Stab wounds: penetration, track examination and skin shape
THE CONTEXT
The depth, track and external appearance of a stab wound depend on the weapon, clothing, skin and movements involved.
Factors affecting penetration
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Multiple layers of tough clothing, leather belts and thick leather jackets or coats require greater force for penetration.
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The speed of thrust influences penetration. Stretched skin is easier to penetrate than lax skin.
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A knife striking the skin at a right angle usually penetrates more deeply than one striking at an acute angle.
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When a body falls or runs onto a blade, its forward momentum can be sufficient to cause fatal injury. Easy penetration requires a sharp-pointed knife held firmly; a blunt knife held loosely may be turned aside.
Demonstrating the wound track
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Pliable tubing may be introduced gently; if it passes easily, it may reveal the true track. A probe can then be inserted into the tubing to make it rigid and straight.
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Dissection parallel to, but away from the wound can reveal the track.
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Radio-opaque material or dyes may be injected to demonstrate the wound track by X-rays.
Multiple openings and wound shape
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Rarely, one stab produces multiple skin wounds. A blade may pass tangentially through the arm and re-enter the chest wall, or pass through the edge of a sagging breast and re-enter the thorax.
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Skin wound size and shape depend on the implement and its cutting surface, sharpness, width and shape, as well as the body region, insertion depth, withdrawal angle, thrust direction, blade movement, victim movement and skin tension.
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Stab and incised wounds may be slit-shaped with two acute angles or may gape, depending on their location and orientation relative to Langer's cleavage lines.