crop woman with hand in blood

Mechanical Injuries

DIFFERENT TYPES OF FORCES ACTING OVER THE BODY

✒  Tensile force (traction-strain):

This is a force that causes a body to pull apart and, if strong enough, to separate into parts.

✒  Compressive force (compression-strain):

This is a force that tends to squeeze the body together and, if strong enough, can cause the body to break apart.

  Shearing force (shear-strain):

This is a force that causes one portion of the body to glide across another. This sort of force changes the shape of the body but does not change its volume.

FACTORS THAT AFFECT CAUSATION OF WOUNDS ON THE BODY

✒  Nature of weapon used:

If a sharp weapon is used to shove into the body, the force is concentrated across a tiny impact area. As a result, a deep penetrating injury will occur. The force exerted by a weapon’s broad surface/blunt surface will be dispersed over a broader region of the body. As a result, the damage will be less than with a sharp weapon.

✒  Amount of energy released during the impacting force:

A mass of a specific weight travelling at a specific speed will accumulate a specific quantity of energy.

✒  Type of tissue affected:

When a weapon strikes the skin, the skin becomes more flexible yet less elastic, making it more easily impacted. Because fat is deposited between the supporting connective tissue fibres, the subcutaneous tissues are flexible and pliable. Muscles can withstand impact to a certain amount, but if their elasticity is exceeded, they can be avulsed, ripped, ruptured, stretched, or crushed. The bones are both rigid and flexible. The bone, on the other hand, fractures at the point of maximal convexity of bending when it is flexed past its elasticity limit. Thus bones can fracture.

MECHANICAL INJURY

A blow, crush, cut, or piercing wound causes mechanical stress to any part of the body. Fracture, bleeding, and infection are the most common consequences of mechanical trauma. Mechanical injuries are those caused by blunt, sharp, or firearm-based force.

TYPES OF MECHANICAL INJURY

✔  BLUNT FORCE INJURIES
I.  Abrasion
II. Contusion
III. Laceration
IV. Fractures

✔  SHARP EDGED WOUNDS
I. Incised wounds
II. Chop wounds

✔  PIERCING WOUND
I.  Stab wounds

I. Abrasion

✔  Characterised by loss of epidermal or superficial layer of skin or the mucous membrane as a result of mechanical force.

✔  May involve dermis in rare cases but mainly affects only the epidermis and hence no bleeding can be found. If dermis is involved, bleeding might be present.

✔  When an abrasion heals, it does not leave a scar.

✔  There are 4 types of abrasion:

1.Linear Abrasion/Scratch Abrasion

These abrasions are created by a sharp, thin item sliding over the skin, such as a pin, thorn, barb, or the pointed end of a weapon. It is broader at the start and displays epithelial heaping (accumulation). near the end. The direction of movement of the causative weapon or item is indicated by the accumulation of epithelium.

2. Graze Abrasion/ Scrape abrasion/ Brush abrasion

These abrasions are caused by the sliding of a broad or wider surface against the skin. Graze abrasions are wider at the beginning and narrower as the epithelium heaps up towards the end.

3. Pressure Abrasion / Crushing Abrasion

These abrasions are formed by the direct impact or pressure of an object on the skin, which is followed by a small movement, resulting in the crushing of the skin’s top layer. When the pressure abrasion from crushing dries, it resembles parchment and appears brown to black. For e.g.: Ligature mark

4. Imprint Abrasion / Patterned Abrasion / Contact / Impact Abrasion

These abrasions occur when force is applied perpendicular to the skin, i.e. at a right angle. The direct contact or imprint of the item or weapon on the skin at a 90 degree angle causes these abrasions.

Other types of abrasions which can be observed and are confused with ante-mortem abrasions are contused abrasion, Post-mortem abrasions (Ant bite abrasions) , fabricated abrasions, Nappy abrasions.

🧤 Contused Abrasion:

The weapon or item fails to imprint the pattern or design when the crushing power of the causative object is greater. Capillaries in the dermis will be damaged, resulting in blood extravasation (contusion) around the abrasion. Abraded contusion occurs when the contused region is more noticeable than abrasion. Contused abrasion occurs when the abraded region is more prominent than the contusion.

🧤 Post-mortem Abrasion:

These are the abrasions left behind after someone is dead. These abrasions are dry and pale white in colour. Ant bites are the usually seen post mortem abrasions. The bite marks of ants are generally light and uneven in form (map like). They are typically seen in moist areas of the body such the axilla, groins, and scrotum.

🧤 Fabricated abrasion:

These are abrasions inflicted by a person, either alone or with the assistance of others, with the intent of implicating another person in a false injury accusation.

🧤 Nappy abrasions:

These are abrasions inflicted by a person, either alone or with the assistance of others, with the intent of implicating another person in a false injury accusation.

These abrasions appear in new-borns as a result of skin excoriation in the diaper area, which includes the groin and buttocks. Excoriation is caused by faeces or excreta.

II. Contusion/ Bruise

✔ A contusion is a blood extravasation or collection induced by a rupture of blood vessels caused by blunt mechanical force without loss of tissue continuity.

✔ It is caused by a blunt force blow that crushes or tears the subcutaneous tissue or dermis without breaking the skin or mucous membrane covering it.

✔  Swelling and pain accompany the collection of blood.

✔  There are 8 different types of Contusions / Bruises:

1.Intradermal Bruise:

This bruise is located in the sub-epidermal layer of skin. These bruises are usually observed at the point of application of force and their margins are quite distinct. The object or weapon used can be clearly observed.

2. Subcutaneous Bruise:

These are the most frequent forms of bruises, and they occur in the subcutaneous tissue, typically in the fat layer above the deep fascia, and are thus visible through the skin. This type of bruise is also known as a superficial bruise.

3. Patterned Contusion:

The offending weapon or object’s imprint or pattern is imprinted over the skin. They provide significant information regarding the nature of offending weapon or object.

4. Shifting Bruise/ Deep Bruise:

Bruises that develop at a different location from the actual site of mechanical force. This is due to deep wounds which are formed on the deep tissues.

5. Tram-line contusion/ Rail-road contusion:

Compressions from blows with a rod, stick, whip, or belt, for example, create these contusions. The contusion is defined by two parallel tram-track-like lines of haemorrhages, with an intact skin region in the middle.

6. Six-penny bruises:

These bruises have size resemblance to that of a six penny coin and hence the name. Fingertip pressure causes these discoid shaped bruises with a diameter of roughly a centimetre.

7. Contusion over organs:

All organs can be contused. For e.g. Contusion over brain stem, Contusion of heart. All these may be fatal depending upon the severity.

8. Spectacle hematoma:

Bruises which are caused by extravasations or collections of blood into the periorbital skin and the. Subcutaneous tissues around the eyes.

III. Lacerated wounds

✔ It is a form of mechanical injury which is characterise by splitting, ripping or tearing of tissues due to strong and hard blunt force.

✔ Laceration occurs when tissue is squeezed or stretched beyond its elastic limits, causing tears of the skin or other tissue.

✔ There are 6 types of lacerations:

1. Split laceration/ Incised looking lacerations:

It is caused by a blunt force which splits up the thickness of the skin. It is observed when the skin and soft tissues are crushed between the impacting force and the underlying bone.

2. Stretch laceration:

Stretch laceration occurs when the fixed skin is overstretched till it ruptures. There is localised pressure with pull in this sort of lacerated wound, causing skin ripping. Stretch laceration is caused by a pulling force.

3. Tear laceration:

It is one of the most common form of laceration. Localized impact by strong and blunt force causes ripping of the skin and subcutaneous tissue.

4.  Avulsion laceration/Grind laceration/ Flying laceration:

De-gloving of the skin happens as a result of grinding compression of the tissues to the point where the skin becomes separated from the deeper tissues.

5. Crush laceration:

Crushing of tissues occurs as a result of the grinding and compression forces. This type of damage can result in the whole or partial amputation of the afflicted bodily component, such as a leg.

6.  Cut laceration:

Torn or cut jagged wounds on the deep tissues which can be seen as a cut on the skin.

IV. Incised wound

✔  A mechanical injury known as an incised wound is defined by the ordered solution of skin and tissues by a sharp cutting force.

✔  These wounds may be produced by light sharp cutting weapons like kitchen knife, razor, scalpel etc.

V. Chop wound

✔ Chop wounds are incised wounds that are created by hacking or chopping with a reasonably sharp and heavy instrument.

✔ These wounds are caused by heavy, sharp cutting weapons like an axe, a chopper, or a sword.

✔ The wound is larger and deeper than an incised incision.

✔ The wound’s border may display bevelling if it’s inflicted obliquely.

VI. Stab wounds

✔  A penetrating wound caused by the application of mechanical force along the long axis of a thin or pointed item is known as a stab wound.

🔪  It is based divided into 2 types based on penetration:

✔  Penetrating wounds:

These are stab wounds which terminated inside the tissue, organs, or cavities. There is no exit wound observed in this type.

✔  Perforating wounds:

These are the stab wounds that go all the way through the body. An entry and exit wound caused by the weapon can be observed on the body.

✒  It is divided into 2 types based on causative weapon:

✔  Incised stab wounds:

Stab wounds which are caused by sharp pointed weapons like pointed knife.

✔  Lacerated stab wounds Stab wounds which are caused by blunt or less sharp weapons like fork, screwdrivers etc.

VII. Fractures

✔ A fracture is a break in the continuity of bone caused by the application of mechanical force or another traumatic factor.

✔  The force can be direct or indirect.

✔  Divided into 2 based on etiology
✒  Traumatic fracture
✒  Pathological fracture

✔  Divided into 2 based on displacements
✒  Un-displaced
✒  Displaced

✔  Divided into 2 based on relation to skin and external environment
✒  Simple fracture
✒  Compound fracture or open fracture

✔  Divided into 5 based on pattern of fracture
✒  Transverse fracture
✒  Spiral fracture
✒  Oblique fracture
✒  Segmental fracture
✒  Comminute fracture

✔  Types of  Direct fracture
✒  Focal fracture
✒  Crush fracture
✒  Penetrating fracture

✔  Types of Indirect fracture
✒  Traction fracture
✒  Angulation fracture
✒  Rotational fracture
✒  Vertical compression fracture
✒  Angulation-compression fracture

MEDICO-LEGAL IMPORTANCE OF MECHANICAL INJURIES

✔ Colour changes help in determining the age of an injury.

✔ Size of the wound can be used to assess the level of violence.

✔ The kind and severity of the damage can be determined by its distribution.

✔ The presence of foreign bodies in the wound might reveal the circumstances of the crime.

✔ Abrasions on the assailant’s face suggest a battle.

SOURCES AND REFERENCES

Authored by:

AKHILA PRABHAKAR

BSc Forensic Science

Jain (Deemed-to-be-University)