MECHANICAL INJURIES

INTRODUCTIONAn injury is define as any harm, whatever illegally caused to any person in body, mind, reputation or property as per Indian Panel Code (Sec. 44). In forensic science, the injuries/wounds are produced by physical violence, which break of the natural continuity of any of the tissues of the living body .There are different types of injuries. Trauma is explained as an injury to the body caused by physical, mechanical or chemical factors, which may result in wounds or possible complications. The medical purposes, violence refers to either behaviour that result in injury or both psychological and physical trauma .

Mechanical trauma is an injury to any portion of the body from a blow, crush, cut, or penetrating wound.

MECHANICAL INJURY General principlesA wound is caused by a mechanical force which may be either a moving weapon or object, or the movement of the body itself. In the first case, the counterforce is provided by the inertia of the body, and in the second case by the rigidity of some stationary object against which he falls. A combination of these two events is seen in most cases. Due to the impact between the forward moving force and the counterforce, energy is transferred to the tissues of the body, which causes a change in their state of rest or motion. The human body contains many complex tissues which greatly vary in their physical properties, such as state of solidity, fluidity, density and elasticity, and because of this a change in the state of rest or motion of the body produced by a forceful impact does not affect the tissues uniformly. Some of the energy is spent in moving the body as a whole. But most of the energy may cause non uniform motion of localised parts of the body, due to which the affected tissues will be subjected to compression or to traction strains or to a combination of both. All the body tissues, except those which contain gas, are resistant to compression, i.e., they resist force tending to reduce their· volumes. Mechanical force does not cause compression of the tissue but causes their displacement and deformation, and traction strains are produced in the affected tissues. Such strains may be due to forces causing simple elongation of tissues, but they may be

due to more complex mechanism, such as bending, torsion or shearing.

The complications of mechanical trauma are usually related to fracture ,haemorrhage and infection. They do not necessarily have to appear immediately after occurence of the injury. Slow internal bleeding may remain masked for days and lead to an eventual emergency. Similarly wound infection and even systemic infection are rarely detectable until many days after the damage. All significant mechanical injuries must therefore be kept under observation for days or even weeks.

FACTORS INFLUENCING THE NATURE AND EXTEND OF WOUND

1. The Nature of the Object or Instrument:With a blow from a pointed or sharp-edged weapon,

the force is concentrated over a limited area; due to which deep penetration or incision of the tissues occurs. The hardness of the tissues and the friction of the divided tissues against the sides of the object resist the passage of object through tissues. With a blow from a blunt instrument, the force is distributed over a relatively large area, due to which the damage caused to a unit mass of tissue is less than when the force is concentrated over a smaller area.

2. The Amount of Energy Discharged During Impact:The amount of kinetic energy present in a moving

object is measured by the formula mv2/2, where m =

mass, and v= velocity of the moving object. An object of definite weight moving at a definite speed produces a definite amount of energy. If the weight of the object alone is doubled, the kinetic energy is doubled, but if the velocity only is doubled, the kinetic energy is quadrupled. Therefore, the velocity of the object is more important than the weight.

3. The Conditions under which the Energy is Discharged:Most of the energy liberated in an impact may he

spent in causing generalised movements of the body, which may be sufficient to knock down a person, although the local injury may be minimal. If the body or part of the body struck is immobilized, the greater part of the kinetic energy may be spent in causing localised deformation. If the head is free to move, a blow may cause little damage, but if the head is well supported, a similar blow may cause marked injury to skull.

4. The Nature of the Affected Tissues:Skin: The shape of the skin is readily changed when

struck as it is very pliable and a little elastic. The skin is strongly resistant to traction forces due to the firm coherence of its tough layers of keratinized cells, and it is often not damaged when struck with a blunt instrument, though the underlying tissues may be damaged severely. When crushed against rigid bone, the skin is readily split.

Subcutaneous Tissues: The subcutaneous tissues are very plastic due to their fat content and the pliability of their' supporting connective tissue fibers.

Muscles: The muscles are usually not damaged from blows due to their great plasticity and elasticity but may

be crushed or torn against bone or lacerated by fragments of displaced and broken bone

Bones: The bones are relatively rigid. The bones may bend without breaking when a force is applied, and then may recoil to its normal shape due to its elasticity. A blow to the chest may bend the ribs without fracture, but the thoracic organs may be damaged. Fracture occurs when the bone is bent beyond the limits of its elasticity, which starts at the point of maximum convexity caused by the bending.

Body Fluids and Gases: Fluid is incompressible but is easily displaced. Powerful hydrostatic forces may be produced in a hollow organ which contains fluid due to a blow, which are transmitted equally and uniformly in all directions and may rupture anatomically distant and mechanically weak tissues.

CLASSIFICATION

Mechanical injuries are classified into

1. Abrasions2. Contusions3. Lacerations4. Incised wounds5. Stab wounds6. Fire arm wounds7. Fractures and dislocation

1. ABRASIONAn abrasion is a destruction of the skin, which usually involves the superficial layers of the epidermis only. They are caused by a lateral rubbing action by a blow, a fall on a rough surface, by being dragged in a vehicular accident, fingernails, thorns or teeth bite. Some pressure and movement by agent on the surface of the skin is essential. In its simplest form, the epidermal cells are flattened and their nuclei are elongated. If sufficient friction is applied, partial or complete removal of

the epithelium may occur and the superficial layer of dermis is damaged.

CAUSATIVE AGENT

Hard blunt or hard blunt and rough or pointed end of an object or weapon. Example: stone, stick, needle or any other weapon or rough surface of any other material.

MODE OF PRODUCTION

Abrasions are produced by the impact of the above materials, when friction is caused between the object and the epidermis due to the impact. The direction of force causing the friction may be horizontal (as in scratches or grazes)or tangential or it may be more or less perpendicular (as in pressure or imprint abrasion)

FEATURES OF ABRASION

Abrasions are superficial injuries. But often there is accompanying injury to the subcutaneous or still deeper tissues. At the site of abrasion, there may be oozing

of lymph and sometime very slight oozing of blood. The

lymph or blood which oozes out, and the denuded epithelial

debris , dry up within a few hours to form a scab. Abrasions heal without formation of permanent scars.

TYPES

1. SCRATCHES2. GRAZES3. PRESSURE ABRASIONS4. IMPACT ABRASIONS

MEDICOLEGAL IMPORATANCE

1. From abrasion, the type of the weapon used, can be said. 2. From linear or graze abrasion, the direction of application of force and the relative position of the victim and the assailant can be known.3. From abrasions, time of assault can be roughly assessed. When fresh, an abrasion is red with evidence of oozing of serum and a little blood .By 8-24 hours, there is a reddish scab formation. By 6th day, it is blackish and it starts falling off from the margins 

4. Abrasions sometime give indication about the specific type of offences committed. Nail scratches in the neck of a dead body may be indicative of manual strangulation or throttling may be indicative of killing by smothering.

5. Abrasions may be produced on the vulnerable sites of the dead body during shifting of the body to the mortuary. These postmortem abrasions may be mistaken as antemortem abrasions . These abrasions are present mostly against the vulnerable bony prominences.

Ante-mortem and Post-mortem Abrasions:Abrasions produced slightly before or after death cannot be differentiated even by microscopic examination. In superficial lesions or when decomposition is advanced, differentiation is difficult. After death, the abraded epidermis becomes stiff, leathery, and parchment-like, brown, more prominent, and may be mistaken for burns. On drying, abrasions become dark-brown or even black. In a body recovered from water, abrasions may not be seen on first inspection, but they are easily seen after the skin dries. Abrasions may be produced after death when a body is dragged away from the scene of crime. The distribution of such abrasions depends upon the position of the body while it is being dragged.

2. bruise/ contusionFeatures of bruise When fresh a bruise is reddish in color, slightly raised above the surrounding area, is painful and tender and may or may not have denudation of the covering cuticle .Gradually, it changes in color and subsides by

two weeks. It is usually roundish or takes the shape of the striking part of the weapon. Along with rupture of the capillaries. There is damage in the soft tissue. But the skin is usually spared because skin tissue is quite tough

Type of weapon Impact with hard blunt weapon produces bruise. Example- stone, stick. Impact by a stick or rod will cause two parallel linear bruises along the two margins of the impact, with a pale gap intervening, the breadth of

which correspond with the diameter of the stick. From this kind of bruise, the type of the weapon used, can be known.FACTORS WHICH INFLUENCE THE FORMATION AND APPEARANCE OF A BRUISE

1. Quantity of force used- A greater force is more likely to cause a bruise. 2.

Quality of force- A hard blunt force will cause a bruise, but a soft blunt force may not. Thus, striking with a stone will produce a bruise, but covering the part of the body with a rug before hitting with a stick may not produce a visible bruise. No bruise may be apparent externally, because the impact being soft, there may not be any rupture of capillaries underneath the skin.

But it may cause deep bruise or haematoma adjacent to the bone because, the applied force causes the soft tissue to strike the hard bone, resulting in the rupture of the capillaries and venules there.

3. Site of application of force A greater force may even not produce any bruise on the anterior wall of the abdomen due to toughness and yielding force absorption capacity of the tissue there .But bruises are easily produced against a bony prominence, say malar prominence because the capillaries in the subcutaneous tissue rupture easily in between the bone underneath and the hard blunt force applied on the surface.

4. Sex Females bruise easily due to delicacy of tissue in them including the vessels, and also due to more subcutaneous fat in them. Vessels present in the fatty tissue are more likely to be ruptured on application of force than the vessels present in the tough fibro muscular tissue. 5. Age Infants, young children and very old persons bruise more easily than young adults. In infants and young

children, it is due to delicacy of tissue including vessels and more amount of subcutaneous fat.

6. Certain pathological conditions Persons suffering from some disease (example- leukaemia vitamin ”K” deficiency ),bruise easily without application of much force. These persons may even develop haemorrhagic spots without application of any force. 7. Complexion of the person A bruise appears more prominent in a fair complexioned person. In dark-skinned persons ,it may not be well appreciated.

PATTERNED bruise

The design on the surface of the weapon maybe imprinted on the bruise. Such a bruise is called a patterned bruise. Example – bruises caused by a cycle chain or motor vehicle grill. A bruise caused by the roundish end of a weapon is circular in shape. When caused by the margin of the circular end of the weapon, it is crescent shaped. If caused by the body of a rod or stick then two parallel lines of bruises appear with a gap in between , which is roughly equal to the breadth of the weapon.

Medico- legal Importance:

1) Patterned bruises may connect the victim and the object or weap, e.g., whip, chain, cane, ligature, vehicle; etc.

2) The age of the injury can be determined by color changes.

3) The degree of violence may be determined from their size.

4) Character and manner of injury may be known from its distribution. (a) When the arms are grasped, there may be 3 or 4 bruises on one side and one larger bruise on the opposite side, from the fingers and thumb 'respectively, indicating the position of the assailant in front of, or behind the victim.

(b) Bruising of the arm may be a sign of restraining a person.

(c) Bruising of the shoulder blades indicates rum pressure on the body against the ground or other resisting surface.

(d) In manual strangulation, the position and number of bruises and nail marks may give an indication of the method of attack or the position of the assailant.

(e) Bruising of thigh especially inner aspect, and of genitalia indicates rape.

(5) In the case of fall, sand, dust, gravel or mud may be found on the body.

Bruises are of less value than abrasions because:

(1) Their size may not correspond to the size of the weapon.

(2) They may become visible several hours or even one to two days after the injury.

(3) They may appear away from the actual site of injury.

(4) They do not indicate the direction in which the force was applied

LACERATIONS

In laceration there is breach of continuity of tissue involving depth more than the covering epithelium of skin or that of an organ. Lacerations are caused due to impact by hard blunt and rough weapons or objects.

Features

Shape – Usually irregular. Margin – Irregular. Floor – Tags of tissue may be seen passing across the floor .Dimensions – length or length and breadth both are more than the depth of the injury .Foreign substances at the site of laceration – Many of these injuries being sustained on roads or due to fall etc., often the lacerations gave dust or such materials adhered to their floors . These foreign materials may sometime help to find out the place of occurrence of the injury or assault

Types:

1) Split Lacerations: Splitting occurs by crushing of the skin between two hard objects. Scalp lacerations occur due to the tissues being crushed between skull and some hard object, such as the ground or a blunt instrument.

Incised-like or Incised-looking Wounds- Lacerations produced without excessive skin crushing may have relatively sharp margins. Blunt force on areas where the skin is close to bone, and the subcutaneous tissues are scanty, may produce

a wound which by linear splitting of the tissues, may look like incised wound.

2) Stretch Lacerations: Overstretching of the skin, if it is fixed, will cause laceration. There is localised pressure with pull which increases until tearing occurs and produces a nap of skin, which is peeled off the underlying bone or deep fascia. This is seen in the running over by a motor vehicle, and the flap may indicate the direction of the vehicle. They can occur from kicking, and also when sudden deformity of a bone occurs after fracture, making it compound.

3) Avulsion: An avulsion is a laceration produced by sufficient force (shearing force) delivered at an acute angle to detach (tear oft) a portion of a traumatized surface or viscous from its attachments. The shearing and grinding force by a weight, such as lorry wheel passing over a limb may produce separation of the skin from tile underlying tissues (avulsion) over a relatively large area. This is called "flaying". The underlying muscles are crushed, and the bones may he fractured. The separated skin may show extensive abrasions from tile rotating frictional effect of tile tyre, but one portion is still in continuity with adjacent skin. Internally, organs can be avulsed or torn off in part or completely from their attachments.

4) Tears: Tearing of the skin and tissues can occur from impact by or against irregular or semi-sharp object, such as door handle of a car. This is another form of overstretching.

5) Cut Lacerations: Cut lacerations may be produced by a heavy sharp-edged instrument. The object causing a

lacerated wound crushes and stretches a broad area of skin, which then splits in the centre. The edges are irregular and rough, because of tile crushing and tearing nature of the blunt trauma. Frequently, the skin, at the margins is abraded due to the flatter portion of the striking object rubbing against the skin as it is indented by the forceful blow.

Medico-legal Importance:

(1) The type of laceration may indicate the cause of the injury and the shape of the blunt weapon.

(2) Foreign bodies found in the wound may indicate the circumstances in which the crime has been committed.

(3) The age of the injury can be determined.

INSICED WOUNDS

Incised wounds are cuts or slashes produced by the sharp edge of a weapon like, knife, razor, sword etc.

Mode of infliction

By drawing or saw like movement of the weapon on the body surface when the weapon is rather light like, a knife or razor ,by striking the sharp edge on the body when the weapon is heavy or moderately heavy like, axe ,sword etc.

Features of incised wounds

1. Shape – The shape of an incised wound is elliptical or it is spindle shaped. It maybe oval if the wound gaps much. .The

shape of the incised wound may change in its curvature due to elasticity, creases and cleavages of the skin and the direction of the underlying muscle.

2. Length of the wound - Length of an incised wound is greater than breadth and depth. Length of the wound does not correspond with the length of the blade of the weapon when the incised wound is caused by drawing or sawing. It may correspond when the wound is caused by striking.

3. Breadth – Breadth of an incised wound primarily depends on the thickness of the effective part of the blade i.e., the thickness of the blade at that level upto which the edge of the weapon has gone in the tissue. But the breadth depends much on the elasticity of the skin of the area and direction of the fibres of the muscle underneath the skin, in relation with

the length of the wound. If the underlying muscle fibres

are cut across their length then, contraction or shortening of the cut muscle fibres on both sides of the incised wound will cause widening of the gap (bread) of the wound.This does not happen if themuscle fibres not cut across or if the fibres run along the length of the incised wound.

4. Angles - The angles at both ends of the incised wound is sharply defined. 5. Margin – Margins of an incised wound are well defined, cleanly cut and sharp. 6. Floor – Floor of the wound is also sharply cut and divided. 7. Haemorrhage – As the vessels are also sharply cut, there is

excessive external haemorrhage. If the haemorrhage is

from a vein then bleeding occurs in drops, which is stellate in appearance. If it is from the arterial source, then there is spurting effect and the bleeding occurs in jets

8. Hesitation cuts – These are also termed “tentative cuts”. These are multiple superficial cuts placed around the beginning part of the main wound, in cases of suicide. These superficial tentative or hesitation cuts indicate hesitation or indecisive state of mind of the suicide, before he finally inflicts the deep fatal wound on his own body.

9. Defence wounds :These are in most occasions , incised wounds though abrasions; bruises, lacerations or punctured wounds also may be sustained in defence for self protection.

Defence cuts may be present on the palmar aspects of the hand if, when attacked with a sharp cutting weapon, the victim holds the blade of the weapon to escape the assault. In such a case there may be incised wounds on the palmar aspects of more than one finger, but all of them are expected to be in one line, if the blade of the weapon is single edged.

Medicolegal aspects of incised wound

1. Incised wounds are usually suicidal, then homicidal and only occasionally accidental. Suicidal incised wounds are usually placed in front and sides of the neck or sometimes in front of the wrists, to cut the radial artery to bleed to die. 2. Direction of application of force – From the tailing and bevelling, the direction of application of force can be known.

3. Cause of death – In case of incised wound there is excessive external bleeding. Death therefore in many cases occur due to haemorrhage and shock. In case of cut-throat injury ,death, in addition, may occur due to asphyxia due to choking of the respiratory passage by blood.

CHOP WOUNDS

Chop wounds are incisedwounds produced by striking withsharp cutting, heavy or moderatelyheavy weapons, like axe, sword etc .These wounds are comparatively deeper and broader than the incised wounds produced by drawing or saw like movement

of light sharp cutting weapons Abrasions or contusions

maybe produced at the margins due to friction with the surface of the thick and heavy blade. These wounds usually have bevelling also. Bevelling – When a sharp cutting heavy or moderately heavy weapon is used (striking) tangentially or a tan angle to the body, then there is flapping at one margin of the wound at the cost of the other margin.

STAB WOUND

Punctured or stab wounds are deep wounds produced by the pointed end of a weapon or an object , entering the body .Depth is the greatest dimension of punctured wound

Causative Weapon : Punctured wounds may be caused by the tip of a knife, arrow, needle. Punctured wounds may also be caused by an object or weapon having no pointed end, e.g., blunt end of an iron rod. The pointed weapon may or may not have sharp edge. Example: spear (have pointed end but may or may not have sharp edge), needles (have pointed end but no sharp edge), end of an iron rod (not pointed or sharp edged)

Varieties of punctured wounds

1. Perforated Wound Here part of the weapon passes through the whole thickness of any part of the body, e.g. when the tip of a weapon enters the body through anterior surface of the chest and exits out through the posterior surface of the chest. In a perforated wound there will be two outer or external wounds with a single strike,(a) wound of entrance, the wound through which the weapon enters the body and(b)wound of exit, through which the tip of the weapon comes out of the body

2. Penetrated wound. Here the wound terminates inside a body cavity or viscous , e.g. penetrating wound ending inside the abdominal or chest or cranial cavity.3. Punctured or stab wound without causing penetration to a body cavity or without perforating the whole thickness of the body. Here the tip of the weapon terminates inside the body except in a body cavity

Features of punctured wounds

1. Shape The shape of the wound of entrance in case of stab wound depends mostly on the shape of the weapon or shape of the edge of a weapon.

When a double edged pointed weapon is used , the external wound is elliptical, spindle shaped or slit-like in appearance. In spindle shaped or elliptical wounds produced by double edged weapon, both the margins and angles will be sharp,

clean and well-defined. When a single-edged pointed weapon is used, the external wound will be triangular or wedge-shaped. In wedge-shaped wounds produced by single-edged pointed weapons two margins and one angle will be sharply defined

2. Margin: When stabbed with double-edged sharp cutting pointed weapon, both the margins of the elliptical external wound will be clean cut ,regular, sharp and well defined. When caused by a single-edged sharp cutting pointed weapon, the wedge shaped external wound will have two long, clean cut, regular, well defined margins with one short irregular margin. When caused by pointed or blunt ended weapon without any sharp edge, then the margin will be irregular, uneven with abrasion ,contusion and even tears

3. Depth : Depth is the greatest dimension of a punctured wound. The depth of the wound usually depends on the length of the weapon or the blade of the weapon upto which it enters in the body. If the whole length of the blade of the weapon enters the body, then surrounding the wound of entrance there will be a contusion or abrasion due to friction or pressure by the hilt or blade-guard of the weapon.

If the whole length of the weapon does not enter the body then, there will not be any hilt mark in the form of abrasion or bruise. In such cases, the depth of the wound will not correspond with the length of the blade of the weapon. Similarly, in case of a perforated wound, when a part of the weapon comes out through the wound of exit, the depth of the wound will not give the length of the blade of the

weapon even though, hilt mark may be present around the wound of entrance indicating that, whole length of the blade has passed through the tissue.

4. Hilt mark: Most of the sharp cutting pointed weapons have a hilt or hand guard in between the butt and the blade, so that, during use the hand will not slip down over the blade of the weapon and get injured .When in a stab wound, the whole length of the blade is pushed inside the body then the hilt strikes against the skin around the wound of entrance and keeps its mark over there in the form of abrasion or

occasionally in the form of bruise. Thus, hilt mark has

two importances. If there is abrasion due to hilt around the wound, we can say that, that wound is the wound of entrance and that the whole length of the blade of the weapon was pushed inside the body and the weapon has a hilt

5. Haemorrhage: In case of stab wound internal haemorrhage is more than the external haemorrhage due to injury to internal vessels. The extent of internal haemorrhage may not be guessed until the body is dissected open.

6. Injury to the internal organs: In stab wounds, injury to the vital internal organs is more common and is the real danger. Stab wounds over the head, neck, chest or abdomen are obviously more dangerous due to possible injury to the vital organs

7. Examination of punctured wounds require extra vigil, because, these wounds have greater depth which cannot be examined from outside and because, punctured wounds are expected to cause injury to the vital organs of the body and extensive internal haemorrhage. The depth and direction of the track of the wound should not be attempted from outside with the help of a probe. Such an attempt may cause further extension of the depth or extension in a new direction during probing.

Medicolegal importances of stab wounds

1. About the nature of the injury: Generally speaking, stab wounds are most commonly homicidal, next in occurrence suicidal and lastly accidental.

Homicidal stab wounds are usually more than one in number, all are quite deep ,may be located anywhere on the body ,including self unapproachable parts. In homicidal cases, the covering clothes usually bear corresponding cut marks or tears. Defence wounds and marks of resistance may be present on the body .Foreign materials like foreign scalp hair or shirt-button etc. may be found in the tightgrip of the hand of the victim in a state of cadaveric spas

m. The weapon of offencemay not be available on the spot.

Suicidal stab wounds are located on the approachable parts of the body, more commonly over the left side front of chest, neck and lower abdomen. The main wound maybe only one. The coveringclothes may not bear corresponding cut marks as that may be partly removed from the area while doing the act. The weapon may be held in the hand in

a state of cadaveric spasm, or it may be present near death.

No defence wounds or marks of resistance will be present on the body, but some self-inflicted incised wounds may be present on the other approachable parts of the body. The place of occurrence will not be disturbed and it may be a secluded place, not approachable to others. Sometimes a suicidal note may be

left behind by the suicide. In some cases the suicide might have tried some other method before stabbing himself to death .Evidence in support of this may be present on the body.

2. From the shape and size of the external wound and the depth, the type of the blade of the weapon used can be said.

FRACTURESFractures may be caused by direct or indirect violence.

1. Fissured fractures: These are linear fractures of cracks in the bone involving the whole thickness of the bone or one or the other table only. They are caused by forcible contact with a broad resisting surface like ground , blows with an agent having a relatively broad striking surface or from a fall on the feet or buttocks.The fracture starts at the point of impact and runs parallel to the direction of the force. If the head is supported when struck, the fracture may start at the counter pressure. The fracture line tends to follow a devious course and is usually no more than hair’s breadth.

2. Depressed fractures: in this portions of fractured bones are driven inward into the skull cavity. Their pattern often resembles the weapon or agent which caused it.They are

caused by blows from heavy weapons with a small striking surface eg; stones , sticks, hammer.

3. Comminuted fractures : In this the bone is broken into several pieces . They are caused by a fall from height , vehicle accidents and from blows by weapons with a large striking surface, eg; heavy iron bar, axe, thick stick. Fissured fissures may radiate for varyind distances from athe area of comminution.

4. Pond or Indented fractures : This is a simple imbucklingof the skull which results from the obstetric forceps blade, a blow from a blunt object or forcible impact against some protruding object.

5. Gutter fractures : They are caused when part of the thickness of the bone is removed so a s to form a gutter , eg; glancing bullet wounds . They are usually accompanied by irregular depressed fractures to the inner table of the skull.

6. Ring or foramen fractures: It is fissured fracture which encircles the skull in such a manner that its anterior third is separated at its junction with the middle and posterior thirds.But usually the term is applied to a fracture, e=which runs about 3 to 5 cm.outside the foramen magnum at the back and sides of the skull and passes forwards through the middle ears and roof of the nose due to which skull is sepearted from the spine.They are rare and occur after falls from a height into feets or buttocks. This drives the vertebral column into the skull.

7. Perforating fractures: These are caused by fire arms or pointedsharp weapons like dagger or knives or axe.The weapon pass through both tables of the skull leaving more or less clean cut opening.

8. Diastic or sutural fractures : Seperation of the suture occur in young person due to a blow on the head with blunt instrument.

FIRE ARM INJURY

They are usually recognized without difficulty. The injuries produced by fire arms vary depending on the projectile, the muzzle velocity, distance, angle of firing and part of the body involved.

The type of wound produced by a firearm depends on several factors including:

a) Nature of the weapon

b) Composition of the missile

c) Range

d) Tissues traversed by the missile

e) Direction of fire

The Weapon

Ballistics is the study of firearms and ammunition. It is a very highly specialized and complex science and cannot be fully

discussed here, but certain basic principles can be considered.

There are two main types of guns:

Those firing single missiles, e.g. rifles and pistols

Those firing a mass of small missiles (shot) - shotguns.

Rifles and pistols are rifled weapons i.e. there is rifling (spiral grooving) of the inside of the barrel which imparts spin to the bullet, ensuring a stable flight by the gyroscopic effect produced.

The long-barrelled weapons (rifles) have a high muzzle velocity and are accurate over a long range (2,000-3,000 yards on average).

The short-barrelled weapons (pistols) have a low muzzle velocity and are accurate over a relatively short range (400-600 yards on average).

Pistols may be revolvers or automatics (semi-automatics). Revolvers fire bullets from chambers in a revolving metal cylinder. After the bullet is fired, the cartridge case remains in the cylinder and must be removed by hand. The “automatic” is a self-loading weapon, and the ammunition is stored in a magazine in the handle of the gun and is fed into

the barrel of the gun as each bullet is fired. After the bullet is fired the empty cartridge case is automatically ejected from the gun.

The calibre of these guns is expressed as the internal diameter of the barrel e.g. .38 inch, .45 inch or 9mm. The basic unit of ammunition is the cartridge (or round), made up of the cartridge case, the primer, the powder and the bullet. Bullets are made of hard solid metal and fit into a cartridge case (usually brass) that contains the powder, which explodes when the firing pin on the hammer of the gun hits the cartridge case and ignites the primer, forcing the bullet from the gun. Hollowing out the tip of the bullet (hollow-points; dum-dums) causes the bullet to shatter or deform on contact causing greater damage.

Shotguns have a smooth bore i.e. the inside of the barrel is smooth. The gun fires a cartridge composed of a mass of lead pellets which fan out after being fired. The effect at close range is that of one solid missile, but at a distance it is that of several individual pellets. A bullet fired from a rifled gun bears scoring (scratches) imparted by the inside of the barrel. This scoring is characteristic of the weapon, providing a "fingerprint" which can be used to identify the weapon from which a bullet was fired.

It is therefore important that bullets recovered at autopsy should NEVER be handled directly by metal forceps or other hard instruments which might alter the scoring pattern.

Such bullets should be wrapped in protective wadding for transportation to the forensic laboratory. Note that the cartridge case bears marks produced by the firing mechanism from which it is possible to identify the gun that was used. It should also be treated with great care.

Bullet Wounds

Entry Wounds

The features vary depending on the range from which the weapon is fired—contact, close (intermediate) range or longer (indeterminate) range.

A gunshot wound is a controlled explosion and the bullet is accompanied from the gun by a jet of flame, a cloud of gas, burning and unburnt grains of gunpowder and soot from burnt gunpowder. Entry wounds may show the stigmata of the explosion to a lesser or greater extent.

(A) Contact wound

The muzzle is pressed against the skin. The heat of the discharge causes scorching or charring of the wound. The

gases produced by the explosion of the cartridge enter, stretch and split the skin producing a stellate or cruciform tear. The tissue at the margin of the wound may contain soot and powder.

(B) Close range (Intermediate range)

The wound is inflicted at less than arm's length i.e. < 2 - 3 feet. The particles of partly burnt or unburnt powder from the muzzle are driven into the skin around the entrance wound giving a stippled appearance called "powder tattooing" or "powder burns". The area may be blackened by soot. Soot may be wiped off the skin, but powder tattooing cannot be wiped off. The bullet hole may be round or split, the latter being relatively common when there is underlying bone.

(C) Longer (Indeterminate) `range

The range is > 2 - 3 feet. The gun is too far from the skin for the products of the explosion to have any effect. Therefore the appearance of the wound is due entirely to the bullet. The wound is usually round (but may be split by "tail-wag" if the gun is fired from the extreme of its effective range causing the bullet to lose its gyroscopic spin and start to tumble).

Marginal abrasion/Abrasion collar/Abrasion ring

The margin of the entry wound in some close range and longer range injuries may be abraded (“marginal abrasion”, “abrasion collar” or “abrasion ring”) as the bullet inverts the skin and abrades the epidermis as it enters. The shape of this abrasion may help in determining trajectory.

Grease ring

The inner edge of the abrasion collar may be black due to grease or lubricating oil and metal particles from the bullet.

Exit wounds

These show none of the stigmata of the explosion or soiling seen in the entry wound. An exit would may be the same size as the entry wound, but may be smaller or larger depending on the range, type of weapon, type of bullet, the tissues being traversed by the bullet, etc.

In a contact shot the entry wound is split by the explosive gases and is therefore usually larger than its corresponding exit wound. However, if the bullet comes out carrying bone e.g. a shot to the skull, the exit wound may be larger than the entry.

In a distant shot the exit wound may be the same size or slightly smaller than the entry. In general, exit wounds tend to be split with irregular, everted edges. As a rule, exit wounds DO NOT show an abrasion collar, but exceptionally,

this may occur if the skin was pushed up against a hard surface, e.g. concrete wall or floor at the time the bullet exited. This is known as a shored exit wound.

CONCLUSION Forensic expert determine the direction of impact, the type of object that caused it and how often the contact was made, often they're made by blows from a hammer or axe head. Bite marks are also a form of crushing wounds. With a knife or incised wounds the crime scene investigator must make a distinction between cut and stab or puncture wounds and among different types of piercing implements such as an ice pick or small knife. Most knives have a flat edge and a sharp edge which can be seen in the wound angels. Some wounds are defensive such as cuts made on the palms or fingers of a victim's hands. Some time cuts are associated with suicidal gestures are known as hesitation wounds as the person attempts to inflict self-damage. As with all instances of a firearms offence that results in an injury, measurements are taken along with photographs to aid in the identification of the weapon used, it is necessary for a Forensic expert. Powder residue samples are taken and if the victim dies as a result of their gunshot wound, the round is removed for ballistic analysis from the corpse at the autopsy stage. The forensic scientists and investigating officer scour the crime scene looking not only for the weapon involved as they are sometimes disposed of but also for spent shell casings and/or loose rounds that were fired but did not hit their intended

targets and imbedded themselves in nearby walls, doors or the ground.

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Sharon R. Sexual Assault: The MedicalLegal

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