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Forensic Medicine & Toxicology - Chapter 7: Mechanical Injuries

Sources: Parikh's Textbook of Medical Jurisprudence FMT; DiMaio's Forensic Pathology, 3rd Ed.

LONG ANSWER QUESTIONS

Q1. Classify Mechanical Injuries. Write in Detail on Abrasions. Differentiate Antemortem and Postmortem Abrasion.

Classification of Mechanical Injuries

Mechanical injuries are caused by physical force acting on the body. They are classified as:

Abrasions - Injury to superficial layers of skin
Bruises (Contusions) - Extravasation of blood into tissues without breach of skin surface
Lacerations - Tearing of skin and underlying tissues by blunt force
Fractures - Break in continuity of bone
Incised wounds - Caused by sharp-edged instruments (cuts)
Stab wounds - Deeper than wide, caused by pointed or sharp instruments
Firearm injuries (Gunshot wounds)

Special medicolegal categories (used irrespective of weapon):

Defence wounds - Sustained while defending
Self-inflicted wounds
Injury patterns - Patterned injuries indicative of specific weapons

Abrasions - Definition and Classification

An abrasion is an injury involving only the superficial layers of the skin. It is caused by friction and/or pressure between the skin and some rough object or surface. It bleeds very slightly, heals rapidly in a few days, and leaves no scar.

Classification of Abrasions (based on manner of production):

Type	Mechanism	Features
1. Scratch	Sharp object (pin, thorn, fingernail) running across skin	Linear; torn epithelium piled up at the distal end, indicating direction of force
2. Graze	Broad skin surface slides across rough surface	Also called "brush burn" or "friction burn"; contaminated with grit; seen in traffic accidents/dragging; direction indicated by serrated border initially and heaped epithelium at the end
3. Imprint/Pressure/Contact abrasion	Direct impact/pressure of an object crushing the cuticle	Also called "patterned abrasion"; stamps a reproduction of weapon shape on skin (e.g., ligature mark in hanging, tyre pattern in run-over)

Medicolegal Significance of Abrasions:

Indicate the site of application of force (unlike bruises, they do not shift)
Show direction of force (direction of heaped epithelium)
Help identify the nature of the weapon (e.g., patterned abrasions)
Can indicate the age of the injury (color changes)
Presence of vital reaction distinguishes antemortem from postmortem

Age of an Abrasion:

Fresh: Bright red
12-24 hrs: Scab forms (dried blood/serum/lymph + injured epithelium); scab is initially red
2-3 days: Scab becomes reddish brown
4-7 days: Scab falls off (heals from periphery by epithelial growth)
~10 days: Complete healing

Antemortem vs. Postmortem Abrasion

Feature	Antemortem Abrasion	Postmortem Abrasion
Color	Reddish brown	Dark brown to black
Texture	Soft, moist	Parchment-like (from drying of exposed surface)
Margins	Blurred, indistinct (due to vital reaction)	Sharply defined (absence of vital reaction)
Vital reaction	Present (inflammatory response, exudate)	Absent
Confusion with	-	May be mistaken for burns
Histology	Evidence of inflammatory cell infiltration	No vital reaction on histology

Note: In case of doubt, histological examination for evidence of vital reaction is confirmatory. Abrasions should also be distinguished from: postmortem injuries by insects/ants, excoriation from excreta, and pressure sores. (Parikh's Textbook of FMT)

Q2. Classify Injuries. Differentiate Antemortem Wounds from Postmortem Wounds. Discuss the Cause of Death from Wounds.

Antemortem vs. Postmortem Wounds

Feature	Antemortem Wound	Postmortem Wound
Bleeding	Profuse, spurting from arterial vessels	Little, oozes slowly; no spurting
Clotting	Blood clots in and around wound	No true clotting
Vital reaction	Present (redness, swelling, neutrophil infiltration)	Absent
Wound retraction	Present (edges gape due to elasticity)	Absent or minimal
Bruising	Present around wound	Absent (postmortem lividity may mimic)
Healing	Evidence of repair if death delayed	No healing changes
Histology	Inflammatory cells (PMNs) present	Absence of inflammatory infiltrate
Colour of abrasions	Reddish brown, soft	Dark brown/black, parchment-like

Causes of Death from Wounds:

Immediate causes - Hemorrhage (external or internal), Air embolism, Injury to vital centers (brain, spinal cord), Cardiac tamponade
Early complications - Traumatic shock, Fat embolism, Acute respiratory failure
Delayed complications - Sepsis/infection, Tetanus, Gas gangrene, Peritonitis, Pulmonary embolism, Wound dehiscence

Q3. Enumerate the Effects of Bomb Explosive Injuries. What are the Methods to Identify Mutilated Bodies?

Effects of Bomb/Explosive Injuries

Explosive injuries are classified into four types:

Type	Mechanism	Injuries
Primary	Blast wave (overpressure) striking the body	Blast lung, tympanic membrane rupture, bowel perforation, gas-filled organ injury
Secondary	Flying fragments/shrapnel from device	Penetrating lacerations, puncture wounds, embedded foreign bodies
Tertiary	Body thrown by blast wind, striking surfaces	Fractures, blunt force injuries, traumatic amputations
Quaternary	Burns, toxins, crush, inhalation	Flash burns, chemical injuries, crush injuries

Specific effects:

Ruptured tympanic membranes (most sensitive blast indicator)
Blast lung: haemorrhagic contusion without external mark
Bowel perforation from pressure wave
Traumatic amputation of limbs
Multiple penetrating wounds from shrapnel
Flash burns (superficial; face and exposed parts)
Blast amnesia from cerebral concussion
In confined spaces: greater mortality from pressure wave reflection

Methods to Identify Mutilated Bodies

When a body is badly mutilated or fragmented, the following methods are used:

1. Visual/Physical Methods:

Physical appearance: height, weight, build, sex
Scars, tattoos, deformities, moles
Clothing, jewellery, personal belongings

2. Anthropological Methods:

Skeletal examination for age (epiphyseal fusion, dental eruption), sex (pelvis, skull morphology), and stature (long bone measurements)

3. Fingerprint Analysis:

Dactyloscopy - comparison with ante-mortem records
Even decomposed/macerated skin: fingerprint ridges may be restored

4. Dental (Odontological) Methods:

Comparison of dental records (fillings, crown work, missing teeth, X-rays)
Most reliable in aircraft/mass disaster identification

5. DNA Profiling:

Most definitive method
Comparison with biological samples from family members
Mitochondrial DNA useful when nuclear DNA is degraded
Used in mass disasters (e.g., 9/11, tsunami)

6. Radiological Methods:

Antemortem vs postmortem X-ray comparison
Implants, surgical hardware, fracture patterns

7. Serological Methods:

Blood grouping from tissue/bones

8. Forensic Facial Reconstruction:

Skull-based computerized facial reconstruction

Q4. Define Firearm. Draw and Describe the Parts of the Shotgun Cartridge. Describe the Pattern of Entrance Wounds Produced by a Shotgun at Various Ranges.

Definition of a Firearm

A firearm is a weapon that propels a projectile by the combustion of a propellant (gunpowder). All firearms consist of: a grip or stock, a trigger, a hammer, and a barrel. When the trigger is pulled, the hammer strikes the firing pin against the cartridge base, igniting the primer and then the main powder charge, propelling the bullet down the barrel. (DiMaio's Forensic Pathology)

Parts of the Shotgun Cartridge (Shell)

A shotgun shell (cartridge) consists of:

┌─────────────────────────────────────────┐
│  SHOT PELLETS (birdshot/buckshot)        │
│  GRANULAR POLYETHYLENE FILLER           │
│  PLASTIC WAD (wading)                   │
│  PROPELLANT POWDER                       │
│  PRIMER                                  │
│  BRASS/BRASS-COATED STEEL HEAD          │
│  PLASTIC TUBE (body/case)               │
└─────────────────────────────────────────┘

Components:

Plastic tube (body): The main cylindrical case
Brass head: Reinforced base containing the primer
Primer: Ignites when struck by firing pin
Powder: Propellant (flake or ball powder)
Wad/Wading: Separates powder from shot; can be paper/composite or plastic; acts as a gas seal; can produce stippling on skin at close ranges
Shot pellets: Birdshot (small game) or Buckshot (large game); no. 12 to 000 buck
Granular polyethylene filler: Cushions shot pellets; can produce stipple marks identical to powder tattooing

Shotgun gauge refers to the number of lead balls of that bore diameter that make up 1 pound (e.g., 12-gauge = 12 lead balls make 1 lb). The 12-gauge (bore 0.729 in.) is most commonly encountered.

Shotgun Entrance Wounds at Various Ranges

Range	Wound Characteristics
Contact (muzzle touching skin)	Circular wound ~= bore diameter; edges seared and blackened by hot gases; hard-contact: no soot surrounds entrance but edges are seared; head wounds produce massive bursting destruction of skull; most contact wounds are suicidal
Close range (a few cm)	Circular wound; powder soot present; powder tattooing begins >1-2 cm; wad may penetrate and be found in wound track; intermediate/close-range wounds nearly as mutilating as contact because pellets still travel as a mass
Intermediate range (~60-90 cm)	Shot pellets begin to scatter; wound still largely a single mass; powder tattooing present (flake powder up to 60 cm; ball powder up to 90-125 cm); wad separates and may produce separate puncture
Long/distant range (>2-3 m)	Multiple separate pellet entry wounds scattered over a wide area; classic "pepperhole" or "buckshot scatter" pattern; no soot or tattooing; each pellet produces its own entry wound with small abrasion collar

"At close range, the shotgun is the most formidable and destructive of all small arms." (DiMaio's Forensic Pathology, p. 237)

Q5. Classify Firearms. Difference Between Entry and Exit Wounds Due to Bullet Injury. How Will You Assess the Range of Firing?

Classification of Firearms

A. Based on Barrel:

Rifled firearms (rifled barrel - has spiral grooves): Handguns (revolvers, pistols), Rifles, Machine guns
Smooth-bore firearms (no rifling): Shotguns

B. Based on Action/Operation:

Single shot - One shot per loading
Repeating/Semi-automatic - One shot per trigger pull, auto-reloads
Automatic - Fires continuously while trigger is held

C. Based on Size:

Long arms - Rifles, shotguns (shoulder-fired)
Short arms (handguns) - Pistols, revolvers

D. By Cartridge type:

Rimfire (e.g., .22 LR) - primer in the rim
Center-fire (e.g., 9mm, .308) - primer in the center of the base

Difference Between Entry (Entrance) and Exit Wounds

Feature	Entry Wound	Exit Wound
Size	Smaller, roughly = caliber of bullet	Larger and more irregular
Shape	Round or oval (punched out)	Stellate, slit-like, crescent, circular, or completely irregular
Edges	Regular, inverted	Everted (skin pushed outward)
Abrasion collar/ring	Present (characteristic); may be concentric or eccentric	Absent (EXCEPT in "shored exit wounds")
Beveling (skull)	Internal beveling (hole is smaller externally, larger internally)	External beveling
Contamination	May have soot, tattooing, wad marks (at close range)	No powder residue
Soiling	May have grease/dirt ring (from bullet jacket)	Clean edges
Number	Usually 1 (unless multiple)	Can be 1 or multiple (if bullet fragments)

Shored exit wounds: When the skin is reinforced by a firm surface (wall, floor, chair) at the moment of bullet exit, the everted margin impacts and gets abraded - producing an irregular band of abrasion around the exit. This can be confused with an entrance wound.

Why exit wounds are larger:

The spin that stabilized the bullet in air is NOT effective in tissue (greater density)
Bullet yaws and may end up traveling base-first by the time it exits
Bullet may be deformed during passage
Both factors present a larger bullet profile at the exit site (DiMaio's Forensic Pathology)

Assessment of Range of Firing

Range of firing is determined by the presence and character of gunshot residue around the entrance wound:

Feature	Contact	Close (<30 cm)	Intermediate (30-90 cm)	Distant (>90 cm)
Soot (blackening)	Baked into/around wound	Present; can be wiped away	May be wiped away	Absent
Powder tattooing	Not typically seen	Present	Present (cannot be wiped off)	Absent
Muzzle stamp	Muzzle impression on skin	Absent	Absent	Absent
Searing of edges	Yes (hard contact)	No	No	No
Wad marks	Wad enters wound	Wad may be near wound	Wad makes separate mark	Absent

Key points for assessment:

Soot (carbon/fouling): deposited within 30 cm (12 in.) for virtually all handguns
Powder tattooing (stippling): Unburned/partially burned powder grains embed in skin; CANNOT be wiped away; present at:
- Flake powder: up to 45-60 cm (18-24 in.) for center-fire handguns
- Ball powder: up to 75-105 cm (30-42 in.)
- Shotgun (flake): up to ~60 cm; (ball): up to ~90-125 cm
Muzzle contusion ring: In hard-contact wounds, the muzzle stamps into the skin
Wound morphology: Contact wounds have characteristic seared, blackened edges with stellate tearing in loose skin over bone (e.g., head)
Examination of clothing should accompany wound examination
Chemical tests (e.g., Dermal Nitrate Test / Harrison-Gilroy Test for GSR on hands)

SHORT NOTES

Classification of Lacerations

A laceration is a wound where skin, mucosa, or underlying tissues are torn by blunt force. Classified based on manner of production:

Split laceration (incised-like wound):
- Due to blunt, nearly perpendicular impact
- Skin crushed between underlying bone and weapon
- Linear split, may mimic incised wound
- Common on scalp, face, hands, lower legs
- On close examination: jagged edges, tissue bridging, no sharp cut
Stretch laceration:
- Due to overstretching by blunt tangential impact
- Produces a flap, with flap direction indicating force direction
- Example: scalp hitting windscreen; run-over injuries
Avulsion:
- Due to horizontal impact tearing tissue away from its bed
- Skin is peeled off (degloving)
Tears:
- Due to irregularly directed force
- Irregular, ragged edges
Internal laceration:
- Impact exceeds tensile strength of a deep organ (e.g., liver, spleen)
- No external breach of surface

Characteristics of lacerations (vs. incised wounds):

Edges: Irregular, ragged, inverted
Tissue bridges: Present in wound depths
Contamination: Often present (grit, foreign material)
Bruising of edges: Present
No scar if superficial; may scar if deep

(Parikh's Textbook of FMT)

Difference Between Entry and Exit Bullet Wounds

(See detailed table in Q5 above - same topic, short note version below)

Feature	Entry	Exit
Size	Smaller	Larger
Abrasion collar	Present	Absent (except shored)
Edges	Inverted	Everted
Skull beveling	Internal	External
Soot/tattooing	May be present	Never present
Shape	Regular (round/oval)	Irregular (stellate/slit)

Fabricated Wounds

Fabricated (self-inflicted / simulated) wounds are wounds deliberately inflicted by the victim themselves to:

Feign an attack and accuse another person (false accusation)
Claim compensation (insurance fraud)
Gain sympathy or avoid duty/responsibility
Malingering

Characteristics of fabricated wounds:

Usually multiple, superficial wounds
Located on accessible parts of the body (anterior surface, non-dominant hand side)
Incised type most common (razor, knife, glass)
Parallel/grouped wounds in a small area (hesitation marks)
Wound edges: Clean, regular
Absence of defence wounds
No injury to clothing over the wound site
Vital structures are usually avoided
Typically seen in: wrists, forearms, chest, abdomen
May be associated with psychiatric illness

Differences from homicidal wounds:

Homicidal wounds tend to be on the back, neck, areas not accessible to oneself
Homicidal wounds often deeper, more irregular
Defence wounds typically absent in fabricated; present in homicidal
Hesitation cuts (tentative, parallel superficial cuts) are characteristic of fabricated/self-inflicted wounds

(Parikh's Textbook of FMT)

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