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Stab Injuries - Complete FMT Pedagogy

Sources Used

• DiMaio's Forensic Pathology, 3rd Ed (DiMaio)
• P.C. Dikshit Textbook of Forensic Medicine and Toxicology (Dikshit)
• Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology (Parikh)
• Schwartz's Principles of Surgery, 11th Ed
• Roberts and Hedges' Clinical Procedures in Emergency Medicine

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1. DEFINITION AND CLASSIFICATION

• Incised wounds (cuts/slash - length > depth)
• Stab/puncture wounds (depth > length)
• Chop wounds (heavy sharp weapons, e.g., axe)

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2. BIOMECHANICS AND MECHANISM

Force Required to Penetrate Skin

Factors Affecting Depth and Force Required (Dikshit)

1. Nature of weapon - A sharp, slender weapon passes more easily; a blunt-pointed weapon requires more force
2. Part of the body stabbed - Soft areas like the anterior abdominal wall are easily pierced; areas with underlying bone (skull) resist penetration
3. Age and build of the victim - Healthy muscular adults are less susceptible to deep penetration; children with softer skin sustain deeper injuries with less force

Skin-to-Organ Distances (DiMaio, Connor et al. CT study)

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3. CHARACTERISTICS OF STAB WOUNDS - FMT PRACTICAL EXAMINATION

1. Dimensions of the weapon
2. Type of weapon
3. Taper of the blade
4. Movement of knife within the wound
5. Depth of thrust
6. Direction of thrust
7. Amount of force used

3a. LENGTH

• Length of the wound is usually slightly less than the width of the weapon due to the elasticity of skin
• In most instances, the wound will have gaped across the centre forming a long ellipse
• Extent of gaping depends on anatomical location (over joints, axilla, groin), and whether the axis crosses Langer's lines
• After a stab, edges must be manually apposed to record the true dimension - this is a critical medicolegal step
• The wound appears considerably longer once edges are approximated
• Length is more if lateral movement of the weapon or body occurs

3b. BREADTH

3c. DEPTH

• Depth is the greatest dimension - the length of the wound track
• Equal to or less than the length of the blade
• May exceed blade length if the knife is plunged with sufficient force to indent the abdominal/chest wall
• Do NOT probe a stab wound in a living patient with a metal probe - risk of dislodging clots and causing hemorrhage. Use a pliant rubber tube or radiopaque dye injection followed by X-ray

3d. MARGINS

• Sharp and clean with a sharp weapon
• Irregular and abraded with a blunt-pointed weapon (screwdriver, broken glass)
• A hilt mark (technically "guard mark") may be seen at the angles of the wound if the full length of the blade entered

3e. ANGLES (Corners) - Most Important FMT Practical Point

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4. SHAPES OF STAB WOUNDS AND LANGER'S LINES

Langer's Lines (Cleavage Lines) and Wound Shape

Shape is Also Influenced By:

• State of skin tension/relaxation at time of stabbing
• Movement of the blade or the victim
• Whether the flat surface of the blade entered obliquely (beveled margin on one side, undermining on the other)
• Depth of insertion (whether guard/ricasso contacted skin)

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5. TYPES OF WEAPONS AND WOUND PATTERNS

A. Single-Edged Knife (Kitchen/Pocket/Folding Knife)

• Most common weapon; typical blade 4-5 inches
• Wound: one acute angle, one squared/blunted angle
• If blade inserted up to ricasso: wound can be squared at both ends
• If guard (crossguard) contacts skin: patterned guard abrasion visible around the wound entry
  • Symmetrical = knife driven straight in
  • Prominent above wound = knife angled downward at entry

B. Double-Edged Weapon (Dagger, Stiletto, Bayonet)

• Wound: both angles acute/pointed
• Hilt mark may be seen if blade driven to full length
• Parikh case illustration: double-edged wound with prominent hilt mark

C. Ice Pick / Awl / Stiletto

• Small, inconspicuous circular or oval puncture
• May resemble insect bites or small lacerations
• Can be easily missed at autopsy - require careful examination

D. Scissors

• Closed scissors: Linear stab wound with abraded margins (tip splits rather than cuts)
• If screw protrudes, may produce an angular laceration in mid-portion of one skin margin
• Open scissors (blades separated): Produce two parallel stab wounds per thrust

E. Screwdriver (Flat-Head)

• Produces a linear or slightly angular wound

F. Phillips Screwdriver

• X-shaped point produces a circular or cruciform wound - highly characteristic

G. Fork

• Barbecue fork: Multiple penetrating wounds corresponding to number of prongs
• Kitchen fork: Superficial, small parallel punctures

H. Broken Glass / Porcelain

• Cutting ability can equal or exceed a surgical scalpel
• Produces incised or stab wounds depending on mechanism
• Margins may be irregular depending on nature of glass

I. Pen / Pencil / Unconventional Objects

• Can penetrate deeply into soft tissue and vital structures
• DiMaio case: ballpoint pen perforated the skin, muscle, and ligaments, penetrated the atlanto-occipital junction and perforated the spinal cord

Summary Table: Weapon vs. Wound Pattern

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6. WOUND TRACK AND DIRECTION

• Nature of weapon
• Approximate dimensions
• Thrusting force (from depth)
• Position of assailant and victim at time of assault
• Whether suicidal, homicidal, or accidental

• Track is evenly cut with no tissue bridging (unlike lacerated wounds)
• Direction of track gives information about relative positions
• Track should not be probed with a metallic probe in the living - use pliant rubber tube or contrast X-ray
• Wound of exit (if present): smaller, with everted edges when a tapering weapon is used

Suicidal vs. Homicidal Stab Wounds

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7. WOUND HEALING - PHASES

Phase 1: Hemostasis (Immediate - Hours)

• Platelet degranulation, clot formation
• Release of PDGF, TGF-β, VEGF
• Vasoconstriction via sympathetic and cytokine pathways
• Sets the stage for inflammation

Phase 2: Inflammation (Days 1-5)

• PMNs (neutrophils) arrive first (24-48 hrs)
• Macrophages dominate by day 3-5 - coordinate debridement and growth factor release
• Histamine, prostaglandins increase capillary permeability
• Keratinocytes begin migration across wound surface within 24-48 hours (re-epithelialization)
• Surface becomes impermeable to water within 24-48 hours in sutured wounds

Phase 3: Proliferation / Fibroplasia (Days 4-21)

• By day 4-5: fibroblasts begin synthesizing collagen (predominantly Type III initially, then Type I)
• Significant tensile strength gain begins around day 5
• Tensile strength increases rapidly for days 6-17, more slowly for a further 10-14 days
• Granulation tissue forms; angiogenesis occurs

Phase 4: Remodeling / Resolution (Weeks to Months - up to 1 year)

• Type III collagen replaced by Type I
• Scar tissue remodels and strengthens for up to 1 year
• Maximum scar strength = ~80% of original unwounded skin - never fully restored
• Collagen formation essentially complete in 21-28 days but scar widens for another month

Healing by Intention

• First intention (primary): Wound edges approximated (sutured) within 24 hours; heals with minimal scar
• Second intention (secondary): Open wound; heals by contraction, collagen formation, and epithelialization; more scar tissue

Age Estimation of Wound (FMT relevance)

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8. WRITING A STAB WOUND - PRACTICAL REPORT FORMAT

The entry wound is a punctured-incised wound, elliptical in shape. It is located in the left upper thorax above and lateral to the nipple, 15 inches below the top of the head, and 7 inches to the left of the midline. It is 1 inch long (1.25 inches when the edges are apposed) and 1/4 inch wide at the skin surface. It is horizontally oriented. The lateral corner is blunted and the medial corner is acutely angulated. There is no abrasion or bruising at the wound margin. The track is 5 inches deep, evenly cut, directed from left to right, front to back, and angulated slightly downward. No tissue bridging is noted. The track perforates the chest wall through the third intercostal space, perforates the lingula of the upper lobe of the left lung, the pericardial sac, and penetrates the heart perforating the left ventricular wall. The entire wound track is infiltrated with blood and 1000 ml of liquid and clotted blood is found in the left chest cavity. There is no exit wound.

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9. KEY FMT PRACTICAL EXAM POINTS (MCQ/Short Answers)

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10. NOTE ON GRIEVOUS HURT: IPC Section 320 and BNS Section 116

Under IPC Section 320 (now replaced by BNS Section 116)

1. Emasculation - Loss of masculine power due to direct trauma to genitalia or indirect (lumbosacral trauma); applicable only to males; both testes must be affected
2. Permanent privation of sight of either eye - Corneal scarring, retinal detachment, any permanent visual impairment of either eye
3. Permanent privation of hearing of either ear - Rupture of tympanic membrane causing even partial permanent hearing loss in either ear
4. Privation of any member or joint - Loss of function or anatomical separation of any body part capable of performing a distinct function
5. Destruction or permanent impairing of power of any member or joint - Permanent functional loss of any joint or organ; injury must be permanent
6. Permanent disfiguration of head or face - Context-dependent: a small scar on a young woman's face may qualify; a large scar on an elderly man's face may not. The impact on the person matters.
7. Fracture or dislocation of a bone or tooth - All fractures including hairline fractures, even outer table of skull fractures; even tooth dislocation qualifies
8. Any hurt that endangers life, or causes severe bodily pain or inability to follow ordinary pursuits for 20 days - "Ordinary pursuits" = daily activities (eating, bathing, toileting); inability to go to office alone for >20 days is not sufficient; the attending physician must evaluate nature/site of injury, treatment, and presence of infection

BNS vs. IPC - Key Changes Relevant to FMT

FMT Relevance of Grievous Hurt in Stab Injuries

• Category 7 if it causes a bone fracture (e.g., stab wound with rib fracture)
• Category 8 if it endangers life (pneumothorax, hemopericardium, organ perforation) or causes severe pain/disability for >20 days
• Category 4/5 if it results in permanent loss of function (e.g., nerve injury, tendon severance)

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