Lacerations may involve deep tissues or internal organs despite limited external skin injury.
Avulsion
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In wheel-related avulsion, separated skin may show abrasions from tyre friction while one portion remains continuous with adjacent skin.
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Internal organs can be partly or completely torn from their attachments. Hair trapped in machinery can cause scalp avulsion.
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Shearing may separate underlying soft tissue from fascia or connective tissue while the skin shows no injury. The resulting pocket may fill with blood.
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This concealed shearing injury is usually seen on the back of the thighs of pedestrians struck by motor vehicles.
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Extreme avulsion may tear an extremity or even the head from the body.
Tears and cut lacerations
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Tears can result from impact by or against irregular or semisharp objects, including a car door handle, broken glass or a rough projecting object.
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A tear is another form of overstretching and is deeper at its starting point than at its termination.
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Heavy, relatively sharp-edged instruments such as an axe, hatchet or chopper may produce injuries described as cut lacerations, usually with abraded and bruised margins. The passage advises avoiding this term.
Deep injury without external laceration
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Hair may prevent external scalp laceration even when inner scalp layers are lacerated.
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A padded instrument or a broad striking surface may cause severe skull fractures without external laceration.
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Internal organ lacerations may result from fractured bone fragments, traction or strain shears, stretching of visceral attachments, or hydrostatic forces.
General margin characteristics
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Laceration margins are irregular, ragged and uneven, with pointed or blunt ends and minute marginal tears.
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Crushing and tearing can undermine laceration edges, particularly over bony areas such as the skull.