MECHANICAL INJURIES

An injury is any harm, whatever illegally caused to any person in body, mind, reputation or property (Sec. 44, LP.C.). Mechanical injuries (wounds) are injuries produced by physical violence. A wound or injury is a break of the natural continuity of any of the tissues of the living body.

 'The question of wounds may be raised in a Court of law in both civil and criminal cases.

Classification:

(I) Mechanical Injuries:

   1) Abrasions 2) Contusions 3) Lacerations 4) Incised wounds

   5) Stab wounds 6) Firearm wounds 7) Fractures and dislocations

(II) Thermal Injuries:

1) Due to cold: a) Frostbite b) Trench foot c) Immersion foot

(2) Due to heat: a) Burns: b) Scalds

(III) Chemical Injuries:

a) Corrosive acids b) Corrosive alkalis

(IV) Injuries due to electricity, lightning, X-rays, radioactive substances, etc.

Legally, injuries are classified into:

(1) Simple, and (2) Grievous

General Principles:

A 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.

Factors Influencing the Nature and Extent of Wounds:

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 he 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.

ABRASIONS:

An 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.

An abrasion is a superficial injury, commonly known as a 'graze' or 'scratch'.

This type of wound damages only the epidermis (uppermost skin layer), and should not therefore bleed. However, abrasions do usually extend into the dermis causing slight bleeding.

Abrasions are commonly caused by a 'glancing' impact across the surface of the skin, but if the force is directed vertically down onto the skin surface it may be termed a 'crush' injury.

These wounds are seen where an object has struck the skin (eg a blow from a fist), or where the injured person has fallen onto a rough surface, such as road.

Abrasions may be 'linear', or commonly known as a single 'scratch', whereas if a broader surface is affected, it is called a 'graze' or 'brush abrasion' (eg where a motorcyclist is thrown from their vehicle, and comes into contact with the road surface in a skidding fashion). Such an abrasion often covers a relatively large area of skin, and is often called a 'friction burn' in lay language.

Abrasions are of four types:

1.     Scratches  2. Grazes  3. Pressure abrasions  4. Impact abrasions

Age of the Abrasions:

The exact age cannot be determined.

Fresh:                    Bright red.

12 to 24 hours:      Lymph and blood dries up leaving a bright scab.

2 to 3 days:           Reddish-brown scab.

4 to 7 days:           Epithelium grows and covers defect under the scab.

After 7 days:          Scab dries, shrinks and falls off.

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.

Medico-legal Importance:

1) They give an idea about the site of impact and direction of the force.

2) They may be the only external signs of a serious internal injury.

3) Patterned abrasions are helpful in connecting the wound with the object which produced them.

4) The age of the injury can be determined, which helps to corroborate with the alleged time of assault.

5) In open wounds, dirt, dust, grease or sand are usually present, this may connect the injuries to the scene of crime.

6) Character and manner of injury may be known from its distribution.

(a) In throttling, crescentic abrasions due to fingernails are found on the neck.

(b) In smothering, abrasions may be seen around the mouth and nose.

c) In sexual assaults, abrasions may be found on the breasts, genitals, inside of the thighs and around the anus.

(d) Abrasions on the face of the assailant indicate a struggle.

(e) Abrasions on the victim may show whether the fingernails of the assailant were long, irregular or even broken.

BRUISES / contusion

Bruises are caused by blunt trauma / injury to tissues, resulting in damage to blood vessels beneath the surface. Blood leaks out ('extravasation') into surrounding tissues from damaged capillaries, venules and arterioles. Bruises may be surface bruises, or deeper within tissues or organs.

Unlike abrasions, the characteristics of the object causing a bruise cannot easily be determined, because blood tends to spread out in a diffuse manner from the site of injury, particularly along fascial planes. Indeed, this phenomenon results in the apparent 'shifting' of bruises after time. For example, a scalp injury may result in a black eye. Bruses may also 'appear' after some days due again to the same phenomenon of blood tracking along tissue planes, and pathologists often re-examine a body again to look for such bruising.

Intra-dermal bruises, however, provide an exception to this general rule, as they are superficial - lying just under the epidermis. In this case, there may be good correlation between the bruise seen and the characteristics of the causative object.

Contusion is an effusion of blood into the tissues, due to the rupture of blood vessels, caused by blunt trauma. Contusions may be present not only in skin but also in internal organs, such as the lung, heart, brain and muscles. The bruise is usually situated in the corium and subcutaneous tissues, often in the fat layer. In contusion, there is a painful swelling, and crushing or tearing of the subcutaneous tissues usually without destruction of the skin. The extravasated blood is diffusely distributed through the tissue spaces, and tile margins are blurred. Bruises may be seen in association with abrasions (abraded-contusion) or lacerations. When a large blood vessel is injured, a tumour-like mass called haematoma is formed. A fresh bruise is usually tender and slightly raised above the surface of the skin, and even a deep-seated bruise shows some swelling when compared with tile opposite limb or part of tile body. A bruise has lighter color in tile centre because extravasated blood is pushed outward by the impact. Mongolian spot (hyperpigmented skin in the lumbosacral region) should not be confused with contusion.

Size: Bruises vary in size from pinhead to large collections of blood in the tissues. The size of a bruise is slightly larger than the surface of the agent which caused it as blood continues to escape into the area. Development of marked tissue swelling in the vicinity of a bruise usually results in loss of its original shape. As a general rule, the greater the force of violence used, the more extensive will be the bruises, but size and shape are modified by the following factors.

(1) Condition and Type of Tissue: If the part is vascular and loose, such as face, vulva, scrotum, a slight degree of violence may cause a large bruise, as there is sufficient space for blood to accumulate. If the tissues are strongly supported, and contain firm fibrous tissues and covered by thick dermis, such as abdomen, back, scalp, palms and soles, a blow of moderate violence may produce a comparatively small bruise.

(2) Age: Children bruise more easily because of softer tissues and delicate skin and old persons bruise easily because of loss of flesh and cardiovascular changes.

(3) Sex: Women bruise more easily than men, because the tissues are more delicate and subcutaneous fat is more. Fat people bruise easily,' because of greater volume of subcutaneous tissue. A slight pressure with the fingers on the arm of a woman, and especially if she is obese and not accustomed to work or exercise, may produce a definite bruise.

(4) Color of Skin: Bruising is more clearly seen in fair-skinned persons than those with dark skin, in whom they may be better felt than seen. The areas of extravasated blood appear darker even on heavily pigmented Negroid skin. If the body is embalmed, skin bruises become more prominent probably (1) by forcing of additional blood into the damaged area, (2) increased transparency of overlying skin, and (3) formation of a dark pigment complex.

(5) Natural Disease: When the vessels are diseased as in arteriosclerosis, bruising occurs very easily and may even result from coughing or slight exertion. In children, small bruises may be caused by the violent coughing as in whooping cough. In purpura haemorrhagica, leukaemia, haemophilia, scurvy; vitamin K and prothrombin deficiency and in phosphorus poisoning, bruising may 'be out of all proportion to the' amount of violence used.

(6) Gravity shifting of the Blood: Bruises do not always appear at the site of impact. Blood escaping from deep tom vessels may be prevented from reaching the skin at the point of impact, because of fascial plane arrangements at the injured area. The bruise may appear at a relatively distant place, where the fascial pattern permits it to reach the surface (ectopic bruising).

The Age of Bruise:

At first: Red.

Few hours to 3 days: Blue.

4th day: Bluish- Black to brown(haemosiderin).

5 to 6 days: Greenish (haematoidin).

7 to 12 days: Yellow (bilirubin).

2 weeks: Normal.

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.

incised wounds

Incised wounds are sharp cut-like injuries, made by knives or broken glass etc.

The edges of the wound will vary according to the nature of the cutting edge of the object, in that a razor will leave regular margins, whereas an axe may leave the wound margins crushed and bruised, resembling a laceration.

Slash Wounds:

These are wounds where the length is greater than the depth, eg a slice wound across the skin. If the wound involves major blood vessels, it can be life threatening, but in general, they are not as serious as stab wounds.

Stab Wounds:

These are wounds where the depth of injury is greater than the length. They penetrate more deeply than slash wounds and tend to come into contact with vital organs in the chest and abdomen.

Stabbing is the most common mode of homicide in the UK, due to the strict control of guns.

Stab wounds are caused most obviously by knives, but are also caused by bayonets and swords, as well as scissors and even blunter instruments such as screwdrivers.

These types of wounds have the following features,

Causes:

l) Striking the body with the edge of Sharp-cutting weapon,

2) By drawing the weapon, and

3) By using the weapon like a saw in which case there may be more than one cut in the skin at the beginning of the wound which merge into one at the end.

A curved weapon like a sickle produces a stab from the pointed end, and incised wound from the blade, sometimes with an intervening intact skin. When the skin becomes folded under the cutting edge of the weapon, a single movement of a sharp weapon may produce a series of incised wounds, separated one from another by bridges of normal skin.

Characters:

l) Margins 2) Width 3) Length 4) Shape

5) Hemorrhage 6) Direction 7) Bevelling cut

CHOP WOUNDS: They are deep gaping wounds caused by a blow with the sharp-cutting edge of a fairly heavy weapon, like a hatchet, an axe, a sabre, or a cleaver. The dimensions of the wound correspond to cross-section of penetrating blade. The margins are sharp and may show slight abrasion and bruising with marked destruction of underlying organs. If the edge is blunt, the margins are ragged and bruised. Undermining occurs in the direction towards which the chop is made. When the whole blade strikes the body at the same time, the depth may be same throughout the wound. Usually the lower end (heel) of the axe strikes the surface first, which produces a deeper wound than the upper (toe) end.

STAB OR PUNCTURED WOUNDS:

Stab wound is penetrating injury caused by sharp and/or pointed objects, such as knife, dagger, nail, needle, spear, arrow, screw driver, etc. penetrating the skin and the underlying tissues that is deeper than its length and width on skin. This can occur by driving the object into the body or from the body's pressing or falling against the object. They are called penetrating wounds, when they enter a cavity of body. When the weapon enters the body on one side and comes out from the other side, perforating wounds or through-and-through puncture wounds are produced. The wound of entry is larger with inverted edges, and the wound of exit is smaller with everted edges, due to tapering of blade. The victim of a fatal penetrating injury may not show signs and symptoms of injury until many hours have passed.

Characters:

1) Margins: The edges of the wound are clean-cut. There is usually no abrasion or bruising of the margins, but in full penetration of the blade, abrasion and bruising may produced by the hilt or the handle. The margins may be abraded, and ragged if the cutting edge is blunt. The mark will be symmetrical, if the knife strikes the skin at right angle. If the knife strikes in a downward angle, the mark will be prominent above the stab wound, and if the knife strikes in an upward angle, the abrasion will be below the stab wound.  In oblique stab wounds, a knife striking from the right will have an abrasion on the right side and vice versa.

(2) Length: The length of the wound is slightly less than the width of the weapon up to which it has been driven in, because of stretching of the skin. Deliberate lateral, forward, or backward movement of the weapon during its withdrawal from the body tends to widen the wound, and the length will be more than the maximum width of the blade.

3) Depth: The depth (length of track) is greater than the width and length of the external injury. It is not safe to find out the depth of a stab wound by introducing a probe, because it may disturb a loose clot and may lead to fatal hemorrhage, or cause serious damage.

LACERATIONS:

These wounds are commonly known as 'gashes, tears or cuts' of the skin. The skin surface is split or torn following blunt trauma, and the force causes the full thickness of the skin to be damaged. Lacerations therefore bleed profusely.

Areas of the body that are commonly the site of lacerations are those with underlying bony support, such as above the eyebrows, on the scalp and face, or over the knees etc, whilst they are less common on areas of the body that are softer such as the buttocks.

Contact with motor vehicles may also cause splitting of the skin due to grinding type movements over the surface.

They are caused by blows from blunt objects, by falls on hard surfaces, by machinery, traffic accidents, etc, If the force produces bleeding into adjacent tissues, the injury is a 'contused-laceration' or 'bruised-tear'. If the blunt force produces extensive bruising and laceration of deeper tissues, it is called "crushing" injury. The force may be produced by some moving weapon or object or by a fall.

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 thee underlying bone or deep fascia. This is seen in the running over by a motor vehicle, and the flap may indicate thee 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 viscus 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.

DEFENCE WOUNDS:

Defence wounds result due to the immediate and instinctive reaction of the victim to save him, either by raising the arm to prevent the attack, or by grasping thee weapon. If the weapon is blunt, bruises and abrasions are produced on the extensor or ulnar surfaces of the forearms, wrists, backs of the hands and knuckles. The size and shape of the bruises depends upon the attacking object. Fractures of the carpal bones, metacarpals and digits may occur. There may also he defence bruises and abrasions on the thighs and a cut may be seen in the web between the base of the thumb and index finger. If the weapon is sharp, the injuries will depend upon the type of attack, whether stabbing or cutting. In stabbing with a single-edged weapon, if me weapon is grasped a single cut is produced on the palm of the hand or on the bends of the fingers or thumb. If the weapon is double-edged, cuts are produced both on the palm and fingers. The cuts are usually irregular and ragged, because the skin tension is loosened by gripping of the knife. When attacked, the victim usually holds up the hand or forearm and receives cuts on the hand, wrist, ulnar border of the forearm and on the fingers. They are often irregular in depth and distribution. A typical knife defence wound is seen in the web between the base of the thumb and index finger, when the blade is grasped. Rarely, defence wounds are found on the feet or legs, e.g. when the victim kicks at the knife, or curls up and tries to cover vital areas with his legs. Defence wounds indicate homicide. Defence wounds are absent if the victim is unconscious, or is taken by surprise, or attacked from the back, or under the influence of alcohol or drugs.

SELF INFLICTED AND FABRICATED WOUNDS:

Self-inflicted wounds are those inflicted by a person on his own body. Fabricated wounds (fictitious, forged or invented wounds) are those which may be produced by a person on his own body, or by another With his consent. They may be produced for the following reasons.

1) To charge an enemy with assault or attempted murder.

2) To make a simple injury appears serious.

3) By the assailant to pretend self-defence or to change the appearance of wounds, which might connect him with the crime.

4) By policemen and watchmen acting in collusion with robbers to show that they were defending the property.

5) In thefts by servants or messengers for the above reason.

6) By prisoners, to bring a charge of beating against officers.

7) By recruits to escape military service.

8) By women to bring a charge of rape against an enemy.

Fabricated wounds are mostly incised wounds, and sometimes contusions, stab wounds and burns. Lacerated wounds are rarely fabricated. Incised wounds are usually superficial, multiple and parallel. The direction is from behind forwards on the top of the head, from above downwards on the upper arm, from below upwards on the forearms, variable on the legs and vertical on the abdomen. Stab wounds are usually multiple and superficial and seen about the left arm or shoulder and sometimes on the chest. Burns are superficial and seen usually on me left upper arm. The clothes are not cut and if cuts are seen they are not compatible with the nature of the wounds. The history of me assault is incompatible with the injuries.

Therapeutic Wounds:

These are wounds produced by doctors during the treatment of a patient, such as surgical stab wounds of me chest for insertion of chest tubes, of the abdomen for drains, thoracotomy and laparotomy incisions, incisions on the wrists, antecubital fossae and ankles, and tracheostomy incisions. Some of these wounds may be mistaken for traumatic wounds, e.g. a surgical stab wound of me chest for putting a drainage tube. Sometimes, a traumatic wound may be enlarged and included in the surgical procedure, or a drainage tube may be put in a homicidal stab wound.

 FORENSIC BALLISTICS

REFERENCES:

Textbook of Forensic Medicine and Toxicology:

 www.forensicindia.com (Department of Forensic Medicine, A.M.U. Aligarh)