Understanding Mechanical Injuries and Forensic Implications

Apr 27, 2025

Lecture on Mechanical Injuries

Presenter

  • Dr. Shilpa Singh
  • Postgraduate in Forensic Medicine from Armed Forces Medical College, Pune

Topic

  • Mechanical Injuries

1. Abrasion

  • Definition: Superficial denudation of skin/mucous membrane.
    • 2D Injury: Only length and breadth, no depth.

Types of Abrasion

  1. Scratch/Linear Abrasion

    • Caused by pointed objects (e.g., needle, thorn).

  2. Graze/Sliding/Scrape/Grinding Abrasion

    • From dragging on a broad rough surface (e.g., road traffic accidents).

  3. Pressure/Crushing Friction Force Abrasion

    • Due to pressure, common in ligature marks, hanging, strangulation.

  4. Imprint Abrasion

    • Caused by a rough object impression (e.g., radiator grille, teeth marks).

Mechanism

  • Tangential force: Linear or graze abrasion.
  • Compression force: Patterned abrasion (e.g., teeth marks, vehicle rims).

Healing and Medical Legal Importance

  • Heals rapidly, minimal bleeding, no permanent scab.
  • Timing of abrasion can indicate the time of injury.
    • Fresh Injury: Bright red, minimal bleeding.
    • Scab Colors Indicating Time Since Injury:
      • Reddish (12-24 hours)
      • Reddish-brown (2-3 days)
      • Dark brown (4-5 days)
      • Brownish scab (5-7 days)
      • Scab fallen off (7-10 days)
  • Determines direction of injury, causative weapon, timing, and place of occurrence.

Artifacts in Abrasion

  • Mimic abrasion, leading to misdiagnosis.
  • Caused by insects, animals, excreta, etc.

Antemortem vs. Postmortem Abrasion

  • Antemortem: Can be anywhere, shows stages of healing.
  • Postmortem: On bony prominences, lacks redness, no healing process.

2. Contusion

  • Definition: Known as bruise, extravasation of blood under intact skin due to capillary rupture.
  • Factors Affecting Bruise Appearance:
    • Site, vascularity, age, sex, skin color, underlying diseases.

Types and Healing of Contusion

  • Patterned Bruises: Intradermal bruises with minimal bleeding over ridges.
  • Healing Timeline:
    • Red (fresh, <1-2 hours)
    • Blue (reduced hemoglobin, few hours - 1 day)
    • Brown/Black (hemosiderin, 2-3 days)
    • Green (hematoidin, 5-7 days)
    • Yellow (bilirubin, 7-10 days)
    • Normal skin (10-15 days)

Special Types of Bruises

  • Migratory Bruise: Seen distant from impact site due to blood seepage.
    • Common in cranial fractures.
  • Battle’s Sign: Bruising behind the ear, indicates basilar skull fracture.
  • Black Eye/Spectacle Hematoma: Bruising around eyes.

Medical Legal Aspects of Bruises

  • Identification of causative object, time since injury, differentiation from artificial bruises.
  • Artificial Bruises: Can be caused by plants or chemicals mimicking genuine bruises.

Summary

This lecture covered the definitions, types, mechanisms, and medical legal importance of mechanical injuries, focusing on abrasions and contusions. Understanding the characteristics and healing stages of these injuries is crucial for accurate forensic analysis.

Full transcript