Factors determining wound severity: contact area, energy and immobilization
THE CONTEXT
The nature and extent of a wound depend on the striking object, the energy delivered and the conditions under which that energy is discharged.
Tissue failure and the striking object
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Soft tissues rupture when stretched beyond their tensile strength.
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A sharp-edged object concentrates force over a small area, point or line, producing deep penetration or clear tissue separation. Tissue hardness resists its passage.
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A flat blunt instrument involves a larger surface area and dissipates energy, reducing damage per unit mass of tissue compared with a narrow object.
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Instrument irregularities or a curved body surface can reduce the actual contact area and increase damage. A fall against a projection may therefore cause more serious injury than a similar fall against a flat surface.
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Deformation or breakage of a plastic instrument consumes energy and increases both the area of impact and the period over which energy is discharged.
Mass and velocity
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Doubling mass doubles kinetic energy, whereas doubling velocity increases kinetic energy fourfold.
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Velocity therefore has a greater influence on energy than mass. A light bullet can have great destructive power because of its high velocity.
Movement versus localized injury
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When much of the impact energy produces generalized body movement, the person may be knocked down while sustaining little local injury.
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When the body or struck part is immobilized, a greater part of the force produces localized tissue damage.