Abrasions: mechanism, depth, scab formation and scratches
THE CONTEXT
Abrasions result from pressure and movement at the skin surface. Their depth and pattern reflect the abrading surface and the manner of contact.
Mechanism and depth
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Abrasions arise from friction against a rough surface or compression with rubbing, including falls, dragging, fingernails, thorns and teeth bites.
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Pressure and movement of the agent over the skin are essential. In the simplest injury, epidermal cells flatten and their nuclei elongate.
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Sufficient friction may partially or completely remove the epithelium and damage the superficial dermis.
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Greater surface roughness and faster skin movement produce deeper injury.
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Deeper subepidermal damage may cause superficial scarring. Occasionally, full-thickness skin damage occurs in an irregular, interrupted pattern, with intact epidermis remaining within the abrasion.
Surface covering and clinical features
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Lymph and blood exude over the raw surface and form a protective scab or crust.
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Typical abrasions are simple injuries that bleed slightly, heal rapidly and do not scar; the passage separately describes scarring when deeper damage occurs.
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Large abrasions may cause severe pain and bleeding.
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The size, situation, pattern and number of abrasions should be recorded.
Scratches and fingernail marks
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A scratch is a linear abrasion with length but no significant width, or a very superficial incision depending on the agent.
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A point scratch may be produced by the tip of a knife or razor. Scratches can also result from fingernails, pins or thorns passing across the skin.
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The scratching object pushes surface layers ahead of it, leaving a clean area at the start and tags at the end.
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Static gripping by fingernails may produce straight or curved marks, 1–2 mm broad, with a wide start and narrow end.