Mechanical Injuries: Abrasion, Contusion & Laceration
Forensic Medicine · Injuries · lean revision notes
Mechanical Injuries: Abrasion, Contusion & Laceration
Mechanical injuries are physical wounds produced by the application of mechanical force (blunt or sharp). For NEET PG, the highest-yield cluster is the trio of blunt-force injuries — abrasion, contusion (bruise) and laceration — because their distinction by causation, wound-edge characters and medico-legal value generates a steady stream of one-liner MCQs (ageing of a bruise, patterned abrasion, laceration vs incised wound).
Definition & Legal Framework
An injury (Section 44 IPC, now Section 2(14) BNS 2023) is "any harm whatever illegally caused to any person in body, mind, reputation or property." A wound is a breach in the natural continuity of any tissue. Forensically, injuries are classified by the type of force / weapon.
| Class | Sub-type | Causative agent |
|---|---|---|
| Mechanical | Blunt force | Abrasion, contusion, laceration |
| Sharp force | Incised wound, chop wound, stab/puncture | |
| Firearm | Entry/exit wounds | |
| Thermal | Heat / cold | Burns, scalds, frostbite |
| Chemical | Acid / alkali | Corrosive burns |
| Physical (other) | Electricity, lightning, X-ray | — |
High-yield: Abrasion, contusion and laceration are blunt-force mechanical injuries. Incised and stab wounds are sharp-force. This blunt-vs-sharp divide underlies almost every distractor in the MCQ.
Simple vs grievous hurt
Hurt (S.319 IPC / S.114 BNS) is bodily pain, disease or infirmity. Grievous hurt (S.320 IPC / S.116 BNS) has 8 (now expanded) clauses — the classic mnemonic "FEED PEDS": Fracture/dislocation, Emasculation, Eye (permanent privation of sight), Disfiguration of face/head, Privation of any member/joint, Ear (loss of hearing), Destruction/impairment of any member/joint power, Severe — danger to life or 20-day (now interpreted) hospitalisation/inability to follow ordinary pursuits.
1. Abrasion
An abrasion is the most superficial mechanical injury — destruction of the epidermis (skin or mucous membrane) caused by friction against a rough surface, without breaching the full thickness of the dermis. It may extend to the superficial papillary dermis (hence may exude serum/lymph and a little blood from dermal papillae, but typically does not bleed heavily or scar).
Types of abrasion (high-yield)
| Type | Mechanism | Classic example |
|---|---|---|
| Scratch (linear) | Sharp/pointed object drawn across skin | Fingernail, thorn, pin |
| Graze / brush / sliding | Tangential rubbing over rough surface | Road-traffic "gravel rash" |
| Pressure / imprint / patterned | Crushing of epidermis under sustained pressure | Ligature mark, tyre tread, teeth bite |
| Impact / contact | Perpendicular crushing force | Radiator grille mark |
High-yield: A patterned (imprint) abrasion reproduces the shape of the offending object — ligature mark in hanging/strangulation, teeth marks of a bite, tyre tread in run-over, weave of clothing. These are medico-legally most valuable because they identify the weapon.
Direction of a graze abrasion
The superficial epidermal tags / heaped-up epithelium pile up at the terminal (far) end — the end where the force came to rest. The skin is piled up away from the point of commencement, so the abrasion is deeper at the start and tapers/heaps at the end, indicating the direction of force.
High-yield: In a graze abrasion, epidermal tags accumulate at the end opposite to the point of impact → the direction of the abrading force is from the shallow/smooth end towards the heaped-up end.
Ageing of an abrasion (colour of scab)
| Age | Appearance |
|---|---|
| Fresh (≤12 h) | Bright red, moist, exuding serum |
| 12–24 h | Reddish, lymph/serum dries → scab forming |
| 2–3 days | Reddish-brown scab |
| 4–7 days | Dark brown / blackish scab, epithelium grows under it |
| After ~7 days | Scab falls off, depigmented area, no permanent scar |
Medico-legal importance of abrasions
- Indicate site of impact and direction of force.
- Patterned abrasions identify the weapon/object.
- Manner: nail abrasions on neck → throttling; on thighs/breasts → sexual assault; "abraded margin" around a contused-lacerated wound → blunt impact.
- Postmortem abrasions (e.g. from dragging) are yellowish, parchment-like, translucent, with no colour change and no vital reaction.
High-yield: A brown, dry, parchment-like, leathery patch is the classic description of a postmortem abrasion / pressure abrasion (dries due to loss of moisture). Antemortem abrasions show vital reaction (redness, scab).
2. Contusion (Bruise)
A contusion (bruise) is an extravasation of blood into the tissues due to rupture of small blood vessels (capillaries and venules) beneath an intact skin, caused by blunt force. The skin surface is not breached — this distinguishes it from abrasion and laceration.
Pathophysiology & factors affecting bruising
The size of a bruise does not always correspond to the force used; it depends on:
- Age: children and the elderly bruise easily (loose subcutaneous tissue, fragile vessels). Adults with firm tissue bruise less.
- Sex: females bruise more readily (more subcutaneous fat).
- Site / tissue laxity: lax vascular areas (eyelids, scrotum, face) bruise easily; tightly bound areas (palms, soles, scalp over bone) bruise poorly.
- Disease: haemophilia, scurvy, thrombocytopenia, leukaemia → spontaneous/exaggerated bruising.
- Colour of skin affects visibility (harder to see in dark skin).
Patterned & special bruises
- Tram-line (railway-track) bruising: Two parallel lines of bruising with a central pale (spared) zone — pathognomonic of a blow with a rod/stick/cane. Mechanism: blood is forced laterally from under the rod to the margins, vessels rupture along the edges while skin directly under the rod is compressed bloodless.
- Six-penny / ectopic bruise (gravitational shift): Bruise appears at a site distant from the point of impact because extravasated blood tracks along fascial planes under gravity — e.g. a blow to the forehead surfacing as a "black eye"/spectacle haematoma around the eyes the next day.
- Come-out / delayed bruise: Deep bruise (e.g. in muscle) not visible initially, becomes apparent over 1–3 days as blood reaches the surface.
High-yield: Tram-line bruising = blow with a cylindrical rod / stick. Central pallor with two parallel margins of bruising.
Ageing of a bruise by colour change (MOST-TESTED TABLE)
Colour change is due to sequential breakdown of haemoglobin: haemoglobin → biliverdin (green) → bilirubin (yellow) → haematoidin/haemosiderin.
| Age of bruise | Colour |
|---|---|
| Fresh / immediate | Red |
| Few hours – 1 day | Blue / bluish-black (dark purple) |
| 2nd–3rd day | Bluish-brown |
| 4th day onwards | Green (biliverdin) |
| 5th–6th day | Yellow (bilirubin) |
| 7th–14 days | Normal — disappears |
High-yield: Sequence of bruise colour = Red → Blue → Bluish-black → Green → Yellow → Normal. The first colour to appear from haemoglobin breakdown is green (biliverdin, day 4); the last is yellow (bilirubin). The earliest colour change useful for ageing is GREEN.
High-yield: Bilirubin (yellow) is the last pigment to be metabolised → yellow is the final colour before resolution. In the eye / sclera, no colour change occurs (no tissue to metabolise pigment), so a subconjunctival haemorrhage stays bright red until it clears.
Mnemonic for colour sequence: "Really Bad Bruise Goes Yellow" — Red, Blue, Blue-brown, Green, Yellow.
Artificial / fabricated & feigned bruises
- Marking-nut (Bhilawanol / Semecarpus anacardium) juice produces a vesico-bullous, irregular, "ink-spot"/tongue-shaped lesion mimicking a bruise — classic exam fact for fabricated injury to support a false charge. The margins are well-defined, dark brown to black, often linear or with a vesicle, itchy, and lie on accessible body parts; chemical (potassium dichromate, marking-nut oil) testing confirms it.
Postmortem staining vs bruise (differentiation — exam favourite)
| Feature | Bruise (antemortem) | Postmortem lividity |
|---|---|---|
| Site | At point of impact (anywhere) | Dependent parts only |
| Elevation | Often swollen/raised | Not raised |
| Cut section | Clotted blood in tissues, extravasated | Blood inside vessels, no extravasation |
| Washing/pressure | Does not disappear | Lividity fixed only after a time |
| Colour uniformity | Variegated (ageing colours) | Uniform |
| Vital reaction | Present | Absent |
3. Laceration
A laceration is a tear or split of the skin and underlying soft tissues produced by blunt force that crushes and stretches the tissue beyond its elastic limit. Unlike an incised wound (sharp, clean), a laceration is irregular and ragged.
Characteristic features (vs incised wound)
- Margins: irregular, ragged, contused, abraded, swollen, bruised.
- Tissue bridges: strands of intact tissue (nerves, vessels, connective tissue) bridge the depth of the wound — the single most important sign of a laceration.
- Hair bulbs / hair follicles crushed, not cleanly cut.
- Foreign material (dirt, grease, glass) often present.
- Bleeding is less than incised wounds (vessels crushed → retract & thrombose).
High-yield: Tissue bridging (intact strands across the wound base) is the hallmark that distinguishes a laceration (blunt) from an incised wound (sharp, no bridging). This is the single most repeated MCQ point.
Types of laceration
| Type | Mechanism / appearance |
|---|---|
| Split laceration | Crushing of skin between two hard objects, e.g. blow to scalp over bone — splits and mimics an incised wound (caution!) |
| Stretch laceration | Overstretching of skin → flap, e.g. run-over, kick |
| Avulsion / grinding | Tangential force grinds/peels skin off (degloving), e.g. wheel rolling over limb |
| Tear / cut laceration | Skin torn by irregular/semi-sharp object, e.g. broken glass, blow with an axe's blunt edge |
High-yield: A split laceration over a bony prominence (scalp, eyebrow, shin) can closely resemble an incised wound — but careful inspection reveals abraded/bruised margins and tissue bridges → it is a laceration. This is a classic medico-legal pitfall and frequent MCQ.
Comparison: Laceration vs Incised Wound (CRITICAL TABLE)
| Feature | Laceration (blunt) | Incised wound (sharp) |
|---|---|---|
| Margins | Irregular, ragged, bruised, abraded | Clean-cut, well-defined, everted |
| Tissue bridges | Present | Absent |
| Width vs length | Length usually > breadth, depth variable | Length always > depth & breadth |
| Bleeding | Less (vessels crushed) | Profuse (vessels cleanly cut) |
| Hair bulbs | Crushed | Cleanly cut |
| Foreign bodies | Often present | Usually absent |
| Surrounding skin | Contused / abraded | Normal |
| Healing | Slow, with scarring/infection | Faster, less scarring |
Stepwise medico-legal approach to a mechanical injury
Describe every wound systematically → so the report stands in court:
- Number of the wound (label each).
- Type — abrasion / contusion / laceration / incised etc.
- Site — exact, with reference to a fixed bony landmark + distance from heel (for hanging/firearm).
- Size — length × breadth × depth (in cm).
- Shape — linear, oval, crescentic, stellate.
- Margins / edges — clean / ragged / abraded / everted.
- Direction (of force / wound axis).
- Age — colour (bruise), scab (abrasion), healing stage.
- Antemortem vs postmortem — vital reaction.
- Foreign bodies — present / absent.
- Likely weapon and manner (homicidal/suicidal/accidental).
Causation chain to remember: Blunt force → friction = abrasion; → vessel rupture under intact skin = contusion; → tissue tears = laceration. Sharp force → clean split = incised.
Vital reaction & ageing of wounds (the antemortem/postmortem question)
A vital (supravital) reaction indicates the injury occurred during life:
- Local: redness, swelling, margin retraction, bleeding, coagulation, abundant RBCs in tissue.
- Microscopic timeline: neutrophils infiltrate within ~4–12 h; macrophages by 2–3 days; collagen/fibroblasts by ~4–6 days; haemosiderin (Perls' Prussian-blue positive) by ~24–72 h indicating older bruise.
High-yield: Enzyme histochemistry — a vital injury shows enzyme changes within minutes: ATP/esterase depletion at the wound edge, and increased aminopeptidase, acid phosphatase, ATPase at margins within ~1 hour — used to date wounds and confirm antemortem nature.
Key differentials & "look-alikes" (favourite distractor pairs)
- Abrasion vs postmortem pressure mark → vital reaction & parchmenting.
- Bruise vs postmortem lividity → site, extravasation on cut section.
- Bruise vs artificial (marking-nut) injury → vesicle, accessible site, chemical test.
- Laceration (split) vs incised wound → tissue bridges, abraded margins.
- Incised wound vs incised-looking laceration over bone → margins.
- Chop wound (heavy sharp weapon, e.g. axe) → has features of both incised (clean cut into bone) and contused/lacerated margins.
Recently asked / exam angle
- "Earliest colour change in a bruise useful for ageing?" → Green (biliverdin, ~day 4). Frequently combined with "last colour = yellow (bilirubin)."
- "Tissue bridges are seen in?" → Laceration (NOT incised wound).
- "Tram-line/railway-track bruise indicates?" → blow with a stick/rod (central pallor).
- "Marking-nut juice produces?" → fabricated/artificial bruise (vesico-bullous, tongue-shaped).
- "Patterned abrasion of medico-legal value?" → ligature mark, tyre marks, teeth bite.
- "Direction of a graze abrasion is given by?" → heaped-up epidermal tags at the terminal end.
- "Parchment-like, leathery, yellow-brown skin patch?" → postmortem abrasion (dried skin).
- "Black eye appearing a day after a forehead blow?" → gravitational/ectopic (come-out) bruise.
- "Which colour change does NOT occur in a subconjunctival bruise?" → none — it stays red (no tissue to metabolise pigment).
- Image-based questions: identify abrasion vs laceration vs incised from a photo (look for margins & bridges).
Rapid revision
- Abrasion, contusion, laceration = blunt force; incised & stab = sharp force.
- Abrasion = epidermal injury; heals without scar; epidermal tags pile at the terminal end → gives direction.
- Patterned (imprint) abrasion = highest medico-legal value (ligature, tyre, teeth).
- Postmortem abrasion = dry, brown, parchment-like, no vital reaction.
- Contusion = blood extravasation under intact skin; size ≠ force always; elderly & children bruise easily.
- Bruise colour sequence: Red → Blue → Blue-brown → Green (day 4) → Yellow (day 5–6) → gone (~2 weeks).
- First colour useful for ageing = green (biliverdin); last = yellow (bilirubin).
- Tram-line bruise (central pallor) = blow with a rod/stick; ectopic bruise tracks under gravity.
- Marking-nut (Semecarpus anacardium) juice = artificial bruise, vesico-bullous on accessible parts.
- Laceration hallmark = TISSUE BRIDGES + irregular, abraded, contused margins; bleeds less than incised.
- Split laceration over bone mimics an incised wound — check margins & bridges.
- Bruise vs lividity: bruise = extravasated clotted blood in tissue at impact site; lividity = intravascular, dependent, uniform.