Mechanical Injuries: Definition, Classification, Abrasions, Contusions, and Lacerations

1. DEFINITION OF INJURY AND WOUND

2. CLASSIFICATION OF INJURIES

A. Based on Causative Agent

• (a) Blunt force: Abrasions, Contusions/Bruises, Lacerations, Fractures and dislocations, Crush injuries
• (b) Sharp force: Incised wounds (cuts), Stab wounds, Chop wounds
• (c) Firearm wounds
• (d) Blast/Explosion wounds

• Cold: Local hypothermia, Frost bite, Trench foot, Immersion foot, General hypothermia
• Heat (local): Burns, Scalds
• Heat (general): Heat stroke, Heat exhaustion, Heat cramps

• Corrosives (acids and alkalis)
• Irritants (weak acids and alkalis)

• Electricity, Lightning, X-rays, Radioactive substances

B. Legal Classification (BNS)

1. Hurt (Simple) - Section 114, BNS
2. Grievous hurt - Section 116, BNS

C. Medicolegal Classification

1. Suicidal
2. Homicidal
3. Accidental
4. Defense wounds
5. Fabricated wounds

D. In Relation to Death

1. Antemortem
2. Postmortem

3. ABRASIONS

Definition

Mechanism

Features

• Vary in size depending on the extent of body surface exposed
• Bleed slightly; heal rapidly; scar is usually not formed
• Large abrasions can cause severe pain and bleeding
• The size, situation, pattern, direction (tailing) and number should be noted

Types of Abrasions

• Most common type
• Show uneven, longitudinal parallel lines (grooves/furrows) with epithelium heaped up at the ends, indicating direction of force
• Epidermis scraped away, destroyed or detached
• Graze abrasions are commonly seen in road accidents
• A scraping injury over a large area caused by violent lateral rubbing is called "Brush burn or gravel rash"
• "Friction burn" (scuff/brush abrasion) is an extensive, superficial, reddened excoriated area with little or no linear mark (seen in motorcyclists ejected from vehicles)

• Caused by crushing of the superficial layers of the epidermis
• Associated with a bruise of the surrounding area
• Include ligature marks in hanging (parchment-like, pale-yellow to brownish), muzzle contusion pattern in contact gunshot wounds, tyre marks from vehicles
• The best examples are: ligature marks in hanging, tyre marks, bite marks, contact gunshot muzzle marks

• The pattern of the object is reproduced on the skin surface
• The pattern left by the object helps identify the weapon
• Examples: rope marks, chain marks, tyre treads, fabric patterns

• Caused by the tip of sharp and pointed objects (knife, thorn, fingernails, needle, pin)
• A scratch has length but no significant width
• Surface layers of skin are collected in front of the object - the scratch is deeper and wider at the start (head) and tapers toward the end (tail)
• Fingernail (Crescentic) Scratch Abrasions: 1-2 mm breadth, about 0.5-1 cm long. Presence on:
  • Neck - indicates strangulation or attempted strangulation
  • Breast and inner thighs of women - indicates sexual molestation

Age of Abrasion (Approximate)

Antemortem vs Postmortem Abrasions

Medicolegal Importance of Abrasions

1. Site of impact and direction of force - The tailing of epithelium indicates the direction in which the force was applied (the heaped-up end marks where the force ended)
2. Only external evidence of deeper injury - may be the only visible sign of a deeper, potentially fatal injury
3. Nature of the surface causing the injury - rough/road surface, fingernails, rope, etc.
4. Patterned abrasions identify the weapon - muzzle pattern, tyre mark, ligature mark
5. Extraneous material - foreign particles (dust, grease, sand) may connect injuries to the scene of crime
6. Character and manner of injury from distribution:
   • Crescentic abrasions on neck - throttling
   • Around mouth and nose - smothering
   • On breasts, genitalia, inner thighs, around anus - sexual assault
   • On face of assailant - indicates struggle
   • Nail marks reveal if assailant's nails were long, irregular, or broken
7. Age of the injury can be approximately determined
8. Postmortem abrasions from dragging may be distinguished from antemortem ones

4. CONTUSIONS (BRUISES)

Definition

Situation

Features

• Painful swelling and crushing/tearing of subcutaneous tissues, usually without destruction of skin
• Extravasated blood is diffusely distributed through tissue spaces; margins are blurred
• May be seen with abrasions (abraded contusion) or lacerations
• A large vessel injury produces a tumour-like mass called a hematoma
• Petechial bruises are finely mottled/stippled; when larger and confluent they are called ecchymoses
• Fresh bruise: tender, slightly raised
• When skin is lax, as around the eye (black eye/periorbital ecchymosis), bruising spreads widely

Shape and Patterned Bruises

1. A fingertip produces a rounded bruise; 3-4 bruises on one side and one larger on the opposite side = gripping by fingers and thumb
2. A punch/fist - rounded bruise
3. Thick stick end - round; length of stick - elongated and irregular
4. Rod/stick/whip - two parallel linear hemorrhages (railway/tram-line type) because the vessel in the center is compressed and blood is displaced to both sides while vessels at the margins rupture
5. Broad flat weapon (plank) - parallel bruises separated by apparently normal tissue
6. Belt/strap/chain - definite imprint
7. Suction/biting during sexual activity - elliptical patterned bruises on neck or breasts (petechial hemorrhages, may reproduce shape of lips)

Age Estimation of Bruises (Color Changes)

• Hemoglobin → Hemosiderin + Hematoidin + Bilirubin (by enzymatic action)
• Change of color begins at the periphery and extends inward to the center

Factors Affecting Appearance of Bruises

• Depth of bleeding (deep bruises may not show for hours or days)
• Amount of bleeding
• Environmental lighting
• Overlying skin color
• Age (elderly persons: bruises are larger; children: change color rapidly)
• Vascular diseases (e.g., purpura, hemophilia) - bruises appear more easily
• Site: lax tissue (eyelid) bruises spread widely; bruises may track along tissue planes and appear at a site distant from the injury (shifting contusion, e.g., black eye after a blow to the forehead)

Medicolegal Importance of Contusions

1. Patterned bruises may connect victim to the object/weapon (whip, chain, cane, ligature, vehicle)
2. Age of injury can be approximately determined by color changes
3. Degree of violence may be estimated by their size
4. Character and manner of injury from distribution:
   • 3-4 bruises on one side and 1 larger on opposite side - grasping
   • Bruising of arm - restraining a person
   • Shoulder blade bruising - firm pressure against the ground
   • Manual strangulation - position and number of bruises and nail marks indicate method and position of assailant
   • Bruising of inner thigh and genitalia - indicates rape/sexual assault
5. Foreign particles (dirt, dust, grease, sand) in open wounds may connect injuries to scene of crime
6. Why bruises are less forensically reliable than abrasions:
   • Size may not correspond to size of weapon
   • May not become visible for several hours to days after injury
   • May migrate/shift from site of injury
   • May be confused with postmortem lividity
   • Color change timing is unreliable for precise dating

5. LACERATIONS

Definition

Mechanism

Types of Lacerations

• Caused by crushing of the skin between two hard objects
• Scalp lacerations occur due to tissues crushed between skull and blunt object or the ground
• Not undermined; show tissue bridges

• Overstretching of fixed skin causes a flap to peel off the underlying bone/deep fascia
• Seen in motor vehicle run-overs; the flap may indicate the direction of the vehicle
• Produces irregular tearing; foreign material may be found in depth of wound

• A shearing force at an acute angle detaches a portion of the traumatized surface or viscus from its attachments
• A lorry/truck wheel passing over a limb may cause separation of the skin and subcutaneous tissue from the underlying structures

• Lacerations produced in areas where skin is close to bone and subcutaneous tissue is scanty, may look like incised wounds
• Sites: scalp, eyebrows, cheekbones, lower jaw, iliac crest, perineum, and shin
• Differentiating features: tissue bridges present, hair bulbs crushed, irregular wound edges

Characteristics of Lacerated Wounds (vs Incised Wounds)

1. Wound margins are ragged, irregular, and contused (not clean-cut)
2. Edges are swollen by the blunt impact
3. Tissue bridges (bridging fibers of nerves, blood vessels, elastic and connective tissue) cross the depths of the wound - this is the most important distinguishing feature
4. Hair bulbs are crushed (not cleanly divided)
5. Hair and epidermal tags may be driven deeply into the wound
6. Hemorrhage is less than incised wounds - arteries are crushed and torn irregularly, retract, and clot readily (EXCEPT scalp wounds where temporal arteries bleed freely as they are firmly bound)
7. Foreign matter may be found in the wound
8. Shape - usually curved; convexity of curve points toward direction of application of force:
   • Blunt round end - stellate laceration
   • Blunt object with an edge (e.g., hammer head) - crescentic laceration
   • Long thin objects (pipes) - linear lacerations
   • Flat surface objects - irregular, ragged, or Y-shaped lacerations
9. If impact from an angle: the side opposite to the direction of motion is torn free or undermined; the side from which the blow was delivered shows abrasion and beveling

Age of Laceration

• Antemortem: bruising, eversion, gaping, bloodstaining of margins, greater bleeding, vital reaction
• Granulation tissue, fibroblast ingrowth, organizing infiltrate = healing laceration

Complications of Lacerations

1. Severe or fatal bleeding (especially internal organ laceration; scalp temporal arteries)
2. Infection (from skin, weapon, or secondary infection)
3. Continued oozing if over joints/wrinkled areas
4. Fat embolism from crushing of subcutaneous tissue
5. Healing by secondary intention - scarring, possible keloid formation, or sarcomatous change

Medicolegal Importance of Lacerations

1. Type of laceration may indicate the cause of injury and the shape of the blunt weapon (linear = long narrow weapon; stellate = round-ended object)
2. Foreign bodies found in the wound may indicate the circumstances in which the crime was committed
3. Age of the injury can be determined by healing markers
4. Lacerations (along with abrasions and contusions) are the external visible evidence of blunt impact injury - they may be the only external sign of deeper, sometimes fatal injury to internal structures
5. Suicidal lacerations - usually situated on exposed parts of the body, mostly on the same side
6. Homicidal wounds - usually seen on the head
7. Fall on head - abraded scalp surface is circular and completely surrounds the laceration
8. Pattern of footwear may be imprinted on the skin in kicking injuries

6. COMBINATIONS OF ABRASIONS, CONTUSIONS, AND LACERATIONS

• Punching (clenched fist): abrasions and contusions; laceration over bony prominences; on face - split lips, fractured teeth/nose/jaw, "black eye"
• Kicking/stamping: abrasions, contusions, and sometimes lacerations (more severe than punching); may produce deep abdominal injuries and rib fractures; footwear pattern may be imprinted

"Abrasions, contusions and lacerations are the external visible evidence of blunt impact injury which may be the only external sign of deeper and sometimes fatal injury of deeper lying structures."

• KS Narayan Reddy's Essentials of Forensic Medicine and Toxicology, 36th Edition, p.196