Mechanisms and identifying patterns of weapon-related bruises
THE CONTEXT
Different objects produce characteristic contusion patterns through compression, stretching and displacement of blood.
Mechanism of parallel contused lines
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A rod dents the tissues inward and stretches the sides of the dent. Marginal vessels rupture, while vessels at the compressed base remain uninjured.
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Pressure displaces blood from the base towards the sides. When the skin returns to its normal position, the two sides remain as contused lines with apparently unchanged intervening skin.
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Blood infiltration along the edges can make a bruise from a long rigid weapon wider and irregular.
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A rigid stick striking a curved, pliable region such as the buttocks may produce a contusion extending over the whole curved surface.
Patterns associated with different objects
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The edges of a broad flat weapon, such as a plank, may produce parallel bruises separated by apparently normal tissue.
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Whip bruises are elongated, curve over prominences and may partially encircle a limb or the body. Their two parallel lines are separated by a distance roughly equal to the whip's diameter.
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Pliable cane bruises resemble whip bruises but never encircle a limb or curve around the sides of the body.
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Straps, belts and chains leave definite imprints. Woven, spiral or plaited ligatures may also produce patterned bruises.
Other patterned injuries
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Contact injuries from firearms may produce abrasion with bruising that outlines the weapon's muzzle.
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Patterned bruising also occurs in motor car accidents.
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Suction or biting on the neck or breasts during sexual activity produces elliptical patterned bruises, often composed of petechial haemorrhages that may become confluent.
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These suction or bite-related bruises may reproduce the shape of the upper and lower lips.