the arteries of Willis circle.

(2)(2) Posttraumatic intracerebral hemorrhage Posttraumatic intracerebral hemorrhage

Hemorrhages into the brain arising directly from impacts are called posttraumatic intracerebral hemorrhage.

Posttraumatic intracerebral hemorrhage usually develops near the surface of the brain.

A single deep-seated hemorrhage is usually due to some disease process. Emotional excitement or physical exertion may precipitate an intracerebral hemorrhage in an arteriosclerotic and hypertensive subject.

Indications which assist in the differentiation of natural hemorrhages from traumatic ones include:

(a) The age of the subject;

(b) The site and the extent of the hemorrhage;

(c) The presence of vascular lesions in the

cerebral vessels;

(d) Signs of cardiac hypertrophy and generalized

arteriosclerosis.

Delayed posttraumatic cerebral apoplexy

In posttraumatic intracerebral bleedings, there is an important pathologic entity named delayed traumatic cerebral apoplexy.

This term was first created by Böllinger in 1891. He observed that, after a posttraumatic interval of days or even weeks, a hemorrhagic effusion was found in the substance. Since then many cases concerning with such a type of cerebral apoplexy have been reported. But the mechanisms of the condition are not well known.

(3)(3) Cerebral contusions Cerebral contusions

i. Definition

Cerebral contusions are circumscribed areas of brain tissue destruction which are accompanied by extravasations of blood into the affected tissues.

Contusions are found most commonly in the cortex of the brain, but they occur also in the deeper tissues.

In the cortex contusions are often covered by a narrow zone of intact cerebral tissue, which appear frequently wedge-shaped and are surrounded by numerous petechiae.

ii. The types of cerebral contusions

Three kinds of cerebral contusions: coup, contre-coup and intermediate cerebral contusion.

(a) The coup contusion lies beneath the injuries of

the head at the site of impact.

(b) The contre-coup contusion is found in a

somewhat less compact distribution in the

diametrically opposite area.

(c) The intermediate contusion develops at midline

structures of the brain such as callus, capasula

interna, basal ganglion, and hypothalamus,

by the impact of blow to the top of the head.

(4)(4) Traumatic cerebral edema Traumatic cerebral edema

i. Definition Cerebral edema of trauma-origin is an increase in th

e fluid content of the perivascular and pericellular spaces of the brain by blow applied to the head.

ii. Appearances of the cerebral edema The macroscopic criteria on a diagnosis of generaliz

ed edema : A flattening of the cerebral gyri or convolutions with o

bliteration of the sulci. A herniation of the inner portions of the temporal poles

through the tentorial hiatus. Herniation of the cerebellar tonsils through the foramen

magnum.

7. Injuries of the heart7. Injuries of the heart

Injuries of the heart include penetrating and non-penetrating ones. In forensic practice, non-penetrating injuries of the heart are of greater forensic interest.

Non- penetrating injuries of the heart may be caused by impact to the chest by blows, fall from height or traffic accidents, which may range from functional disturbance such as cardiac concussion to cardiac structure damage, such as pericardial rupture, cardiac rupture, cardiac contusion, and valvular ruptures. All these injuries can be fatal.

Section 3 Firearm InjuriesSection 3 Firearm Injuries

Firearm injuries can be divided into gunshot wounds

due to penetration of the bullet and explosion

wounds caused by explosion of ammunition.

Gunshot wounds that are caused by penetration of

the bullet into the body are called gunshot wounds

or ballistic missile injuries.

In most of the bullet injuries there are usually an

entrance wound, a bullet track in the tissues and an

exit wound.

i. The classification of gunshot wound according to the firing distance

(a) The contact entrance wound: when the gun is

fired with the barrel closely contacted with the skin.

(b) The near contact entrance wound: when the gun is

fired with the barrel partially contacted with the skin.

(c) The close range entrance wound: when the gun is

fired within 30 cm.

(d) The medium-distance entrance wound: when the gun

is fired within 100 cm.

(e) The distant entrance wound: when the gun is fired

beyond 100 cm.

ii. The features of gunshot wounds

(a) Entrance wound of the bullet The diameter is smaller than the caliber of the

bullet, especially when a pistol is discharged beyond range of 15cm or rifle beyond 100cm.

The entrance wound is circular in shape and is surrounded by a narrow zone of desquamation and bruising of the skin known as contusion collar.

At the moment of penetration, the bullet may rub against the inner edge of the entrance wound. The inner edge of the wound may be covered by the dirt on the bullet to form grease collar.

The entrance wound is usually oval when a bullet strikes the skin obliquely.

The entrance wound may be surrounded by blackening due to fired powder and soot deposited around the wound if a pistol is discharged at a range of 15cm and a rifle within a range of 100cm.

When a pistol or rifle is discharged very close to or in contact with the surface of the skin, the gases may pass into the tissues with the bullet and cause considerable laceration of the skin and subcutaneous tissues. Under these conditions the entrance wound has a cruciate appearance.

At close range there is usually some burning

blackening and tattooing of the skin around the

entrance opening, while the hair in the region of

the wounds often singed.

In contact gunshot wounds, the whole of the

discharge passes into the tissues through the bullet

entrance opening. The burning blackening or soot

and powder deposited are found in the depths of

wound.

iii. The wound track of the bullet The path that a bullet penetrates through the tissues in t

he body is called the wound tract of the bullet. A bullet track is situated between the entrance wound and the exit wound, or between the entrance wound and the site of lodgment of the bullet .

A bullet usually travels through the tissues in a straight line. However, a bullet may be deflected from its course when meets the resistance of the tissues, especially when a bullet strikes the bone.

During its travel through the tissues the bullet may turn, wabble, deform or fragment to cause a considerable damage to the tissues.

iv. The exit wound of the bullet Irregular in shape with its edge everted and torn. Bur

ning blackening and tattooing are not seen in relation to the wound.

Usually larger than entrance wound. But in the case of contact entrance wound, exit wound may be smaller than the entrance wound.

In most of the skull injuries, the bullet passes completely through the skull and as it enters the skull from without, it produces a clean-cut hole in the outer table and a larger hole in the inner table. At its point of exit wound from within, the hole in the outer table is larger than the hole in the inner table.

The track of a bullet through the brain tissues varies greatly.

At long ranges, a bullet at high velocity may pass through the skull in a straight line and produce little damage to the brain tissues away from its immediate track.

Considerable damage may be produced if the bullet is deflected from its course within the skull.

At closer ranges, a high–velocity bullet may produce explosive effects in the brain tissues, which are resulted from the dispersion of the bullet energy through out the brain tissues.