A laceration is a tear in tissue caused by either a shearing or a crushing force (Figure 4.8). Just as with contusions, one can have lacerations of internal organs as well as the skin. Lacerations of the skin tend to be irregular with abraded contused margins. They are caused by blows from blunt objects, falls, or impact from vehicles. The appearance of the laceration may not accurately reflect the instrument that produced it. Thus, a steel rod might produce not only a linear laceration of the scalp, but also a Y-shaped one. As a general rule, however, long, thin objects, such as pipes and pool cues, tend to produce linear lacerations, while objects with flat surfaces tend to produce irregular, ragged, or Y-shaped lacerations. Just as with contusions, determining the age of lacerations is difficult.
Lacerations occur most commonly over bony prominences, such as in the head, where the skin is fixed and can more easily be stretched and torn. Since different components of soft tissue have different strengths, there is usually incomplete separation of the stronger elements, such as blood vessels and nerves, so that when one looks into the depth of the laceration, one sees "bridges" of tissue running from side to side (Figure 4.9). The presence of bridging proves decisively that one is not dealing with an incised wound. The depths of the laceration should be explored for the presence of foreign material that could have been deposited there by the weapon or surface that caused the laceration.
If the blow or impact that causes a laceration is delivered at an angle, rather than perpendicular to the surface of the body, one will find undermining of the tissue on one side, which indicates the direction that the blow was delivered (Figure 4.10). The other side of the laceration, the side from which the blow was coming, will be abraded and beveled.
While most lacerations have irregular, abraded, even contused margins, if an individual is struck with a heavy object having a relatively sharp edge along the impacting surface, the wound produced may greatly resemble an incised wound (Figure 4.11). Careful examination of the wound, however, will usually reveal at least some abrasion of the margin, plus bridging in the depths of the wound. Occasionally, a very dull knife may produce an incised wound with abraded margins. Again, careful observation of the edges and base of the wound with a dissecting microscope usually makes differentiation
between an incised wound and a laceration relatively easy. In some instances, however, differentiation is not possible. Differentiation of a laceration from an incised wound of the head in a decomposed body is often not possible.
An avulsion or avulsive injury to the outside of a body is a form of laceration where the force impacting the body does so at an oblique or tangential angle to the skin, ripping skin and soft tissue off the underlying fascia or bone. Thus, tires passing over an extremity may avulse soft tissue off the bone. In a case of extreme avulsion, an extremity or even the head can be torn off the body. Internally, organs can be avulsed or torn off in part or in toto from their attachments.
A variation of an avulsive laceration is one produced by shearing forces, where the skin shows no signs of injury but the underlying soft tissue has been avulsed from the underlying fascia or connective tissue, creating a pocket that may be filled with a large quantity of blood. This injury is occasionally encountered on the backs of the thighs of pedestrians struck by motor vehicles. As the hood of the car impacts the back of the thigh and lifts up the pedestrian, it imparts a shearing force to this region, avulsing the skin and subcutaneous tissue off the fascia and creating pockets where blood can accumulate.
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