Pattern Injuries and Their Recognition

Intro to Patterns - Defining Dents

• Pattern Injury: Injury whose physical characteristics (shape, size, details) mirror portions of the causative object or instrument.
• "Dents": Refers to these tell-tale imprints, impressions, or markings on skin or deeper tissues.
• Significance in forensics:
  • Weapon identification (e.g., ligature, firearm muzzle, footwear).
  • Mechanism elucidation (e.g., impact, pressure, sliding).
  • Crucial for linking injury to a specific object or perpetrator.
• Can be seen in: Contusions, abrasions, lacerations, burns.

⭐ Tram-track bruises (parallel linear bruises with a central clear area) are highly suggestive of impact by a rod-like or cylindrical object.

Blunt Force Patterns - Impact's Echo

• Injury mirrors object/surface features. Key for weapon ID under BNS investigations.
• Abrasions (Patterned):
  • Pressure abrasion: Prolonged compression, minimal force
  • Impact abrasion: Direct perpendicular force creating object impression
  • Tyre marks (RTA), ligature marks (hanging, strangulation) - leathery
  • Muzzle imprint (contact firearm shot) - distinguish from cartridge case impacts
• Contusions (Bruises):
  • Tram-line/Railway-line: Rod impact. Central pallor, parallel bruises. 📌 Rod's twin tracks.
  • Finger-pad: Grip marks (throttling, abuse).
  • Suction/Bite marks.
• Lacerations:
  • Stellate: Over bony prominences (scalp).
• Fractures:
  • Depressed skull: Weapon shape (hammer).
  • Ring fracture: Skull base (fall on feet/buttocks).
  • Bumper fracture: Pedestrian tibia/fibula (impact height).

⭐ Tram-line bruise: Results from impact with a linear object; central area is compressed causing pallor, while adjacent capillaries rupture causing parallel linear bruises.

Sharp & Thermal Patterns - Cutting Clues & Burning Brands

• Sharp Force:
  • Incised Wounds: Longer than deep, clean edges, no tissue bridging. Minimal bruising. Precise forensic terminology essential for BNS documentation.
  • Stab Wounds: Deeper than long. Shape may indicate weapon (single/double-edged). Hilt abrasions. 3D scanning enhances wound analysis.
  • Hesitation Marks: Superficial, parallel cuts near fatal wound (suicidal pattern).
  • Defence Wounds: On hands/forearms (ulnar aspect), indicates struggle under BNS provisions.
• Thermal (Burns):
  • Patterned: Imprint of hot object (e.g., iron, cigarette). Shape is key evidence.
  • Scalds: Hot liquids/steam. Irregular margins, "splash" patterns, follows gravity.
  • Pugilistic Attitude: Post-mortem limb flexion (heat-induced muscle coagulation). Not vital reaction.

  ⭐ Soot in airways or COHb levels indicate antemortem burns. 10% threshold requires comprehensive interpretation with other toxicological findings for definitive BSA evidence.

Special Patterns - Bites, Ligatures, Firearms

• Bite Marks:

  • Human: U-shaped pattern; inter-canine 3-4.5 cm (adult), 2.5-3.0 cm (small adult/child), <2.5 cm (deciduous teeth). DNA from saliva.
  • Animal: V-shaped pattern; deeper punctures.
  • Significance: Perpetrator ID, abuse.

• Ligature Marks:

  • Hanging: Oblique, non-continuous, runs upwards to knot; above thyroid.
  • Strangulation: Horizontal, encircling; at/below thyroid.
  • Pattern of material may imprint.

• Firearm Wounds (Entry):

  • Contact: Muzzle imprint, charring, stellate (bone).
  • Close (<15 cm): Soiling, burning, dense tattooing.
  • Intermediate (15-60 cm): Tattooing (density ↓).
  • Distant (>60 cm): Abrasion collar, bullet wipe.
  • Exit: Larger, irregular, everted. No tattooing/soiling.

  ⭐ Bevelling of bone: internal (entry) or external (exit) in firearm skull fractures indicates bullet direction.

High‑Yield Points - ⚡ Biggest Takeaways

• Pattern injuries distinctly reproduce characteristics of the object or weapon used.
• Essential for weapon identification, understanding mechanism of injury, and event reconstruction under BSA evidence standards.
• Common examples: tram-line bruises (rod/pipe), ligature furrows, tyre tread marks, bite marks.
• Bite marks show individual characteristics; however, their use for linking suspect to victim through dental patterns has limited scientific validation and high false positive rates in modern forensic practice.
• Imprint abrasions clearly depict the impacting surface (e.g., grille, muzzle).
• Patterned contusions can reveal shapes like belt buckles or fingertip pressure.