Lacerations: directional signs, tissue bridges, bleeding and vitality
THE CONTEXT
Wound structure can help interpret the direction of blunt impact, while healing and vital reactions help assess timing and antemortem occurrence.
Direction of impact
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With a downward course of the striking object, the lower wound margin is likely to be more bruised and undermined than the upper margin.
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Equal undermining on all sides indicates perpendicular impact.
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With impact from an angle, the side opposite the direction of motion is usually torn free or undermined. The side from which the blow was delivered is abraded and bevelled.
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A laceration is usually curved, with its convexity pointing towards the direction of application of force.
Tissue findings and bleeding
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Deeper tissues divide unevenly because their components have different strengths, leaving tissue bridges across the wound.
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Tissue bridges contain nerves, blood vessels, and elastic and connective tissue fibres.
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Hair bulbs are crushed, and hair or epidermal tags may be driven deep into the wound. Foreign matter may also be present.
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Haemorrhage is generally limited because arteries are crushed and irregularly torn, allowing retraction and ready clotting.
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Scalp wounds are an exception: temporal arteries bleed freely because they are firmly bound and unable to contract.
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Gaping results from the pull of elastic and muscular tissues.
Shape, size and depth
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Depth depends on the thickness of soft tissues at the injury site and the force applied. Wound shape and size may not correspond to the causative object.
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A blunt round end may produce a stellate laceration.
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A blunt object with an edge, such as a hammer head, may produce a crescentic patterned laceration.
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Long, thin objects such as pipes tend to produce linear lacerations. Flat surfaces produce irregular, ragged or Y-shaped wounds.
Age and antemortem occurrence
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Age determination is difficult unless there are clear healing signs, such as granulation tissue, fibroblast ingrowth or an organising infiltrate.
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Antemortem lacerations show bruising, eversion, gaping, blood-stained margins, greater bleeding and vital reaction.