Topic 2: Forensic Pathology — Wound Classification, Medicolegal Aspects of Injuries, Ante-mortem vs. Post-mortem Wounds
Introduction to Forensic Pathology
Forensic pathology is the branch of medicine that deals with the determination of the cause and manner of death through the examination of a corpse. The postmortem examination (autopsy) is its primary tool. A thorough understanding of wound classification, healing patterns, and the distinction between ante-mortem and post-mortem injuries is essential for every FMGE candidate.
Classification of Wounds
Wounds are broadly classified as mechanical, thermal, chemical, and electrical. Each category has distinct features, medicolegal implications, and characteristic findings.
Mechanical Wounds
Abrasions (Excoriation): Abrasions involve the superficial layer of the skin — the epidermis — without breaching the basement membrane. They heal by epithelialization within 3–5 days without scar formation. The forensic importance of abrasions lies in indicating the point of impact, the direction of force, and sometimes the pattern of the weapon.
Types of abrasions include: scratches (linear, caused by pointed objects), grazes (broad superficial denudation from friction), pressure abrasions (from blunt force — may reproduce the weapon’s surface pattern), and impact abrasions (full-thickness epidermal loss at the point of impact, often showing the weapon’s impression). Age determination of abrasions relies on colour: red/serous (fresh, hours), black/dry scab (1–3 days), brown/pigmented (4–7 days), and fading discoloration (7–10 days).
Contusions (Bruises): Contusions result from blunt force that ruptures subcutaneous blood vessels, causing extravasation of blood into the tissues without breaching the skin. The spread of a contusion depends on tissue looseness — the face and eyelids show extensive spread due to loose areolar tissue, while the scalp shows limited spread because of tight fascial attachments.
Colour progression of bruises is a reliable indicator of age: red/blue/purple appears within 1 day, dark blue/violet at 1–3 days, green at 4–7 days, yellow at 7–10 days, and brown fading at 10–14 days. Critically, the size of a bruise does not indicate the severity of the underlying injury — elderly individuals and those with chronic alcoholism can develop massive bruising from seemingly trivial trauma due to fragile blood vessels and coagulopathies. Tardieu’s spots are old petechial haemorrhages seen in chronic alcoholism and malnutrition, indicating vascular vulnerability.
Lacerations: Lacerations are tears or splits in the skin and underlying tissues caused by blunt force that exceeds the skin’s elastic limit. Their margins are irregular, bruised, and contused — unlike the clean edges of incised wounds. Hair bulbs are crushed rather than cleanly cut. Types include: split lacerations (over bony prominences such as scalp, eyebrows, and perineum), stretch lacerations (skin stretched beyond its elastic limit), crushing lacerations (tissue crushed between an object and underlying bone), and avulsion (tissue torn away exposing underlying structures). Lacerations typically show tissue bridges on the wound floor.
Incised Wounds: Produced by sharp-edged weapons such as knives, blades, glass, or metal cutting through tissue. Key features include clean, sharp, and everted margins; wound length exceeding the depth of the weapon; absence of tissue bridges; and more profuse haemorrhage due to clean transection of blood vessels. They may be suicidal, homicidal, or accidental. Hesitation wounds (superficial, multiple, parallel, clustered cuts) typically indicate suicidal intent — the victim hesitates before committing to the fatal act.
Stab Wounds: Produced by pointed weapons such as knives, daggers, or spears. The external wound may be deceptively small, but internal injury can be extensive — penetration of viscera or major vessels can be fatal. The direction of the wound track is crucial for reconstructing the incident.
Firearm Wounds
The examination of firearm wounds requires understanding of the entry wound, exit wound, and the range of fire.
Entry wound characteristics: Generally smaller than the exit wound (the bullet compresses on impact), edges are inverted, an abrasion collar (contusion ring) is present due to friction and heat, soot blackening is present when fired at close range, and tattooing (stippling from unburnt powder granules) is present at close range (within approximately 25 cm).
Exit wound characteristics: Larger, irregular, with everted margins; no abrasion collar; no soot or tattooing.
Range of fire estimation: Contact range — muzzle imprint, soot blackening, and tattooing all present; close range (within 1 metre) — tattooing and soot both present; medium range (1–2 metres) — tattooing present but soot absent; distant range — entry wound alone without tattooing or soot.
In skull fractures, internal beveling (inward indentation of bone at the point of impact) indicates entry, while external beveling (outward indentation) indicates exit.
Thermal Injuries — Burns
Burns are classified by depth:
- Superficial (first degree): Erythema only; epidermis intact; heals in 3–5 days
- Superficial partial thickness (second degree): Blistering; epidermis and superficial dermis involved; heals in 10–14 days
- Deep partial thickness (deep second degree): Blisters may be absent; heals in 3–4 weeks with scarring
- Full thickness (third degree): Charred or leathery; all skin layers destroyed; requires skin grafting
The Rule of Nines for adults assigns 9% body surface area to each upper limb, 18% to each lower limb, 9% to the head and neck, 18% each to the anterior and posterior trunk, and 1% to the perineum. In children, the head accounts for a larger proportion.
Special burn patterns include: pugilistic attitude (flexion of all limbs in defensive posture seen in prolonged burning), heat haematoma (subperiosteal haemorrhage suggesting immersion burn in children), glove-and-stocking pattern (differential immersion in burning liquid), and cafe-au-lait marks (characteristic of electrocution rather than burns).
Electrical Burns
Electrical injuries follow Ohm’s Law (Current = Voltage ÷ Resistance). Low-resistance tissues (nerves, blood vessels, muscle) conduct current more readily than high-resistance tissues (skin, bone, fat). Wet skin dramatically reduces resistance, increasing current flow and heat generation (Joule heating). Death mechanisms vary: ventricular fibrillation is most common in low-voltage electrocution (below 1000V), while asystole and respiratory muscle paralysis are seen with high voltage (above 1000V).
Difference Between Ante-mortem and Post-mortem Wounds
| Feature | Ante-mortem Wound | Post-mortem Wound |
|---|---|---|
| Margins | Everted, inflamed | Clean, sharp, not everted |
| Haemorrhage | Present, often clotted | Absent or minimal |
| Vital reaction | Present (leucocyte infiltration, capillary dilation) | Absent |
| Tissue reaction | Inflammatory changes; healing attempted | No reaction |
| Survival time | Minutes to hours (depends on vital organ involvement) | Instantaneous — no vital response |
The presence of vital reaction — the body’s inflammatory response to injury — is the single most reliable indicator that a wound was inflicted during life. Histologically, wound healing progresses through recognizable stages: no inflammatory cells at 0–6 hours (pure haemorrhage), early polymorphonuclear infiltration at 6–12 hours, leucocyte infiltration with macrophages at 12–24 hours, granulation tissue and fibroblasts at 24–48 hours, capillary ingrowth and early collagen at 3–5 days, active fibroblastic proliferation at 5–10 days, and scar formation after 14 days.
Medicolegal Classification of Injuries Under IPC
The Indian Penal Code classifies injuries as follows:
- Section 319 IPC — Hurt: Whoever causes bodily pain, disease, or infirmity to any person
- Section 320 IPC — Grievous Hurt: Includes emasculation, permanent privation of sight or hearing, destruction of reproductive capacity, permanent disfigurement of head or face, fractures or dislocations of bones, and any injury that causes severe bodily damage or danger to life
- Section 322 IPC — Voluntarily Causing Grievous Hurt: The act of causing such hurt deliberately
- Section 325 IPC — Punishment for Voluntarily Causing Grievous Hurt: Imprisonment up to 7 years
- Section 326 IPC — Grievous Hurt by Dangerous Weapons: Acids and weapons specifically — imprisonment up to life
- Section 300 IPC — Murder: When death is caused with clear intention to cause death or bodily injury sufficient to cause death
- Section 304 IPC — Culpable Homicide Not Amounting to Murder: When death results from an act with the intention of causing bodily injury but not with the intention to cause death
Regional Injuries — Key Patterns
Head injuries are the most common cause of traumatic death. Scalp lacerations bleed profusely due to the rich anastomosis of superficial temporal, occipital, and supraorbital arteries. Extradural haemorrhage (between skull and dura) is classically associated with temporal bone fracture damaging the middle meningeal artery; patients present with a characteristic lucid interval followed by deterioration. Subdural haemorrhage (between dura and arachnoid) results from tearing of bridging veins; venous accumulation is slower, making it common in elderly and alcoholic patients. Diffuse Axonal Injury (DAI) results from rotational acceleration causing widespread white matter damage and carries a high mortality rate.
Thoracic injuries causing death include rib fractures (especially ribs 4–9) leading to pneumothorax or flail chest, cardiac tamponade (blood in the pericardial sac causing death by impairing cardiac filling — can occur with trivial chest trauma if prior pericardial adhesion exists), and aortic rupture (usually at the isthmus just distal to the left subclavian artery due to sudden deceleration).
Wound Documentation
Proper documentation is medicolegally essential: written description with exact measurements, body diagrams, photographs with scales, wound swabs for microbiology or histology, and preservation of clothing. The chain of custody for all evidence must be maintained.